Research ArticleModification of Waste Aggregate PET for Improving theConcrete Properties

Zoe Harmonie Lee,1 Suvash Chandra Paul ,1,2 Sih Ying Kong ,1 Susilawati Susilawati,1

and Xu Yang 3,4

1School of Engineering, Monash University Malaysia, Bandar Sunway 47500, Malaysia2Department of Civil Engineering, International University of Business Agriculture and Technology, Dhaka 1230, Bangladesh3School of Highway, Chang’an University, Xi’an 710064, China4Department of Civil Engineering, Monash University, Clayton, Victoria 3800, Australia

Correspondence should be addressed to Xu Yang; xyang2@mtu.edu

Received 24 June 2019; Accepted 26 November 2019; Published 19 December 2019

Academic Editor: Xuemei Liu

Copyright © 2019 Zoe Harmonie Lee et al. +is is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

Disposal of plastic wastes causes negative impacts including degradation of land and ocean and climate change. Reusing plasticwastes in concrete is one of the effective methods of reducing plastic disposal. Polyethylene terephthalate (PET) is one of the mostabundantly available plastic wastes as it is commonly used for plastic bottles and food containers.+is paper investigates the effectsof treating PET wastes using hydrogen peroxide solution (H2O2) and calcium hypochlorite solution (Ca(ClO)2) before in-corporating in concrete as coarse aggregate replacements. +e physical and mechanical properties of concrete were analyzed forthree different percentages, namely, 10%, 20%, and 30%, replacement of natural aggregates with plastic aggregates. For allpercentage of replacements, it was found that chemically treated plastic aggregates have no effects on the fresh density, but theslump decreased due to roughened surface of treated plastic aggregates. Chemical treatment improved the bond strength betweencementitious matrix and plastic aggregates and reduced the gap at the interfacial transition zone (ITZ). +ese phenomenacontributed to the improvement the compressive strength and lower the permeability and porosity.

1. Introduction

+roughout the years, the quantity of plastic consumptionhas increased due to its reasonable cost, flexibility, dura-bility, and global industrialization. According to a statisticsdone by the National Solid Waste Management Departmentof Malaysia, plastic wastes are the second largest of the totalsolid wastes produced in Malaysia [1]. +e slow rate ofdegradation and the large amount of plastic wastes producedby human activities results in large area of landfills arerequired. Incineration is not a viable disposing method dueto the toxic fumes released which is detrimental to theenvironment and human health. Recently, research havesuggested reusing plastic wastes in concrete as natural ag-gregate replacement to reduce the exploitation of naturalresources, and it could minimize the negative environmental

impacts by construction [2]. Plastic wastes are cheap due toabundant in supply. +erefore, reusing plastic wastes as asubstitution for natural aggregates is feasible because it iseconomical and environmental friendly. Commonly, twoforms of plastics are used in concrete, namely, plastic ag-gregates and plastic fibres. Amongst the two, application ofplastic aggregates is more economical and simpler as itgenerally involves less number of processing steps comparedwith that of fibres.

+ere are different types of plastic waste aggregatesavailable for concrete applications. Polyethylene tere-phthalate (PET) is widely used domestically and discardedafter single use. PET is normally used to manufacture plasticbottles, food containers, and cloth fibre. Research showedthat incorporating plastic aggregates in concrete can be usedfor construction applications as it can reach strengths as high

HindawiAdvances in Civil EngineeringVolume 2019, Article ID 6942052, 10 pageshttps://doi.org/10.1155/2019/6942052

as that of normal concrete [3]. Alqahtani et al. [2] stated thatsubstitution of PET in concrete could also be applied forconstruction of pavements and roads, where high strength isnot required. Multiple studies were performed to study theincorporation of plastic waste in concrete, by replacing 10 to30% of natural coarse aggregates. Subramani and Pugal [4]determined that a 20% percentage substitution was opti-mum, as the compressive strength decreased considerablywhen the plastic content was higher. Nevertheless, moststudies just randomly replaced the plastic aggregates inconcrete and observed their influences in mechanical anddurability properties.

Incorporating plastic aggregates into concrete changesthe consistency and homogeneity of mixture properties suchas workability and density. Experiments performed by Saikiaand de Brito [5] showed that the workability of freshconcrete was affected by the surface and texture of aggregatesplastic aggregates. +e smoother surface texture of plasticaggregates produced concrete with higher slump comparedto typical concrete made from natural aggregates. +erefore,as the amount of plastic aggregates increased, the slumpincreased due to a larger area of smooth surface. It was alsofound that the density of concrete decreased proportionallywith increasing replacement of plastic aggregates, as plasticshave lower density than natural aggregates [6, 7].

It was reported that the strength contributed by recycledPET to the mixture was lower than natural fine aggregates [8].+e trend identified by research showed that the compressivestrength reduced with increasing percentage of plastic ag-gregates in concrete. +e reduction in compressive strengthwas caused by the weak adhesive strength between plasticaggregates and cement paste, due the hydrophobicity ofplastics. +e hydrophobicity also further restricted the diffu-sion of water into concrete, which was important for cementhydration [9]. Hannawi et al. [10] concluded that the largegaps at the interfacial transition zone (ITZ) in concrete withplastic aggregates reduced the concrete compressive strength.

Research findings concluded that the porosity and waterpermeability of concrete with plastic aggregates were higherthan those of typical conventional concrete. Islam et al. [11]deduced that the weak bonding at the ITZ between cementpaste and plastic aggregates contributed to higher porosityand permeability. During cement hydration, redistributionof calcium-silicate-hydrate (C-H-S) allows the pores in theITZ to be partially filled. Depending on the width andcontent of aggregates, individual aggregates in ITZ can beinterconnected, which highly affected the permeability andtransport properties of concretes [12]. +rough scanningelectron microscope (SEM) analysis, Pezzi et al. [13] ob-served that the number of voids increased with largeramount of PET aggregates being used. +e results showedlarge gaps and cracks between cement paste and plasticaggregates, which indicated a weakening in bond.

It was concluded from various reviews that the mainreason behind all the changes in the properties of concrete isthe weak bonding between plastic aggregates and cementpaste. Some research has suggested improving the bonds byperforming surface modification using chemical treatments onthe plastic aggregates. It is expected that the characteristics of

the ITZ may be affected by a chemical reaction between theaggregates and the cement paste [14]. However, only limitedstudies have been performed on this topic. A successful studyperformed byNaik et al. [15] demonstrated that treating plasticusing an oxidizing agent could strengthen the bond of plasticto cement, thus producing concrete with higher strength. +isstudy investigated plastic treatment using 3 oxidizing agents:water, bleach (hypochlorite), and bleach with sodium hy-droxide (alkaline bleach) on concrete properties. As theamount of plastic aggregates in concrete increased, thecompressive strength of concrete decreased as predicted, butthe compressive strength was greatly improved after theplastics underwent chemical treatment. Naik et al. [15] furthertheorized that the reaction between the plastic and oxidizingagent created reactive chemical species on the plastic surfacethat could take part in cementitious reaction. Treatment withhypochlorite introduces the R-OH (alcohol) and R-COOH(carboxylic acid) species to the polymeric chain of plastic.+ese species are polar and hydrophilic, which allows strongerhydrogen bonds to be formed. +e polarity also increased thereactivity between the plastic aggregates with the cement paste.

Very limited studies have been conducted for chemicallytreated plastic aggregates used in concrete. +erefore, thisstudy was performed to add more insights of chemicallytreated plastic aggregates for concrete application. +echemical treatment was performed using hydrogen peroxidesolution (H2O2) and calcium hypochlorite solution(Ca(ClO)2). +e effects of chemical treatment on work-ability, density, compressive strength, and permeability wereinvestigated. Finally, analysis of variance (ANOVA) isperformed at 5% significance level to check any significantdifference between the means of the groups statistically.

2. Methodology

2.1. Materials. Materials used in this study include water,ordinary Portland cement (OPC), sand as fine aggregates,crushed rocks, and PET plastic aggregates as coarse aggre-gates. Crushed PET wastes were used to replace coarseaggregates with different percentages. +e plastic aggregateswere produced by crushing recycled plastic bottles and foodcontainers using a machine into sizes ranging from 10 to20mm. Before mixing with concrete, the plastic aggregateswere treated separately by soaking in different oxidizingagents for 24 hours.+en, the treated plastic aggregates wereair-dried to ensure there was no additional water orchemicals on the surface. +e oxidizing agents used were2.5%wt. hydrogen peroxide solution (H2O2) and 5%wt.calcium hypochlorite solution (Ca(ClO)2), which is used inbleaching powder as well. +e plastic aggregates treatedusing water (H2O) was used as control. Figure 1 shows PETplastic aggregates before and during the treatment process.

2.2. Concrete Mix Design. +e concrete mix design wascalculated based on British Standard (BS) of mix pro-portioning. In this study, coarse aggregates (natural crushedrocks) were replaced with 0%, 10%, 20%, and 30% of plasticaggregates by volume. To determine the mix proportions,

2 Advances in Civil Engineering

the combined specific gravity of the aggregates was calcu-lated. Sieve test and Pycnometer test were conducted todetermine the fineness modulus and specific gravity of theaggregates. Figure 2 shows the results of the sieve analysis.+e specific gravity of the fine, coarse, and plastic aggregateswas 2.79, 2.85, and 1.3, respectively. +e mix designs for theplastic aggregate concretes (PAC) are shown in Table 1.

2.3. Preparation of Specimens. Casting and compaction weredone according to BS1881-108:1983. Concrete cubes werecasted using 100×100×100mm moulds for compressivestrength tests. For permeability testing, 150×150×150mmcube samples were casted in accordance with BS EN12390-8:2000. Compaction was done using a vibrating table. Vi-bration was stopped once no air bubbles could be seen at thesurface and a smooth surface was obtained. +e castedspecimens were covered to prevent moisture loss duringhardening of concrete. After 24 hours, the specimens weretaken out from the moulds and cured in water for 7 days and28 days. Curing was done in accordance with BS 1881-111:1983.

2.4. Testing Methods. To evaluate the fresh concrete prop-erties, slump and density were measured in accordance withBS 1881-102:1983 and BS EN12350-6:2009, respectively. +eslump test was performed using a cone mould and a tampingrod. +e density test was performed by filling a containerwith concrete mix and then compacting and weighing thecontainer. Hardened concrete cubes were tested for com-pressive strength at ages of 7 and 28 days, in accordance withBS 1881-116:1983. +e concrete cubes were tested using acompression machine with a loading rate of 2500N/s.Permeability of hardened concrete was obtained by mea-suring the depth of water penetration after samples weresubjected to pressure for 72 hours, as stated in BS EN12390-8:2000. For the purpose of the test, a digimatic concreteimpermeability apparatus was used.

To evaluate the microstructure of the concrete speci-mens, a SEM was used to obtain images under high mag-nification. Elemental identification was also performed usingenergy-dispersive X-ray spectroscopy (EDX) analysis. +etest was done on 3 samples to compare the gap betweentreated plastic aggregates (using H2O, H2O2, and Ca(ClO)2)and the cementitious matrix. +e concrete samples werecured for 28 days and coated with platinum (Pt) to obtain a

a

(a)

b

(b)

Figure 1: Sample of PET plastic aggregates (a) before treatment and (b) during the chemical treatment process.

0102030405060708090

100

0 5 10 15 20 25

Perc

enta

ge p

assin

g (%

)

Sieve size (mm)

River sand

PET plasticCrushed rocks

Figure 2: Sieve analysis of plastic, fine, and coarse aggregates usedin this study.

Table 1: Concrete mix design used in this study.

Mixture %plastic

w/cratio

Water(kg/m3)

Cement(kg/m3)

F.A(kg/m3)

C.A(kg/m3)

P.A(kg/m3)

M0 0 0.6 230 383 971 896 0M10 10 0.6 230 383 929 679 179M20 20 0.6 230 383 903 486 347M30 30 0.6 230 383 882 305 509

Note: w/c ratio: water-cement ratio; F.A: fine aggregates; C.A: coarse ag-gregates; P.A: plastic aggregates.

Advances in Civil Engineering 3

clearer image under the microscope. Using backscatteredelectron mode, an accelerating voltage of 15 kV with mag-nification of 20,000 was set for all three samples.

3. Results and Discussion

3.1. Fresh Concrete Properties. Fresh concrete properties ofslump and density were measured for concrete with differentproportion of treated plastic aggregates using either H2O,H2O2, or Ca(ClO)2. Figure 3 shows the fresh density results forconcrete with various plastic aggregate amounts. Overall, thefresh densities decreased with increasing the amount of plasticaggregates as expected. Since plastic aggregates have a lowerdensity than natural coarse aggregates, the overall weight ofconcrete is reduced, thereby producing a lighter concrete.

+e typical density of normal weight concrete rangesbetween 2200 and 2400 kg/m3, while lightweight concretedensity is below 2200 kg/m3 [9]. From the results shown inFigure 3, the density of concrete with plastic aggregates wasbelow 2200 kg/m3, thereby being classified as lightweightconcrete. +e potential application of plastic aggregatesconcrete (PAC) may noticeably reduce the dead load ofwhole structure which is an important design consider-ation. Comparing the fresh densities of PAC treated withthree different types of oxidizing agents, no distinct pat-terns could be observed from the results. It could beconcluded that different chemical treatment used in thisstudy has insignificant impact on the density of theconcrete.

Figure 4 presents the slump values of PAC using variousamounts of treated plastic aggregates. Overall, the resultsindicated that slump increased with an increasing per-centage of plastic aggregates. +e increase could beexplained by the smoother surface and texture of plasticaggregates as compared with natural coarse aggregates, eventhough the PET aggregates surface area-to-volume ratio forplastic aggregates was higher than that of the natural coarseaggregates. Furthermore, smooth surfaces have weakerbinding force to cement paste as the area of contact is lesser.

In addition, it was found that the slump values variedslightly between the control and other two chemicals used inPAC. Amongst the three oxidizing agents, the slump valuefor Ca(ClO)2 was the lowest, followed by H2O2 and H2O.+e plastic aggregates undergo surface modification due tooxidation reaction with oxidizing agents, and Ca(ClO)2 isthe strongest oxidizing agent, followed by H2O2 and H2O[16]. Treating the plastic with Ca(ClO)2 may modify theinitially smooth surface to be more angular and rougher,resulting in more contact and higher friction between theparticles, therefore causing a lower slump and workability.

3.2. Compressive Strength. +e 7-day and 28-day compres-sive strengths for all mixtures are presented in Figure 5.Overall, the results showed a decrease in compressivestrength as the percentage replacement increased for all PACtypes. Compressive strengths for 10% and 20% replacementswere higher than the minimum compressive strength re-quired for structural concrete, which is approximately

0

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0 10 20 30

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sity

(kg/

m3 )

PAC replacement (%)

ControlH2O

H2O2Ca(ClO)2

Figure 3: Fresh density of concrete with various percentage re-placements of plastic aggregates with different chemical treatments.

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PAC replacement (%)H2O2Ca(ClO)2

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Figure 4: Slump of concrete with various percentage replacementsof plastic aggregates with different chemical treatments.

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ngth

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H2O 7 dayH2O 28 dayCa(ClO)2 7 day

Ca(ClO)2 28 dayH2O2 7 dayH2O2 28 day

Figure 5: Compressive strength of concrete at 7 and 28 days.

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17MPa [9]. +is further proved that concrete with plasticaggregates can be used in structural applications, providedthat the percentage replacement is lower than 30%.

Overall, the compressive strength for concrete withchemically treated plastic aggregates was higher than that ofthe control PAC. +is could be attributed to the differentbond strength between the cement paste and plastic ag-gregates. After being treated with chemicals, oxidation ofplastic surface allows a stronger bond to be formed betweenplastic and cement paste, due to the reduced hydrophobicityafter surface modification. It could be seen from Figure 5that the highest compressive strength was obtained by usingplastic aggregates treated with Ca(ClO)2 for all percentagereplacement for both 7-day and 28-day strengths. Ca(ClO)2is a stronger chemical as compared with H2O2, resulting in ahigher polarity of the plastic surface after treatment, thusallowing stronger hydrogen bonds to be formed, comparedwith weaker bonds such as hydrophobic interactions andvan der Waals force, i.e., intermolecular forces between themolecules are formed on the surface of untreated plastics.

+e percentage of improvement in compressive strengthdue to chemical treatment was not consistent for differentpercentage replacements of coarse aggregates by plastic ag-gregates. As shown in Table 2, the percentage increment ofcompressive strength compared to the control samples fluc-tuated for different percentage replacements, where the lowestmagnitude of increase was observed for 10% replacement.+ismight be due to the difference in proportion of plastic andnatural coarse aggregates in the mixtures. Replacing 10% ofplastic aggregates does not significantly affect the homogeneityof the concrete mixtures as much as higher percentages ofreplacements. +e percentage of natural coarse aggregates isstill considerably higher than the plastic aggregates re-placement. +us, it can be said that as the percentage re-placement increases, the effect of chemically treating the plasticaggregates on concrete strength will be more prominent.

Univariate statistical analyses like ANOVA was done onthe 7-day and 28-day compressive strength results for threetreatment groups, H2O, H2O2, and Ca(ClO)2, for all percentagereplacements. +e statistical analysis was performed to de-termine the effectiveness of chemicals treatment for plasticaggregates to improve concrete compressive strength. AnANOVA test could indicate if there are significant differencesbetween the means of the groups statistically but does not tellwhere the differences lies, if there are any. +e Post hoc TukeyHonest Significant Difference (HSD) test was performed todetermine which of the specific groups’ mean was different.+ese analyses were carried out with 5% significance level.

In ANOVA, the null hypothesis states that there is nosignificant difference between the means of groups. ANOVAis based on the assumption that the samples have the samevariances. Homogeneity of variance is first checked usingLevene’s test. It is conducted to determine if the ANOVAtest can be further performed, as a violation of the test showsthat there is a probability of falsely rejecting the null hy-pothesis. In Levene’s test, if the p value is more than 0.05,then the variances are statistically same. As shown in Table 3,all the p values are more than 0.05, which means that there isno violation on the assumption of homogeneity of variance.

+e output of one-way ANOVA F test is a p value thatstates there is a significant statistical difference betweenmeans of group when the p value is less or equal to 0.05. +eresults for p values in Table 3 for all PAC groups have valuesless than 0.05, indicating the null hypothesis can be rejected.+e p values are very low and close to zero, which showscompelling evidence against null hypothesis. +is meansthat there is an overall effect of chemically treating the plasticaggregates on strength. As discussed previously, this effect isknown to positively increase the 7-day and 28-day com-pressive strengths.

To quantify effects of chemical treatment, themagnitude ofmean differences between groups was calculated using partial-eta square (η2p). A higher value of η2p indicates higher mag-nitude of differences. Most of the results in Table 3 show thatthe differences are large, indicating strong effect of chemicaltreatment on the concrete compressive strength. Table 4presents the results of the Tukey HSD test. +e mean dif-ferences between each pair of means in categories 1 and 2 werecompared to obtain the statistical significance, p(sig). +isidentifies specifically which groups or chemical can increasethe compressive strength when p(sig) is less than 0.05.

+e results validated the previous findings that as thepercentage of plastic replacement increases, the effect ofchemical treatment on the 7-day and 28-day strength be-comes more substantial. Also, the values corroborates thatCa(ClO)2 treatment is the most effective in increasing thestrength of concrete as compared to the control PACstrength. For 10% replacement, the usage of H2O2 on plasticaggregates does not have any significant impact on thestrength as compared to the control, but using Ca(ClO)2shows a change. For 20% replacement, the usage of H2O2 onplastic aggregates has an impact on the 7-day strength butnot the 28-day strength. For 30% replacement, treatingplastic aggregates with H2O2 indicates an improvement forboth 7- and 28-day strengths, but the usage of Ca(ClO)2 iseffective in increasing all strengths for 20% and 30% re-placements. +us, using the chemicals, Ca(ClO)2 and H2O2,to treat the plastic has significant differences than using

Table 2: Percentage increase in compressive strength as comparedto the control PAC (H2O).

Type ofchemicaltreatment

M10 M20 M307-day(%)

28-day(%)

7-day(%)

28-day(%)

7-day(%)

28-day(%)

H2O2 2.7 1.8 14.0 1.8 11.3 25.2Ca(ClO)2 6.94 6.9 38.8 13.2 24.4 55.9

Table 3: Statistical analysis results for compressive strength.

TypeM10 M20 M30

7-day 28-day 7-day 28-day 7-day 28-dayLevene statistic,p value 0.248 0.135 0.313 0.077 0.130 0.383

ANOVAp value 0.010 0.002 0.000 0.000 0.001 0.000

η2p 0.402 0.498 0.901 0.905 0.913 0.934

Advances in Civil Engineering 5

H2O, but predominantly, Ca(ClO)2 produces better strengthresults.

3.3. Water Permeability and Porosity. +e water penetrationrate was tested for three concrete samples incorporated withdifferent types of treated PETaggregates. +is was only donefor 20% replacement, as the main purpose was to comparethe effect of different chemical treatments on the waterpermeability. It was previously determined that 10% plasticreplacements do not show significant effect on the concretewhile 30% is not suitable for structural application purposes.+erefore, 20% replacement was considered to be the mostoptimum percentage of replacement.

From Figure 6, it could be seen that the height of waterpenetrated into the concrete under pressure was the highestfor the control PAC, followed by the PAC with H2O2- andCa(ClO)2-treated PET aggregates. Table 5 shows the waterpenetration rate for each of the PAC type. Compared withthe control, the reduction in the rate was 1.5% and 6.6% forPAC with H2O2 and Ca(ClO)2, respectively. +ese resultscorroborate with the inverse relationship between perme-ability and compressive strength, as the control PAC pro-duces the lowest strength and PAC with Ca(ClO)2-treatedPETaggregates has the highest strength for any percentage ofPET replacements.

Generally, the bonding strength between cement pasteand PET aggregates also influences the permeability ofconcrete. +e permeability of the concrete decreased whenPET aggregates were treated using chemicals, as the in-troduction of stronger bonds reduced the gap between the

cement paste and plastic aggregates. When the gaps betweenparticles reduced, the number of pores decreases and thepore system becomes more discontinuous and ineffective intransportation of fluid, thereby causing permeability todecrease. As discussed previously, it is evident that a strongeroxidizing agent helps forming in a stronger bonding betweenplastics and cement paste, meaning that the concrete withplastic treated using Ca(ClO)2 is expected to have smallergaps in between the particles, thus lowering the permeabilityas compared with H2O2.

Permeability can also be related to porosity in terms ofthe amount of water infiltrating the pores of the concretesamples. It can be deduced that for a less permeableconcrete, the porosity also decreases as there are less dif-fusive pathways available for the water to permeate throughthe pores. +erefore, the PAC with Ca(ClO)2-treatedplastic aggregates can have the lowest permeability andporosity.

3.4. Microstructure Analysis. Figure 7 shows images fromthe SEM, and Figure 8 shows the EDX analysis of elementscompositions in the different concrete mixes. C-S-H foil-like

Table 4: Post Hoc Tukey HSD test showing the statistical significance (p(sig)) between the three groups.

Category 1 Category 2M10 M20 M30

7-day 28-day 7-day 28-day 7-day 28-day

H2OH2O2 0.402 0.537 0.001∗ 0.249 0.024∗ 0.020∗

Ca(ClO)2 0.008∗ 0.002∗ 0.000∗ 0.000∗ 0.001∗ 0.000∗

H2O2H2O 0.402 0.537 0.001∗ 0.249 0.024∗ 0.020∗

Ca(ClO)2 0.113 0.020∗ 0.000∗ 0.000∗ 0.012∗ 0.004∗

Ca(ClO)2H2O 0.008∗ 0.002∗ 0.000∗ 0.000∗ 0.001∗ 0.000∗H2O2 0.113 0.020∗ 0.000∗ 0.000∗ 0.012∗ 0.004∗

∗+e mean difference is significant at the 0.05 level.

Water penetrationheight

(a) (b) (c)

Figure 6: Water penetration depth for PAC with PET aggregates treated with (a) H2O, (b) H2O2, and (c) Ca(ClO)2.

Table 5: Water penetration rates for different chemical treatmentsused on PET aggregates.

Type of treatment Water penetration rate (mm/hr)H2O 1.96H2O2 1.93Ca(ClO)2 1.83

6 Advances in Civil Engineering

fibres and bundles can be seen along with plate-like calcium-hydroxide (C-H) morphology. It can be observed that thePET treated with H2O has smooth surfaces, whereas therough surfaces can be seen in PET treated with H2O2 andCa(ClO)2. Figure 7(b) shows that the PET treated by H2O2has holes and uneven surfaces. In Figure 7(c), the PETtreated by Ca(ClO)2 has cracks and more groove lines inaddition to some holes. +is validates the findings whichpreviously concluded that the concrete with Ca(ClO)2-treated plastic aggregates has the roughest surface and lowestslump values.

As stated previously, treating the PET aggregates withchemicals causes the surface to roughen due to oxidation.Chemical oxidation modifies the surface of PET aggregatesby introducing polar groups so that hydrogen bonds can beformed between the cement paste and PET aggregates toimprove adhesive properties. Without chemical treatment,the bonds formed are nonpolar van derWaals force, which isconsidered to be weaker.

+e improvement in bonding was also observed from theSEM images, which showed the quality of interaction be-tween the cement paste and the PETplastic aggregate in theITZ. By comparing the gap size, the largest gap could beobserved in the control PAC while the smallest gap wasobserved in the PAC with Ca(ClO)2-treated plastic aggre-gates.+emeasured gaps between the cement paste and PETaggregate for H2O, H2O2, and Ca(ClO)2 were given as605 nm, 490 nm, and 347 nm, respectively. +erefore, it canbe concluded that PET aggregates treated with Ca(ClO)2

shows the highest bonding strength between the cementpaste and aggregates, which can be related to a concrete withhigher compressive strength, lower permeability, andporosity.

Based on the results from the elemental analysis in EDXin Figure 8, Ca, C, Si, O, and Al element peaks could befound in all images spectrums selected at the cement matrix.+e low Al peak at the cement matrix indicates a low amountof ettringite. Needle-shaped ettringite crystals can be seendispersed around the cement matrix. Ettringite is notbeneficial at the later ages in concrete as it will reduce thedurability of concrete and cause cracking. At severe envi-ronments, ettringite becomes highly unstable. Minoramounts of secondary ettringite are still acceptable inhardened concretes.

+ere are relatively high peaks for Ca in the spectrums atthe cement paste. Ca/Si ratio is an important factor for thehydration of cement, which affects the strength of concrete.+e ratio of Ca/Si was also determined from the spectrumsfor cement paste in all EDX images in Figure 8. +e Ca/Siratio for the concrete with different plastic aggregates treatedusing H2O, H2O2, and Ca(ClO)2 was 5.5, 4.9, and 3.3, re-spectively. A lower Ca/Si ratio typically gives higher strengthfor any hydration times. For a decreasing Ca/Si ratio, themolar volume C-S-H phases decreases, resulting in a largercontact area between cement matrix and aggregates,stronger bonding, and compressive strength. [17].

In summary, PET waste obtained from the bottles andfood containers can be reused as plastic aggregates for

C-S-H

Ettringite

PET

(a)

PET

Cementpaste

(b)

PET

C-S-H

Ettringite

Cementpaste

(c)

Figure 7: SEM images showing the contact between cementitious matrix and PET plastic aggregate treated with (a) H2O, (b) H2O2, and(c) Ca(ClO)2.

Advances in Civil Engineering 7

concrete. When the PET aggregates are chemically treatedbefore being incorporated in concrete, an improvement inthe physical and mechanical properties can be achieved. Forapplication of the study, PAC can be used in structural andnonstructural applications as the minimum compressive

strength is achieved, provided that the percentage re-placement is not above 30%. Some of the applications in-clude road, highways, pavements, and medians. +erefore,there is a potential for this method to be advanced in theconstruction industry.

0 1 2 3 4

Spectrum 1

5 6 7 8 9 10

keVFull scale 2096 cts cursor: 0.000

C

Ca

CaO PtPt

Pt

(a)

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0 1 2 3 4 5 6 7 8 9 10keVFull scale 1436 cts cursor: 0.000

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(b)

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0 1 2 3 4 5 6 7 8 9 10keVFull scale 3422 cts cursor: 0.000

C

Ca

Ca

Pt

PtPt

O

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(c)

Figure 8: EDX analysis showing the elemental compositions of concrete in PET plastic aggregate treated with (a) H2O, (b) H2O2, and(c) Ca(ClO)2.

8 Advances in Civil Engineering

4. Conclusion

+is research work contributed to the development ofchemically treated waste polyethylene terephthalate (PET)aggregates in concrete. In this study, PET aggregates weretreated using three different types of oxidizing agents such asH2O, H2O2, and Ca(ClO)2. From the outcome of this study,the following conclusions can be drawn:

(i) +e workability of concrete decreases when theplastic aggregates were treated using a strongeroxidizing agent of Ca(ClO)2. +e slump value ofplastic aggregate concrete (PAC) was found to belower in the Ca(ClO)2-treated waste PETaggregatesthan the PET treated with H2O and H2O2.

(ii) Concrete with PETsatisfies the lightweight concretedensity specification. +e density of PAC reducedas the percentage of PET replacement increased.Chemical treatment has no effects on the density ofconcrete.

(iii) +e compressive strength of PAC also reduced asthe percentage of PET replacement increased.Chemical treatment on plastic aggregates was ef-fective in improving compressive strength ofconcrete. Amongst the treatments used, Ca(ClO)2showed the highest improvement of concretecompressive strength.

(iv) From univariate statistical analysis of ANOVA andPost Hoc Tukey test, it was further established thatPET aggregates treated using Ca(ClO)2 had morestatistical significant effects on the compressivestrength than H2O and H2O2.

(v) Chemical treatment on plastic aggregates reducesthe porosity and permeability of concrete. PACmixed with PET aggregates treated with Ca(ClO)2showed a lower permeability than the PET treatedwith H2O and H2O2.

(vi) In the control mix, weak bonding due to relativelylarge gaps between the cementitious matrix andPET aggregates was proved by the SEM imageanalysis. However, the bonding was improved byreducing the gaps between the matrix and aggre-gates for concrete with Ca(ClO)2-treated PET ag-gregates, followed by concrete with H2O2-treatedPET aggregates.

(vii) +e elemental analysis results revealed that theconcrete with Ca(ClO)2-treated PET aggregatesdemonstrated the lowest Ca/Si ratio which validatesthe improvement in the compressive strength ofPAC.

In the end, limited research has been done to analyze theeffects of chemically pretreating the waste PETaggregates onconcrete properties. Further studies on the flexural andtensile strengths of PAC with chemically treated PETas bothcoarse and fine aggregates can be conducted to widen theapplication of PAC. Also, further works can be performed toinvestigate the effects of other types of chemicals which

might have stronger oxidizing power to promote betterbinding of PET aggregates to the cementitious matrix andthus producing concrete with higher strength. Finally, long-term durability of PAC can be analyzed such as thermalproperties and corrosion attack to investigate the resistanceof PAC towards environmental and surrounding changes.

Data Availability

All the data used in this study can bemade available from thecorresponding author upon request.

Conflicts of Interest

+e authors declare that they have no conflicts of interest.

References

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