EFFECT OF RECYCLED CONCRETE AGGREGATES ON THE LONG …

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Civil Engineering Theses Civil Engineering

Fall 12-19-2019

EFFECT OF RECYCLED CONCRETE AGGREGATES ON THE LONG-EFFECT OF RECYCLED CONCRETE AGGREGATES ON THE LONG-

TERM, ELASTIC, TOTAL DEFLECTION AND STRENGTH OF TERM, ELASTIC, TOTAL DEFLECTION AND STRENGTH OF

PRECAST PRESTRESSED HOLLOW CORE CONCRETE SLABS PRECAST PRESTRESSED HOLLOW CORE CONCRETE SLABS

Lizeth Marisol Gomez Santana University of Texas at Tyler

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Recommended Citation Recommended Citation Gomez Santana, Lizeth Marisol, "EFFECT OF RECYCLED CONCRETE AGGREGATES ON THE LONG-TERM, ELASTIC, TOTAL DEFLECTION AND STRENGTH OF PRECAST PRESTRESSED HOLLOW CORE CONCRETE SLABS" (2019). Civil Engineering Theses. Paper 16. http://hdl.handle.net/10950/2323

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EFFECT OF RECYCLED CONCRETE AGGREGATES ON THE LONG-TERM,

ELASTIC, TOTAL DEFLECTION AND STRENGTH OF PRECAST PRESTRESSED

HOLLOW CORE CONCRETE SLABS

by

LIZETH MARISOL GOMEZ SANTANA

A thesis submitted in partial fulfillment

of the requirements for the degree of

Master of Science in Civil Engineering

Department of Civil Engineering

Michael J. McGinnis, Ph.D., Committee Chair

College of Engineering

The University of Texas at Tyler

August 2019


Tyler, Texas

This is to certify that the Master's Thesis of

LIZETH MARISOL GOMEZ SANTANA

has been approved for the thesis requirement on

August 6, 2019 for the degree Master of Science in

Civil Engineering

Dedication

I dedicate this thesis to the members of my family who came before me. I would like to

thank my family: my father José del Refugio Gómez Brambila, my mother Maria

Guillermina Santana García and my siblings Guillermo and Gisselt for their support. I’d

like to thank my siblings for their enthusiasm, as soon as Guillermo and Gisselt found out

I had been given admissions at UT Tyler they wanted to immediately pack up my things

and ship me off to graduate school. Thank you Guillermo and Gisselt for your support

that first difficult semester. Thank you Gisseltita for taking on an adventure with me and

helping me move to Tyler. I would also like to thank the Rivera Balderas family

especially my friends Brenda, Emmanuel and Raymundo for supporting me both

emotionally and spiritually.

Acknowledgements

I would like to thank my advisors Dr. Michael J. McGinnis, Dr. Michael V.

Gangone and Dr. Yahya C. Kurama from the University of Notre Dame for their

guidance, patience and commitment to their profession as educators. I would like to thank

Mr. Adam Reihl from Stresscore, Inc. based out of South Bend, Indiana for their support,

technical expertise and assistance in providing the test specimens. I would also like to

thank the National Science Foundation (NSF) for their support in funding this project. I

would like to express my gratitude to Dr. Gokhan Saygili who provided encouragement,

wisdom and laughter. I would also like to express my gratitude to Dr. Torey Nalbone for

his constant support and his reminders to keep calm and carry on. I would like to thank

my colleagues who assisted me during the laboratory testing: David Etheridge, Aqil

Sheraze, Alireza and Armin Yazdanshenas, Luis Mendoza Morales, Ashmita Wasti and

Prajwol Sharma.

i

Table of Contents

List of Tables ..................................................................................................................... iii

List of Figures ..................................................................................................................... v

Abstract ............................................................................................................................ xiii

Chapter 1 Introduction ...................................................................................................... 15

1.1 Introduction ............................................................................................................. 15 1.2 Organization of thesis ............................................................................................. 16 1.3 Symbols and notation .............................................................................................. 18

Chapter 2 Literature Review ............................................................................................. 21

2.1 Concrete mixtures with Recycled Concrete Aggregate (RCA) .............................. 21

2.2 Use of RCA in reinforced concrete applications .................................................... 23

2.3 Properties of recycled concrete aggregates from precast/prestressed members ..... 25 2.3.1 Use of RCA in prestressed concrete .................................................................... 27

Chapter 3 Test specimen description ................................................................................ 29

3.1 Concrete properties: mix design ............................................................................. 30 3.1.1 RCA particle size distribution .............................................................................. 33 3.2 Manufacturing and casting conditions .................................................................... 35

3.3 Concrete stiffness (Ec) ............................................................................................ 35 3.4 Specimen geometry and casting conditions ............................................................ 40

3.5 Shipping .................................................................................................................. 41

3.6 Curing conditions .................................................................................................... 42

3.7 Replacement percentage ......................................................................................... 43 Chapter 4 Long term test description ................................................................................ 44

4.1 Test matrix .............................................................................................................. 44

4.2 Slab loading and diagram pictures .......................................................................... 45 4.3 Slab layout in laboratory ......................................................................................... 45 4.4 Loading procedure .................................................................................................. 48 4.5 Instrumentation ....................................................................................................... 49

Chapter 5 Deformations under instant and long-term constant loading ........................... 52

5.1 Deflection data ........................................................................................................ 52 5.1.1 Long-term deflection ........................................................................................... 52 5.1.2 Deflection magnifier ............................................................................................ 64

5.1.3 Instant (Elastic) deflection. .................................................................................. 69 5.1.4 Inelastic deflection ............................................................................................... 71

5.2 Long-term deflections ............................................................................................. 72 5.3 Service load stress ................................................................................................... 73 5.4 Weather conditions ................................................................................................. 74 5.5 Conclusions ............................................................................................................. 78

Chapter 6 Bending test description ................................................................................... 79

6.1 Test set up ............................................................................................................... 79

ii

6.2 Equipment ............................................................................................................... 81

6.3 Load procedure ....................................................................................................... 82 6.4 Instrumentation ....................................................................................................... 82

Chapter 7 Bending test results .......................................................................................... 86

7.1 Moment capacity ..................................................................................................... 86

7.2 Development length ................................................................................................ 87 7.3 Cracking load, maximum load to failure and code capacity ................................... 88 7.4 Cracking deflection ............................................................................................... 101 7.5 Modulus of elasticity from load vs. midspan displacement curves ...................... 101 7.6 Quarter-point deflection plots ............................................................................... 102

Chapter 8 One-way shear test description ...................................................................... 115

8.1 Test set-up ............................................................................................................. 115 Chapter 9 Results of one-way shear tests ....................................................................... 119

9.1 Theoretical shear capacity and moment capacity ................................................. 119 9.2 Moment and shear demand ................................................................................... 121

9.3 Results of four-point shear tests ............................................................................ 122 Chapter 10 Punching (two-way) shear test set up ........................................................... 137

10.1 Punching shear test set up ................................................................................... 137 Chapter 11 Punching (two-way) shear results ................................................................ 141

11.1 Punching shear results ......................................................................................... 141 Chapter 12 Conclusions and future work........................................................................ 148

12.1 Discussion of results ........................................................................................... 148

12.1.1 Deflections ....................................................................................................... 148 12.1.2 Bending strength .............................................................................................. 149

12.1.3 One-way shear strength.................................................................................... 149 12.1.4 Punching (two-way) shear strength ................................................................. 149 12.2 Suggestions for future work ................................................................................ 150

References ....................................................................................................................... 151

iii

List of Tables

Table 1 Section properties, 6SC56.................................................................................... 30

Table 2 Properties of slag ................................................................................................. 30

Table 3 Particle size distribution, slag .............................................................................. 31

Table 4 Properties of fine aggregate, sand ........................................................................ 31

Table 5 Particle size distribution, sand ............................................................................. 32

Table 6 Mix design for each of the slab specimens .......................................................... 33

Table 7 Particle size distribution, RCA ............................................................................ 34

Table 8 Properties of RCA ................................................................................................ 34

Table 9 Compressive strength of cylinder samples, 7-day strength ................................. 37

Table 10 Compressive strength of cylinder samples, (psi) ............................................... 37

Table 11 Modulus of elasticity, Ec, calculated from ACI 318 code ................................. 39

Table 12 Compressive strength and modulus of elasticity from numerical models ......... 39

Table 13 Compressive strength and modulus of elasticity from numerical models,

continued ........................................................................................................................... 40

Table 14 Specimen replacement percentages of virgin aggregate with RCA .................. 43

Table 15 Test matrix of slabs for long-term load testing .................................................. 44

Table 16 Total deflection, ΔT ............................................................................................ 55

Table 17 Deflection magnifier .......................................................................................... 65

Table 18 Instant (elastic) deformation .............................................................................. 70

Table 19 Inelastic deflection ............................................................................................. 72

Table 20 Total, elastic and long-term deflection .............................................................. 73

iv

Table 21 Service load stress vs. available stress (psi) ...................................................... 74

Table 22 Development length (ld) ..................................................................................... 88

Table 23 First cracking load ............................................................................................. 91

Table 24 Maximum load to failure and code capacity ...................................................... 92

Table 25Maximum load to failure and shear demand vs. shear capacity ......................... 92

Table 26 Cracking deflection .......................................................................................... 101

Table 27 Modulus of elasticity, Ec, from load vs. midspan displacement curves .......... 102

Table 28 Beam (one-way) shear slab lengths tested ....................................................... 118

Table 29 One-way shear demand and capacity ............................................................... 124

Table 30 Moment demand and capacity ......................................................................... 124

Table 31 Negative moment demand versus negative moment capacity ......................... 126

Table 32 Maximum load to failure, two-way (punching) shear test ............................... 142

v

List of Figures

Figure 1 Hollow core slabs ............................................................................................... 29

Figure 2 Particle size distribution curve, slag ................................................................... 31

Figure 3 Particle size distribution curve, sand .................................................................. 32

Figure 4 Gradation curves of RCA sample ....................................................................... 34

Figure 5 Average compressive strength (psi) based on Table 9 ....................................... 38

Figure 6 (a) NDS 56 day (b) ND20 56 day (c) ND30 56 day (d) ND40 56 day (e) ND60

56 day ................................................................................................................................ 38

Figure 7 Modulus of elasticity of samples from Table 11 ................................................ 39

Figure 8 Prestressing strands ............................................................................................ 40

Figure 9 Slipformer ........................................................................................................... 41

Figure 10 Hollow core concrete slabs curing ................................................................... 41

Figure 11 Shipping route .................................................................................................. 42

Figure 12 Unloading from flat bed truck .......................................................................... 42

Figure 13 Brecknell electronic crane scale ....................................................................... 45

Figure 14 Slab layout in laboratory .................................................................................. 46

Figure 15. Slab layout in laboratory ................................................................................. 47

Figure 16 Laboratory slab layout ...................................................................................... 47

Figure 17 Slab layout outside ........................................................................................... 48

Figure 18 Slab loading diagram ........................................................................................ 48

Figure 19 Instrumentation for long-term loading ............................................................. 50

vi

Figure 20 Dial gauge used for verification of long-term service loading from string

potentiometers ................................................................................................................... 51

Figure 21 NDS long-term deflection ................................................................................ 55

Figure 22 ND20 long-term deflection............................................................................... 56




Figure 26 NDS 1 block long-term deflection ................................................................... 60

Figure 27 NDS 2 blocks long-term deflection .................................................................. 61

Figure 28 Long-term deflection, inside slabs ................................................................... 62

Figure 29 Long-term deflection, outside slabs ................................................................. 63

Figure 30 Long-term deflection, all slabs ......................................................................... 64

Figure 31 ND20 deflection magnifier ............................................................................... 65




Figure 35 NDS 1 block deflection magnifier .................................................................... 67

Figure 36 NDS 2 blocks deflection magnifier .................................................................. 68

Figure 37 Single load slabs, deflection magnifier ............................................................ 68

Figure 38 Rainfall data during long-term deflection testing ............................................. 75

Figure 39 Temperature and humidity data, outside slabs ................................................. 76

Figure 40 Temperature and humidity data, inside slabs ................................................... 77

vii

Figure 41. Bending test set up, ND S................................................................................ 80

Figure 42. Bending test set up diagram ............................................................................ 80

Figure 43 Bending test set-up ........................................................................................... 81

Figure 44. Enerpac hydraulic pump and pressure gauges ................................................. 82

Figure 45 Data acquisition system .................................................................................... 83

Figure 46 Model 100, data acquisition hardware .............................................................. 84

Figure 47 String potentiometer ......................................................................................... 84

Figure 48 Load cell, model Omegadyne LC8400-213-200k ............................................ 84

Figure 49 Slab and instrumentation set up ........................................................................ 85

Figure 50 Load cell calibration curve ............................................................................... 85

Figure 51 NDS 1 block, uneven surface ........................................................................... 91

Figure 52 Applied load vs. midspan displacement up to cracking for ND20 ................... 91

Figure 53 Failure loads of flexural bending test specimens ............................................. 92

Figure 54 Loading diagrams for bending tests ................................................................. 93

Figure 55 Load vs. midspan displacement of NDS slab up to cracking load ................... 93

Figure 56 Load vs. midspan displacement of ND20 slab up to cracking load ................. 94




Figure 60 Load vs. midspan displacement of NDS 1 block slab up to cracking load ...... 96

Figure 61 Load vs. midspan displacement of NDS 2 blocks slab up to cracking load ..... 96

Figure 62 Loading and re-loading load-displacement curve of NDS during loading test 97

viii

Figure 63 Loading and re-loading load-displacement curve of ND20 during loading test

........................................................................................................................................... 97


........................................................................................................................................... 98


........................................................................................................................................... 98


........................................................................................................................................... 99

Figure 67 Loading and re-loading load-displacement curve of NDS 1 block during

loading test ........................................................................................................................ 99


loading test ...................................................................................................................... 100

Figure 69 Load vs. midspan displacement averages for all slabs ................................... 100

Figure 70 NDS (a) bending test set-up (b) bending test set-up (c) cracked section left (d)

cracked section right (e) cracked section ........................................................................ 104

Figure 71 ND20 (a) bending test set-up (b) bending test cracked section left (c) bending

test cracked section right (d) bending test cracked section left (e) bending test cracked

section ............................................................................................................................. 105

Figure 72 ND30 (a) bending test set-up (b) bending cracked section left (c) bending

cracked section right ....................................................................................................... 106

Figure 73 ND40 (a) bending test set-up (b) bending test set-up (c) bending test cracked

section left (d) bending test cracked section right .......................................................... 107

ix


test cracked section right ................................................................................................. 108

Figure 75 NDS 1 block (a) bending test set-up (b) bending test cracked section left (c)

bending test cracked section right (d) bending test cracked section ............................... 109

Figure 76 NDS 2 blocks (a) bending test set-up (b) bending test cracked left (c) bending

test cracked section right ................................................................................................. 110

Figure 77 NDS deflection plots ...................................................................................... 111

Figure 78 ND20 deflection plots..................................................................................... 111




Figure 82 NDS 1 block deflection plots ......................................................................... 113

Figure 83 NDS 2 blocks deflection plots ........................................................................ 114

Figure 84 One-way shear test set up NDS ...................................................................... 117

Figure 85 One-way shear test set up ND60 .................................................................... 117

Figure 86 One-way shear test set up, all other slabs ....................................................... 118

Figure 87 Cross-section of slab showing shear area ....................................................... 121

Figure 88 Example loading diagrams for one-way shear tests, NDS ............................. 122

Figure 89 Applied load at failure for slab specimens undergoing one-way shear .......... 125

Figure 90 Load vs. midspan displacement of slab NDS during one-way shear testing .. 126

Figure 91 Load vs. midspan displacement of slab ND20 during one-way shear testing 127


x



Figure 95 Load vs. midspan displacement of slab NDS 1 block during one-way shear

testing .............................................................................................................................. 129

Figure 96 Load vs. midspan displacement of slab NDS 2 blocks during one-way shear

testing .............................................................................................................................. 129

Figure 97 NDS (a) one-way shear set-up (b) one-way shear set-up (c) one-way shear

cracked section left (d) one-way shear cracked section left (e) one-way shear cracked

section right (f) one-way shear cracked section .............................................................. 130

Figure 98 ND20 (a) one-way shear test set-up (b) one-way shear cracked section left (c)

one-way shear cracked section right (d) one-way shear cracked section underside ....... 131

Figure 99 ND30 (a) one-way shear test set-up(b) one-way shear test cracked section left

(c) one-way shear cracked section right (d) one-way shear cracked section midspan ... 132

Figure 100 ND40 (a) one-way shear test set-up (b) one-way shear test cracked section left

(c) one-way shear test cracked end of slab (d) one-way shear test cracked section right133

Figure 101 ND60 (a) one-way shear test set-up (b) one-way shear cracked section (c)

one-way shear cracked section left (d) one-way shear cracked section end (e) one-way

shear cracked section right .............................................................................................. 134

Figure 102 NDS 1 block (a) one-way shear test set-up (b) one-way shear cracked section

left (c) one-way shear cracked section right (d) one-way shear cracked section end (e) one

way shear cracked section underside .............................................................................. 135

xi

Figure 103 NDS 2 blocks (a) one way-shear test set-up (b) one-way shear cracked section

left (c) one-way shear cracked section right (d) one-way shear cracked section slab

underside ......................................................................................................................... 136

Figure 104 Steel donut used in punching shear tests ...................................................... 138

Figure 105 Punching (two-way) shear set-up ................................................................. 138

Figure 106 Punching shear test, overhead view .............................................................. 139

Figure 107 Punching (two-way) shear test set-up........................................................... 139

Figure 108 Punching shear test box formation supports ................................................. 140

Figure 109 Failure load of two-way (punching) shear.................................................... 142

Figure 110 NDS (a) punching(two-way) set-up (b) punching(two-way) set-up(c)

punching (two-way) shear cracked section, South side (d) punching(two-way) cracked

section, North side (e) punching(two-way) cracked section, South side ........................ 143

Figure 111 ND20 (a) punching (two-way) shear test set-up (b) punching (two-way) shear

cracked section (c) punching (two-way) shear cracked section ...................................... 144

Figure 112 ND30 (a) punching (two-way) shear set-up (b) punching (two-way) shear




Figure 114 ND60 (a) punching (two-way) shear test set-up (b) punching (two-way)

cracked section (c) punching (two-way) cracked section end ........................................ 146

Figure 115 NDS 1 block (a) punching (two-way) shear test set-up (b) punching (two-

way) shear cracked section (c) punching (two-way) shear cracked section end ............ 146

xii

Figure 116 NDS 2 blocks (a) punching (two-way) shear test set-up (b) punching (two-

way) shear cracked section ............................................................................................. 147

xiii

Abstract

EFFECT OF RECYCLED CONCRETE AGGREGATES ON THE LONG-TERM,

ELASTIC, TOTAL DEFLECTION AND STRENGTH OF PRECAST PRESTRESSED

HOLLOW CORE CONCRETE SLABS

Lizeth Marisol Gomez Santana

Thesis Chair: Michael J. McGinnis, Ph.D.


August 2019

Concrete constitutes the largest portion of construction and demolition waste

generated each year in the United States. The Environmental Protection Agency (EPA)

estimates that the total production of construction and demolition of concrete waste

during 2015 was 381.8 million tons. In order to reduce the economic and environmental

effects of waste concrete, researchers have begun to incorporate it into concrete mixtures.

However, the inherent variability in mechanical properties between RCA sources makes

it difficult to quantify the maximum permissible replacement of natural aggregate and the

end-result properties of concrete. This project investigates the use of recycled concrete

aggregates (RCA) obtained from a precast prestressed concrete plant in the manufacture

of prestressed hollow core concrete slabs. Seven full scale slabs were tested in two ways

(1) under long term static bending loads to investigate long term deflection behavior, and

(2) under short term loading in bending, beam (one-way) shear and in punching (two-

way) shear.

The results indicate that slabs with RCA generated larger long-term service

deflections. With regards to strength testing the slabs with RCA performed just as well, if

xiv

not better, than slabs with no RCA. Overall, this testing indicates RCA is a viable option

in the efforts to help improve sustainability while maintaining a safe design.

15

Chapter 1

Introduction

1.1 Introduction

Replacing natural aggregate in concrete is a methodology undertaken to reduce

both the costs of construction and negative impact to the environment. A literature review

of this endeavor shows that recycled concrete aggregates (RCA) are a common ingredient

in road base.

RCA are of practical and economic use in the construction industry. Currently, a

large portion of RCA are used as substitutes for natural aggregates in road base (FHWA,

2004). Construction codes and standards do not provide sufficient guideline as to the use

of RCA in structural applications. Therefore, further work is needed to ascertain their

suitability in heavy structural and industrial applications. Previous work indicates that the

inclusion of RCA negatively impacts the properties of concrete specimens. However,

even with these findings RCA may remain a suitable option for structural applications.

The University of Texas at Tyler and The University Notre Dame have

collaborated on the study of RCA on various occasions. These efforts have occurred both

as collaborations between UT Tyler and Notre Dame as well as graduate work carried out

by the individual institutions. The collaborative efforts of UT Tyler and Notre Dame have

led to studies on the design of concrete mixtures with RCA (Knaack and Kurama, 2011;

Knaack and Kurama, 2013a), service load deflections of RCA concrete (Knaack and

Kurama, 2013b), creep and shrinkage (Knaack and Kurama, 2015a) and sustained service

load deflections (Knaack and Kurama, 2015c) as well as strength and stiffness impact of

16

RCA (McGinnis et al., 2017a). Furthermore, work was also done on the effect of RCA on

time dependent deformations on reinforced concrete beams (Knaack and Kurama, 2015b;

Knaack and Kurama, 2018). Work has been undertaken on the mechanical properties of

precast prestressed concrete (Brandes and Kurama 2018a; Brandes and Kurama, 2018b;

Brandes and Kurama, 2018c; Brandes and Kurama, 2016). The economic and

environmental impacts of RCA use have also been investigated (Davis et al., 2015; Davis

et al., 2016; McGinnis et al., 2017a; McGinnis et al., 2017b; Knaack and Kurama, 2018;

Azúa et al., 2019).

This study investigates the use of RCA in precast prestressed hollow core slabs

with varying percentages of natural aggregate replaced by RCA. The replacement

percentages were as follows: 0%, 20%, 30%, 40% and 60%. The precast prestressed

hollow core concrete slabs were: (1) subjected to long term loading for a period of 3

months and (2) were loaded to failure in flexural bending, beam (one-way) shear and

punching (two-way) shear. Existing literature published by the Precast/Prestressed

Concrete Institute indicates detailed guidelines for the design of hollow core concrete

slabs; however, the existing design document does not delve into the use of RCA in these

concrete specimens.

1.2 Organization of thesis

This document is organized as follows:

Chapter 2 presents a review of the previous work undertaken by members of this research

team. This material includes studies on the properties of RCA and its use in reinforced

concrete and precast prestressed concrete.

17

Chapter 3 provides a description of the properties of the concrete mixtures and aggregates

used in this study as well as manufacturing and casting conditions and curing conditions

of the test specimens.

Chapter 4 details the test matrix of variables and samples tested as well as loading

conditions, loading procedures and instrumentation used.

Chapter 5 presents the results of long-term service loading including climatic data,

service load deflections, elastic and inelastic deformations, long-term deflections as well

as service load stress calculations

Chapter 6 provides a description of the bending test set up and procedure as well as the

equipment and instrumentation used.

Chapter 7 provides the bending test results and pictures including calculations of

development length, cracking load and cracking deflections and moment capacity as well

as modulus of elasticity calculated from load vs. midspan displacement

Chapter 8 provides a description of the beam one-way shear test set up as well as

accompanying diagrams

Chapter 9 provides results of the beam one-way shear tests including theoretical shear

capacity and moment capacity and moment and shear demand

Chapter 10 presents the test set-up for the punching (two-way) shear tests as well as

accompanying diagrams

Chapter 11 presents the results of the punching shear tests.

Chapter 12 provides summary and conclusions of the work undertaken in this research

investigation.

18

1.3 Symbols and notation

a, moment arm

a’, moment arm

A, area

ARCA, water absorption of RCA

Aslag, water absorption of slag (used as natural aggregate)

cb, distance from centroid to bottom of the section

ct, distance from centroid to top of the section

DCW, demolition construction waste

dp, depth of prestressing steel

DRCA, deleterious material content of RCA

Ec, modulus of elasticity, Young’s modulus

f’c, compressive strength

f'c,Target, target compressive strength, psi

FHWA, Federal Highway Administration

fpe, effective prestress

fps, stress in prestressing strand at nominal flexural strength

I, moment of inertia

Ie, effective moment of inertia

l, effective span length, bending tests

l’, effective span length, one-way shear tests

ld, development length of prestressing strand

19

Mcapacity, mfg., moment capacity, manufacturer calculation

Mcapacity, moment capacity

Mcr theoretical, mfg., theoretical cracking moment, manufacturer calculation

Mcr theoretical, theoretical cracking moment

Mcr, cracking moment

MLOAD, moment due to applied load

Mmax, maximum moment

MSW, moment due to self-weight

MTotal, total moment

OPEN SEES

P, applied load

RCA, recycled concrete aggregate

Vci, flexure shear strength

Vcapacity, mfg., shear capacity, manufacturer calculation

Vcapacity, shear capacity

VLOAD, shear force due to applied load

VSW, shear force due to self-weight

VTotal, total shear force

β, deflection magnifier

Δel, elastic deflection

ΔLT, long-term deflection

Δmax, maximum deflection

20

ΔT, Total deflection

σb, available, available stress at the bottom of the section

σb, due to load, stress at the bottom of the section due to applied load

21

Chapter 2

Literature Review

2.1 Concrete mixtures with Recycled Concrete Aggregate (RCA)

Thus far, the use of RCA has been restricted primarily to its use in subbase

materials in transportation applications. The Federal Highway Administration (FHWA)

conducted a survey of each states’ use of RCA in road construction. This brief

investigation found that the primary use of RCA was as base material (FHWA, 2004). In

order to better utilize this material several studies have investigated the properties of

RCA from different sources in order to quantify the RCA properties and their impact on

the strength, stiffness, creep and shrinkage of RCA concrete mixtures (Knaack and

Kurama, 2013b; Knaack and Kurama, 2015a; Knaack and Kurama, 2015b; Knaack and

Kurama, 2015c; Knaack and Kurama, 2018; Brandes and Kurama, 2018a; Brandes and

Kurama, 2018b; Brandes and Kurama, 2018c). Studies have also probed the effects of

absorption, ARCA, and deleterious material content, DRCA, of RCA source material on the

performance of RCA concrete. (McGinnis et al., 2017a). Secondly, aside from studying

RCA properties, designers must determine the methodology for incorporating RCA in

concrete mix design. In a 2013 study by Knaack and Kurama, researchers probed three

different methods of incorporating RCA into concrete mixtures (Knaack and Kurama,

2013a). The three methods studied were the: (1) direct weight replacement (DWR), (2)

direct volume replacement (DVR) and (3) equivalent mortar replacement (EMR). Studies

show that these three methods produce similar results with regards to compressive

strength and modulus of elasticity of the samples; however, the workability of the

22

mixture is greatly affected by use of the equivalent mortar method (EMR). Therefore,

Knaack and Kurama (Knaack and Kurama, 2013a) opted to use the direct volume

replacement method. In this method, a given volume of natural concrete aggregate is

replaced by an equal volume of RCA. Per Knaack and Kurama (Knaack and Kurama,

2013a), the direct volume replacement is the most efficient method for RCA applications

because this method produces RCA mixtures that most mimic the workability of natural

aggregate concrete mixtures. Furthermore, this methodology is in line with standard mix

design practice (Knaack and Kurama, 2013a). Concluding that the most important

considerations for use of RCA are the pre-qualification of high-quality source material.

Researchers found that the two most important indicators of quality for RCA are the

water absorption of RCA, ARCA, and the deleterious material content, DRCA (Knaack and

Kurama, 2013a). This study produced and proposed a set of equations that may help to

predict the compressive strength of an RCA mixture given the properties, such as

absorption (ARCA) and deleterious content (DRCA), of an RCA source as well as the

replacement percentage of natural aggregate by RCA. These equations may also be used

to design a concrete mixture by back calculating the allowable values of deleterious

material by setting an allowable maximum strength loss or stiffness loss. Researchers

also identified as a barrier to full-use of RCA in concrete mixtures the effect on the secant

modulus of elasticity of the mixture that would then lead to larger service load deflections

rather than simply the compressive strength (Knaack and Kurama, 2013a; Knaack and

Kurama, 2011).

23

Furthermore, the inclusion of RCA into concrete has shown to decrease CO2

production while simultaneously increasing the amount of water needed to process and

clean the RCA. Therefore, the use of RCA offers a complicated tradeoff where CO2

emissions are reduced but water consumption increases (Azúa et al., 2019). In general,

studies show no distinct pattern in the variability of RCA properties with regards to the

geographical origin of RCA, processing and type or deleterious material present (Knaack

and Kurama, 2013a). Additionally, the size and gradation of aggregates was also found to

affect the properties of the RCA concrete mixes. Results show a marked increase in the

stiffness and compressive strength with a decrease in maximum aggregate size by moving

from ASTM #57 to ASTM #8 aggregates (McGinnis et al., 2017a) as well as decrease in

f’c and Ec with an increase in ARCA and DRCA (Knaack and Kurama, 2013a).

2.2 Use of RCA in reinforced concrete applications

Several authors have investigated the effect of RCA on normal strength reinforced

concrete mixtures. These studies show similar trends, in general: (i) RCA has higher

absorption and LA abrasion loss, lower stiffness (largely due to adhered mortar) and is

sometimes more angular than natural aggregate (NA) (McGinnis et al., 2017a), (ii) an

increase in RCA content is found to decrease the modulus of elasticity, compressive

strength and shear strength (Knaack and Kurama, 2015b) with the effect on modulus of

elasticity being the greatest, (Knaack and Kurama, 2015c) (iii) an increase in RCA

increases the creep and shrinkage (Knaack and Kurama, 2015a; Knaack and Kurama,

2013b), and lastly (iv) an increase in RCA increases service load deflections (Knaack and

Kurama, 2018).

24

Studies have probed the use of RCA in reinforced concrete. These studies have

investigated the creep and shrinkage of RCA mixtures (Knaack and Kurama, 2015a;

Knaack and Kurama, 2013b), short-term and long-term service load deflections (Knaack

and Kurama, 2018) and the effect of RCA on modulus of elasticity and compressive

strength (Knaack and Kurama, 2015c). Research conducted utilizing a time-dependent

numerical model on an open source software (OPEN SEEES) shows that the limiting

factor for usage of RCA is the large service-load deflections (Knaack and Kurama, 2018).

In another study by Knaack and Kurama, the largest negative effect of RCA was shown

to be the stiffness of the mixture while the least affected property was the compressive

strength (Knaack and Kurama, 2015c). The large decrease in stiffness is likely due to the

increased porosity and absorption and decreased mechanical resistance of RCA. The

investigations detailed above found several important trends in RCA use: (i) an increase

in percent of RCA replacement leads to an increase in instantaneous (Malešev et al.,

2010) and long-term deflection, (ii) increase in RCA content results in a large decrease in

modulus of elasticity, Ec, and tensile strength, f’t, but a mild decrease in compressive

strength, f’c (Knaack and Kurama, 2015b.)

Knaack and Kurama (2015b) also probed the effect of RCA on flexural and shear

strength (Knaack and Kurama, 2015b). In this study, the flexural and shear strength

dropped slightly with percent increase of RCA. However, the study also found that the

use of shear reinforcement could circumvent the decrease in shear strength. This study

concludes that the controlling parameter with regards to the tensile strength of concrete is

the quality of RCA and not the quantity (Knaack and Kurama, 2015b). Furthermore, this

25

study proposes that the factors affecting compressive strength and modulus of elasticity

are the RCA replacement ratio, water absorption, ARCA, and deleterious material content,

DRCA. Other studies on the use of RCA are mostly conducted outside the United States

and show that the flexural capacity of reinforced concrete beams is not greatly affected

using RCA even at 100% replacement of natural aggregates (Knaack and Kurama,

2015b). Some studies also indicate that the initiation of shear cracking occurs at lower

service loads in RCA mixtures; this phenomenon is thought to indicate a weaker RCA-

cement paste interlock (Etxeberria et al., 2007).

The performance of concrete mixtures made with high quality aggregates such as

those derived from precast operations also follow the trends indicate above: these

mixtures have lower modulus of elasticity with increase in RCA percent as well as

increased creep and shrinkage strains (Soares et al., 2014a; Limbachiya et al., 2000).

Furthermore, a study by McGinnis et al. concluded that the strength and stiffness

decreases in RCA concrete can be managed by the prequalification of aggregates before

their inclusion in RCA mixtures (McGinnis et al., 2017a). Additionally, this study also

proposed a set of design equations to estimate the effects of RCA on both strength and

stiffness; however, these equations were more complex than those proposed by Knaack

and Kurama (Knaack and Kurama, 2013a).

2.3 Properties of recycled concrete aggregates from precast/prestressed members

Several studies have probed the use of RCA for precast elements (Soares et al.,

2014a; Limbachiya et al., 2000; Pérez-Benedicto et al., 2012; Soares et al., 2014b;

López-Gayarre et al., 2015). Traditionally, the standards for precast elements and the

26

quality control measures at precast facilities account for a higher level of quality as

compared to other sources of RCA, such as demolition and construction waste (DCW).

Most of these studies discussed here cite the high quality and uniformity in precast

members as the reasoning for selection as a reliable RCA source.

In a study by Soares et al., the aggregates used have a substantial amount of

residual mortar attached to the recycled aggregate. This residual mortar leads to an

increase in the porosity of the aggregates (Soares et al., 2014a). In general, research

shows contradicting results regarding the effect of RCA on the compressive strength of

concrete when compared to a standard mixture. Limbachiya et al. found that RCA could

be included in concrete mixtures with up to a 30% replacement of natural aggregate

without negatively affecting the compressive strength of concrete (Limbachiya et al.,

2000). On the other hand, Soares et al. found that the compressive strength of concrete

for 10% and 20% replacement was lowered by, approximately 2.3%, however, for 30%,

40%, 50% and 100% replacement of natural aggregate by RCA the compressive strength

was higher by 6% (Soares et al., 2014a). This shows a lack of a clear relationship

between compressive strength and percent replacement. The use of a superplasticizer

(SP) was found to further increase the compressive strength of concrete. A 100% RCA

mixture with SP and without SP were compared. The mixture with SP had a higher

compressive strength. Findings show that this compressive strength increase is likely due

to a quickening of the hydrating process (Soares et al., 2014a).

27

2.3.1 Use of RCA in prestressed concrete

The efficacy of utilizing RCA within a precast concrete facility is that the

properties of the RCA are known (Brandes and Kurama, 2018a). In order to utilize RCA

in precast prestressed concrete members the bond strength between the prestressing

strands and the concrete must be investigated (Brandes and Kurama, 2018a; Brandes and

Kurama, 2016). There are two important points of concern regarding bonding between

prestressing strands and concrete: the chemical and mechanical bond and the bond

strength (Brandes and Kurama, 2016).

One important consideration of the mechanical bond between the concrete and the

prestressing strand is the development length. In a study by Brandes and Kurama, ASTM

A1081 tests were conducted to ascertain the chemical and mechanical properties of the

seven-wire prestressing strand (Brandes and Kurama, 2018a). The strength and stiffness

of the concrete mixtures used was compared. No significant differences were found

between strength and stiffness gain rate between the RCA and natural aggregate concrete

cylinders.

In a study by Brandes and Kurama, researchers utilized RCA made from crushed

discarded precast prestressed concrete members (Brandes and Kurama, 2018b). As noted,

the use of RCA material from these types of sources ensures the high quality of RCA

aggregates. The results of this study showed that using RCA increased the compressive

strength of concrete. Furthermore, the study compared the effects of traditional RCA

(obtained from construction demolition) to the effects of RCA from precast prestressed

sources on the properties of concrete. Results show that the concrete specimens with

28

RCA from demolition waste had greater shrinkage strains than the concrete specimens

manufactured with discarded precast prestressed concrete (Brandes and Kurama, 2018b).

Few studies have probed the use of RCA in prestressed concrete (Brandes and

Kurama, 2018a; Brandes and Kurama, 2016; Brandes and Kurama, 2018b; Brandes and

Kurama, 2018c; Gonzalez-Corominas et al., 2017). In one study by Brandes and Kurama,

investigators used RCA in precast prestressed members (Brandes and Kurama, 2018c).

This study utilizes RCA as replacement for natural aggregate in precast prestressed

production of up to 100% replacement. In general, the study found that the usage of RCA

yielded concrete mixtures with lower stiffness and larger creep and shrinkage strains

(Brandes and Kurama, 2018c). In this study, the use of RCA caused an increase in

compressive strength and a decrease in tensile strength and concrete stiffness. This

decrease in stiffness is often associated with the residual mortar paste attached to RCA

particles that is substantially less stiff when compared to the natural aggregate, in this

case crushed limestone (Brandes and Kurama, 2018c). In conclusion, this study saw a

minor decrease in the cracking shear force and initial stiffness which, in turn, led to larger

displacements during shear loading and failure (Brandes and Kurama, 2018c). On the

other hand, some studies indicated that the use of RCA has little to no effect on the

mechanical properties of precast concrete (Gonzalez-Corominas et al., 2017). These

contradicting research findings provide the space for further testing of RCA in precast

prestressed members.

29

Chapter 3

Test specimen description

This study probes the use of RCA in hollow core prestressed concrete slabs. The

test specimens used were manufactured at STRESCORE, Inc. located in South Bend,

Indiana. These hollow core concrete slabs were manufactured with varying amounts of

RCA. In this study, different concrete mixes are made by replacing 20%, 30%, 40% and

60% of the coarse aggregate volume with RCA. The hollow core concrete section is 6”

deep and 48” inches wide. There are eight 4” diameter hollow cores that span the entire

length of the slab; there are 5 prestressed strands that run through the ribs (between two

cores) of the slab. Figure 1 below shows a cross section of the hollow core prestressed

concrete slab and Table 1 shows the section properties.

Figure 1 Hollow core slabs

30

Table 1 Section properties, 6SC56

Section properties, 6SC56

A in.2 188

I in.4 764

ct, in. 3

cb, in. 3

dp, in. 4.75

Weight, psf 49

f'c,Target 6,500

3.1 Concrete properties: mix design

The concrete mixtures were made using air-cooled blast furnace (slag) provided

by Beemsterboer Aggregates based out of Gary, Indiana. These aggregates meet the

requirements of INDOT #9 (INDOT, 2019). The properties of slag including specific

gravity and absorption as well as particle size distribution curve are shown in Table 2,

Table 3 and Figure 2. The fine aggregates used in this research program are sand acquired

from the South Bend, Indiana Rieth-Riley plant. The properties of this fine aggregate are

shown in Table 4, Table 5 and Figure 3. The concrete mix designs utilized in this study

are shown in Table 6. Finally, Table 6 shows that all mixtures are made with 500 lbs of

cement while the standard mixture NDS is made with 525 lbs. This discrepancy is not

considered during analysis.

Table 2 Properties of slag

Properties of air-cooled blast furnace (Slag)

Bulk specific gravity Absorption

2.407 3.20%

31

Table 3 Particle size distribution, slag

Properties of air-cooled blast furnace (Slag)

Sieve

No.

Diameter,

mm

%

passing Specification, INDOT 9

1" 25 100% -

3/4" 19 100% 100

1/2" 12.5 64.0% 60-85

3/8" 9.5 41.3% 30-60

No. 4 4.75 10.3% 0-15

No. 8 2.36 5.5% 0-10

No. 200 0.075 1.7% 0-2.5

Figure 2 Particle size distribution curve, slag

Table 4 Properties of fine aggregate, sand

Properties of Sand

Bulk specific gravity Absorption

2.603 4.70%

0%

20%

40%

60%

80%

100%

0.010.1110100Per

cent

pas

ing s

ieve,

%

Particle size, mm

Particle size distribution curve, Slag

32

Table 5 Particle size distribution, sand

Sieve analysis, Sand

Sieve No. Diameter, mm % passing Specification

1/2" 12.5 100%

3/8" 9.5 100% <100

No. 4 4.75 99.6% 95-100

No. 8 2.36 87.7% 80-100

No. 16 1.18 71.1% 50-85

No. 30 0.6 51.3% 25-60

No. 50 0.3 20.2% 5-30.

No. 100 0.15 2.0% 0-10

No. 200 0.075 0.6% 0-3

Pan - 0.0

Figure 3 Particle size distribution curve, sand

0%

20%

40%

60%

80%

100%

0.010.1110100

Per

cent

pas

ing s

ieve,

%

Particle size, mm

Particle size distribution curve, sand

33

Table 6 Mix design for each of the slab specimens

Material ND Standard ND20 ND30 ND40 ND60

Sand 1637 lb 1637 lb 1637 lb 1637 lb 1637 lb

RCA - 282 lb 423 lb 565 lb 846 lb

Slag 1506 lb 1205 lb 1054 lb 904 lb 631 lb

Cement 525 lb 500 lb 500 lb 500 lb 500 lb

VC6100 (plasticizer) 11 oz 11 oz 11 oz 11 oz 11 oz

Air entrainer 10 oz 10 oz 10 oz 10 oz 10 oz

Water #1 10.0 gal 10.0 gal 10.0 gal 10.0 gal 10.0 gal

3.1.1 RCA particle size distribution

The RCA utilized in this study was obtained from STRESCORE, Inc. Two large

samples of aggregates were shipped from STRESCORE, Inc. to the University of Texas

Tyler in Tyler Texas where they were sent for analysis to East Texas Testing

Laboratories (ETTL). The particle distribution curve of this aggregate sample is shown in

Figure 4 and Table 7. The specific gravity, relative density and absorption of RCA are

shown in Table 8. The RCA used for the concrete mixture proportioning of the hollow

core slabs was not sieved to specific gradation it is assumed that the gradation of the

RCA used in the slabs is like that shown above. According to the literature the absorption

of natural aggregate is typically lower than that of RCA.

34

Figure 4 Gradation curves of RCA sample

Table 7 Particle size distribution, RCA

Sieve analysis, RCA

Sieve No. Diameter, mm % passing

3" 75 100.0%

2" 50 100.0%

1" 25 100.0%

3/4" 19 100.0%

1/2" 12.5 80.4%

3/8" 9.5 53.1%

No. 4 4.75 14.0%

No. 8 2.36 5.9%

No. 16 1.18 5.4%

No. 200 0.075 1.7%

Table 8 Properties of RCA

Properties of RCA

Average apparent specific gravity Average specific gravity, SSD Absorption

2.59 2.327 7.66%

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

0.010.1110100

Per

cent

pas

ing s

ieve,

%

Particle size, mm

Particle size distribution curve

35

3.2 Manufacturing and casting conditions

The concrete specimens tested in this study correspond to hollow core concrete

slab type 6SC56 manufactured by STRESCORE, Inc. based out of South Bend, Indiana.

The hollow core slabs were manufactured on February 8th, 2018. Temperatures during

casting remained below freezing at 4° F. The factory daily production report shows a

moisture content of 4%. The slabs were initially cast as 17-foot-long sections but were

cut down to 15-foot-long sections in order to fit them into the university structures

laboratory.

3.3 Concrete stiffness (Ec)

During manufacturing concrete cylinders were cast for each of the mixtures used.

The cylinders were broken at 28 days, 56 days and 129 days (shortly after the end of

large-scale tests). Cylinders were tested for tensile and compressive strength in

accordance with ASTM C39/C39M-18 (ASTM C39/C39M-18). The results of the

compressive strength tests are shown in, and Table 10 as well as in Figure 5. Figure 5

shows that the compressive strength of each concrete mixture does not rise uniformly

over time. This lack of uniformity in compressive strength is due to the lack of proper

consolidation of cylinder samples and the dryness of the concrete mixture. Many concrete

samples had excessive voids such as the NDS cylinders, shown in Figure 6, and,

therefore, yielded low compressive strengths. The compressive strength values shown in

Table 10 lower than 5,100 psi were excluded from any further analysis including the

calculation of the modulus of elasticity, Ec.

36

The compressive strength values were later used to calculate the elastic modulus of

concrete, Ec. The elastic modulus of concrete was calculated using 𝐸𝑐 = 57,000√𝑓′𝑐

(ACI 318). The elastic modulus of concrete calculated using ACI 318 is shown in Table

11 and Figure 7. Figure 7 presents the modulus values for all three tests. The elastic

modulus is highest for mixtures NDS, ND20 and ND30.

The compressive strength, f’c, and modulus of elasticity, Ec, was also calculated

using the numerical models presented by McGinnis et al., 2017a and Knaack and

Kurama, 2013a. A value of deleterious material content, DRCA, of only 1% was assumed

since the RCA was directly processed on site from discarded precast elements and did not

come from a demolition yard. These are shown in Table 12 and Table 13. The models

proposed by Knaack and Kurama, 2013a tend to underestimate both the compressive

strength and modulus of elasticity.

37

Table 9 Compressive strength of cylinder samples, 7-day strength

Mix 1 2 3 Avg.

NDS 5152 5968 6437 5852

ND20 5320 5573 4717 5203

ND30 5899 5912 6071 5961

ND40 5750 6248 6084 6027

ND60 4545 5572 5438 5185

Table 10 Compressive strength of cylinder samples, (psi)

Compressive strength of concrete cylinder samples (psi)

NDS ND30 ND60

Specimen # Specimen # Specimen #

1 2 3 Avg. 1 2 3 Avg. 1 2 3 Avg.

29

day 7,380 7,140 7,510 7,343 7,140 6,740 7,120 7,000 5,980 6,850 7,030 6,620

56

day 7,590 3,990 3,690 7,590 7,150 7,990 8,250 7,797 5,030 5,010 7,960 7,960

129

day - 8,551 6,964 7,758 6,868 7,416 7,034 7,106 7,393 8,009 6,570 7,324

ND20 ND40

Specimen # Specimen #

1 2 3 Avg. 1 2 3 Avg.

29

day 3,990 6,640 7,390 7,015 6,580 3,850 3,710 6,580

56

day 7,300 7,990 5,930 7,073 3,920 7,620 8,020 7,820

129

day 4,704 8,898 5,695 7,297 5,840 7,917 4,180 5,979

38

Figure 5 Average compressive strength (psi) based on Table 9

(a)

(b)

(c)

(d)

(e)

Figure 6 (a) NDS 56 day (b) ND20 56 day (c) ND30 56 day (d) ND40 56 day (e) ND60

56 day

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

NDS ND20 ND30 ND40 ND60

Co

mp

ress

ive

stre

ngth

, p

si

29 DAY 56 DAY 129 DAY

39

Table 11 Modulus of elasticity, Ec, calculated from ACI 318 code

Modulus of elasticity, Ec, (psi)

29 day 56 day 129 day

NDS 4,884,515 4,066,621 5,020,370

ND20 4,417,653 4,793,877 4,571,504

ND30 4,768,962 5,033,028 4,804,934

ND40 3,913,262 4,602,551 4,407,468

ND60 4,637,713 4,415,201 4,878,081

Figure 7 Modulus of elasticity of samples from Table 11

Table 12 Compressive strength and modulus of elasticity from numerical models

Knaack and Kurama, 2013a

Slab ARCA Aslag D Replacement

% Ec, psi f'c, psi

NDS 7.66% 3.20% 1.00% 0% 4,595,487 6,500

ND20 7.66% 3.20% 1.00% 20% 4,073,545 6,534

ND30 7.66% 3.20% 1.00% 30% 4,073,545 6,584

ND40 7.66% 3.20% 1.00% 40% 4,073,545 6,634

ND60 7.66% 3.20% 1.00% 60% 4,073,545 6,734

4,300,000

4,400,000

4,500,000

4,600,000

4,700,000

4,800,000

4,900,000

5,000,000

5,100,000

5,200,000

NDS ND20 ND30 ND40 ND60

Ec,

psi

29 day 56 day 129 day

40

Table 13 Compressive strength and modulus of elasticity from numerical models,

continued

McGinnis et al., 2017a from compressive strength tests, 129 days

Slab Target, f'c Grade Ec, psi f'c,

psi Ec, psi

NDS 6,500 12.5 4,595,487 6,500 5,020,370

ND20 6,500 12.5 4,810,428 7,006 4,868,915

ND30 6,500 12.5 4,827,615 7,073 4,804,934

ND40 6,500 12.5 4,844,802 7,139 4,727,393

ND60 6,500 12.5 4,879,176 7,272 4,878,081

3.4 Specimen geometry and casting conditions

The prestressed hollow core concrete slabs were manufactured through an

extrusion process. The prestressed tendons are first run throughout the entire length of the

casting yard and are attached to thick metal plate on the end of the bed as shown on

Figure 8. The concrete mix is batched and then introduced into the hopper at the top of

the slipformer as shown in Figure 9. The slabs are extruded onto a bed and allowed to

cure. During curing time, the slabs were covered with black plastic sheathing to keep

them moist as shown in Figure 10. The hollow core slabs were then removed from the

casting yard and loaded into a truck for delivery. A member of this research team was

present during casting to ensure quality.

Figure 8 Prestressing strands

41

Figure 9 Slipformer

Figure 10 Hollow core concrete slabs curing

3.5 Shipping

The specimens were transported from the manufacturing plant to the University of

Texas at Tyler structures laboratory on a flat-bed truck at 5 days curing age. The shipping

route is shown in Figure 11; Figure 12 shows the unloading process which followed the

manufacturers recommended lifting scheme to avoid cracking the slabs.

42

Figure 11 Shipping route

Figure 12 Unloading from flat bed truck

3.6 Curing conditions

The hollow core prestressed concrete slabs were left to harden and cure until 28

days at which point long term loading began. The slabs were left to cure for a period of

three weeks in their long-term loading configuration as described in section 4.3 (later

shown in Figure 16 and Figure 17). The temperature and humidity conditions were stable

within the laboratory; however, the two test specimens left to cure outside, specimens

NDS 1 block and NDS 2 blocks, were cured outside and exposed to the elements. These

two outside specimens are were exposed to large variations in temperature and rainfall

43

events. The rainfall data is for the period between initial arrival of the test specimens and

end of long-term loading and will be discussed further in section 5.4.

3.7 Replacement percentage

The replacement percentages of virgin aggregates with RCA investigated in this

study are shown in Table 14. Three standard mixture, NDS, specimens were tested; the

variables studied were different curing conditions and load levels for the three NDS test

specimens.

Table 14 Specimen replacement percentages of virgin aggregate with RCA

Specimen # Specimen name Replacement percentage

1 NDS 0%

2 ND20 20%

3 ND30 30%

4 ND40 40%

5 ND60 60%

6 NDS 1 Block 0%

7 NDS 2 Blocks 0%

44

Chapter 4

Long term test description

4.1 Test matrix

A total of seven slabs were tested in this study. Five of the slabs were placed

inside the structural laboratory while the remaining two slabs were cured and tested

outside. The slabs arrived on February 14th and were cured in-situ in what would be their

final position for long-term load testing. The test matrix showing the slab properties,

aging conditions and test configurations are shown in Table 15.

Table 15 Test matrix of slabs for long-term load testing

Mix Length Width Section type P, total load (lbs)

Testing

Environment

NDS 15 feet 46 in.

5 strand, six inch corefloor,

6SC56 4,134 Inside

ND20 15 feet 46 in.


6SC56 4,134 Inside

ND30 15 feet 46 in.


6SC56 4,134 Inside

ND40 15 feet 46 in.


6SC56 4,134 Inside

ND60 15 feet 46 in


6SC56 4,134 Inside

NDS 1 block 15 feet 46 in.


6SC56 3,992 Outside

NDS 2

blocks 15 feet 46 in.


6SC56 8,226 Outside

45

4.2 Slab loading and diagram pictures

The slabs were loaded utilizing concrete blocks measuring 46” wide and 23.5” tall

that were manufactured in the university structures laboratory. The blocks were weighted

with a Brecknell electronic crane scale with a 6,000 lb capacity with a ± 0.1% of full

scale capacity accuracy shown in Figure 13. The blocks weighed approximately ± 4000

lbs each and were placed on top of the concrete slabs and supported by two square hollow

tubes measuring ¾” x ¾” and 1/8” thick. These tubes were placed 12” to the left and right

of the center line of the slab.

Figure 13 Brecknell electronic crane scale

4.3 Slab layout in laboratory

The concrete slabs were transported into the structures laboratory and placed in

their testing position on two 3 ½” x 3 ½”x ½” angle steel sections placed at 6” from the

edge of the slab. The long-term laboratory testing included five slabs that were placed

inside the structures laboratory and two slabs placed outside. Of the three standard

concrete mixture slabs two were placed outside, one with a single load block (NDS 1

block) and one with two load blocks (NDS 2 blocks). The last standard mixture slab

46

(NDS) was placed inside the laboratory. In this study, both the curing conditions and the

long-term loading were variables studied. The indoor slabs maintained a constant load of

4134 lbs while the outside slabs were one singly loaded slab and a doubly loaded slab

with 3992 lbs and 8226 lbs loads, respectively. Here buckets of dried aggregates were

used to increase the weight of the concrete blocks to match that of the heaviest block

thereby creating similar loading conditions across all tests. The laboratory slab layout is

shown in Figure 14 - Figure 16. The outside slab layout is shown in Figure 17. In

addition, the slab loading diagram is shown in Figure 18.

Figure 14 Slab layout in laboratory

47

Figure 15. Slab layout in laboratory

Figure 16 Laboratory slab layout

48

Figure 17 Slab layout outside

Figure 18 Slab loading diagram

4.4 Loading procedure

The slabs were loaded by lifting the load blocks from the staging area in the

laboratory utilizing the double girder overhead crane. The blocks were placed on two ¾”

steel square tubes that served as shims and spanned the full width of the slabs to provide

a uniform loading condition.

49

4.5 Instrumentation

The slabs were tested utilizing two string potentiometers placed at midspan at

each side of the span with the wire attached to a 3/16” diameter steel rod. The steel rod

was glued to the top of the slabs utilizing a JB Weld epoxy. Figure 18 shows a diagram of

the slab instrumentation and set-up and Figure 19 shows pictures of the instrumentation

set-up. Additionally, a dial gauge was attached to one side each slab. The dial gauges

used are shown in Figure 20. These dial gauges were utilized as backup for long-term

deflection measurements. Further discussion on the use of these dial gauges is provided

in Chapter 6.

50

Figure 19 Instrumentation for long-term loading

51

Figure 20 Dial gauge used for verification of long-term service loading from string

potentiometers

52

Chapter 5

Deformations under instant and long-term constant loading

5.1 Deflection data

Long-term deflection of slabs is discussed in this chapter as well as discussions on

instant (elastic) deflection, inelastic deflection and long-term deflection. Long-term

deflection was monitored by two string potentiometers on either side of the concrete slab.

Each string potentiomenter was attached to a steel rod glued at the midspan as shown in

Figure 18 and Figure 19 of chapter 4. In addition, a dial gauge was attached to one side of

the slab at 6” from the center to verify the string potentiometer measurement. Each day a

picture was taken of each dial gauge to track deflection. During this experimental

program, no considerations were made for the camber of the precast prestressed hollow

core concrete slabs.

5.1.1 Long-term deflection

The slabs were monitored for long-term loading utilizing the setup described in

chapter 4 for a period of 13 weeks from March 8th to June 9th, 2018. The following

graphs in Figure 21 - Figure 27 show the long-term deflection over time for each slab.

Each slab was instrumented with two string potentiometers (one on each side) and one

dial gauge. The asterisks in the deflection plots indicate the string potentiometer and dial

gauge placed on the same side of the hollow core concrete slab. The three measurements

(taken from the two potentiometers and the one dial gauge) are averaged as follows: the

dial gauge deflection value is averaged with one potentiometer (located on the same side)

then this value is taken and averaged with the remaining potentiometer. For example, for

53

test specimen NDS the deflection values from CH16 were averaged with the dial gauge

deflection value. Then, the average of CH16 and the dial gauge deflection value is

averaged with the second potentiometer in CH7.

The individual deflection curves for each slab are shown in Figure 21 - Figure 27.

Additionally, Figure 28 shows the deflection averages for the inside slabs, Figure 29

shows the deflection averages for the outside slabs and Figure 30 shows the deflection

averages for all slabs. These figures have curves from the two string potentiometers, dial

gauge and a fourth curve showing an average of the three instruments. The four different

curves in each graph tend to follow the same curvature in each individual test. The total

deflection for each slab is shown in Table 16. The use of RCA was seen to increase the

total deflection up to 40% replacement of natural aggregate by RCA. On average, the

total deflection of the inside slabs was approximately 203 thousandths of an inch except

for slab ND40 which had a total deflection of approximately 228 thousandths of an inch

(12.39% higher than the total deflection average of the inside slabs.). Slab NDS 1 block

had a total deflection of 285 thousandths of an inch, 40.30% higher than the average of

the inside slabs. This higher total deflection might be due to manufacturing

imperfections, namely the uneven surface of the specimen. Slab NDS 2 blocks deflected

a total of 768 thousandths of an inch. This specimen had double the load of the other test

specimens, and, therefore, larger total deflection values were expected. In conclusion, the

general trend shows that the deflection of the inside slabs increases with increasing RCA

content except for ND60. Some irregularities present in the curves specifically the

54

outside specimens NDS 1 block shown in Figure 26 and NDS 2 blocks shown in Figure

27 are due to weather conditions. This will be discussed in section 5.3.

55

Table 16 Total deflection, ΔT

Total deflection, ΔT (x 10-3 inch)

Slab ΔT

NDS 187

ND20 192

ND30 206

ND40 228

ND60 202

NDS 1 block 285

NDS 2 blocks 768

Figure 21 NDS long-term deflection

0

50

100

150

200

250

28 38 48 58 68 78 88 98 108 118 128

Def

lect

ion,

(x 1

0-3

inch

)

Age of specimen (days)

CH 13 CH 16* Dial gauge* NDS avg.

56

Figure 22 ND20 long-term deflection

0

50

100

150

200

250

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n,

, (x

10

-3in

ch)


CH 1* CH 4 Dial gauge* ND20 avg.

57


0

50

100

150

200

250

300

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n,

, (x

10

-3in

ch)


CH 1 CH 4* Dial gauge* ND30 avg.

58


0

50

100

150

200

250

300

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n,

, (x

10

-3in

ch)



59


0

50

100

150

200

250

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n,

(x 1

0-3

inch

)



60

Figure 26 NDS 1 block long-term deflection

0

50

100

150

200

250

300

350

400

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n,

(x 1

0-3

inch

)


CH 13* CH 16 Dial gauge* NDS 1 block avg.

61

Figure 27 NDS 2 blocks long-term deflection

0

100

200

300

400

500

600

700

800

900

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n,

(x 1

0-3

inch

)


CH 7 CH 10* Dial gauge* NDS 2 blocks avg.

62

Figure 28 Long-term deflection, inside slabs

0

50

100

150

200

250

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n (

x 1

0-3

inch

)


NDS avg. ND20 avg. ND30 avg. ND40 avg. ND60 avg.

63

Figure 29 Long-term deflection, outside slabs

0

100

200

300

400

500

600

700

800

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n (

x 1

0-3

inch

)


NDS 1 block avg. NDS 2 blocks avg.

64

Figure 30 Long-term deflection, all slabs

5.1.2 Deflection magnifier

The deflection magnifier was calculated for each slab by diving the deflection of

each slab by the deflection of NDS (e.g. ND20/NDS). These values are shown in Table

17 and Figure 31 -Figure 37. This value shows how quickly the deflection of each slab

progresses as compared to the progression of downward deflection of the control sample

NDS (inside slab). The deflection magnifier values in Table 17 show that at first the

progression of the slab deflection for ND20 and ND60 is slower than NDS (inside slab).

Additionally, the progression of deflection for NDS 2 blocks is more than three times as

0

100

200

300

400

500

600

700

800

28 38 48 58 68 78 88 98 108 118 128D

efle

ctio

n (

x 1

0-3

inch

)


NDS avg. ND20 avg. ND30 avg. ND40 avg.

ND60 avg. NDS 1 block avg. NDS 2 blocks avg.

65

fast as NDS, and, towards the end of the long -term service load testing the deflection of

NDS 2 blocks proceeds nearly three times as fast as NDS.

Table 17 Deflection magnifier

Deflection magnifier, β

ND20 ND30 ND40 ND60 NDS 1 block NDS 2 blocks

7 days 0.945 1.040 1.168 0.991 1.192 3.476

1 month 0.991 1.063 1.192 1.048 1.144 3.456

2 months 1.017 1.085 1.212 1.068 1.242 3.642

3 months 1.030 1.096 1.222 1.075 1.432 3.985

Figure 31 ND20 deflection magnifier

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

28 48 68 88 108 128

Def

lect

ion m

agn

ifie

r


NDS/NDS ND20/NDS

66



0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

28 48 68 88 108 128

Def

lect

ion m

agn

ifie

r


NDS/NDS ND30/NDS

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

28 48 68 88 108 128

Def

lect

ion m

agn

ifie

r


NDS/NDS ND40/NDS

67


Figure 35 NDS 1 block deflection magnifier

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

28 48 68 88 108 128

Def

lect

ion m

agn

ifie

r


NDS/NDS ND60/NDS

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

28 48 68 88 108 128

Def

lect

ion m

agn

ifie

r


NDS/NDS NDS 1 block/NDS

68

Figure 36 NDS 2 blocks deflection magnifier

Figure 37 Single load slabs, deflection magnifier

0.8

1.2

1.6

2

2.4

2.8

3.2

3.6

4

28 48 68 88 108 128

Def

lect

ion m

agn

ifie

r


NDS/NDS NDS 2 block/NDS

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

28 48 68 88 108 128

Def

lect

ion m

agn

ifie

r


ND20/NDS ND30/NDS ND40/NDS

ND60/NDS NDS 1 block/NDS

69

5.1.3 Instant (Elastic) deflection.

The instant deflection was also recorded for each slab. The instant deflection at

application of load was calculated by graphing the deflection vs. time curve from the

beginning of the loading period and taking an average value from the first hour after the

application of load. These values were compared to the theoretical instant (elastic)

deflection values calculated using the effective moment of inertia, Ie based on ACI 318-

14 section 24.2.3.5. The values for instant deformation are shown in Table 18. The

effective moment of inertia, Ie, was calculated using the compressive strength of concrete

at the time of application of load, 28 days curing age. The compressive strength values

used for slabs NDS, NDS 1 block and NDS 2 blocks were from the same concrete

cylinder specimens given that the three concrete slabs were made from the same mix,

NDS.

The measured elastic deflections increased with an increase in RCA content. The

elastic deflection increased from NDS to ND30 and ND40; however, the performance of

ND60 is like that of NDS. Elastic deflections then increase for NDS 1 block and NDS 2

blocks. The measured elastic deflection of all test specimens with one block was on

average 122 thousandths of an inch. The average elastic deflection for slabs with RCA is

118 thousandths of an inch which is 2.6% higher than the elastic deflection of NDS (115

thousandths of an inch). The higher elastic deformation of slab ND40 and slab NDS 1

block is likely due to imperfections in the test specimen (NDS 1 block had an uneven

surface). Slab NDS 2 blocks had a measured elastic deflection that was twice as large as

the average measured elastic deflection of the slabs with one block due to doubling of the

70

load. The theoretical values for elastic deflection calculated from ACI 318-14 are quite

close to the measured values. The theoretical elastic deflection value for NDS 2 blocks is

higher than the measured value; this is due to the higher applied load.

Table 18 Instant (elastic) deformation

Instant (elastic deformation), Δel, (x 10-3 inch)

Slab String

potentiometers Dial gauge Average ACI 318-14 24.2.3.5 Difference

NDS 122 115 101 115 106 8.03%

ND20 124 101 100 107 109 -2.17%

ND30 104 160 104 118 109 7.52%

ND40 155 128 135 137 112 17.99%

ND60 111 111 109 110 112 -1.60%

NDS 1 block 206 133 119 148 106 28.25%

NDS 2 blocks 348 453 300 362 133 63.29%

71

5.1.4 Inelastic deflection

The test specimens were unloaded at the end of the long-term loading period. The

inelastic deflection was noted and recorded for each slab. Table 19 shows the inelastic

deflection for each test specimen. The inelastic deflection value was calculated using the

same procedure as that for the long-term deflection graphs. The dial gauge deflection

value was averaged with the deflection value of the potentiometer on the same side.

Then, this value was averaged with the remaining string potentiometer.

RCA was seen to seen to increase inelastic deflection up to ND40; then the

inelastic deflection decreased from ND40 to ND60. ND60 has a similar performance than

ND40. Table 19 shows that most slabs had approximately 100 thousandths of an inch of

inelastic deflection while specimen NDS 2 blocks, which had twice as much static load as

the rest of the specimens, had more than twice as much inelastic deflection, 337

thousandths of an inch. The inelastic deflection increases with an increase in RCA

content for up to 40% replacement of natural aggregate by RCA. Slabs with RCA have,

on average, had an inelastic deflection of 105 thousandths of an inch an increase of

20.7% from the inelastic deflection of NDS.

72

Table 19 Inelastic deflection

Inelastic deflection, ΔInelastic, (x 10-3 inch)

Slab String

potentiometers Dial gauge Average

NDS 96 88 69 87

ND20 123 78 99 95

ND30 92 165 82 108

ND40 137 109 120 119

ND60 99 99 93 98

NDS 1 block 165 40 156 100

NDS 2 blocks 372 230 375 337

5.2 Long-term deflections

Long-term deflection was calculated by subtracting the elastic deflection

measured averages from the total deflection presented in Table 16. Increase in RCA

content increased the long-term deflections. Furthermore, no change in long-term

deflection was seen in the performance from ND40 to ND60. The relationship between

elastic, long-term and total deflection is: ΔLT = ΔT- Δel. Long-term deflection is shown

below in Table 20. The long-term and total deflection increases with increase in RCA

content up to 40%. The average long-term deflection for slabs with RCA is 89.5

thousandths of an inch which is 24.3% higher than that of NDS; the average total

deflection of RCA slabs is 207 thousandths of an inch which is 10.7% higher than that of

NDS.

73

Table 20 Total, elastic and long-term deflection

Total, elastic and long-term deflection, (x 10-3 inch)

Slab Total deflection, ΔT Δel ΔLT

NDS 187 115 72

ND20 192 107 86

ND30 206 118 88

ND40 228 137 92

ND60 202 110 92

NDS 1 block 285 148 137

NDS 2 blocks 768 362 406

5.3 Service load stress

The available stress, stress due to service loads and ratio between stress due to

applied load and available stress (stress at cracking of section) are in Table 21. Table 21

shows that the stress due to service loads is approximately two thirds of the available

stress for all slabs except for NDS 2 blocks. NDS 2 blocks has an applied stress/available

stress ratio of 108.34%. This percentage indicates the cracking capacity of the NDS 2

blocks section was exceeded by 8.34% during service loads.

The bottom stress (due to applied loads and self-weight) is calculated as the stress

created by the self-weight moment and applied service load moment while the available

stress is the summation of the stress due to prestressing including all loses and the stress

available from the modulus of rupture of the section calculated as 7.5√𝑓′𝑐.

74

Table 21 Service load stress vs. available stress (psi)

Slab σb, due to load, psi σb, available, psi σb, due to load/σb, available, psi

NDS 926 1,389 66.68%

ND20 926 1,374 67.39%

ND30 926 1,374 67.42%

ND40 926 1,354 68.37%

ND60 926 1,356 68.28%

NDS 1 block 926 1,389 66.68%

NDS 2 blocks 1,505 1,389 108.34%

5.4 Weather conditions

Careful observation showed that the rainfall greatly affected the flexural response

of the concrete slabs. Figure 38 shows rainfall data for the Tyler Texas region during this

testing. Figure 39-Figure 40 show the temperature and humidity data for the outside and

inside slabs. The data for the inside slabs was obtained by means of a temperature and

humidity monitor. The data for the exterior slabs was obtained from the national weather

service database (Tyler Texas Weather Station) and shows rainfall data collected at the

Tyler Pounds Airport rain gauge station. This rainfall data proved to be useful in the

interpretation of the daily deflection readings. The rainfall created an interesting pattern

in the service load deflections of the outside slabs, as shown in Figure 29. On days with

large rainfall, the dial gauge readings were seen to ‘dial back’ an average of 3 to 5

thousandths of an inch (3/1000” – 5/1000”). This ‘dialing back’ corresponded to a

negative deflection upwards due to the increased moisture of the top of the concrete slabs

that led to the expansion of the top surface and thus bending of the slabs that resulted in

upward deflection at midspan.

75

Figure 38 Rainfall data during long-term deflection testing

28-Mar, 2.62

13-Apr, 0.81

21-Apr, 2.22

22-Apr, 0.334-May, 0.6

0

0.5

1

1.5

2

2.5

3

Rai

mfa

ll,

(inch

es)

Date

76

Figure 39 Temperature and humidity data, outside slabs

0

10

20

30

40

50

60

21-Mar 31-Mar 10-Apr 20-Apr 30-Apr 10-May 20-May 30-May 9-Jun 19-Jun

Deg

rees

(°C

)

High temperature (°C) Low temperature (°C)

0

20

40

60

80

100

120


Hum

idit

y (

% R

H)

High humidity (% RH) Low humidity (% RH)

77

Figure 40 Temperature and humidity data, inside slabs

0

5

10

15

20

25

30


Deg

rees

(°C

)

High temperature (°C) Low temperature (°C)

0

10

20

30

40

50

60

70

80

90


Hum

idit

y (

% R

H)

High humidity (% RH) Low humidity (% RH)

78

5.5 Conclusions

In conclusion, the prestressed precast hollow core concrete slabs had an increase

in elastic deflection (by 2.6%), long-term deflection (by 24.3%), inelastic deflection (by

20.7%) and total deflection (by 10.7%) when RCA was used. No trends with increasing

RCA content were noted. For elastic, inelastic and total deflection typically the 40%

RCA slab had the largest deflections and the 60% RCA slab had behavior similar to the

standard slab, NDS. Long-term deflections increased slightly with increasing RCA

replacement. Slab NDS 1 block had larger total and elastic deflection when compared to

the other five slabs loaded with a single block. This trend is likely due to the poor quality

of the specimen (uneven surface). These results show that the replacement of natural

aggregate by RCA is feasible up to 60%. The superior performance of slab ND60 versus

slab ND40 should be investigated further. The elastic deflections calculated using ACI

318-14 were comparable to the measured deflections.

The total deflection of NDS 2 block slab was substantially larger than the total

deflection of the specimens with one load block; this result was expected given the larger

service load applied. Overall, the slab with the highest replacement of RCA, ND60,

showed a comparable performance to that of the NDS slab. Lastly, the deflection

magnifiers reported here show that in general an increase in RCA content quickens the

progression of downward deflection (larger deflection magnifier values).

79

Chapter 6

Bending test description

In this study the flexural strength, one-way shear and punching shear strength of

several hollow core slabs with varying percentages of natural aggregate replaced by RCA

were studied. This chapter describes the flexural bending strength test set-up.

6.1 Test set up

The test specimens were moved into place utilizing the overhead crane and web

slings. The slabs were lifted into the air, turned 90° and positioned between the two steel

wide flange columns. The slab was placed on two W10x54 sections with the web of the

wide flange placed at 6” from the slab end. Figure 41 shows an example of the bending

test set-up for the NDS slab test and Figure 42 shows a diagram of the test set up. All

slabs were tested in bending utilizing a uniform test set up. The location of the two wide

flange supports and the position of the wide flange point loads were constant from one

slab to the next.

80

Figure 41. Bending test set up, ND S

Figure 42. Bending test set up diagram

81

6.2 Equipment

The steel frame in the structures laboratory was utilized for loading. Once the slab

was in place the centerline of the slab was aligned with the center of the load frame, the

steel wide flange sections, hydraulic pump, load cell and plates were set in place as

shown in Figure 43. The slabs were loaded utilizing a RCH603 Enerpac hollow plunger

hydraulic cylinder with a 3” stroke and a 60 ton capacity Enerpac model number

ZU4420MB electric hydraulic pump. The hydraulic pump and its attached pressure

gauges are shown in Figure 44.

Figure 43 Bending test set-up

82

Figure 44. Enerpac hydraulic pump and pressure gauges

6.3 Load procedure

Utilizing the hydraulic pump valve and gauge, the pressure was advanced a

quarter turn at a time extending the hollow cylinder upwards. The hollow cylinder

pressed against the plate, load cell and load frame creating an equal and opposite reaction

that slowly displaced the slab downwards. The hollow cylinder was advanced while

tracking the load and the deflection of the slab at midspan. If the ram had reached stroke

prior to slab failure the slab was unloaded and additional plates were positioned between

the ram and the load frame by space left by the permanent deformation. The test was then

restarted until the slab failed.

6.4 Instrumentation

The string potentiomenters utilized for the long-term loading of the slabs were

also utilized for the large-scale tests. Three steel galvanized angle clips were placed on

both sides of the slab with a 3/16” diameter screws protruding outwards. The clips were

83

located at midspan and quarterspans (45”, 90” and 135”) on both sides of the slab. Then

utilizing the metal loops on the string potentiometer wire, the instruments were attached

to the galvanized steel angles. The clips located at the center of the slab, 90”, were

monitored while loading. The string potentiometers were wired and connected to an

instrunet data acquisition system utilizing a GW Instruments, Inc. Model 100

Analog/Digital Input/Output system with 22 channels, as shown in Figure 45 and Figure

46. The string potentiometers were connected as show in Figure 47 in Channels 1 through

16. The load cell, shown in Figure 48 was also connected to the instrunet data acquisition

system in Channel 22. The slab orientation and instrumentation are shown in Figure 49.

The values were recorded as the hydraulic pressure from the pump was increased. These

values were then plotted against the load applied to track the deflection of the slabs. The

load cell utilized in this study was an Omegadyne LC8400-213-200k with a capacity of

200,000 lbs. The load cell was calibrated before the long-term testing, as shown in Figure

50. The calibration curve was utilized in the analysis of the test data.

Figure 45 Data acquisition system

84

Figure 46 Model 100, data acquisition hardware

Figure 47 String potentiometer

Figure 48 Load cell, model Omegadyne LC8400-213-200k

85

Figure 49 Slab and instrumentation set up

Figure 50 Load cell calibration curve

y = 0.9819x + 1903.4

R² = 0.9999

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000

Load

mea

sure

d (

lbs)

Applied load (lbs)

86

Chapter 7

Bending test results

The hollow core concrete slabs were tested for flexural bending strength, one-way

shear and punching (two-way) shear. This chapter presents the results of the flexural

bending tests.

7.1 Moment capacity

The moment capacity, Mcapacity, was calculated and compared to the moment

demand. The moment capacity was calculated using the strain compatibility method and

the following assumptions and values: (i) the compressive strength, f’c, values used were

the measured strength from 129 days curing strength, (ii) the effective prestress loses

were calculated using the lump-sum method of time dependent losses, here the effective

prestress after all loses is fpe = 144,000 psi, (iii) the theoretical cracking moment is

calculated as the summation of the moment necessary to reach the modulus of rupture of

concrete plus the moment necessary to reach the total stress at the bottom of the section

due to prestress (including all loses) and stress due to bending. Additionally, the

manufacturer’s moment capacity is included and compared to the calculated moment

capacity. Furthermore, it is important to note that the manufacturers calculations are

based on the following conditions: (i) the target compressive strength, f'c,Target = 6,500 psi

is used and (ii) the prestress losses are calculated using the methods stipulated in section

2.2.3 of the PCI Manual for the design of Hollow Core Slabs and walls.

87

7.2 Development length

The development length was calculated for each slab in accordance with ACI

318-14 section 25.4.8.1, and is shown in Table 22, in order to avoid strand slip. The

development length is calculated as a function of fps (the stress in the prestressing strand

at nominal flexural strength). Here fps is calculated using the strain compatibility method.

Here, the development length of the prestressing strand for each slab is approximately 59

inches compared to the available length of 78 inches. This calculation shows that strand

slip did not occur during bending tests.

88

Table 22 Development length (ld)

Slab fps, psi ld, in.

NDS 254,689 59.51

ND20 254,174 59.32

ND30 253,913 59.22

ND40 253,631 59.11

ND60 254,200 59.32

NDS 1 block 254,685 59.51

NDS 2 blocks 254,685 59.51

7.3 Cracking load, maximum load to failure and code capacity

The flexural bending tests were carried out on the entire slab length directly after

long-term loading. The slabs were unloaded from their long-term loading configurations

the day before, and therefore, recovered elastic deflection before the large-scale tests. The

bending set-up indicated in chapter 6 creates a four-point bending where the moment is

constant between the two-point loads. The maximum flexural bending load at failure is

shown in Figure 53. The load versus midspan deflection curves are in Figure 55 - Figure

61 and the load versus midspan deflection curves showing the loading and reloading of

the slabs are in Figure 62 -Figure 69. The tests were terminated when the failure load was

reached. No attempt was made to deform any of the slabs on their yield plateau the same

for every slab.

The cracking load for each slab was determined by taking the coordinates of the

last point on the straight-line portion of the load vs. midspan displacement. Figure 52

shows an example for ND20 where the cracking load was 8,930 lbs and the cracking

deflection was 0.1495 inches. The cracking moment is calculated from the cracking load

and compared to the theoretical cracking moment, Mcr theoretical. The theoretical cracking

89

moment was calculated using the total stress at the bottom of the section due to

prestressing and prestress losses. Table 23 shows the initial cracking load is highest for

NDS and thereafter decreases with an increase in RCA. ND20 and ND30 have a similar

initial cracking load with the initial cracking load of ND30 being approximately 0.71%

higher than ND20. ND40 and ND60 show a uniform decrease in initial cracking load.

Furthermore, the cracking load for slabs NDS 1 block is significantly lower than that of

the other slabs. This lower cracking load is likely due to the irregular and unfinished

surface of the NDS 1 block slab. The initial cracking load for NDS 2 blocks is

substantially lower than that of the other slabs. The lower initial cracking load could be

due to the cracks that were present at the time of load to failure due to the service loads

applied to the section.

The images in Figure 70 -Figure 76 show the flexural bending test set-up as well

as pictures of the cracked sections. The maximum load to failure, moment due to applied

load, MLOAD, and moment due to self-weight, MSW, for each slab is shown in Table 24.The

moment due to applied load is calculated using the moment arm length from a quarter

way from the right edge of the left-most support to the application of the point load, P as

shown in Figure 54.. The moment due to self-weight is calculated using the effective

length as seen in Figure 54. The summation of the moment due to self-weight and the

moment due to applied load is the total moment, MTotal. This total moment is compared to

the moment capacity, Mcapacity. The ratio of moment demand to moment capacity is also

reported in Table 24. All slabs exceeded code capacity except for NDS 1 block; this is

likely due to the uneven surface of the slab as indicated in Figure 51. RCA was seen to

90

improve the moment capacity of the hollow core concrete slabs; ND20, ND30 and ND40

had a higher moment capacity than the standard slab by 10.2%, 5.5% and 7.7%,

respectively. NDS 2 blocks also had a higher moment capacity than the standard slab. On

the other hand, ND60 performed equally as well as the standard slab, NDS. The average

MTotal /Mcapacity ratio for RCA slabs, as shown in Table 24, is 1.20 which is approximately

5.85% higher than that of NDS. The total moment was also compared to the moment

capacity as calculated by the manufacturer, Mcapacity, mfg. The Mcapacity, mfg. is about 1.96%

higher than that the code moment capacity of NDS, as shown in Table 24.

The shear capacity was also compared to the shear demand for these bending

tests. The total shear demand, VTotal, was calculated as the summation if the shear due to

applied load, VLOAD, and shear due to self-weight, VSW. The total shear demand versus

shear capacity is shown Table 25. The VTotal/ Vcapacity ratios for all slabs were well below

1.0 indicating that the test specimens all failed by the intended mode, bending. The

results of the bending tests are within the variability of the materials and methods used in

this study.

The moment capacity calculations by the manufacturer are shown in Table 24.

The moment capacity values calculated by the research team are at most 2.8% lower than

those of the manufacturers.

91

Figure 51 NDS 1 block, uneven surface

Table 23 First cracking load

First cracking, bending

Slab P, Load, lbs Mcr, kip∙ft. Mcr theoretical, kip∙ft. Ratio Mcr theoretical, mfg.,

kip∙ft.

NDS 9,083 27.25 29.85 0.91 30.04

ND20 8,930 26.79 29.43 0.91 30.04

ND30 8,993 26.98 29.25 0.92 30.04

ND40 8,228 24.68 29.03 0.85 30.04

ND60 7,998 24.00 29.46 0.81 30.04

NDS 1 block 5,332 16.00 29.85 0.54 30.04

NDS 2 blocks 6,952 20.86 29.85 0.70 30.04

Figure 52 Applied load vs. midspan displacement up to cracking for ND20

0

2,000

4,000

6,000

8,000

10,000

-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0

Lo

ad (

lbs)

Midspan displacement (in)Channel 13 Channel 4 Average

92

Figure 53 Failure loads of flexural bending test specimens

Table 24 Maximum load to failure and code capacity

Slab

P,

Load,

lbs

a,

inch

l,

inch

MLOAD

kip∙ft.

MSW

kip∙ft.

MTotal,

kip∙ft.

Mcapacity,

kip∙ft.

Ratio MTotal/

Mcapacity

Mcapacity, mfg.

kip∙ft.

NDS 14,351 70.50 165 42.16 4.63 46.79 41.30 1.13 42.11

ND20 15,895 70.50 165 46.69 4.63 51.32 41.13 1.25 42.11

ND30 15,116 70.50 165 44.40 4.63 49.04 41.04 1.19 42.11

ND40 15,435 70.50 165 45.34 4.63 49.97 40.94 1.22 42.11

ND60 14,287 70.50 165 41.97 4.63 46.60 41.14 1.13 42.11

NDS 1

block 11,940 70.50 165 35.07 4.63 39.71 41.30 0.96 42.11

NDS 2

blocks 15,346 70.50 165 45.08 4.63 49.71 41.30 1.20 42.11

Table 25Maximum load to failure and shear demand vs. shear capacity

Slab P, Load, lbs VTotal, kips Vcapacity, kips Ratio VTotal/ Vcapacity

NDS 14,351 8.52 19.72 0.43

ND20 15,895 9.30 20.84 0.45

ND30 15,116 8.91 20.68 0.43

ND40 15,435 9.07 20.49 0.44

ND60 14,287 8.49 19.17 0.44

NDS 1 block 11,940 7.32 21.22 0.34

NDS 2 blocks 15,346 9.02 21.22 0.43

14,351

15,89515,116 15,435

14,287

11,940

15,346

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

ND S ND 20 ND 30 ND 40 ND 60 ND S 1

Block

outside

ND S 2

Block

outside

Fai

lure

load

(lb

s)

Slab

93

Figure 54 Loading diagrams for bending tests

Figure 55 Load vs. midspan displacement of NDS slab up to cracking load

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0

Lo

ad (

lbs)


94

Figure 56 Load vs. midspan displacement of ND20 slab up to cracking load


0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

-0.3 -0.2 -0.1 0

Lo

ad (

lbs)

Midspan displacement (in)

Channel 13 Channel 4 Average

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

-0.7 -0.5 -0.3 -0.1

Lo

ad (

lbs)



95



0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0

Lo

ad (

lbs)


0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

-0.2 -0.15 -0.1 -0.05 0

Load

(lb

s)



96

Figure 60 Load vs. midspan displacement of NDS 1 block slab up to cracking load

Figure 61 Load vs. midspan displacement of NDS 2 blocks slab up to cracking load

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

-1.5 -1 -0.5 0

Lo

ad (

lbs)


0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

-0.3 -0.2 -0.1 0

Lo

ad (

lbs)


97

Figure 62 Loading and re-loading load-displacement curve of NDS during loading test


0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

-3 -2.5 -2 -1.5 -1 -0.5 0

Lo

ad (

lbs)


0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

-3 -2.5 -2 -1.5 -1 -0.5 0

Lo

ad (

lbs)



98



0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

-3 -2.5 -2 -1.5 -1 -0.5 0

Lo

ad (

lbs)


0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

-3 -2.5 -2 -1.5 -1 -0.5 0

Lo

ad (

lbs)


99



loading test

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

-2 -1.5 -1 -0.5 0

Load

(lb

s)

Midspan displacement (in)Channel 13 Channel 4 Series3

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

-3.5 -2.5 -1.5 -0.5

Lo

ad (

lbs)


100


loading test

Figure 69 Load vs. midspan displacement averages for all slabs

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

-3 -2.5 -2 -1.5 -1 -0.5 0

Lo

ad (

lbs)


0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

-0.2 -0.15 -0.1 -0.05 0

Lo

ad (

lbs)

Displacement (in)

NDS ND20 ND30 ND40 ND60 NDS 1 block NDS 2 blocks

101

7.4 Cracking deflection

The load vs. midspan deflection curves up to the cracking load are shown in

Figure 55 - Figure 61. The cracking deflection due to the cracking load is shown in Table

26. The load vs. midspan deflection curve for slab NDS 2 blocks shown in Figure 61 does

not have a distinct straight line load vs. displacement portion as the other slab load vs.

midspan displacement curves in Figure 55 - Figure 60. The NDS 2 blocks slab was

cracked due to service loads as the weight of the two blocks created bottom stress that

exceeded the available stress from the effective prestress of the tendons.

Table 26 Cracking deflection

Slab Cracking

load, lbs Cracking deflection (in.)

NDS 9,083 0.1705

ND20 8,930 0.1495

ND30 8,993 0.1560

ND40 8,228 0.1545

ND60 7,998 0.1482

NDS 1 block 5,332 0.0895

NDS 2 blocks 6,952 0.2030

All slabs were loaded to failure. Figure 62 - Figure 68 show the load vs. midspan

displacement curves. These curves show the loading and re-loading of slabs to failure.

These figures are accompanied by pictures of the cracked sections in Figure 70 -Figure

76.

7.5 Modulus of elasticity from load vs. midspan displacement curves

The modulus of elasticity, Ec, was also calculated from the straight-line portion of

the load versus midspan displacement curves shown in Figure 55 - Figure 61. Modulus of

102

elasticity is back calculated by taking the load and deflection from each point of the

straight-line portion of the load versus displacement plots and using the elastic deflection

for maximum displacement 𝛥𝑚𝑎𝑥 = 𝑃𝑎

24𝐸𝐼∙ (3𝑙2 − 4𝑎2). The equation represents the

maximum displacement based on the loading setup. These values were compared to the

Ec values calculated from the compressive strength cylinders in section 3.3. Table 27

shows a comparison between the Ec value from load vs. midspan displacement and Ec

calculated from the ACI empirical equation which is based on the compressive strength

of the cylinders. The table shows the Ec values calculated from the load vs. midspan

displacement tests are on average 33% higher than those calculated from the compressive

strength tests.

Table 27 Modulus of elasticity, Ec, from load vs. midspan displacement curves

Ec modulus of elasticity (psi)

Slab from load vs. midspan displacement curves 57,000√𝑓′𝑐 % error

NDS 7,577,383 5,020,370 33.75%

ND20 7,581,630 4,868,915 35.78%

ND30 7,551,334 4,804,934 36.37%

ND40 6,821,636 4,727,393 30.70%

ND60 6,952,796 4,878,081 29.84%

NDS 1 block 7,606,445 5,020,370 34.00%

NDS 2 blocks 7,275,630 5,020,370 31.00%

7.6 Quarter-point deflection plots

The deflection curves for all six string potentiometers used during load to failure

testing (including those at midspan) were plotted and are shown in Figure 77 - Figure 83.

Within each bending test, the deflection plots tend to follow a similar trend with the

103

curves for channel 4 and channel 13 showing the largest displacements. The curves for

channels 4 and 13 are larger than the other deflection plots because these two channels

are located at the beam midspan and therefore have the largest deformations. The curves

for the four remaining channels (located at quarter points as shown in Figure 49) tend to

cluster around the same space. This clustering of curves indicates that the deflection at

each of these points is similar. The symmetrical positioning of these string potentiometers

also accounts for the similar deflection values.

104

(a)

(b)

(c)

(d)

(e)

Figure 70 NDS (a) bending test set-up (b) bending test set-up (c) cracked section left (d)

cracked section right (e) cracked section

105

(a)

(b)

(c)

(d)

(e)


test cracked section right (d) bending test cracked section left (e) bending test cracked

section

106

(a)

(b)

(c)

Figure 72 ND30 (a) bending test set-up (b) bending cracked section left (c) bending

cracked section right

107

(a)

(b)

(c)

(d)

Figure 73 ND40 (a) bending test set-up (b) bending test set-up (c) bending test cracked

section left (d) bending test cracked section right

108

(a)

(b)

(c)


test cracked section right

109

(a)

(b)

(c)

(d)

Figure 75 NDS 1 block (a) bending test set-up (b) bending test cracked section left (c)

bending test cracked section right (d) bending test cracked section

110

(a)

(b)

(c)

Figure 76 NDS 2 blocks (a) bending test set-up (b) bending test cracked left (c) bending

test cracked section right

111

Figure 77 NDS deflection plots

Figure 78 ND20 deflection plots

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

0 360 720 1080 1440 1800 2160

Def

lect

ion (

inch

)

Time (seconds)

CH1 CH10 CH4 CH13 CH7 CH16

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

0 360 720 1080 1440 1800 2160

Def

lect

ion (

inch

)

Time (seconds)


112



0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

0 360 720 1080 1440 1800

Def

lect

ion (

inch

)

Time (seconds)


0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

0 360 720 1080 1440 1800 2160

Def

lect

ion (

inch

)

Time (seconds)


113


Figure 82 NDS 1 block deflection plots

0.000

0.500

1.000

1.500

2.000

2.500

3.000

0 360 720 1080 1440 1800 2160 2520 2880

Def

lect

ion (

inch

)

Time (seconds)


0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

4.500

0.000 360.000 720.000 1080.000 1440.000 1800.000

Def

lect

ion (

inch

)

Time (seconds)


114

Figure 83 NDS 2 blocks deflection plots

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

0.000 360.000 720.000 1080.000 1440.000

Def

lect

ion (

inch

)

Time (seconds)


115

Chapter 8

One-way shear test description

8.1 Test set-up

Following the bending test, the specimens were moved into place for one-way

shear testing. Due to the variability in the usable length of slab left after the first test (the

bending test) three different shear test set ups were utilized as shown in Figure 84 -

Figure 86. First, the usable slab length was measured as the distance from the right edge

of the slab (the end of the slab pointing outside of the lab) to the innermost edge of the

nearest flexural crack. In most of the bending tests, the usable length for shear testing was

approximately 90”; however, some slabs only had approximately 72” of usable length.

The tested slab length was thus different for each. The midpoint of the slab length tested

was marked using chalk. Then two W10x54 wide flange sections were placed equidistant

from the test length with their outer edge of the flange placed flush to the edge of the

flexural crack on the left and the end of the slab on the right. Two W12x72 wide flange

sections were placed near the center of the tested span length as load points to distribute

the load. Here the web of the W12x72 sections were placed at 9.875 inches from the

centerline of the shear test length for the ND60 slab, at 15.50 inches from the centerline

of the NDS slab and 12 inches from the centerline of the remaining samples. The usable

length/as tested length of each slab and the distance between the point loads is indicated

for each test in Table 28. During this test, the slabs are loaded by advancing the hydraulic

pump a quarter turn at a time. Here the hydraulic cylinder proceeds to push against the

load frame and create an equal and opposite reaction that bends the slabs downwards.

116

Here the shear tests were loaded to failure. The slabs were loaded until the maximum

stroke of the hydraulic cylinder of 3 inches was reached. The slabs were then unloaded.

At this moment, the permanent deformation of the slab causes the test assembly to

separate from the load frame which allowed for additional metal plates (shims) to be

placed between the hydraulic cylinder and the load frame. The shear test is restarted and

load applied till the span failed.

117

Figure 84 One-way shear test set up NDS

Figure 85 One-way shear test set up ND60

118

Figure 86 One-way shear test set up, all other slabs

Table 28 Beam (one-way) shear slab lengths tested

Slab Usable length of slab

tested (inches) Distance between point loads (inch)

ND S 90 31

ND20 72 24

ND30 72 24

ND40 72 24

ND60 90 19.75

NDS 1 block 72 24

NDS 2 blocks 72 24

119

Chapter 9

Results of one-way shear tests

In order to facilitate the testing procedures all concrete slabs were tested in one-

way shear directly after the bending tests. A useable length of the concrete slab was used

to test the one-way shear capacity of the different specimens. The test set-ups of these

concrete slabs were described in Chapter 8 and detailed in Figure 84 - Figure 86.

9.1 Theoretical shear capacity and moment capacity

The theoretical shear capacity of the prestressed hollow core slabs was calculated

in accordance with section 22.5.8.3.1 as the greater of the flexure shear strength, Vci,

calculated by equation(s) 22.5.8.3.1a and 22.5.8.3.1b from the ACI 318-14 design code.

Here equation 22.5.8.3.1a includes provisions for the maximum moment at section due to

the applied load. The following assumptions were made: (i) the shear area is calculated as

the area of concrete above the center of the steel prestressing strands as shown in Figure

87 and (ii) the effective prestress is taken as fpe = 144,000 psi to calculate the moment

causing flexural cracking at section due to externally applied loads, Mcre. The moment

capacity, Mcapacity, of the section is calculated as described in section 7.1.

Furthermore, the manufacturers calculation of shear capacity is also included. It is

important to note that the manufacturers calculations are based on the following

conditions: (i) the target compressive strength, f'c,Target = 6,500 psi is used and (ii) the

prestress losses are calculated using the methods stipulated in section 2.2.3 of the PCI

Manual for the design of Hollow Core Slabs and walls and is approximately fps= 168,600

120

psi. Finally, due to the short development length, strand slip did occur during one-way

shear tests.

121

Figure 87 Cross-section of slab showing shear area

9.2 Moment and shear demand

During the one-way shear tests the usable length of the slab was supported by two

W10 x 54 sections as well as a third W10 x 54 section that supported the remaining

(unbroken) span of the slab as shown Figure 84-Figure 86 and Figure 88. This additional

support creates a test set-up consisting of two spans instead of a single span. However,

during the application of load the unused span lifts-off of the W10 x 54 section which

then changes the setup from two spans to one. The spacing of the point loads varied for

each slab with the spacing for ND60 being the smallest at 19.75 inches and the spacing

between the point loads for NDS being the largest at 31 inches.

The shear and moment demand due to self-weight is calculated using the effective

length and moment arm shown in Figure 88. The effective span length for test specimen

NDS is 75 inches. The moment due to the applied load is calculated using the moment

arm, a’, shown in Figure 88. The moment arm for NDS is 22 inches.

122

Figure 88 Example loading diagrams for one-way shear tests, NDS

9.3 Results of four-point shear tests

The results of the four-point one-way shear test of the hollow core concrete slabs

are shown in Figure 89. Slabs ND60 and NDS were loaded twice; therefore, the load

versus displacement curves show an unloading and reloading curve. The load versus

displacement curves for each hollow core concrete slab are shown below in Figure 90 -

Figure 96. Photos of the one-way shear test set-up and cracked sections are shown in

Figure 97 - Figure 102.

During one-way shear tests, all slabs exceeded code shear capacity and moment

capacity. Table 29 shows the measured and theoretical one-way shear capacities based on

ACI 318-14 and calculated as described in section 9.1, and

Table 30 shows the moment demand and capacity of each test specimen. All slabs failed

in shear which was the intended failure mode; RCA was seen to improve the shear

123

capacity of the hollow core slabs. The ND20, ND30 and ND40 RCA slabs performed at

73%, 59% and 85% higher than code capacity. ND60 exceeded code capacity by only

25%; therefore, NDS performed better than ND60. The ratio of VTotal/ Vcapacity is much

lower for NDS 1 block (likely due to manufacturing irregularities) and NDS 2 blocks.

The lower shear capacity of NDS 2 blocks is likely lower due to the lower slab capacity

given that the section cracked during the service loading period. The shear capacity as

calculated by the manufacturer Vcapacity, mfg. kip∙ft., is substantially higher than the total

shear and higher than the shear capacity calculated via ACI 318-14. Furthermore, NDS 1

block has a substantially lower VTotal/ Vcapacity and MTotal/ Mcapacity ratios when compared to

the other slabs due to the manufacturing errors in the slab as shown in Figure 51. Finally,

the negative moment (taken as the maximum moment generated by the self-weight) at the

middle support as shown in Figure 84-Figure 86 hand overhanging span as shown in

Figure 88, was not seen to exceed the moment capacity of the section and therefore did

not crack the overhanging span. A comparison of the negative moment capacity versus

negative moment demand is shown in Table 31. Here the negative moment capacity is the

moment necessary to create the available stress at the bottom of section (due to

prestressing and eccentricity). The results of the one-way shear tests are within the

variability of the materials and methods used in this study.

124

Table 29 One-way shear demand and capacity

Slab a',

inch

P,

Load,

lbs

VLOAD, kip

l', inch VSW, kips VTotal, kips Vcapacity, kips Ratio VTotal/

Vcapacity Vcapacity, mfg.

kip∙ft.

NDS 22.0 53,067 26.53 75 1.64 28.17 19.72 1.43 22.92

ND20 16.5 67,227 33.61 57 2.37 35.98 20.84 1.73 22.92

ND30 16.5 60,976 30.49 57 2.37 32.86 20.68 1.59 22.92

ND40 16.5 71,181 35.59 57 2.37 37.96 20.49 1.85 22.92

ND60 27.625 44,648 22.32 75 1.64 23.97 19.17 1.25 22.92

NDS 1

block 16.5 51,664 25.83 57 2.37 28.20 21.22 1.33 22.92

NDS 2 blocks

16.5 54,343 27.17 57 2.37 29.54 21.22 1.39 22.92

Table 30 Moment demand and capacity

Slab a',

inch

P,

Load,

lbs

l', inch MLOAD

kip∙ft.

MSW

kip∙ft.

MTotal,

kip∙ft.

Mcapacity,

kip∙ft.

Ratio MTotal/

Mcapacity

NDS 22.0 53,067 75 48.64 -1.13 47.51 41.30 1.15

ND20 16.5 67,227 57 46.22 -2.20 44.02 41.13 1.07

ND30 16.5 60,976 57 41.92 -2.20 39.72 41.04 0.97

ND40 16.5 71,181 57 48.94 -2.20 46.74 40.94 1.14

ND60 27.625 44,648 75 51.39 -1.52 49.88 41.14 1.21

NDS 1

block 16.5 51,664 57 35.52 -2.20 33.32 41.30 0.81

NDS 2

blocks 16.5 54,343 57 37.36 -2.20 35.16 41.30 0.85

125

Figure 89 Applied load at failure for slab specimens undergoing one-way shear

53,067

67,227

60,976

71,181

44,648

51,66454,343

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000


Block

outside

ND S 2

Block

outside

Load

(lb

s)

Slab

126

Table 31 Negative moment demand versus negative moment capacity

Slab MSW kip∙ft. Mmax neg. kip∙ft.

NDS -6.47 -15.83

ND20 -9.08 -15.83

ND30 -9.08 -15.83

ND40 -9.08 -15.83

ND60 -6.47 -15.83

NDS 1 block -9.08 -15.83

NDS 2 blocks -9.08 -15.83

Figure 90 Load vs. midspan displacement of slab NDS during one-way shear testing

0

10,000

20,000

30,000

40,000

50,000

60,000

-2 -1.5 -1 -0.5 0

Lo

ad (

lbs)


127

Figure 91 Load vs. midspan displacement of slab ND20 during one-way shear testing


0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

-1 -0.8 -0.6 -0.4 -0.2 0

Lo

ad (

lbs)



0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

-0.8 -0.6 -0.4 -0.2 0

Lo

ad (

lbs)



128



0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

-0.8 -0.6 -0.4 -0.2 0

Lo

ad (

lbs)


0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

-1.5 -1 -0.5 0

Lo

ad (

lbs)



129

Figure 95 Load vs. midspan displacement of slab NDS 1 block during one-way shear

testing

Figure 96 Load vs. midspan displacement of slab NDS 2 blocks during one-way shear

testing

0

10,000

20,000

30,000

40,000

50,000

60,000

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0

Lo

ad (

lbs)

Midpsan displacement (in)Channel 13 Channel 4 Average

0

10,000

20,000

30,000

40,000

50,000

60,000

-0.8 -0.6 -0.4 -0.2 0

Lo

ad (

lbs)


130

(a)

(b)

(c)

(d)

(e)

(f)

Figure 97 NDS (a) one-way shear set-up (b) one-way shear set-up (c) one-way shear

cracked section left (d) one-way shear cracked section left (e) one-way shear cracked

section right (f) one-way shear cracked section

131

(a)

(b)

(c)

(d)

Figure 98 ND20 (a) one-way shear test set-up (b) one-way shear cracked section left (c)

one-way shear cracked section right (d) one-way shear cracked section underside

132

(a)

(b)

(c)

(d)

Figure 99 ND30 (a) one-way shear test set-up(b) one-way shear test cracked section left

(c) one-way shear cracked section right (d) one-way shear cracked section midspan

133

(a)

(b)

(c)

(d)

Figure 100 ND40 (a) one-way shear test set-up (b) one-way shear test cracked section

left (c) one-way shear test cracked end of slab (d) one-way shear test cracked section

right

134

(a)

(b)

(c)

(d)

(e)

Figure 101 ND60 (a) one-way shear test set-up (b) one-way shear cracked section (c)

one-way shear cracked section left (d) one-way shear cracked section end (e) one-way

shear cracked section right

135

(a)

(b)

(c) (d)

(e)

Figure 102 NDS 1 block (a) one-way shear test set-up (b) one-way shear cracked section

left (c) one-way shear cracked section right (d) one-way shear cracked section end (e)

one way shear cracked section underside

136

(a)

(b)

(d)

(e)

Figure 103 NDS 2 blocks (a) one way-shear test set-up (b) one-way shear cracked

section left (c) one-way shear cracked section right (d) one-way shear cracked section

slab underside

137

Chapter 10

Punching (two-way) shear test set up

Each hollow core concrete slab was tested to failure in punching shear

immediately after the one-way shear tests. The hollow core prestressed concrete slabs

were repositioned within the loading frame utilizing two web sling straps and the

laboratory 2-ton overhead crane. The straps were positioned carefully at each end and the

slab was hoisted in the air and turned 180°. Once again, the usable length of the slab was

measured as the distance from the interior edge of the closest flexural crack to the

unbroken edge of the slab.

10.1 Punching shear test set up

The usable length was the same for all slabs and was approximately 84 inches

except for the NDS 2 blocks which had a usable length of approximately 66 inches. The

punching shear tests were carried out by using a 1 ½ inch thick 6 inch diameter steel

donut with a 1 inch diameter hole. The steel section assembly was placed at the center of

the remaining usable length (either 42 inches or 33 inches) and centered on top of the

steel donut shown in Figure 104. The steel donut was also placed at approximately 18 1/4

inches from the center over a rib (space between two cores) without reinforcement as

shown in Figure 105. The punching shear test set up is shown in Figure 106 and Figure

107. Steel wide flange sections were placed as supports in a box formation around the

tested span to keep the span from failing due to bending as shown in Figure 108. Metal C

clamps and spring clamps were used to keep the steel sections together as shown in

Figure 110 - Figure 116.

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Figure 104 Steel donut used in punching shear tests

Figure 105 Punching (two-way) shear set-up

139

Figure 106 Punching shear test, overhead view

Figure 107 Punching (two-way) shear test set-up

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Figure 108 Punching shear test box formation supports

141

Chapter 11

Punching (two-way) shear results

11.1 Punching shear results

The maximum load to failure in the punching shear tests is shown in Figure 109

and Table 32. Images for these tests are shown in Figure 110 - Figure 116. The punching

load to failure results show an interesting pattern where the punching shear strength of

the slabs is highest for the ND20 and ND30 test specimens. Test specimen NDS, which is

the standard concrete mixture, has a lower punching shear strength capacity than

mixtures ND20 and ND30. Other than the data point for the NDS test specimen the

punching shear strength seems to decrease with an increase in natural aggregate

replacement past 30% (ND30). Furthermore, the data in Figure 109 shows the punching

shear strength of the NDS 1 block and NDS 2 block slabs also had relatively low

capacities as compared to the ND20 and ND30 specimens. The punching (two-way)

shear capacity of NDS 1 block is significantly lower than all the other test specimens.

This is likely due to the uneven slab surface, as mentioned before. In conclusion, the

punching (two-way) shear capacity of these test specimens varies and does not show a

clear trend. Finally, although not utilized in this study, a quick review of the literature

indicates that the other studies that undertook similar problem statements found that for

hollow slabs the design codes(such as the German DIN 1045) do not accurately estimate

the punching shear capacity of the section. However, showed that utilizing a effective

area of the concrete section versus the gross area might provide better estimations of the

punching shear capacity a study by (Schnellenbach-Held and Pfeffer, 2002). A second

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study by Sagadevan and Rao also found that existing design codes(specifically ACI 318

2014, EN 1992-1-1 and IS 456 200) overestimated the punching shear capacity of hollow

concrete slabs. The study arrived at better results when modifying the design codes by

using effective perimeter and net area(Sagadevan and Rao, 2019).

Figure 109 Failure load of two-way (punching) shear

Table 32 Maximum load to failure, two-way (punching) shear test

Slab Punching Shear (lbs)

NDS 21,303

ND20 23,600

ND30 24,365

ND40 21,686

ND60 17,859

NDS 1 block 17,094

NDS 2 blocks 21,814

21,303

23,600 24,365

21,686

17,859 17,094

21,814

0

5,000

10,000

15,000

20,000

25,000

30,000


Block

outside

ND S 2

Block

outside

Load

(lb

s)

Slab

143

(a)

(b)

(c)

(d)

(e)

Figure 110 NDS (a) punching(two-way) set-up (b) punching(two-way) set-up(c) punching

(two-way) shear cracked section, South side (d) punching(two-way) cracked section,

North side (e) punching(two-way) cracked section, South side

144

(a)

(b)

(c)


cracked section (c) punching (two-way) shear cracked section

145

(a)

(b)

(c)

Figure 112 ND30 (a) punching (two-way) shear set-up (b) punching (two-way) shear


(a)

(b)

(c)



146

(a)

(b)

(c)

Figure 114 ND60 (a) punching (two-way) shear test set-up (b) punching (two-way)

cracked section (c) punching (two-way) cracked section end

(a)

(b)

(c)

Figure 115 NDS 1 block (a) punching (two-way) shear test set-up (b) punching (two-way)

shear cracked section (c) punching (two-way) shear cracked section end

147

(a)

(b)

Figure 116 NDS 2 blocks (a) punching (two-way) shear test set-up (b) punching (two-

way) shear cracked section

148

Chapter 12

Conclusions and future work

The work summarized in this document presents a strong narrative of the efficacy

of RCA as a replacement for natural aggregate in precast prestressed concrete specimens.

Specimens containing 20%, 30% and 40% replacement of natural aggregate by RCA

were found to perform, at times, better than the standard mixture, NDS. Hollow core

concrete slabs ND20, ND30 and ND40 with 20%, 30% and 40% replacement of natural

aggregate by RCA, respectively were found to outperform the NDS slabs in flexural

bending capacity, one-way shear and punching shear. RCA was shown to increase elastic

deflection, long-term deflection, inelastic deflection and total deflection. ND40 had the

largest deflections and ND60 performed much like NDS.

Furthermore, the use of RCA in precast prestressed concrete specimens is also

possible due to the manufacturers ability to recycle their own waste concrete from

previous manufacturing sessions. This internal recycling and reusing of material is

beneficial and efficient because these concrete floor panels are manufactured at plants

that also produce waste concrete; therefore, this project aims to implement the use of

RCA in a controlled environment where the manufacturer is able to certify the properties

of the concrete in order to ensure quality control.

12.1 Discussion of results

12.1.1 Deflections

The total deflection of the slabs was shown to increase with an increase in RCA

content with ND40 having the highest total deflection. NDS 1 block had a substantially

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larger total deflection when compared to the other slabs with a single load block; this was

likely due to the uneven and unfinished condition of the slab. The elastic deflection

followed a similar pattern with an increase in elastic deflection with RCA content. ACI

318-14 code provided good estimates for elastic deflection.

Amongst the two slabs cured outside, NDS 1 block had greater total and elastic

deflection when compared to the other slabs with one load block. Secondly, NDS 2

blocks had the largest elastic and total deflection as was expected of a slab with double

load.

12.1.2 Bending strength

The results of the flexural bending tests do not show a clear relationship between

RCA content and bending strength. The slabs with the highest flexural bending capacity

were ND20 and ND40 as well as NDS 2 blocks. All slabs exceeded code moment

capacity except for NDS 1 block.

12.1.3 One-way shear strength

The one-way shear strength test results show that all specimens failed in moment

except for ND40. Measured shear strengths were compared to code capacity, Stresscore,

Inc. software program and ACI 318-14; all slabs exceeded code capacity.

12.1.4 Punching (two-way) shear strength

The results of the punching shear tests are presented herein. The results of the

punching shear tests were greatly affected by the quality and curing conditions of the test

specimens. For example, test specimen NDS 1 block had many surface imperfections and

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seemed to be ‘patched’. These imperfections are likely due to the inherently dry concrete

mixture used and the likelihood that this specimen was manufactured at the beginning of

the slipformer’s run.

12.2 Suggestions for future work

The University of Texas Tyler and The University of Notre Dame research

partnership has studied the properties of RCA, the effect of RCA on reinforced concrete

specimens (compressive strength, tensile strength, cracking mechanisms) and the effect

of RCA on precast prestressed members (service load deflections, stiffness, and other

mechanical properties). Further work should focus on other mechanical properties of

RCA as well as on-site and in-service performance of RCA specifically in precast

prestressed members. Some suggestions for further work include:

(1) in service performance of hollow core concrete slabs by means of constructing a scale

model within a laboratory space or tracking the performance of specimens used in

exterior projects

(2) investigations on the microstructural properties of RCA aggregates and concrete

mixtures to further explain and understand the performance of RCA mixtures

(3) use of Digital Imaging Correlation software to track the progression of sagging and

deflection in as-built structures and models as mentioned in (1) to assist in calculating

strains and further monitoring the effects of RCA

(4) further investigations on the punching (two-way) shear capacity of the slabs as well as

finite element modeling of the contact effective area for calculation of theoretical, or code

capacity

151

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