Development of Strength and Fracture

Properties of Latex Modified Concrete

Abslract

This paper reports latex modified

concrete (LMC) .~Irength and fracture

properties at ages ranging from 5 hours

and 28 days. The development of strength,

defonnability and fracture properties were

sligthly different from eonveotional con­

crete. Test results indica[e a significant

improvement in reducing and bridging

microcracks,; especially in the prepeak load

region. The load deflection relationship

was obsered: to he highLy linear up to 0.93

of peak lop-d. Fracture toughness and

deformabiE!y increased significantly.

Fracture energy varies from 2.3 to l33.1

N/m, depending on age, and La some degree,

-~~--

SuvimoJ Su,liaranich '

.Tames R. Lundy 2

on notch depth ratio. However, the postpeak

hehavior was quite similar to convenrional

concrete. In the range studied. notch depth

appears to have less effect. compared to

nonnal concrete. The crack mouth opening

displacement control method provided

consistent values which may henefit olher

researchers.

Keyword:

Early llge perfonnance, styrene

butadiene. latex modified concrete.

mierocracb, strength development.

dcformabillty. fracture energy. characteristic

length, prepeak, posfpeak, strain softening,

cmocL

1, Associate; Professor. Civil Engineering Depanment, Faculty of Engineering, Kasetsart

UOlversity, Ph. D. student at College of Engineering, Oregon State University,

2. College of Engineering, Oregon State University, Corvallis. Oregon 9733l.

Introduction

OeteriQf;ltion of the infru~trueturc

may be due to environmental eondilions.

age, material degradation and/or increased

loading spt:elra, Bridge deek deterioration

is one major coneern beeause it affeets

the serviee life, maintenance costs, useT

eonvenience. and safety. Therefore, good

performing repair materials and cost-effec­

tive application of these materials are of

interest.

These repair materials serve two

purposes. First. effeelive materials and

effieiem teehniques reciuce public incon­

venienef', and, as a result. user costs.

Secondly, materials thaI reduce rhe bridge

deek pcnneability also provide a protection

system against <:lggres~ive solution seepage.

The second funetion is believed to delay

the corrosion of reinforcing steel, a major

factor in bridge deek deterioration.

Impermeability and dumbility are

two important faetors whieh are used to

judge the effeetivenes~ of ~ bridge deck

overlays. Low permeability materials that

provide a more effective proteetion system

against the ingress of aggressive solutions

are of interest.

Improved eoncrete propertics.

particul:.l1"ly lower pcnnc<:lbility, can be

achieved by adding admixtnres such as

latex to modify the concrete matriees (l , 5),

Latex modified concrete is the most eom­

man overlay material used for bridge decks

during the last decade (l). Many highway

ageneies eontinue to use this material and

reeonize it~ heneficial qualities..'\lthough

these modified materials generally perfonn

well. distress eontinues to be reported.

Often, dislrt:sses are reported soon after

eonstruction.

The most eommonly reported early

age dislres~es. cracking and delamination.

pennit the ingress of moisture or aggressive

solutions into the substrate. These actions

may contribute to olher snbseqnent dis­

tresses. Therefore. 10 avoid or minimIze

these distresses and achieve better long

term performance. a smdy is necessary to

investigate and understand the material

pror~nies and mcchani~r.1s involv~.

To study the meehanisms involved.

it has been recognized that models based on

fracture mechanics, sueh as the cohesive

cri.lck model, provide a better description of

eraek development in a composite material

like concrele, eompared to the conventional

stress criterial which assumes an immediate

drop to zero stres.s after peak stress (2). In

order to apply [he eohesive erack model to

study early age crack propagation, some

fraeture parameters are needed.

The investigation of maleria.l

properties reported in this paper is a part of

a study illvolving early age perfoffimnce of

laL~x modified concrete bridge deck over­

lays. A test program and subsequent rcsults

for strength development, deformability

and fractnre energy of LMC provide Lhe

necessary information for further sludy,

LlJ1:YUJ'U - n'i'nlJ1P'1lJ

Material: Latex Modified concrete

(LMC)

Polym~rs were first introdueed to

hydrautic-eeme~t system" in 1923 because

of an increased need for durable eom;truction

material. In lnL1, Lefebure, using conven­

tional concrete mixture proportioning, pro­

duced lcllex modified concrete (LMC) and

latex modified 'mortar (LMM) (1). LMC.

defined by the :ACT committee 548. is the

mIxture of Portiand cement. fine and coares

aggrcgates combined wilh orgamc polymers

that are dispcrsed in "",."uer at the timc of

mlXlng(l).

After WWll, natural latex \I,/as

replaced with ;scvcral types of chemkal

polymers, bolh thermoplastic (vinyl-type)

and clastomeric: (styrene- butadiene copoly­

mcr) based. Th¢se materials were developed

and commerdalized to modify thc structure

of concrete sys~ms, Some improved latexes

such as ~tyrene: butadiene have been widely

used in the l,;oocrcle industry, especi<.llly in

bridge deck overlays. This m<.lteriat has been

widely reporteu as providing s;ltisfaetory

protective/preventive systems for bridge

decks due to its excellent properties espe­

cially lower permability and improved

bond str~ngth.

Styrene butadicne, an elastomcric

polymcr, is the copolymerized product of

two monomers, styrene and butadiene.

Latex is typic~l1y included in concrete in

the form of a coUoidal suspension polymer

1f'11n'i''i'lJ'1\1'i' lJn. l19

in water. This polymer latex, usually a

milky-white fluid, eontains small, spherical,

eopolymer particles that vary in size from

about 0.05-5.0 !-1m in diameter. The emul­

sion polymerization of l<.ltex modifies the

conerete Slrueture system through two

processes, cemcnt hydration and film for­

mation. Ohama modelled and cle;lrly

cxplained these processes in three steps (l).

The wide size variation of polymer

particles results in an effectivc void-fill­

ill and a closely-packed system of film

formation. The closely-packed polymer

particles fonn a continuous film on the

surface of the ccment gel-unhydrated

cement particle mixturc. This film will

rctain internal moiqure and enhance curing.

The continuous mau·ix. also bridges some

capillary pores and microcracks. The resul1

is <.l dmslic improvement in some concrCle

plOperties such as tensile strength. flexural

strenglh and permeability (1, .d, 5).

Although a cleal modification

model of the interface zone betwcen

aggregate and cement pastc does not exist. is

likely that the microcracks in this zone, in

LMC. arc effectively bridged by lhe pore

filling and the interfacl' zone is improved

hy the bonding effect (3), Thc.'ie re!iulrs are

reported to reduce microcrack intensity

in concrete subjectd 10 every load level,

even before <.lny load is applied. However,

sudden increased microcrack intensity is

still reported as in convcntional conCrete

in spite of latex modification (3).

The typical LMC pore structure

differs from those of conventional concrete

(Ll). The hardened LMC contains a relatively

small number of single pores. Pores with

radii of 0.2 fJm. or more are signifieantly

rcclucc:c.. Huwl;:wr smaller radii pores (s

75nm.) are increased. (5, 6, 7). The total

porosily tenris to deerease by a~ mueh as

50°/" as the polymer-cement rario (piC)

increases (5).

The effeel.~ of filling large voids

and sealing with polymer reduces gas and

water vapor transmission. This phenomenon

increases material re~islance to liquid

intrusion. Pcnncabiliry tends Iu cUlllilJue

deeren~ing nfter the initjeal 28 dny cunng

period as a function of age (8, 'I),

Typical LMC mIXes eontain

about 5-l0 percent latex solids and have

wlc ratios of about 0.30-0.LlO. The latex to

cement ratios. ranging between 5-20%.

strongly affeet [he mixture properties; nor­

mally 15% is used.

Experiment

Little information is nvailabJe in

the literature on em'ly age properties of

modified concrete. Some properties of

LMC have never been sludied. particnlarly

fracture energy and flexural eurvature at

initi<:l1 cracking. However, 10 order to apply

fracture mechanics 10 failure behavior, if is

necessary 10 determine values for these

parameters. Therefore, and experiment i~

requisite 10 georcrate Ihe fracture parameters

from the test results. These parameters will

be used as input to predict the outcome of

erack propagation and crack mouth opening

displaeement (cmod) in the applieaation

phase of lhe study.

Experimental Program

Sinee there are no standard tests

available for early age eoncrete, especially

for modified eoncreLe, some standard test

methods and specimen preparation teeh­

niques for eonventional concrete were

used, whenever possible. However, dne to

Ine chamcteristics of the m",teri<:ll and tne

limitations of the avaLiable equipment, the

specimen sizes in this stndy differ slightly

from ASTM standards or RILEM recom­

mendations. Sizes similar to those used in

olher studies ("10, "11) were ehosen TO provide

comparative re~;n1ts_

Material

The laboratory work was COIl­

ducted on specimens using a mix similar to

thJt used by the Oregon Department of

Transportation (22). The wi" proportions

and material properlies are shown in Tables

1 lnd 2

P0I11and cement ASTM C-1 ')') type

l. was used for .~pecimen prepnration. In this

study. clean river sand. river gravel and a

styrene-bntadiene polymeric emnlsion were

used. This latex type contains a polymer

eontenL abuuL Ll7- Ll Y"!o of total emnlsion..fhe

approximate weighl is l018.53 kg/m'.

Table 1. Mix proportions of latex modi­

fied concrete used by Oregon

Dep~rlment or Transportation

(22)

~ Maler;a~unt (kg/m') 1 cement 391.5 l sand 963.5 I

gravel B2A.6! II latex 122.' I L_water 63.8~

Note; w/c ~ 0.32

The three point bending. test used

to investigate fracture energy was conducted

with a data acguisition system (12),

A beam size ofl 0.2 by 10.2 by 4 3.2

em. was chosen instead of the standMd

size in ASTM:C3l-91 (13). This size was

selected to reduce the dead weight, to allow

molds to be 'used for both flexure imd

fracture energy leSIS and to compare the

results wilh other published paper (ll).

The ,specimens were cast into

two lifts as suggested in ASTM C3' -91 ,

For the test purposes, the tension side was

designateda'i the top side. After finishing,

the specimens were covered with a plastic

sneet and wet burlap for 2L1 hr. before

demolding. The demolded specimens were

left for an additional 2L1 hr. before being

uncovered and placed in and ambient

environment until tested, similar to the

conventional curing method for LMC.

This procedure was chosen to simulate

field curing.

For early age testing, young con­

crete is too fragile to demold or handle

witham disturbing the material. Therefore,

flexure and fracture energy testing at tnis

stage were conducted in a special plexiglass

mold (fig.l ). The oversize holes allow 100­

gitudinal sliding in the laminated sides to

insure flexibility of the mold thus minimiz­

ing it's influence on testing. The empty

molds were tested for flexure before and

after each specimen was tested, to allow the

influence of the mold to be factored out.

Mi.lterial properties

Fig, Special flexible mold for early age testing

Table 2. Mechanical properties of coarse and fine aggregates

sample 1

sieve mass percentage I retained retained

(gm.) (%)

Sand

"' ~.3 0.69

#8 109.<1 17.72

#;6 86.1 13.95

#30 79.4 ',2.86

#50 221.0 35.80

#100 95.4 15.J5

pan 2l.B 3.53

lolal 61 7..1

fineness

modulus

moisture

content

Gravel

"" 0.0

3/4·' 0.0 -

1/2" 515.0 1l6.31

3/6" 326.0 19,32

pan 271.0

lot.ll 1111.0 I

moisture Jcomem

I

!

sample 2

cum. mass percentage cum.

percentag-e retained retained percentage

retaiued (gm.) I (%) retainedI I

!,

0.69 3.5 0.62 0.62

1 B.cl1 93.6 It.,50 1 7.1 2

32.36 81.2 1 <1.32 3l.<14

45.22 69.4 12.24 J3.68

81.02 192.3 33.90 77 .58

96.J7 1Oil. 7 18.46 96.0<1

- -

27 J.17

12.5 3.97

567.2 266.J8

2.7 J 2,66

.1.02% J.J4%

- - -0.0

- -0.0 -JO.60J6.31 575.0 JO.69

d67.075.63 33.05 n.7 J ,

:'71.0

lfl1J.0

2.74% 2,76%

IIII

Compressive strC'ngth

Standanl cylinders, 15.~ by 30.5

em.. were tested for compressive strengrh

al age$ 0.5, " 2. 3. 7 and 2B days. The

loading rale recommended by ASTM C39­

19y1 ('.3) was used as a gUIdeline. For very

young ages, the loading rate was useu as a

guideline. ror very young ages, the loading

rale was adjusted slightly 10 prevenr sudden

failure and extended the test duration.

Trnsile strength

Although when properly conduc[ed,

the uniaxial tensile lest provides results

that can be characterized as true tensile

strengths for concrete (10), the eharaetcris-·

ties of conerete in early age limits the use

of this test Glethod. The low tensile strength

of the material beeomes a problem because

the speeimen must carry its own weight

for the vertical test, unless sOnle special

arrangements are made- or a horizontal

uniaxial tensile teq is used as an alternative.

The-refore, a :'iimple [est, the split­

ting Tes! was chosen for this study. The

15.2 by 30.:; em. cylindrical specimens were

tested according to ASTM C-c196-91 (13)

at [he same age- as the flexure test. As with

the compression test, the sugges!e-d ASTM

loading rate was used as a guideline and the

range was adjusted slightly for very young

concreted.

M~dulus of Elasticity

The bending tests were conducted

on un notched beams at ages 0.5, 1, 3, 7 and

28 days [0 detennine a modulus of eillscicity

and comp:J.rative fracture energy. A constant

deflection rate was used to control the tesr.

To prevent sudden failurc and to achieve ,\

stable f~lure mechanism for the cor:lplete

load detle-dion curvc, load and dispLlc,_'ment

rates were reduced to zero afrer the peak

load was reached. Thcn. loading ...."as

reapplied. In this study, 10- 2C~ leading

cycles were performed during e<lch test. Thc

1F11f]'i''i'''-I'iWi "-If]. 123

peak load and mid span deflection were

used to calculate the modulus of elasticity.

Fracture energ}'

Although a direct tension test has

be-en recommended by many researchers to

detennine an unambiguow; value of fraeture

energy, the three point bending nOlehed

beam, recommended by RILEM (lJ) was

chosen for this investigation. This decision

wa~ based on procedural simplicity and

equipment availability. Moreover, the young

age of the concrete made iL difficult to

perform the test in a ve-Tlical direetion.

Load was upwi.lrdly applied to 10.2

by 10.2 by .:l3.2 cm. beams (fig.2). a casting

notch on the top side, the tension side,

allowed the measurement of the creack

mouth opening displacement lcomed) and

deflection.

T(l prepare the notch, an aluminum

plate 2 mm. thick was temporarily fixed at

the top of the mold. this plll[e was removed

as soon as possible to avoid cracking. The

notch depth/bcam depth ratios in this study

were 0.2 and I).A.

Specimen Loading

In the nudy of fracture behavior

for concrete-like materia!, postpeak behavior

of particular conl:ern as well as the influence

of loading rate. In this srudy, cmod control

or stram control was: chosen to achieve a

stable test. ThlS chOICe avoided the potenJiai

effect from locatized crushing a[ the loading

point as well as the potential for change in

,oJ .,. iIL~lJ'" 28 LJ'i':;"n 2539

Fig. 2 Test set up for fracture test

internal mierostructure from crack intensity

rtear the cmck tip. This loading control

allowed Ihe study of strain softening which

requires homogenization of the non-uni­

fann deformation process. The closed-loop

servo controHed hydraulic testing machine

enabled cmod to be used to control the test.

A clip gauge measured the crack opening

displacement and sent feedbaek signals to

control machine operations. The machine

was programmed 10 continue applying load

at two selected cmod rates of 0.00003175

and 0.000127 cm.!sec respectively.

It has been shown thai the loading

rates have some int1uence on fracture

energy; the higer the rale, the larger the

fracture energy (15, '23). Kormeling's study

showed that even though the loading

rate increased by a factor of 2000, the

conesponding fracture energy inereased

by only d8 to 82 percent (16), For this

study, therefore, loading ratcs were chosen

approximately equal to those used in

Konneling's study. In addition, the selected

loading rate should provide the complete

pre and post peak load-displacement rela­

tionship in a short time compared to the test

age of the speeimen. The chosen loading

rates, based on these criteria, provide the

maximum load 10 be reached in about 50­

120 seconds, compared to 90 seconds for

conventional concretc in Brameshuber and

Hilsdorf's study (ll).

The effect of two different loading

rates i1) also of interest although no reports

have becn found in the literafure. To

invesllgate this effect, three point bending

tests were conducted on specimens of

similar age and from the same batch. The

resuhs indicated that only a small difference

occurred in fracture energy, G f (6.2'1'0). As

a result, the testing program was conducted

Ilsing the selected rates.

In addition to cmod, mid span The ftrst experiment deals with the general

defleetion was also recorded through a strength properties of LMC. The second

LVDT (Linear Vertieal Differential Trans­ deals with fracture properties from bending

ducer). The measurement is based on the beams.

referenee neutral axis to avoid any error General strength properties geueraled by, localized crushing at the

The development of compre.'isive support. This potential error. reported in strength. modulus ofela."ticity, tensile strength some studies (17), may result in a difference and tlexural strength are shown in tigures 3 up to rio in the area of the load-deflection and 11. Between the ages of 5 and 9 hours, curve. It rna)' also came a ')ignifiulOt the ratio of t~ to ft decreases from about shifting. from 25- JDO~k" in reported mid B.O to 5.2 and then increases again after span deflection (ll). Before testing, beam about 9 hours. ll1is trend (fig.s) showed that dimensions ,and span were carefully the minimum ratio was reached at about lO measured. hours. This time period i~ greater than the

initial setting time but close to the final Test Results scuing time as reported by Ohama (1). A

The results of t\VO different similar Irend is reported for conventional

experiments are reported in this seellon. concrete (ll).

STRENGTH DEVELOPMENT VS TIME COMPRESSIVE STRENGTH

~, 4:00 1-'--'--~---'---~--~--'--T20.00 iL , I " IL.

0

~ 3.50 I' __ ---l---- -----Jl. ~ 1800

:r: [ .-- --+-------! _,----. ' 16.00 " ~

~ 3,00 .----.- r------=···-i···o .. 14,00 ~ )Ii'" -."---- -,----;

~

" "if. <i c ~ 0 ~ ::: ,~' -AT"· /:_-·__-+'~~~_~_·L~~~.~: "

-.:

w 0 0 " ~~' i ' ...£' r 0

(J) 1.50 H-I~t- 8.00 ~

V>~ I II (Z i [d}O -,co~ 1.00 ~f----t-~t-----t--t-----,---+----1 ~

o 4.00 0

t---+--{2.00~ '0,.5 0 ""---f-~~~-~--+-j .... ····~_+-I " 0

w0 0 : -----+---~-- 0.00 o 100 ZOO 300 400 500 500 70G

TJME. HR.

__.. .----.J

Fig. 3 Development of compressive strength and modulus of elasticity with time

I

, '" ~fUJV1 26 lh';:;1t1 2539

,--------T~N-S-,L~~-TR-E-NG-T-H-V-E-RS-U-S-T,~-E-~'-----I SPLITTING AND FLEXURAL STRENGTH

8000.00 -,---._- - I ._.~- ~--T4GOO

D ~ I I *1

§ 0000,00, ~ 7:f~/ '/ ,1---- --- -.---f 2500 ~ t;; 4000.00 L "": •. ----- ~- ==en ,! -.- ' --~2000:; .---l ," -' i I I C'r2 3000.00 -A--- ; -- --,--- - --- ---- 1500 ~

c­::J ~

...: 1000.00t- -- -- - -- ~-- '- I '~,oo : "- 0.00 -- - 1 :.- , 0 -J- -------l---­

o 200 400 600 800 1000 1200 TIME, HR.

L Fig. 4 Dcn'/opmeul of tensile strelJth with lime

----------, 'Ie oc!ual - ­ lilic,i ... aet~al - f11leeJ I

J

~ o

1000 I

____J

Hi'·"··4]11I I'

" i

TIME, HR.

COMPRESSIVE - TEN~.U STRENGTH VS TIME MAIN TEST PROGRAM

,-' I

- iT I'TI,

rr'Ti ,, - _._. ! ,

of, 1

I

,) I

,- .. , I , ,

'~ ," ,

t+ 1'1 I I I , I

I I, ~-,,

r+ , ,

IiJJ, I ' I,

I, , ,

I , , , ' ,L.J

I !1 I i+­ , , -- ."-. - -._­4,00

1

5,00

9.00

5,00

800

10.00

7.00

, ii' iii

I,

Fig. 5 De~'eJopmenl of $lrenglh ratio with lime

---- ----

L1J:tt1fJl.l - n'mD1P1lJ 1f'11n'M'lJ""11 lJn. 127

The calculated flexural stresses and then increased agam with time. The

versus time based on the uncracked section change in deformabitity performance

and the peak load for both notched and continued up to age 28 days whereas, the

unnotched beam are ploUed in tigure. 6. defonnability in normal concrete afrer l2

It is recogniz.e,d that Ihe computed stress hours. appeared unaffected by age (ll).

at (he critical section of the notched beam Because of the characteristics of early age connot be accurarely evaluated by eonven­ LMC, eonsiderable attention should be paid tional methods due to the effeet of induced to each procedure step, casting, handling, flexural stress, shear stress and the notch and test setting. Variation in test results for effect itself. However, these curves show early age specimens may be due to these the same trend of increasing strength with effects as well as the limited number of test time.

specimens uscd in this study. The plo! of mid span dcfle(:tion

Fracture properties.at peak load over time (fig.?) indicates Ihe

changing deformability with the age of A typical load-cmod and load­

LMC. Thispattem differs slightly from mid span deflection is shown in Figure 8.

nonnal concrete (11). For early age LMC, ln this case. stable crack growth is obtained.

the deform.ability decreased and reached Three types of behavior were observed

minimum at about 24 hours (aid = 0.2) from the load-deflection curve. The curve

FLEXURAL ~,TRENGTH- TiME NOTCHED AND UNNClTCHED BEAM Cm~PARISON

~ooo.oo o

,'I II'I

~ I ! ,

}' •• I

II l!~ ... __L._:=;: 7000 DO

! I, , I ,2: 6900_00

u I I I~ 59 00 .0 0

~ ,/ ,~ I~ (f) 4-000,00

II III ! !i,

j ; cH'-- f . , ' I", I,:·unnccII;- , . .c

~ I I I - I , ,

-----

!~ , .. L----t ,;'1 300000 :.-',,

U. :1Ii! :;" w 'notthe-,- ­CJ 2000_00 . "

I -~.~.~

~ ~

, , I , " ,, ,, lIf,/0;

~. .

i<1000.00 -, -,.,

II ,I " I • ! III0_00 [ ---I

1 100 1DOCO 10 1000

AGE, HP

I )I( ocl. 0_2

L__ ~ __ ovg...D.4_

Fig. 6 Development of flexural strength with time

----

128 1f'11n'l'l1J~1'l 1Jn.

,----------_._--_.._.- ­

. DEFORMBIlTY-TIME MID S,::lAN DEFLECTlm~- AGE RELATIONSHIP

1

.~ ::::: ~ +~T~tJt+ITfh~*~~~::::: ~ E 6.0000-' h-1+l+\lL-'LJ-~-Iftt-' U!m.1 z1 . I 'Illill LI ; ; -I~ . 00024

2'5.0000 I ilt'IIIII-;ci" ,"/ -+- ',\ '0,0022 §0

c~

c, o z

"1 00014~ 2.0000 I It·Ill',-rrc~y:ri.:-r·· I ~ ~ 1.0000 1 - 11'1,lf ~ I:~-:;I ,,' '~;.I1000"2 ~ ,,0.0000 .--, ~I-·- W --l-i--L---i- --'+I-I,Looolo

1 100 10 1000

/lGE, HR. I

I~ '-l L _ .

Fig. 7 Del-'elopment of deformabiJit.r with time

Typl,(AL LOAD-CMOD--MID SPAN DEFLECTION NOTCHED AND UN NOTCHED BEAM l

::::r-II-=t--~I=-'1- +- 1~---::L-1 I, L ~UN8 dell elmo , 1_-1 -1-- --j

SOOO - 1-;-1 - - I--r----ri----ll ,

; 4000 A'- t-± ---+ ---1-- t= I

1080 ,1/ '--Kf' -~.-t-- .-+----L -~-. I,~ if -~.L____ I L '

1 o II "--..f==~~ . 1 . -----j

0.0000 20.0000 40.DOOO 60.0000 80.0000 1 00.0000 120.0000 140.0000 DISPLACEMENT. mm/l 00I

I_NOTE: NB.=.NOTCHED BEAM. UNB=UNNOTCH~D BEAM _

C~CD OEFLECT!DN /-lEI .~CTION~I, ----------'

Fig. 8 Typical relationship of load-crack mouth opening and load-mid

span deflection of both notched and unnotched beams

LlIlf1[JU - n'i'fll)11'11J

exhibited linearly up to poinr a. This point

is considered the "elastic limit" in thi!\

study, according to ACI 5l1L1. lR-82 (lB).

Beyond this point. nonlinear perfonnance

was observed. The increasing load produced

increasing deformation which reflecled

some strain 'hardening effect. Beyond

peak load, increasing deformalion with

decreasing load reflected POSl peak lension

:;;oftening in the same manner a:-; eonven­

tional eonerete (l9).

No information has been found to

define the transition point from linear to

nonline<lr eonfiguration. In Ihis study, the

"ela:;;tie limit" was chosen in the following

manner.

A third degree polynomial reV'es­

sion wa:;; u:;;ed lO fit the data up to 95 pereent

of maximnm 10ad in the post peak region.

The fitted curve provided a R =-quare value

not less than :0.99. Another regression line

was used to fit the linear part of the eurve.

Zaitzev's study (19) showed that eonven­

tional concrete was linear up to 65 pereent of

maximum str~ss in stress-strain relation­

ship. However. from the trial regressions in

this study, it was fonnd that linear regre.~sions

from 65 to 90 pereent of the peak load,

predominantly 85 percent of peak load. ,provided bihcR square values (R = 0.98 ­

0.99). Therefore. the linear regression line

up to 85 percent of peak load was chosen as

a reference line. The elastic point for this

~tlldy was chosen when the difference of

load between {he two tegression lines ,H the

1P11n'5"5'1Jfl11 1Jn. 129

same deformation was equal to or slightly

greater than 5 percent of peak load. From

this criteria, the load associated with the

lenstic limit, Pe, and the ratio of Pe/Pmax

were- determined.

From the calculated Pe/Pmax.,

using 5 percent eriteria, there is no evidenee

of signifiennt change in this parameter

wilh time (p = 0.:;355) (fig. 9). There is a

statistically signifieant differenee between

me;m values of Pe/Pma:ot when considering

the notch depth ratio effect (p ""' 0.0005)

(fig. 10). However, using a criterion of 1

pereent difference in peak load as an

arbitrary transition point, no difference was

observed.

Although the load-defonnation of

LMC ha.~ a similar trend as eonventional

concrete (11, 17), the ratio of Pe/Pmax is

higher in this study, eompared to Kim's

study (17). The Pe/Pmax values are 0.693

and 0.9J6 compared to 0.3 and 0.82 for

notch depth ratios 0.2 and 0.L1 respectively.

The results agree with the general eoncept

of modified pore strueture due to the latex

film fonnation which is believed to have a

pronounced effeet especially in the interface

zone. The reduced or bridged microcrack in

this zone affeets the transition from linear to

nonlinear re:;;ponse.

From the test results, all :;;pecimens

showed a bilinear relationship berween the

mid :-.pan defleetion and cmod. This finding

is similar to nonnal concrete results reponed

in Kim's study (l7). The slope S1 in the first

13011"11n'1'1l!A111!n. l'l'il!~ 28 th::41i1 2539

Fig. 9 Relationship between Pe/Pmax. with time

_- ~ -- Pe/Pnlox v'S NOTCH DEPTH RATIO - - - ­

1 1.0D~-·~I-··-I-T~I--

095- --t.~-t - L---4-i , ;, I · ~ 090t----l~ r .~~

".+ II--j ·r­0.80 IL.--1- I -- I J

0.) 0.1 0.2 0.3 0.4- 0.5

~ NO_TC_f RATIO ..__D_EPT~ ~.-.J

Fig. 10 Relationship between Pe/Pma.,. with notch depth

-- ---

portion of the curve reflects the non-panern constant (1 7).

variation when taking age and notch depth The load-deflection cneve of

effect into considerlltion. unnotched beams (curve c in fig. 8) is slighlly

Howe~er, the performace of the different from notched beams. Althouth the

beam after post cracking mdicate,~ a strong cyclic load was manually applied after the

relationship between mid span deflection peak load to restrain the suddenly released

and cmod as shown in the typical curve fractnre energy, all unnOlched beams showed

(figurc 11). From qatis.tital analyses, there a tendency to slightly decrease in both Joad

is no evidenc~ of a relationship between and displacement. However, this observa­

the slope, S2, and time (p ~ 0.51:;5). (ion is based on a limited number of test

Furthermore. there is no significant differ­ samples.

ence between' mean values from different The fracture energy is determined

noteh depth ratios (p = 0.0595). This rela­ according to the RILEM recommendation.

tionship is shown in figure l2. Therefore, from the area under the load-mid span

this parameter; 52, is assumed co be eonstant deflection curve. The calculated Gf varies

This assumption agrees with Kim's study from 2 3 to "l33.l N1m. depending on age

on conventional concrete in which this and, to some degree on nolch dep[h ratiu.

parameter has been proposed as a material from statiSltCal analy.'ies, there is :ilrong

I TYPICAL 'AI] SP4N DEFLECTION VS CMO-D- ~_.. -- ---'1· NOTrHFn RF Af./

I 9O..ooJO~. ·-1 - T I-I~ ~ I §"aooOQt-·-·-I~·-- r-1~1 I [,".0000)··-1- -r---l·-•.~·I·~I i

I E 50.0000 l._ +-- ~L __ I "I--.-j I ! 500COo J- T -+7f"-i ~--..j ~ 'Oocoo 1-_ ~-·-k:"SfI-+- ~

.~ :~~~1?f/1 C=j ]==rq D DODD 20,ODCO 400'.)00 60.0:)00 80.0000 100.0000 120.0000

1

L. CMOD' rn~/10:J __. J

Fig. 7' l)picaJ bilinear relationship between mid ~piln deflection and cmod

-------------

, .J\32 1"'1f11'1lJ?i'11 lJn. ~i'llJ'Yl 28 L~:1'1t1 2539

-~-------- ­

51, CPE 52 'vS TIME IMAI~j TEST PROGRAM

I

I

1

10.00 1110000

TIME, HR,

I -',,~jd=(U (J/d~~l ,LJ

L_.__..~_~~=_=...:=_____='_~ --.J

Fig. 12 Relationship between stope 82 with time

,-- - - - ---_.- - ---- _ ....­

FRACT JRE ENERGY VS TIMF I U.lOO & MID S='AN DEfLECTION COMPARISONI

IOJOOOO'ilT\lI'n- T ~ITTTT-RmIJJ08 I ::~~~~ r---::r-t=l~1 t ~ Llllf+ii-t-loHI~: I 700000 +--1- j :1:1 i1litffil- . c

: :::::~-T[+I+mI-+-r=t~1 .-iJ-' ,.fttt:: ~ ;00000- +-+glfi'. 111 ' ·:tfru·_.,~o, " 20.0000 - - +-+- __ - _ _ . _ ---++ -'. IC.OOOO _TI: ,.' .'"::tt ," -+~r-Imol C'.0000 -I~---J-t-++ -.. I-------t--~ , .--+-W--W-+H-o

1.00 100.00 10.00 1000.00

TIME. HR.

I ~

Fig. J3 Del-'elopment of the calculated value.., from the area under

load-mid span deflection and load-cmod ffith time

LlJ'lf1tJU - fl':i'fll)1I'1lJ

<!videnee of a linear relationship between

fracture energy o.nd time for bOlh notch

deprh ratios, 0.2 and O.L1 ( P O.OODl in buth

cases.)

The cakulnled value of Of from

the deflectiun is very close to the value from

("mod as shown 10 fig. l3. However, dead ,

weight appears to have a significant effect

in fracture energy, especially for early age

specimens. At an early age (up to 24 hours),

the effect of de~d weigth varies twm 35­

350':". This effe~t decreases with (fig. 13).

After 2.4 hours, the effeet of dead weight is

primarily in the'range of 1:,-- '10%.

The relationship of fracture energy, and time is fitted as shown in fig. 1,t:R =

.891) using lhe,c4uatiou: Of - - o.nAl oj.

0,0799 In (age-hr.) - O.0686Inage - hr, r +

0,10825 (a/d)

The intluen(~e elf notch depth ralio

on fracture energy appear,~ to h;oIYe less

effe.ct in LMC, compared to normal con­

crete. The effect is not clearly demonstrated

in this study (fig. l4).

For unnotched beams the fracture

energy is clearly higher [han notched beams

regardkss of the notch depth ratio. This is

due to Ihe larger amounts of microcracks

produced nct'ore the fracture process

lOne WaS fully developed. The ratio of

G( (unnotched beam to uotched beam)

varied from 3.2 to l.2 but there was no

specific relationship, due [0 age, shown in

thi~ study (fig. 1L1). The same trend was also

observed fnr the relationship between Gf

and compressive slTeuglh (fig. 15).

~ _"!_d=_C_.z_-_~_'_../_'O_0,~_"'_~_r~a_"_h~ ~----

Fig. 14 Effect of notched depth un fracture energy with time

, .. I.fUJl1 28 1J1:;1U 2539

1--" ~RA~TLlR£ ENERCY 'IS COMPRESSI\r~E STRENGTH----'-- -- ~ 'I FOR NOTCHED AND UNNO-CHED BEAM

1400000 f-I-'---~J>-p-i08

1200000 I;'NOTJH£D B"~* /1/ t/J t: 100.C000 ;' / -I /' /o¥ I

~ 80,0000 ~"-+ :f /t ---+~ / +-=-J,CO'5 '"c z : ,/'" //f;----/. I 0.4 J)

~ ::::::IXf4~ft+-I::200000~Lj -'- I'. -+1- 'l' 0,1

0

0.0000 -I*--'--t --.,-.L---.--+--_.---+-.-----l-.-- °I 000 500 10.lJO 1~ O'J 20.00 25.00 30.00 350(J

COMPRESSIVE STRENGTHN ,"P8N8 t h d o e: =Jnno c e beam I

L_ I "'_ a/d=0,L _ 0 __aid=O:~ _' '.- .REG.o/d=U,Z-.--- REG a/_d=O.4] _

Fig. 15 Relationship between fracture energy and compressive strength

Another parameter considered in is of particular concern, may be based on

fracture mechanics of concrete WiJS charac­ two criteria. The first criterion involve.s [he

teri<;tic length. 1 .This arbitrary parameter, period when LMC has low tensile strength, m

defined by fraclure energy. modulus of high fel f l , the second criterion involves

elasticity and tensile strength, r,mged the period when the matcrial has low

between 160-2LlOO mm. depending on defonnability. From these criteria, a par­

specimens ilge. LMC showed largcr values ticular duration of interest may range from

of len ; about 3 8 times compared to the sligthly less than 9 hours to grcater than '.ill

conventional early r1ge concrete up to l day hours.

(ll). However, this parameter dramatically 2. It is recognized that. in con­

decreased with time and reached the range crete -like material, stress transferring

of conventional concrete (2DO-400 mm,) mechanisms change with increasing defor­

at abom 28 oays lfig. 16). malion. At peak load, for conventional

concrete the stress transferring capacity can

Discussion and conclusions be explained by the effect of strength and

1. From the test results. the criti­ stiffness of aggregates, mortar matrix: and

cal time when early age cracking in LMC the bond capacity between matrix and

Fig. 16 Development of characteristic length with time

x Cc

of normal concrete in which G f decreases

as notch depth ralio inereases (17, 20).

Generally the lower the ratio. the higher the

probability of available eoarse aggregates

in Ihe critical st'l:!ion, In the' macro level

of concre'te', coarse aggregates .lei as

inclusions or crack arrestors. The increased

length of possible crack paths results in a

higher resistance for crack propagation and

a higher Gr.

However in the case of LMC, bOlh

pore structure in the matrices and interface

zones are improved by film formation.

This film fannation may provide' a more

pronouneed effect than the inclusion effecl

from aggregates as found in normal con­

crete. In short, the effect from aggregates as

'-----. , -­

aggre'gate (1 s). For LMC. theeontribution

of latex film in bridging mierocracks and

improving bond slrength in the interfaee

zone' are probably responsible for th..

different performance,

This beneficial contrihution can be

se'en from the increasing ratio of Pe/Pmax,

Furthermore. Ihis effect appears to provide

ductility improvement. In this study, there

was a greater ratio of mid span defleetion

al failure to mid span deflection at peak

load. 10"':33,; compared to a ratio of 5-6 for

normal c0ncrele (17).

Th~ fracture energy of unnotche'd

beams was' higher than notched beams.

In this study, the effect of notch depth ratio

on fracture energy is in contrast to studies

found in normal concrete. In short, rhe effect

of notch deprh ratio is not as clearly dem­

onstrated as in conventional concrete.

3. LMC's development of Gf

v.'ith time differs slightly from conventional

concrete. LMC has the tendency to continue

developing Gf to 28 days whereas with

normal concrete, after 3 day, age seems to

have less effect on fracture energy.

.1. When considering the single

fracture parameter of LMC, characteristic , kllgth, Ie::: EG f / ( the modulus of elas­

ticity should be derived from either a

rension, or flexure test. Sinee latex film

is p'articularly noticeable in (arger-deforma­

tions, the modulus of elasticity in tension is

about '.( times lower than the modulUS of

elasticity in compression ("21). This is not

rhe case for normal concrete in which the

modulus of elasticity is assumed to be the

same.

In summary. latex film formation

affects LMC strength rlevelnpment,

deformability and failure mechanisms,

The improvemem. especiaUy in tensile und

flexurul strengrh should provide better per­

formance WhCll non-structural failUIt: is

of particular concern. This may minimiz.e

l:arly age distresses iu bridge deck overlay

which some factors such as environmental

effects, the effect from traffic iu the adjacent

}aTJ.es or shrinkage effeci may re involved.

The fracture energy development strongly

depends on time up to 28 days, At later

,oJ .,. " Lf'llJ'YI 28 u'l:::'i'lu 2539

ages, the observed values were comparable

to normal concrete.

Reference

l. National Cooperative Highway

Research Program. Latex-Modified Con­

cretes and Mortars, Synthesis of Highway

Practice 179, editor V, Ramakrishnan,

Washington D. c., August, 199"2 .

2, M. Wecharatana and S.P. Shah,

Prediction of Nonlinear Fracture Process

Zone In Concrete, Journal of Engineering

Mechanics Vol. 109 No.5, 1983,

3. Soroushian Parviz and Tlili

Atef, Latex Modification effects on Meeha-­

nisms of Microcrack Propagation in

Concrete Material. Transportation Research

Record 1301. Washingtion D,C., 1 QQl.

Lt. S.L. Mamsin, Microstructure.

Pore characteristics and Chloride Ion

Penetration in Conventional Concrete and

Concrete Containing Polymer Emulsion,

ACI SP 99-8, David W. Fowler Editor,

Detroit, ',987.

5. Y. Ohama, Priuciple of Latex

Modification and Some Typical Properties

of Latex Modified and Concrete, ACI

Material Journal Title no. 8Ll-M-Ll5,

Nov.lDec. lifa?

6. Y. Ohama and K,Demura,

Pore Sixe Distribution and Oxygen

Diffusion Resistance of Polymer Modified

Mortars, Cement and Concrete Research

Vol. 21 No. 5213, March/May 1091.

l"-J'lf1EJU - n1nlJ1"""-J

7. G.i G. Hoff et. al. Chemical

Polymer and Fiber Additive for Low Main­

tenance Highway. NOYES Data Corp.,

Newjersy. 1977.

8. David Whiting and W. Dziedzic,

Chloride Permeability of Rigid Concrete

Bridge Deck: Overlays. Transportation

Research Record l2:M, Transportation

Research Hoari;!, Washington D.C., 1991.

9. Dvw Chemical USA, LOllg­

Lasting Bridge DeLks with Modified

Concrete, Technical Paper: Form no. 181­

1129-87.1'?e]..

10. Ptopcrties of Set Concrete

CEA State of Art Report, Materiaux et

Construction voL llJ No. 84, 1981.

11. W. Brameshuber and H.K.

Hilsdorf. De'lOeiopment of Strength and

Defonnability of Very Young Concrete.

SEM/RILEM. International Conference

on Ffilcture of Concrete and Rock. Texas.

19 87.

12, Validyne Engineering Corp.

UPC 607, PC' Sensor Interface Card:

Imtruction Manual Revision 2.0 CA. 1990

B. American Society of Testing

Matcrials. 1992 Annual Books of ASTM

Standards Section 4.0: Conslruction. Vol 0,4

02: Concrete 'and Aggregate. PA, 1997.

J 4. A. Hillcrborg, Results of the

Three Compartive Test Series for Delerming

the Fracture' Energy Gf of Concrete,

Materiaux et Constructions Vol. 18 NO.1 07.

1986,

15. RILEM. Fractnre Mechanics

of Concrete- Application Part A, a third draft

of a report over the State of Art, RILEM.

Sweden. 1988.

l6. Kormcling, H. A.. Strain Rate

and Temperature Behavior of Steel Fiber

concrete in Tension, doctoral Thesis, delflh

University of Technology. 1986.

17. Suk Ki Kim, The Constant

Fracture Angle Model For Cementitious

Material, Dissert;ltion (Draft), New Jersey

Institute of Technology, 1991.

18. ACI Committee 554, Statc

of The Art Report on Fiber Reinforced

Concrete, ACI Sil4.1 R - 82, Conerete

Inlernational design :md Construction,

Nov. 1982

19. Y. Zaitsev. Cnlck Propagation

in Composite Material. Fraclure Mechanies

of Concrete. FH. Wittmann editor, Elsevier

Science Publishers. Amsterdam, 1983.

20. P. Nallalhambi. B.L. Karihaloo

and B.S. Heaton. Effect of Specimen and

Crack Sizes. Water Cement Ralio and Coarse

Aggregate Texture upon Fracture Toughness

of Concrete, Magazine of Concrete Re­

search, VoL 36 No. 129 Dec .. 1984.

21. Parviz S. and A. Tlili, Effect

of L~tex Modification on rhe Failure

Mechanism and Engineering Properties.

ASTM STP 1176 Polymer Modified

Hydraulic-Cement f1,Iixture. Kuhlman/

Walters editor. PhdadclphiLl, 1993.

22. Oregon Department of Trans­

portation, Bridge deck overlay field reports

between 1989-1993, Oregon, 1989- 1 993,

138 11"l1f1'i'ilJilI1'i lJf1,

23. E. Bruhweiler, FR. Wittmann

and K. Rokugo, Influence of rate of luaJing

on fracture energy and strain softening

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Research. Activities compiled by F.R.

Wittmann, Laboratories des Materiaux de

Construction, Lausanne, 1988.

Acknowledgements:

The Principal author acknowledges

many fruitful discussions with Professor

=.:=':= _: = _: = -- = _:=::=.. - - -; =-

Methi Wecharatana of the New Jersey

Institute of Technology. The valuable

instrumentation assistance of Mr. Andy

Brickman of OSU is gmteful acknowledged.

Also. the fmancial support of the Depart­

ments of Civil Engineering. Oregon State

University and Kasetsarl University are

appreciated. Finally, material supplied by

Dow Chemical Company are greatly appre­

ciated.