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Contents lists available at ScienceDirect

Sustainable Cities and Society

jou rna l h om epage: www.elsev ier .com/ locate /scs

echanical properties and ASR evaluation of concrete tiles withaste glass aggregate

abio Paiva Cotaa, Caio Cesar Damas Meloa, Tulio Hallak Panzeraa,∗,loizio Geraldo Araújoa, Paulo Henrique Ribeiro Borgesb, Fabrizio Scarpac

Department of Mechanical Engineering, University of São João del-Rei – UFSJ, Prac a Frei Orlando, 170, São João del-Rei, BrazilFederal Centre for Technological Education of Minas Gerais – CEFET/MG, Department of Civil Engineering, Belo Horizonte, BrazilAdvanced Composites Centre for Innovation and Science, University of Bristol, UK

r t i c l e i n f o

rticle history:vailable online xxx

eywords:aste glassetakaolin

a b s t r a c t

This work describes a statistical design of experiments (DoE) testing campaign on 396 samples to eval-uate the effect of replacing quartz aggregate in concrete with waste glass, and Portland cement withmetakaolin to develop a novel generation of sustainable concrete tiles. The properties assessed were bulkdensity, permeability, dynamic modulus and length changes due to alkali-silica reaction (ASR) expan-sion. Metakaolin (MK) was used to replace Portland cement (PC) to verify the possibility of obtaining

ustainabilitySR expansiononcrete tiles

lower ASR expansion. Higher permeability and lower bulk density were obtained when the quartz wasreplaced with glass particles. The statistical analysis also confirmed that the dispersion of 15 wt% of MKwas able to mitigate any possible ASR expansion caused by the presence of coarse glass particles. Thecomposite mixes evaluated in this work constitute promising materials to be used in concrete tiles orsimilar Q2semi-dry compacted products.

© 2015 Published by Elsevier Ltd.

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. Introduction

Glass has been widely used since the middle Ages and its useas been extensively increased in the 21st century. Glass hasemarkable characteristics, such as the relatively easiness of man-facturing, a transparent surface, resistance to abrasion, safety andurability (Topc u & Canbaz, 2004). The amount of waste glass (WG)as gradually increased over recent years due to an ever-growingse of glass products (Park & Lee, 2004). United Nations estimatehat out of 200 millions of tonnes of waste generated worldwideach year, 7% is represented by of glass (Topc u & Canbaz, 2004).he use of recycled WG in glass manufacturing reduces the overallnergy consumption, use of raw materials and decreases dam-ges to related machinery. However, not every type of WG cane recycled into new glass products because of the impurities andndesired mixed colours (Shi & Zheng, 2007). The non-recyclableG constitutes a problem for the disposal of solid waste, as glass is

Please cite this article in press as: Cota, F. P., et al. Mechanical propertieSustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.20

non-biodegradable material (Khmiri, Chaabouni, & Samet, 2013).or this reason, there is an impelling need to develop new appli-ations for mixed waste glass (Shi & Zheng, 2007). A potential way

∗ Corresponding author. Tel.: +55 32 33792603; fax: +55 32 33792525.E-mail address: panzera@ufsj.edu.br (T.H. Panzera).

ttp://dx.doi.org/10.1016/j.scs.2015.02.005210-6707/© 2015 Published by Elsevier Ltd.

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to use WG is within the manufacturing of construction materials,mainly mortars and concretes. The construction industry does con-sume a significant amount of mixed materials, residues and wastes(Khmiri et al., 2013). Among various types of urban solid waste,glass (if finely ground) may replace Portland cement in mortars andconcretes and act as a reactive supplementary material (pozzolan)(Schwarz, Cam, & Neithalath, 2008; Shayan & Xu, 2006). Glass alsopresents remarkable physical characteristics as a composite dis-persion (Tan & Du, 2013), i.e., low water absorption (Topc, Boga,& Bilir, 2008) and lower density when compared with traditionalconcrete aggregates. However, high amounts of WG decrease notonly the concrete weight, but also the compressive strength due tothe weak adhesion with the cement paste (Topc u & Canbaz, 2004).

The main factor limiting the addition of glass particles incement-based materials is however the well-known expansivealkali-silica reaction (ASR) (Mitchell, Beaudoin, & Bellew, 2004;Taha & Nounu, 2008a; Topc et al., 2008). The amorphous silicain glass is likely to be attacked by the alkaline environment pro-vided by the porous solution of the cement paste, giving rise to themonomer Si(OH)4, which further react with cement alkalis, such

s and ASR evaluation of concrete tiles with waste glass aggregate.15.02.005

as Na+, K+, and with Ca2+ to form a gel-like structure (ASR gel) (Du& Tan, 2013; Maraghechi, Shafaatian, Fischer, & Rajabipour, 2012).The ASR gel can absorb water and swell inside the microstructureof concrete, resulting in internal stress. Once the internal stress

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eodpmttArzrtewfTteH

oBoaBmpc2

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a

(

Table 1Chemical composition and physical properties of Portland cement and metakaolin.

Portland cement Metakaolin

ChemicalCaO (%) 64.14 0.2SiO2 (%) 19.45 56.0Al2O3 (%) 4.75 36.0Fe2O3 (%) 3.12 2.0SO3 (%) 2.85 –CO2 (%) 1.13 –MgO (%) 0.80 0.2K2O (%) 0.66 1.5Na2O (%) – 0.1TiO2 (%) – 1.0Loss on ignition (%) – 2.5Physical

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xceeds the strength of concrete, severe cracking and damage mayccur (Du & Tan, 2013). The degree of expansion of ASR gel isependent on the valence and relative concentrations of cationsresent in the ASR gel (Rodrigues, Monteiro, & Sposito, 2001). Someethods have been used to mitigate the ASR expansion, such as

he employment of low-alkalis cement and the reduction of water-o cement ratio (i.e., the availability of free-water in the system).nother method considered to reduce the ASR effect consists ineplacing the Portland cement with pozzolans, because the poz-olanic reaction products retain alkalis in their structure and alsoeduce the free OH− ions that attack amorphous silica and starthe process (Kandasamy & Shehata, 2014; Ling & Poon, 2011). Sev-ral studies have also shown that using lithium-based admixtures,hich form silica-gel products, do not absorb water and, there-

ore, do not swell (Kandasamy & Shehata, 2014; Ling & Poon, 2011;an & Du, 2013). Another alternative to reduce the effect of ASR ishe inclusions of fibres in concrete, which delay the formation andxtent of cracks (Turanli, Shomglin, Ostertag, & Monteiro, 2001;addad & Smadi, 2004).

The effect of size, content and composition of glass aggregatesn the formation of ASR has been well documented (Saccani &ignozzi, 2010), and there is general agreement that the reductionf the size of glass particles contributes to decrease of crack prop-gation phenomena (Farshad, Hamed, & Gregor, 2010; Penacho,rito, & Veiga, 2014). The dispersion of fine particles (glass powder)ake a positive contribution, given that glass powders undergo a

ozzolanic reaction with the presence of alkaline activator (lime,ement and alkalis) that creates hydration products (Taha & Nounu,008a).

.1. Research significance

Previous studies have shown the effects of WG on the propertiesf concrete, as well as the employment of pozzolanic materials toitigate ASR. However, much research has focused on structural

oncrete rather than prefabricated elements such as concrete tiles.he latters have a particular mix design: (i) the mixes are very dryecause they need to be extruded; (ii) the particle size envelope ofggregates is different (from 0.15 to 5 mm). Fine pozzolans (such asetakaolin or silica fume) are not usually employed in those mixes

ecause they demand too much mixing water or superplasticizers.he first lower the strength; the latter has little effect on dry mixesor extruded concrete. So, the majority of concrete tiles mixes willontain only pozzolans or fillers with fineness in the same order ofagnitude of Portland cement, which are blastfurnace slag, fly ash

r limestone fillers.This paper presents three contributions to the concrete science

nd sustainability:

(i) Study on the addition of metakaolin in the mixes used forextruded concrete: this pozzolan is very effective to miti-gate ASR, but it may adversely affect the properties of theconcrete tiles. The mixes are even drier and the compactionmay worsen; porosity and permeability could jeopardize themechanical properties and durability as well.

(ii) To the authors’ knowledge, recycled glass is not employed asaggregate in the manufacturing of concrete tiles. This study,therefore, presents the characterization of alternative mixesfor concrete tiles with the aim to develop sustainable roofingelements for cities worldwide.

iii) Statistical analysis was used to ensure that the results are reli-

Please cite this article in press as: Cota, F. P., et al. Mechanical propertieSustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.20

able and have a statistical significance. This is often forgottenin the development of building materials. For those involvedin the development of new products, it is important to deter-mine not only the individual factors that significantly affect the

BET specific surface (m2/g) 0.47 24Density (g/cm3) 3.12 2.65

properties of the materials, but also the interaction betweenthe factors themselves and their level of significance.

This paper describes an experimental analysis based on a fullfactorial design. It investigates the effect of partial replacement ofthe natural aggregates with WG and Portland cement (PC) withmetakaolin (MK) in the properties of sustainable concrete tiles.The ANOVA study employed a level of significance of 5%, i.e., 95%probability of the effect being significant.

2. Materials and methods

2.1. Raw materials

A rapid-hardening Portland cement (ASTM III) was used as mainbinder. The cement was produced by Holcim-Brazil. The metakaolin(MK) was supplied by Metacaulim do Brasil (Brazil), and the quartzaggregate by Moinhos Gerais (Brazil). Table 1 shows the chemicalcomposition and the physical properties of the Portland cementand metakaolin used. The chemical composition was determinedby x-ray fluorescence; loss on ignition according to the ASTM C114;specific surface using a Quantachrome High Speed Gas SorptionAnalyser (BET); density according to the Le Chatelier method –ASTM C188-14). The pozzolanic activity of MK was determinedusing the Chapelle method, which calculates the amount of calciumhydroxide that reacts with one gram of pozzolan. The result was1000 mg Ca(OH)2/g, which indicates that the MK used is a high poz-zolanic material. A local recycling plant in São João del Rei (Brazil)supplied the WG particles, which were ground in a lab mill machineto obtain different particle sizes.

2.2. Experimental planning

Three experimental factors were investigated in this work: theglass particle size, the glass particle fraction and the addition ofmetakaolin. Table 2 shows an aggregate particle size distribu-tion (PSD) used in the production of concrete tiles as well as theparticle size envelope used in the work. The PSD was always con-stant in order to keep the same rheology for all the experimentalconditions. Three levels of particle size range were consideredfor the quartz/glass replacement: 4–10 US-Tyler, 10–20 US-Tylerand 20–60 US-Tyler (Table 2). The quartz particles were partiallyreplaced by glass particles at 7.5 wt% and 15 wt%. The MK replacedPortland cement at 7.5 wt% and 15 wt% (Bashar & Ghassan, 2008).

s and ASR evaluation of concrete tiles with waste glass aggregate.15.02.005

Design of experiment (DOE) is a systematic method based ona regression model to determine the relationship between factorsaffecting a process and the output of that process. In other words,it is used to find cause-and-effect relationships. This information

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Table 2Quartz particle size distribution for cementitious tiles and work setup.

General particle size distribution forconcrete tiles

Particle size envelopeused in this work (%)

Sieve US-Tyler – (mm) Retained (%)

4 US-Tyler – (5 mm) 04–10 US-Tyler(15.0 wt%)

5 US-Tyler – (4 mm) 57 US-Tyler – (2.8 mm) 11.49 US-Tyler – (2 mm) 15.89 10–20 US-Tyler

(40.0 wt%)16 US-Tyler – (1 mm) 27.0832 US-Tyler – (0.500 mm) 28.44 20–60 US-Tyler

(30.0 wt%)

ip(vritotr(

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dTtdttb‘pwta

wttvo

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Fig. 1. Cylindrical samples for the physical testing.

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60 US-Tyler – (0.250 mm) 10.91 60–100 US-Tyler(15.0 wt%)115 US-Tyler – (0.125 mm) 1.28

s needed to manage process inputs in order to optimize the out-ut. The design of experiments (DoE) and the analysis of varianceANOVA) are used to evaluate not only the direct effect of indi-idual factors, but also their mutual interaction when affecting theesponses at a confidence interval of 95%. A full factorial design (nk)s made from all possible combinations of the experimental fac-ors (k) and its respective levels (n). The DoE approach was basedn a randomized design to eliminate redundant observations ando reduce the number of tests, in order then to obtain statisticallyobust information about the interactions existing among variablesJeff Wu & Hamada, 2000).

A full factorial design of 3221 was conducted in this work, givingighteen experimental conditions (Table 3). Eleven samples wereabricated for each experimental condition and replicate. Two repli-ates were adopted in this experiment, providing a total of 396amples. A replicate consists on repeating the experimental con-ition so that the error associated to the individual response cane estimated. The magnitude of this error is important to identifyignificant effects attributed to the factor selection. Three samplesepresenting the reference conditions were also produced with nolass particle inclusions (see Table 4).

The statistical software Minitab 16 was used to perform theesign of experiment (DOE) and the analysis of variance (ANOVA).he P-values from ANOVA (Table 5) indicate which effects are sta-istically significant based on the examination of the experimentalata from replicates #1 and #2. If the P-value is less than or equalo 0.05, the effect is considered to be significant. A ˛-level of 0.05 ishe level of significance that implies a 95% probability of the effecteing significant. The results are presented via ‘main effect’ and

interaction’ plots. The main effect of a factor can be only inter-reted individually if there is no evidence that it does not interactith other factors. The factors that interact should be considered

ogether when one or more interaction effects with superior orderre significant (Jeff Wu & Hamada, 2000).

The value of ‘R2 adjusted’ exhibited in the ANOVA provided howell the model predicts responses for new observations. The closer

he coefficient is to 1 (or 100%), suggests models of greater predic-ive ability. The R2 values for the responses of this particular workaried from 77.80% to 99.73%, which indicates satisfactory accuracyf the models.

The response variables investigated in this work were the bulkensity, the oxygen permeability, the dynamic modulus of elastic-

ty and the length changes due to the ASR expansion. Cylindricalnd prismatic samples were prepared to perform the experimentalests.

.3. Mixing, casting and curing

Please cite this article in press as: Cota, F. P., et al. Mechanical propertieSustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.20

.3.1. Cylindrical samplesThe semi-dry concrete batches were mixed in a Hobart mixer

ollowing the BS EN 12390-2 standard (BS EN 12390-2, 2009). The

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Fig. 2. Prismatic samples for the ASR testing.

water-to-cement ratio (w/c) and binder-to aggregate ratio (b/a)were kept constant at 0.42 and 0.28, respectively, for all formu-lations. This w/c is sufficient to permit fully hydration of cement,as well as adequate compaction of the concrete samples. Cylindri-cal samples (Fig. 1) were produced by compaction with a Marshallhammer. This equipment is commonly used in foundry sand testingto make specimen of moulding sand by compaction. This equip-ment can be used in laboratory to reproduce the compaction levelof extruded concrete products. In this work, a constant mixing mass(215 g) and 25 hammed-blows were considered for each sample,resulting in cylinders with approximately 48 mm of height and50 mm of diameter (from the dimensions of the steel mould). As theconcrete is semi-dry, the cylinders can be immediately demouldedafter the compaction. Bleeding has been reported as an issue whenWG is incorporated into concrete, because of the intrinsic smoothsurface and the very low water absorption of the glass particles(Taha & Nounu, 2008b). However, no samples in this work haveshown signs of bleeding, likely because of the low mix moistureused for the concrete roof tiles. After demoulding, the samples werethoroughly wrapped with a plastic film to avoid desiccation andthen transferred to an oven for curing at 50 ◦C for 6 h to reproducethe thermal curing at a concrete plant. After this short-term curingregime, the samples were subsequently cured at laboratory condi-tions (20 ◦C and 60 ± 5 R.H.) for 28 days prior to testing. At this age,the cement is predominantly reacted and the pozzolanic reactionhas already started.

2.3.2. Prismatic samplesA prismatic metallic mould (25 × 25 × 285 mm) was used to

manufacture the samples for the ASR tests. Screws were embed-ded at the two ends of the samples to fix them in a length gaugeapparatus, which was used to measure the ASR expansion follow-ing ASTM C1260 (ASTM C1260, 2007). In this case, the sampleswere not compacted but rather vibrated. At first, prisms containingmetakaolin and recycled glass presented a rough surface finishingwhen w/c = 0.42, which may be caused by the combination of a finepozzolan and sharp particles of RG in the mixes. A higher w/c ratio(0.55) was then employed for all formulations subjected to ASRaccelerated testing, in order to prevent any surface roughness that

s and ASR evaluation of concrete tiles with waste glass aggregate.15.02.005

could affect the results (Fig. 2).The mortar was poured into the moulds followed by 3 min

of vibration. The filled moulds were kept at room temperature

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Table 3Full factorial design 3221.

Setup Glass (G) particlesize (US-Tyler)

wt% of G wt% of MK Setup Glass (G) particlesize (US-Tyler)

wt% of G wt% of MK

C1 [4–10] 7.5 0.0 C10 [10–20] 15.0 0.0C2 [4–10] 7.5 7.5 C11 [10–20] 15.0 7.5C3 [4–10] 7.5 15.0 C12 [10–20] 15.0 15.0C4 [4–10] 15.0 0.0 C13 [20–60] 7.5 0.0C5 [4–10] 15.0 7.5 C14 [20–60] 7.5 7.5C6 [4–10] 15.0 15.0 C15 [20–60] 7.5 15.0C7 [10–20] 7.5 0.0 C16 [20–60] 15.0 0.0C8 [10–20] 7.5 7.5 C17 [20–60] 15.0 7.5C9 [10–20] 7.5 15.0 C18 [20–60] 15.0 15.0

Table 4Reference conditions.

Reference Glass particle inclusion (wt%) Quartz particle inclusion (wt%) Metakaolin inclusion (wt%)

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RC3 0.0

∼20 ◦C) for 24 h; subsequently the samples were taken out of theoulds.

.4. Experimental

.4.1. Bulk densityThe dry bulk density of the concrete cylinders was calculated by

ividing the dry weights (after 24 h of drying at 105 ◦C) by the bulkolume of the samples. The bulk volume was calculated based onhe dimensions measured with a calliper.

.4.2. Oxygen permeabilityOxygen permeability measurements were carried out using the

eeds permeameter described by Cabrera and Lynsdale (Cabrera Lynsdale, 1988). The intrinsic permeability (k) in (m2) may bealculated as:

= 4.04 · 10−16 · Q · P2 · L

A · (P21 − P2

2 )(1)

In Eq. (1), L is the length of the specimen [m], A is the cross-ectional area of specimen [m2], Q is the flow rate [cm3/s], P1 is thebsolute applied pressure [bar] and the P2 rate is measured. Theonstant 4.04 × 10−16 accounts for the compressibility and viscos-ty of the oxygen and the units selected. Prior to testing, the samples

ere oven dried at 105 ◦C for 24 h. Two samples were tested for eachxperimental condition, and replicate and the mean were recorded.

Please cite this article in press as: Cota, F. P., et al. Mechanical propertieSustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.20

.4.3. Dynamic modulus of elasticityThe dynamic modulus of elasticity was calculated based on the

esonance of vibration in the longitudinal mode following the rec-mmendations of the BS 1881:209 standard (BS1881-209, 1990).

able 5-values from analysis of variance (ANOVA).

Factors Bulk density

Main FactorsGlass particle size (GS) 0.000

Glass particle fraction (GF) 0.000

Metakaolin addition (MK) 0.000

Interaction

GS × GF 0.015

GS × GF 0.982

GF × MK 0.518

GS × GF × MK 0.054

Variance 0.0110100

R2 (adj) (%) 90.18

00 000 7.500 15.0

An Erudite MkIV equipment was used to measure the fundamentalaxial resonance frequency of the cylindrical samples at 28 days.The dynamic modulus of elasticity depends on the length-L (inmm), density-� (in kg/m3) and resonance frequency-n (in Hz) ofthe concrete as shown in Eq. (2):

ED = 4 · n2 · L2 · � · 10−15 (2)

2.4.4. ASR expansionThe ASR expansion was measured according to the ASTM

C1260 standard (ASTM C1260, 2007), which implies the use ofthe prismatic samples described in Section 2.3.2 and a length gageapparatus. The test rig consisted of a standard metal structure, adigital length gauge (accuracy of 0.001 mm) and a standard bar forlength calibration. The length of the samples before testing wasfirstly recorded when they were demoulded at 24 h. The sampleswere then immersed in 1 N NaOH solution at 80.0 ± 2.0 ◦C, and thelength changes measured at 1, 3, 10, 14 and 28 days. The ASR expan-sion – L (%) – was calculated as follows:

L = Lx − Li

G× 100 (3)

Eq. (3) correlates the specimen length for the period Lx [mm], theinitial specimen length Li [mm] and the nominal specimen lengthG [mm].

3. Results

s and ASR evaluation of concrete tiles with waste glass aggregate.15.02.005

Table 5 shows the results of the analysis of variance (ANOVA).The results will be presented via ‘main effect’ and ‘interaction’ plots.The factors highlighted in bold in Table 5 were evaluated witheffect plots. Table 6 shows the results for the reference conditions

Oxygen permeability Dynamic modulus ASR expansion

0.003 0.000 0.0000.043 0.000 0.0040.238 0.000 0.868

0.803 0.000 0.0010.135 0.000 0.3940.548 0.000 0.2820.446 0.000 0.000

4.42 × 10−5 1.19346 0.007172777.80 93.22 99.73

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Table 6Reference conditions.

Properties RC1 RC2 RC3

Bulk density (g/cm3) 2.15 ± 0.01 2.12 ± 0.02 2.09 ± 0.01Permeability (×10−5 m2) 7.1 ± 3.15 8.2 ± 3.65 8.4 ± 2.83Dynamic modulus (GPa) 33.09 ± 2.80 37.79 ± 2.12 36.97 ± 2.04ASR expansion 0.009 ± 0.006 0.033 ± 0.004 0.003 ± 0.028

Me

an

bu

lk d

en

sit

y (

g/c

m^

3)

15.07.50.0

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2.13

2.12

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2.09

2.08

2.07

2.06

2.83 %

F

cmdod

3

vosiw

tl2tc

tt(sc

6ofiact

3

Mn

Glass particle fraction

Me

an

Bu

lk d

en

sit

y (

g/c

m^

3)

15.0wt%7.5wt%

2.12

2.11

2.10

2.09

2.08

2.07

2.06

[4 - 10 ][10 - 20 ][20 - 60 ]

(US-Tyler)sizeparticleGlass

change from 4–10 to 10–20 US-Tyler cannot be easily explained. Infact, this change in the glass particle size (GS) did not statisticallyaffect the density of the composites (Table 5).

Me

an

Pe

rme

ab

ilit

y (

m^

2)

15.0wt%7.5wt%

0.000 135

0.000 130

0.000 125

0.000120

0.000115

0.000110

0.000 105

0.000 100

33%

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ig. 3. Plot of the main effect of the metakaolin (MK) on the mean bulk density.

onstituted by quartz particles and cement/metakaolin replace-ents with 0 wt% (RC1), 7.5 wt% (RC2) and 15 wt% (RC3)

ispersions. Few changes in the properties of the mortars werebserved by the MK inclusions; however a slightly increase in theynamic modulus was noticed.

.1. Bulk density

The bulk density data varied from 2.01 g/cm3 to 2.17 g/cm3. P-alues lower than 0.05 show that all main factors and an interactionf factors like glass particle size (GS) and glass particle fraction (GF)ignificantly affect the bulk density (see Table 5). In this case, thenteraction (GS×GF) and the main factor metakaolin addition (MK)

ill be evaluated via effect plots.Fig. 3 shows the main effect plot of metakaolin addition on

he mean bulk density. The use of metakaolin in lieu of Port-and cement reduced the bulk density of the composites by nearly.83%. This behaviour can be attributed to the lower density ofhe metakaolin (2.65 ± 0.08 g/cm3) compared to that of Portlandement (3.12 ± 0.10 g/cm3).

Fig. 4 shows that the replacement of quartz with glass par-icles (7.5% and 15%) also reduced the bulk density becausehe density of the glass (2.47 ± 0.09 g/cm3) is lower than quartz2.69 ± 0.11 g/cm3). Ismail and Al-Hashmi (2009) observed theame trend in density when replacing quartz with glass particles inoncrete.

The change in density for different envelopes (4–10, 20–60 and0–100 US Tyler) may be attributed to different particle packingr porosity at the interface transition zone (ITZ). In other words,ner particles of WG (e.g. 20–60 US Tyler) present higher surfacerea of glass particles with angular shape, which may reduce theompaction and density thus increasing the porosity and reducinghe density.

.2. Oxygen permeability

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The permeability varied from 2.80 × 10−5 to 22.68 × 10−5 m2.ost of the values are higher than the reference formulation (with

o WG) (Table 6). P-values in Table 5 show that the glass particle

Fig. 4. Sensitivity of the mean bulk density versus glass particle size (GS) and frac-tion (GF).

size (GS) and the glass particle fraction (GF) significantly affectedthe permeability. Fig. 5 shows the variation of the oxygen perme-ability versus the glass particle fraction. The graph indicates thata large replacement of quartz with glass particles led to a signifi-cant increase in permeability (33%), which is in line with the densityresults (Section 3.1). The angular shape of WG, as well as poor adhe-sion between the two phases (WG and matrix), possibly increasedthe presence of pores around the interface transition zone and,consequently, the permeability.

Fig. 6 shows the variation of the oxygen permeability versus theglass particle size (GS). The replacement of fine quartz (20–60 US-Tyler) with glass particles provided an increase of nearly 79% inpermeability. Similar to the density results, this behaviour mightbe attributed to the larger particle surface area achieved by thefine WG particles that led to the increase of the amount of pores atthe interface. The slight drop in permeability when glass particles

s and ASR evaluation of concrete tiles with waste glass aggregate.15.02.005

Glass particle fraction

Fig. 5. Variation (main effect plot) of the mean permeability versus the glass particlefraction (GF).

ARTICLE ING ModelSCS 252 1–8

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ig. 6. Sensitivity of the mean permeability versus the glass particle size (GS).

.3. Dynamic modulus of elasticity

The dynamic modulus varied from 16.21 GPa to 26.92 GPa,hich is significantly lower than those of the reference formu-

Please cite this article in press as: Cota, F. P., et al. Mechanical propertieSustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.20

ations (without WG), which varied from ∼33 GPa to ∼38 GPaTable 6). Fig. 7 reveals a third order interaction effect plotGS×GF×MK) for the mean value of the dynamic modulus. The

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PRESSd Society xxx (2015) xxx–xxx

replacement of quartz from 7.5 wt% to 15 wt% glass particles con-tributed to a slight decrease in the dynamic modulus, except whenglass particle size of 4–10 US-Tyler was used (Fig. 7a). In that casea sharper reduction is observed. But overall Fig. 7a and b showsthat a rise in the dynamic modulus is observed when larger glassparticles were added. The use of metakaolin did not substantiallycontribute to a variation of the dynamic modulus. In general, theresults of density, permeability and dynamic modulus have a goodcorrelation, i.e., formulations of concrete tiles with lower densitypresented higher permeability and lower dynamic modulus.

3.4. ASR expansion

The ASR expansion measured after 28 days varied from −0.011to 0.427. A third order interaction effect significantly affects the ASRexpansion (Table 5). The largest ASR expansion was obtained whenthe composites were manufactured with coarse glass particles[4–10 US-Tyler], using higher percentage of glass particles (15 wt%)and no addition of metakaolin (Fig. 8). In contrast, the compositemade from fine glass particles, lower GS fraction and high levelof metakaolin presented the lowest alkali aggregate expansion.

s and ASR evaluation of concrete tiles with waste glass aggregate.15.02.005

(Fig. 8a). Farshad et al. (2010) reported that the formation of expan-sive gel occurs inside the cracks of the glass particles. Larger glassparticles lead to higher crack sizes when compared to the smaller

etakaoli n inclusion

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Fig. 9. ASR expansion versus time (days): effect of the glass particles size.

nes, meaning that coarse glass particles are more prone to start anlkali-silica reaction than the fine glass ones. The use of metakaolinitigated the alkali-aggregate expansion in all the formulations

tudied (Fig. 8b and c). The inclusion of 15.0 wt% of metakaolinas sufficient to compensate the ASR expansion within the accept-

ble limits prescribed by the ASTM C1260 standard (ASTM C1260,007) (0.10%). Pozzolanic materials such as metakaolin are ableo dissolve silica particles forming C–S–H, therefore inhibiting theormation of the expansive gel (Farshad et al., 2010).

The increase of fraction of glass particle fraction led to anncrease of the ASR expansion mainly when a small amount of

etakaolin was added. The formation of an expansive gel dependsn the presence of amorphous silica within the glass particles. These of 15 wt% of metakaolin neutralized the ASR expansion in thewo cases when 7.5 wt% or 15 wt% of glass particles were dispersedFig. 8c).

The ASR expansion was measured after different times (1, 3, 7,0, 14 and 28 days). The evolution of the ASR expansion is alsoresented in Figs. 9–11 to further highlight the effect of each fac-or. Fig. 9 shows the time history of the ASR expansion for C1, C7nd C13 composites, which were fabricated with the same frac-ion of glass (7.5 wt%) and metakaolin (0.0 wt%), but different glassarticle size (4–10 US-Tyler, 10–20 US-Tyler and 20–60 US-Tyler,espectively). Similarly to what was observed in Fig. 8, the ASRxpansion increased with increasing particle size; however, after0 days of accelerating ASR testing, C1 composite presented a sig-ificant expansion (0.21%) after 28 days, which exceeds the limitecommended by the ASTM C1260 code (ASTM C1260, 2007).

Two pairs of composites (C1–C4 and C13–C16) were selected tohow how the ASR expansion was affected by two different WG

Please cite this article in press as: Cota, F. P., et al. Mechanical propertieSustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.20

article sizes (4–10 US-Tyler and 20-60US-Tyler). Those compos-tes contained no MK inclusion (Fig. 10). C4 and C16 composites

ere fabricated with high level of glass (15 wt%) and presented

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Fig. 11. ASR expansion against time (days): effect of metakaolin inclusion.

higher expansions. The samples C1, C4 and C16 exceeded the limitexpansion recommended by ASTM C1260 (ASTM C1260, 2007). Itis possible to note that the reference composite C1 (without WGand MK) did not expand. The formulation C13 (with 7.5 wt% quartzreplacement constituted by 20–60 US-Tyler WG, 0% MK inclusion)is interesting from an application point of view, as the expansionat 28 days was well under the limit threshold.

Another two series of composites, with different metakaolin lev-els (0.0 wt%, 7.5 wt%, and 15.0 wt%) were selected to identify theeffect of this pozzolan on the ASR expansion. Fig. 11 shows for-mulations C1, C2 and C3 (all with WG particle size 4–10 US-Tyler,7.5 wt% glass particle), and C13, C14 and C15 (all with WG parti-cle size 20–60 US-Tyler, 7.5 wt% WG). The inclusion of 7.5 wt% ofmetakaolin (C2) was not able to maintain the expansion below therecommended limit for the first series. The situation was differentfor the second series (C13-C15), for which an expansion well belowthe threshold limit was observed when 7.5 wt% (C14) and 15 wt%(C15) of MK replaced the Portland cement in the composites.

4. Conclusions

This paper has shown the effect of waste glass fraction, its par-ticle size and also metakaolin fraction (as replacement of 7.5% and15% Portland cement) on the properties of concrete tiles, as well ason the expansion of these composites due to alkali-silica reaction.The use of metakaolin and glass particles reduces the bulk density,in particular when glass has been used to replace the smaller quartzparticles. The permeability is also significantly affected by the useof the waste glass particles; an increase of 79% is observed com-pared with the control specimens when fine quartz particles werereplaced. The dynamic modulus of the composites was higher whenlarge glass particles were added, although the metakaolin did notaffect substantially this property. Composites containing coarserglass particles were more prone to expand due to alkali-silica reac-tion. It is also possible to conclude that either 7.5 wt% or 15 wt% ofwaste glass may be used in composites, without deterioration ofthe mechanical properties and the durability to alkali-silica reac-tion, as long as 15% of metakaolin replaces the Portland cement.These results are quite significant, because they indicate a clearpath to design and manufacture new classes of sustainable mate-rials for tiles and semi-dry compounds. Other levels of Portlandcement replacement (<7.5% and >15%) were not studied; so theresults and conclusions based on the statistical analysis are limitedto this replacement envelope.

s and ASR evaluation of concrete tiles with waste glass aggregate.15.02.005

Acknowledgements

The authors would like to thank FAPEMIG and CNPq for the Q4financial support provided.

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