STUDY OF DOSAGE AND PRODUCTION OF STRUCTURAL BLOCKS IN

CONCRETE WITH INCORPORATION OF MICRONIZED POLYETHYLENE

TEREPHTHALATE

José Bezerra da Silva1,a, Ana Maria Gonçalves Duarte Mendonça2,b*, John Kennedy Guedes

Rodrigues3,c, Yane Coutinho Lira 4,d, Daniel Beserra Costa 5,e

1 Process Engineering Ph.D student, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil;

2 Researcher Professor, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil;

3 Associate Professor, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil;

4 Civil Engineering student, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil;

5 Civil Engineering Master Student, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil;

abezerra1decufcg.edu@gmail.com,

bana.duartemendonca@gmail.com,

cprofkennedy@hotmail.com,

d yane_coutinho@hotmail.com,

e daniel.beserra@gmail.com

KEYWORDS: Alternative Materials, Micronized PET, Concrete, Structural Blocks.

ABSTRACT

In recent years, the construction sector has been target of incorporation of diverse types of materials,

since some of them have similar composition to natural raw materials. The search for efficient and

environment harmless products has encouraged researches about products from renewable sources and

whose exploration is beneficial to the exploratory society. The use of residues has showed to be a good

alternative in the reduction of impact caused by the disorderly consume of raw materials and the

reduction of disposition areas, when considering the growing volume of discharged residues every year

around the world. Due to the high volume of generated residue caused by the inadequate discharge of

PET, its reuse is indispensable. This work aims to develop a dosage study and production of concrete

structural blocks with micronized Polyethylene Terephthalate incorporated. From the mix design

obtained, it was established a content of 2.5%, 5.0%, 7.5% and 10% of PET replacing fine cement and

it was evaluated the compressive strength at the ages of 7 and 28 days. It was observed that for all ages

the replacement of cement by PET promoted a reduction in the strength compared to the reference

concrete, but the results satisfied the values established by test method ABNT NBR 6139/2008.

1. INTRODUCTION

Nowadays, the use of new materials in the production of structural blocks around the world has

grown, as well as the possibility of offering alternative materials, whose main concern is the balance

between environmental, technological and economic aspects.

The search for efficient and less environment harmful products has encouraged the development

of researches about products from renewable sources and whose exploration generates benefits to the

exploratory society. The use of residues has proved to be a good alternative in the reduction of impacts

caused by raw products disordered consumption and reduction of disposal areas, considering the

growing volume of discharged residues every year around the world.

Polyethylene Terephthalate (PET) is one of the most widely produced thermoplastics in the

world. In Brazil, the main application of PET is the packaging industry (71%) [1]. Food and packaging

industries correspond to 32% of the Brazilian market of polymers, including the use of PET to

carbonated beverages packaging.

Due to the high quantity and variety of polymers application and their long degradation time,

they are considered environment villains, once they occupy a considerable volume in landfills.

However, environmental problems are not caused by polymers but by their inadequate discharge.

Systematic polymers recycling is the solution to minimize this environment impact.

The broad demographic growth that happened from the second half of the past century has

demanded constructive practices that meet the high demand for edifications. In this context, the use of

concrete hollow blocks to masonry has consolidated due to the advantages provided in the execution

and the costs, allying quality and productivity, mainly due to the dimension accuracy.

Even though each type of concrete has distinct and diversified characteristics, according to [2]

concretes can be classified into two groups: “plastic” and “dry” concretes. Basically, the difference

between them resides in the quantity of water requested to ensure workability within the limits imposed

by molding process. Plastic concretes, after homogenization of constituents, form a plastic and easily

consolidated mixture, and the air voids are removed using simple equipment, for instance immersion

vibrators. From this group can be cited conventional concrete used in reinforced concrete structures

and self-compacting concrete used in precast elements.

In dry concretes, the quantity of water used in kneading is substantially lower than the used in

plastic concrete, providing characteristics of slightly wet concrete, and the moisture varies from 6 to

8% [3]. The mixture must be thick enough to allow immediate demolding but with enough moisture to

allow an adequate distribution inside the molds during mixture and vibration operations.

According to [4,5,6], cohesion is a decisive factor in the proportioning of mix designs and in the

moisture content of dry concrete. If the mixture is slightly cohesive, which is the case of low filler

content mixtures, the block in fresh state will crack. Very cohesive mixtures, besides hindering molds

filling process, will require greater compaction and, thus, elevate production costs. The materials used

in the production of hollow blocks are the same used in conventional concrete mixtures: cement,

aggregates and water, and the specifications of each material are intrinsically linked to the fabrication

process.

Due to the immediate demolding and the reduced permanence time at industries, once they can

be traded from seven days after molding, normally HES Portland cement type V is used (ABNT, 1991).

The mix designs used in concrete blocks are usually poorer than the ones used in structural concretes,

varying between 1:4 and 1:14, depending on the function of the block, whether it is structural masonry

or just sealing.

The aggregates (coarse and fine) must be proportioned aiming to obtain a low voids index, and

also considering that the maximum dimension of coarse aggregate must not exceed half of the smallest

dimension, avoiding molding problems, according to NBR 6136 (ABNT, 2008). Due to the low

requested strengths, aggregates from various types can be used since the blocks meet the requirements

set by ABNT.

2. MATERIALS AND METHODOLOGY

2.1 Materials

The materials used in the research were:

Polyethylene Terephthalate (PET): micronized PET supplied by PET Reciclagem company;

Cement: HES Portland cement – Type V;

Fine aggregate: Quartz sand from Paraíba River bed;

Coarse Aggregate: Granitic crushed stone with maximum diameter of 6.3 mm;

Water: Destined to human consumption and provided by Companhia de Águas e Esgoto da

Paraíba (CAGEPA).

2.2 Methodology

In this study, characterization tests of aggregates, cement and micronized PET were performed.

Then, the dosage study of concrete was conducted followed by the determination of properties of fresh

and hardened concrete.

The tests performed in the materials characterization phase are described below.

2.2.1 Materials Characterization

Aggregates Characterization

Grain size Analysis

The grain size test determines the percentage distribution of different grain sizes of aggregate. It

is represented by the grain size curve that shows the passing percentage for each sieve versus the

logarithm of the sieve opening diameter.

The grain size composition test for fine and coarse aggregate was performed according to test

method ABNT NBR 7217:1987.

Specific Gravity Determination

The specific gravity of an aggregate is the ratio between mass and volume, without considering

voids. This value is important in the quantification of materials to be used in concrete mix design.

The specific gravity of sand was determined using Chapman Flask, according to test method

ABNT NBR 9776:1987. Test method ABNT NBR NM 53:2003 was used to determine specific gravity

in coarse aggregate.

Unit Weight Determination

Unit weight of aggregate corresponds to the ratio between the mass of aggregate put in a

container and its volume. This test aims to determine the unit weight of fine aggregate, including voids

and moisture present among grains, and it is important in the determination of mix design. Using this

value, it is possible to convert mix designs from mass to volume during dosage procedure

The test was performed with fine aggregate according to ABNT NBR 7251:1982.

Pulverulent materials content Determination

Pulverulent materials are mineral particles that pass through sieve n° 200 with opening of

75µm, including water soluble materials present in the aggregate.

This test, whose goal is to determine pulverulent materials content in the aggregates destined to

production of concrete, was performed with fine aggregate according to ABNT NBR 7219:1987.

Absorption

It is the increase in mass of a porous solid due to the penetration of a liquid in its permeable

pores, when compared to the mass in dry state.

The absorption of coarse aggregate was determined according to test method ABNT NBR NM

53:2003. Depending on the value obtained, an adjustment in water/cement ratio to the mix design can

be done.

Cement Characterization

Specific Gravity

In the determination of specific gravity for cement, Le Chatelier Flask was used, according to

test method DNER – ME 085/1994.

Fineness Test

It is the determination of the percentage, in mass, of Portland cement whose grain dimensions

are superior to 75 μm, using manual sieving method according to test method ABNT NBR 11579:2012.

It is important to know the fineness value of cements, because when this value is high it means there

was cement hydration and consequently loss of its characteristics. The finner is the cement, the better is

its hydration reaction and mechanic strength of mortar.

PET Characterization

Chemical Analysis – EDX

This test provides important information to industrial and scientific use and consists in

submitting the sample to an X- ray fluorescence, in which physical-chemical components of the

material are identified. The material (PET) was processed in sieve ABNT Nº 200 (opening: 0.074mm)

and the test was performed in an EDX 720 Shimadzu equipment.

X – Ray Diffraction

This technique enables the determination of the structure of crystalline solids, the atomic

arrangement in crystalline reticles or in a sole crystal of a particular substance, based on the

interference patterns of x radiation diffracted by the reticles, allowing the determination of the main

elements that compose the material. The test was performed in a Shimadzu XDR-6000 equipment,

using Cukα radiation, voltage of 40kV, current of 30mA, scanning of 2º< 2ɵ< 30º and λ1.54ª.

Thermal Differential (DTA) and Thermal Gravimetric Analysis (TGA)

Thermal Differential (DTA) and Thermal Gravimetric (TGA) Analysis of PET were performed

using BP Engenharia equipment, RB 3000 Model, operating at 12.5ºC/min. The maximum temperature

in thermal analysis was 300ºC and the reference material used in DTA test was calcined alumina

(Al2O3).

DOSAGE STUDY OF CONCRETE

According to [7], the main goal of concrete dosage is to find a more economic mix to produce a

concrete able to meet specified service conditions, using the available materials

For [8], dosage is defined as:

(...) process through which materials are chosen among the availables,

and it is determined the better proportion among cement, aggregates,

additives and addition, aiming to obtain a material able to meet

determined physical requirements

(...)

(RECENA, 2002, p.16)

According to [9] there is not a stablished methodology to concrete blocks dosage. Most part

of the recommendations comes from vibro press manufacturers.

[10] affirms that concrete blocks need precautions in the dosage process, understood as a set of

operations to the establishment of a mix design, considering the consistency of concrete similar to wet

earth, not plastic consistency. When the concrete presents plastic consistency, it occupies all spaces let

by aggregates, while in concrete for block production there is significant presence of air in the mixture.

At that, it is possible to affirm that concrete for blocks does not follow the principle for plastic

concrete, in which the less the quantity of water, the higher the strength.

Dry concrete has as characteristics a low water/dry materials ratio, great consistency (null slump),

high cohesion and the way the imprisoned air is removed using compacting equipment. [10] believes

that once it is a low water content concrete, the water/cement ratio is not the determining factor of

blocks porosity, once that higher quantities of water improve the mixture workability, reducing intern

friction among grains, achieving a better compaction and improving the strength, as shown in Graph 1.

Graph 1 – Compressive Strength versus water/cement ratio to the same aggregate/cement proportion

Source – OLIVEIRA, 2004.

According to [11], the concrete dosage to production of precast elements, like concrete blocks to

masonry, has the following goals: obtain maximum compactness, mechanic strength compatible with

requirements, compatible durability and acceptable surface aspect.

In the present research, it was used the mix design determined by [12], once it is a concrete with

wet consistency, not plastic, and it does not have a stablished dosage method.

Characterization of fresh concrete and specimens molding

Slump Test

The Slump test was performed according to test method ABNT NBR 67:1998. The determination

of concrete consistency enables the verification of water in the mass, whether it is in excess or lack.

The method is applicable in both laboratory and building site.

Consolidation and Molding of specimens

The process of molding and consolidating in a concrete block industry, using a hydro-pneumatic

vibro press machine, consists on the launching of concrete, consolidation by vibration and mechanic

compaction using rods, demolding of concrete, transport to storage place, initial and proper curing

time.

In this research, once it was not possible to produce concrete blocks with 39x14x19cm because the

vibro press machine in the laboratory had a problem and due to the impossibility of manual molding, it

was decided to mold cylindrical specimens of 5 cm x 10 cm to the mechanic characterization tests.

The consolidation of concrete was made manually in the cylindrical mold, divided in three layers,

each one receiving a compaction energy of 12 blows. The two first layers were consolidated using a

metal rod, while the third was compacted with a tamper. Both the metal rod and the tamper were used

to simulate the consolidation of concrete in hydro pneumatic vibro press machines. The metal rod

simulated consolidation in vibrating table and the tamper simulated mechanic compression by

compaction rod. This type of consolidation was adopted aiming to expel the incorporated air in

concrete, trying to represent the reality found in concrete blocks industries. .

Hardened Concrete

Hardened concrete is the material obtained by the mixture of components after concrete setting.

Mechanic Characterization

For the mechanic characterization of the reference concrete (RC) and the concrete with replacement

in percentage of cement by PET (CPET) cylindrical specimens were produced. The specimens had 5

cm of diameter and 10 cm height and were used in the determination of compressive strength with

replacement of cement by PET in the percentage of 2.5%, 5.0%, 7.5% and 10.0%.

3. RESULTS AND DISCUSSIONS

Physical Characterization of Aggregates

The physical characterization of coarse aggregate used in the research is presented in Table 1.

Table 1 – Physical characterization of coarse aggregate.

Tests Test Method Results

Density ABNT NBR NM 53:2003 s = 2.63 g/cm3

Saturated surface dry specific gravity ABNT NBR NM 53:2003 sss = 2.64 g/cm3

Apparent Specific Gravity ABNT NBR NM 53:2003 a = 2.67 g/cm3

Absorption

ABNT NBR NM 53:2003 Abs = 0.66%

The grain distribution of coarse aggregate is illustrated in Table 2.

Table 2 – Grain size composition of coarse aggregate.

Grain Size Composition (ABNT NBR 7217:1987)

Sieves

(mm)

Retained material

(g)

Percentage in mass (%)

Retained Accumulated

6.3 2382.00 39.70 39.70

4.8 2604.00 43.40 83.10

2.4 955.20 15.92 99.02

1.2 22.20 0.37 99.39

0.6 6.40 0.11 99.50

0.3 5.11 0.09 99.58

0.15 6.04 0.10 99.68

Bottom 18.54 0.31 99.99

Total 5999.49 100.0

Fineness Modulus (FM) 6.19

Maximum Diameter(MD) 6.3mm

As seen in Table 2, the coarse aggregate has a fineness modulus of 6.19 and maximum diameter

of 6.3 mm, having the most part of material retained in sieves with openings of 6.3 mm and 4.8 mm.

From the results, the grain size curve was obtained (Figure 1).

Figure 1 – Grain size curve of coarse aggregate.

Table 3 presents the results obtained in the grain size test for the fine aggregate used in the present study.

Table 3 – Grain size composition of fine aggregate.

Grain size composition (ABNT NBR 7217:1987)

Sieves

(mm)

Retained Material (g) Percentage in mass (%)

Retained Accumulated

2.4 28.95 2.90 2.90

1.2 79.09 7.91 10.81

0.6 326.32 32.65 43.46

0.3 420.85 42.11 85.56

0.15 140.28 14.04 99.60

Bottom 4.00 0.40 100.00

Total 999.49 100.00 -

Fineness Modulus (FM) 2.42

Maximum Diameter(MD) 2.36 mm

The dimensions of aggregates have direct effect on voids, water/cement ratio and workability of

concrete mixtures. The results obtained for maximum diameter and fineness modulus were 2.42 mm e

2.36, respectively. According to the fineness modulus, the sand was classified as fine/medium sand,

belonging to the optimum zone and not presenting deficiency or excess of any particle size, producing

a more economic and workable mortar of concrete. In this way, it was possible to trace the grain size

curve (Figure 2).

Figure 2 – Grain size curve of fine aggregate.

Table 4 presents the results obtained to specific gravity, unit weight and pulverulent materials

content tests for fine aggregate.

Table 4 – Physical Characterization of fine aggregate.

Test Test Method Result

Specific Gravity

(ABNT NBR 9776:1987) 2.618g/cm³

Unit Weight

(ABNT NBR 7251:1982) 1.429g/cm³

Pulverulent Materials Content

(ABNT NBR 7219:1987) 0.07%

According to the results presented in Table 4, it was obtained the specific gravity of fine

aggregate of 2.618 g/cm³ using Chapman Flask (ABNT NBR 9776:1987), as seen in Figure 3.

Figure 3- Determination of specific gravity of fine aggregate using Chapman Flask.

Physical Characterization of cement.

The cement used in the research was a High Early Strength cement type V. The specific gravity

and fineness modulus of cement are presented in Table 5.

Table 5 – Physical characterization of cement.

Test Test Method Result

Specific Gravity

DNER – ME 085/1994 3.10g/cm³

Fineness

ABNT NBR 11579:1991 1.40%

It is observed that the fineness modulus found to HES Portland cement type V was 1.40%,

which meets the maximum value of 12% stablished by test method ABNT NBR11579:1991. The

specific gravity value found was 3.10g/cm³.

Chemical Characterization of Polyethylene Terephthalate - PET

The Polyethylene Terephthalate (PET) used in the research was micronized.

The chemical analysis of PET was performed using X – Ray Fluorescence test. Table 6 shows

the qualitative and quantitative results for chemical composition of Polyethylene Terephthalate.

Table 6 – Chemical composition of Polyethylene Terephthalate.

Determination (%)

Micronized PET

LF SiO2 Al2O3 Fe2O3 CaO TiO2 K2O

0.24 38.70 31.21 14.31 6.76 5.77 3.25

LF: Loss on Fire

According to the results presented in Table 6, it is observed that Polyethylene Terephthalate (PET) is

basically constituted by silica (38.70%), Al2O3 (31.21%), Fe2O3 (14.31%), CaO (6.76%), TiO2 (5.77%)

and K2O (3.25%).

Figure 4 presents Differential Thermal and Thermal Gravimetric analysis of micronized

Polyethylene Terephthalate.

Figure 4 – Differential Thermal and Thermal Gravimetric Analysis of micronized Polyethylene

Terephthalate.

Analyzing the results presented in Figure 4, it is observed the presence of an endothermic peak

at 82°C approximately, related to the change of physical state (solid to liquid), having a significant loss

in PET mass and the occurrence of an exothermic peak at 129°C indicating another change of physical

state (liquid to vapor). From the thermal gravimetric curve, it is observed a total mass loss of 0.24%

Production of concrete and Determination of mechanical properties

Compressive Strength of Concrete fcc

Figure 5 presents the evolution of the average compressive strength with 2.5%, 5.0%, 7.5% and

10% of PET.

Figure 5 – Compressive Strength (fcc) of concrete specimens.

According to the results presented in Figure 5, it is noticeable that the improvement in strength

in the first seven days is high when compared to the improvement at 28 days. This behaviour is caused

by the type of cement used, which was HES Portland cement type V. Besides, this concrete has null

slump. As the strength improvement after the seven first days is not very significant, it is believed that

null slump concrete might be more influenced by weather conditions at the first ages, in other words

curing has great importance to avoid water loss and consequently loss in compressive strength.

4. CONCLUSIONS

According to the results obtained, it is possible to conclude that:

When replacing cement, in the composition of hollow blocks with structural masonry function, by

Polyethylene Terephthalate (PET), there was a reduction in the compressive strength of concrete that

happened to all ages and with all replacement contents of cement by PET. The most unfavourable

condition was observed with the content of 10% of PET in the concrete, presenting a reduction of 1.8

MPa and 2.5 MPa at the ages of 7 and 28 days, respectively. Despite of the reduction in the concrete

strength to the studied mix design, the produced blocks presented compressive strength values above

the values stablished by test method ABNT NBR 6136:1994, which is 4.5 MPa for hollow concrete

blocks to structural masonry and 2.5 MPa for hollow concrete blocks for masonry with no structural

function, according to test method ABNT NBR 7173:1982.

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