1-s2.0-s0950061812002292-main

Construction and Building Materials 36 (2012) 205–215

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Construction and Building Materials

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Durability of mortar using waste glass powder as cement replacement

Ana Mafalda Matos a,⇑, Joana Sousa-Coutinho a,b

a LABEST FEUP, Faculty of Engineering, University of Porto, Portugalb FEUP, Department of Civil Engineering, Faculty of Engineering, University of Porto, Portugal

h i g h l i g h t s

" Glass powder is thoroughly analysed as a partial cement replacement material in mortar." Testing is carried out far beyond the usual mechanical testing and ASR by most authors." Chloride ingress, carbonation, sulphate attack and sorptivity are also considered for durability assessment." SEM demonstrated effect of fine glass particles well encapsulated into a dense matrix." This holistic study confirms that glass powder contributes to sustainability in construction.

a r t i c l e i n f o

Article history:Received 21 August 2011Received in revised form 28 March 2012Accepted 25 April 2012Available online 23 June 2012

Keywords:WasteGlass powderMortarAdditionDurabilityPozzolanic activity

0950-0618/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.conbuildmat.2012.04.027

⇑ Corresponding author. Address: Rua do Dr. RobPortugal. Tel.: +351 225081936; fax: +351 225081441

E-mail address: [email protected] (A.M. Matos).

a b s t r a c t

It is well known that Portland cement production is an energy-intensive industry, being responsible forabout 5% of the global anthropogenic carbon dioxide emissions worldwide. An important contribution tosustainability of concrete and cement industries consists of using pozzolanic additions, especially ifobtained from waste such as waste glass.

Crushed waste glass was ground (WGP) and used in mortar as a partial cement replacement (0%, 10%and 20%) material to ascertain applicability in concrete.

An extensive experimental program was carried out including pozzolanic activity, setting time, sound-ness, specific gravity, chemical analyses, laser particle size distribution, X-ray diffraction and scanningelectron microscopy (SEM) on WGP and resistance to alkali silica reaction (ASR), chloride ion penetrationresistance, absorption by capillarity, accelerated carbonation and external sulphate resistance on mortarcontaining WGP.

Glass particles well encapsulated into dense and mature gel observed by SEM, may help explainingenhanced durability results and thus confirming that waste glass powder can further contribute to sus-tainability in construction.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Concrete is the most commonly used construction material inthe world and it is the second most consumed product on theplanet after water [1].

Today’s annual global cement production has reached 2.8 bil-lion tons, and is expected to increase to some 4 billion tons peryear. At the same time, the cement industry is facing challengessuch as cost increases in energy supply, requirements to reduceCO2 emissions and the supply of raw materials in sufficient quali-ties and amounts [2]. It is estimated that about 0.9–1.0 tons of CO2

are produced for a ton of clinker depending on the type of fuelsused [3].

ll rights reserved.

erto Frias, 4200-465 Porto,.

While cement production in its beginnings only focused on or-dinary Portland cement, later cements with several main constitu-ents were produced by replacing parts of the clinker content bysupplementary cementitious materials [3].

Ecological or environmental benefits of alternative supplemen-tary materials include (1) the diversion of non-recycled waste fromlandfills for useful applications, (2) the reduction in the negativeeffects of producing cement powder, namely the consumption ofnon-renewable natural resources, (3) the reduction in the use ofenergy for cement production and (4) the corresponding emissionof greenhouse gasses [4].

Solid industrial by-products, such as siliceous and aluminousmaterials, as well as some natural pozzolanic materials are increas-ingly being used in the cement and concrete industry. The incorpo-ration of these materials in concrete has been giving encouragingresults regarding the mechanical and durability properties of con-crete [5].

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206 A.M. Matos, J. Sousa-Coutinho / Construction and Building Materials 36 (2012) 205–215

Despite the existence of large amounts of industrial waste suchas blast furnace slag, fly ash, silica fume, slag and agricultural res-idues such as rice husk ash, which have been used for many yearsin large amount as raw materials and components in the cementindustry, there are still many other industrial wastes not usedyet [7], such as waste glass. In fact a few studies have successfullyinvestigated the potential use of finely ground waste glass as a poz-zolanic material focusing on strength development and alkali-silicareactivity [9–18,20–23].

Glass is the result of the merger of several inorganic mineralraw materials, which after undergoing a process of controlled cool-ing becomes a hard, homogeneous, stable, inert, amorphous andisotropic material [8]. Based on the major composition, glass canbe classified into several categories but soda-lime glass is the mostwidely used to manufacture containers, float and sheet glass andtherefore composing over 80% by weight of waste glass [9].

With the exception of Al2O3 and CaO, the percentages of themain constituents of different types of glass are similar [4,6]. Forsoda lime glass the typical glass composition is approximately70% of silica, 13–17% Na2O and 10% CaO [9].

In fact, glass can be considered a pozzolanic-cementitious mate-rial according to the chemical requirements in ASTM C 618 [33] ifthe alkali content is disregarded.

Alkalis can cause alkali-aggregate reaction and expansion ifaggregates are alkali-reactive. Therefore high alkali content of glassis a typical concern for its use in concrete but studies have shownthat finely ground glass does not contribute to ASR [15,20,21]. Thepozzolanic properties of glass are first notable at particle sizes be-low approximately 300 lm. Below 100 lm, glass can have a pozzo-lanic reactivity which is greater than that of fly ash at low percentcement replacement levels and after 90 days of curing [5]. In fact,according to Shi and Zheng [9], ground glass powders exhibit verygood pozzolanic reactivity and can be used as cement replacement.As expected its pozzolanic activity increases as fineness increases[9]. The combined use of other supplementary cementing materialssuch as coal fly ash, ground blast furnace slag and metakaolin canalso decrease the expansion from ASR. Lithium salt can be also veryeffective to prevent ASR expansion of concrete containing glasspowders [10]. In any case compressive strength is often lowerwhen waste glass powder is used as cement replacement, espe-cially at early ages [15,18,20].

Fig. 1. Particle size distributi

The environmental and economic benefits from the reuse ofrecycled waste glass in cement and concrete production can alsobe very significant depending on the end uses and production scale[9].

Therefore the present work besides the usual strength and ASRtesting encompasses a wider range of analysis of effect of wasteglass powder, including pozzolanic activity, setting time, sound-ness, specific gravity, chemical analyses, laser particle size distri-bution, X ray diffraction and scanning electron microscopy (SEM),chloride ion penetration resistance, absorption by capillarity,accelerated carbonation and external sulphate attack. This holisticstudy corroborates that glass powder as a partial replacementmaterial is a waste material that contributes to sustainability inconstruction.

2. Experimental program

2.1. Materials

Typical commercial Type I 42.5R Portland cement was used and commercial sil-ica fume (SF) was employed as a reference pozzolanic material. Waste glass was ob-tained from a recycling glass industry in Portugal where waste glass such as carwindscreens is crushed and sold to the bottle industry. Fine waste glass from thisindustry was ground during 48 h in a ball mill in the laboratory (WGP). Fig. 1 showsparticle size distribution of cement and WGP. X-ray diffraction on WGP showed thatno substantial crystalline phases were detected. Soundness and setting time tests(NP EN 196-3 [36]) were carried out on pastes with 100% CEM I 42.5R (CTL) andon paste with 10% (WGP10) and with 20% (WGP20) cement replacement withWGP. Pozzolanicity test was carried out following NP EN 196-5 [37] on a samplewith 90% of cement and 10% of WGP. Chemical composition and physical character-istics of WGP and cement are given in Table 1. Scanning Electron Microscopy (SEM)was carried out on CEM I 42.5R, silica fume and WGP samples shown in Fig 2.

2.2. Mortar production and workability

Four mortar types were prepared following the procedure described in NP EN196-1 [35] a control mix with 100% cement (CTL), mixes with 10% (WGP10) and20% (WGP20) of waste glass powder as cement replacement and a mix with 10% ce-ment replacement with silica fume (SF). CEN Reference sand for mortar productionand super plasticizer (SP) SikaVisocrete 3000 complying with NP EN 2 [41] wereused.

Mortar workability (measured according to ASTM C 109/90 [31] and ASTM C230[32]) increased with cement replacement with WGP, but SF mortar showed a signif-icant workability decrease so super plasticizer was added. Mix proportions andworkability results are shown in Table 2.

on of cement and WGP.

Table 1Chemical and physical characteristics of cement and glass.

CEM I 45.2R WGP Silica fume

Chemical composition (% mass)LOI 2.61 0.92Insoluble residue 1.33SiO2 20.36 70 >99Al2O3 5.1 1.2Fe2O3 3.12 0.65CaO 62.72 8.7MgO 1.81 3.7Na2O 16K2O 0.35Na2O eq 17SO3 3.44 <0.05Cl 0012 <0005Free lime 1.62Pozzolanic activity Positive Positive

Physical propertiesSpecific gravity (g/cm3) 3.16 2.68 2.20Soundness (mm) �0 �0 �0Initial setting timeWGP10/WGP20 2 h, 20 m/2 h, 15 mCTL 2 h, 30 mFinal setting timeWGP10/WGP20 3 h, 25 m/3 h, 25 mCTL 3 h, 25 m

A.M. Matos, J. Sousa-Coutinho / Construction and Building Materials 36 (2012) 205–215 207

Several test specimens were produced. After demoulding the following day, testspecimens were cured in water at 20 �C in a fog room until testing.

2.3. Strength

Flexural and compressive strength testing was undertaken at 7, 28, 90 and180 days (and 562 days for CTL and WGP10) following the standard procedure inNP EN 196-1 [35]. Results are presented in Fig. 3. The pozzolanic effect of glass pow-der may be assessed with the Activity Index (AI) (Fig. 4) which is the ratio betweenstrength of WGP containing mortar and strength of equivalent control mortar at thesame age.

2.4. Alkali silica reaction (ASR)

The potential risk of alkali-silica reaction in concrete was monitored in accor-dance with the accelerated mortar bar test following ASTM 1567 [34], where twomortar prisms with 25 � 25 � 250 mm were used for each mortar type.

In this test method, higher temperature (80 �C) and increased alkalinity (1 NNaOH) accelerates the reaction. ASTM C 1567 method is not intended to capturethe effect of increased alkalis from glass powder; rather it is used in this study tounderstand the expansion characteristics of plain and modified mortar. In fact thistest method can be used to evaluate the effectiveness of supplementary cementingmaterials in reducing the expansion due to ASR [17].

Two slight modifications were performed when following the procedure inASTM. Instead of 1:2.25:0.47 cement:aggregate:water ratio required in ASTM, theratio used was 1:3:0.5 which is considered in NP EN 196-1 [35]. ASTM C 1567 alsorequires particle size distribution of (reactive) aggregates shown in Table 3, but theparticle size distribution used was the one considered in NP EN 196-1 CEN sand,which was found to be reactive. ASTM C 1567 was followed for the remaining pro-cedure, so immediately after casting, the moulds were covered and demoulded 24 hlater. Then they were preconditioned for a further 24 h in water maintained at80 �C. The lengths of these mortar bars after immersion in hot water, measuredalong the 4 faces of each specimen, were then taken as the initial readings (L0).The mortar bars were subsequently transferred to 1 N NaOH solution maintainedat 80 �C and periodically measured for 14 days.

Therefore the actual length (Lx) of each specimen, on day x is taken as

Lx ¼P4

i¼1Li4

ð1Þ

The expansion of each specimen at day x is given by

e ¼ Lx � L0

250� 100% ð2Þ

Expansion with time is shown in Fig. 5 as well as final expansion in Fig. 6.

2.5. Chloride ion diffusion

The resistance to chloride permeability was evaluated by the CTH Rapid Methodaccording NT Build 492 [44] which is a non-steady state migration method based ona theoretical relationship between diffusion and migration which enables the

calculation of the chloride diffusion coefficient (Dns) from an accelerated test. Anexternal electrical potential is applied axially across the specimen and forces thechloride ions outside to migrate into the specimen. After a certain test duration,the specimen is axially split and a silver nitrate solution is sprayed on to one ofthe freshly split sections. The chloride penetration depth can then be measuredfrom the visible white silver chloride precipitation, after which the chloride migra-tion coefficient can be calculated from this penetration depth as follows:

Dns ¼RTLZFU

:xd � a

ffiffiffiffiffixdp

tð3Þ

a ¼ 2

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiRTLZFU

� er

ð4Þ

e ¼ erf�1 1� 2Cd

C0

� �ð5Þ

where Dns is the apparent diffusion coefficient obtained in a non-steady state migra-tion test (cm2/s), R the gas constant R = 8.314 J/(mol K), T the absolute temperature(K), L the thickness of specimen (cm), Z the ion valence, F the Faraday constant,F = 9.648 � 104 J (V mol.), U the effective voltage applied (V), xd the depth of chloridepenetration measured by using a colorimetric method (cm), t the time of test dura-tion (s), a the laboratory constant, e = 0.764 if external chloride concentration of0.5 M. Cd the concentration of free chloride at which the colour changes when usingthe colorimetric method to measure the chloride penetration depth (kg Cl/m3 solu-tion) and C0 is the concentration of free chloride in the external solution.

Results can be seen in Fig. 7.

2.6. Absorption by capillarity

Absorption by capillarity testing was undertaken on two months old cast testspecimens, approximately 50 mm diameter by 100 mm length generally followingstandard procedure RILEM TC 116-PCD [45]. The samples were put to dry in a ven-tilated heater at 40 �C until constant mass. For the test itself, test specimens wereplaced moulded face downwards, in a shallow water bath. Water level was adjustedautomatically so that the formwork face was dipped to a depth of approximately3 mm. During the test, water was drawn into the core by capillary forces andweighed at time intervals up to 4.5 h from the start of the test [45].

The absorption of water into concrete under capillary action is dependent onthe square-root of time and may be modelled [24] by the following equation:

A ¼ A0 þ St0;5 ð6Þ

where A (mg/mm2) is the water absorption by unit area of concrete surface since themoment the core was dipped in water, S is the sorptivity of the material, t is theelapsed time and A0 (mg/mm2) is the water absorbed initially by pores in contactwith water. The above equation was found to provide a very good fit to the data withcorrelation coefficients of over 0.96 (Fig. 8). The average sorptivity value of eachmortar type is shown in Fig. 9.

2.7. Carbonation

Resistance to carbonation was assessed in accordance with the procedure de-scribed RILEM CPC-18 [44] where test specimens were exposed to 5 ± 0.1% carbondioxide, relative humidity (RH) of 60 ± 5% and temperature of 23 ± 3 �C, in an accel-erated carbonation chamber.

Carbonation depth was evaluated on three test specimens for each mortar type,water cured at 20 �C followed by 2 and 4 months in the chamber. After splitting thespecimens, the surface was cleaned and sprayed with a phenolphthalein pH indica-tor. In the noncarbonated part of the specimen, where the mortar was still highlyalkaline, a purple-red colour was obtained. In the carbonated part of the specimenwhere the alkalinity of mortar is reduced, no coloration occurred. Each value corre-sponds to the mean of twelve measurements taken around the four sides of thefreshly split and sprayed surface of each test specimen. Results can be seen in Fig. 10.

2.8. External sulphate attack

Resistance to external sulphate attack was evaluated according to the Portu-guese standard E-462 [42], on six (1, 2, 3, 4, 5 and 6) mortar prisms of16 � 16 � 160 mm. Test specimens were immersed in calcium hydroxide solutionduring 28 days, measured along the 4 side faces of each specimen and taken as ini-tial readings (L0). Test specimens 2, 4 and 6 were transferred to a sodium sulphatesolution and the others were maintained in calcium hydroxide saturated solution.Readings were taken throughout 26 weeks and sulphate solution was renewedevery 2 weeks. The actual length increase of each specimen on day x is taken as:

ExpCaðOHÞ2 ðxÞ ¼ Lx � L0

1600ð7Þ

ExpSO4 Na2 ðxÞ ¼ Lx � L0

1600ð8Þ

CEM I 42.5 R 200 times enlarged CEM I 42.5 R 1000 times enlarged CEM I 42.5 R 5000 times enlarged

GP 500 times enlarged GP 2000 times enlarged GP 5000 times enlarged

SF 10000 times enlarged SF 20000 times enlarged SF 40000 times enlarged

Fig. 2. Scanning electron microscopy on powder samples.

Table 2Mixture proportions and workability of mortar.

Materials/mortar CTL SF WGP10 WGP20

CEM I 42.5R (g) 450 405 405 360SF (g) 0 45 0 0WGP (g) 0 0 45 90Sand (g) 1350 1350 1350 1350Water (ml) 225 225 225 225SP/C ratio (%) 0 0.34 0 0W/binder ratio 0.5 0.5 0.5 0.5Workability (mm) 200 198 204 206


The expansion for each mortar is taken as:

ExpCaðOHÞ2 ¼ Expð1Þ þ Expð3Þ þ Expð5Þ3

ð9Þ

ExpSO4 Na2 ¼ Expð2Þ þ Expð4Þ þ Expð6Þ3

ð10Þ

The expansion due to sulphate is:

ExpansionðxÞ ¼ ExpSO4 Na2 ðxÞ � ExpCaðOHkÞ2 ðxÞ ð11Þ

Expansion during 26 weeks is shown in Fig. 11.

2.9. Scanning electron microscopy

SEM was also carried out on samples CTL and WGP10 mortar samples cured inwater at 20 �C for 562 days, as shown in Fig. 12, for 2500, 5000, 10,000 and 20,000magnification in order to investigate changes in the cement hydrated microstructure.

3. Discussion

3.1. Chemical and physical properties of WGP

Liu compared composition of soda lime glass in general to flyash, stating that the SiO2 and (Na2O + K2O) contents are muchhigher in glass and (SiO3 + Al2O3 + Fe2O3) is similar [6]. Chemicalcomposition of WGP is in accordance with those values and withresults by other authors using soda lime glass waste in mortarand concrete [14–18].

Considering that no specific European standard covers materialsuch as WGP and that it is mainly composed of silica, WGP proper-ties were compared in Table 4, to requirements for silica fume (NPEN 13263-1 [38]), also for fly ash (NP EN 450-1 [39]) and slag (NPEN 15617-1 [40]). As can be observed glass powder is basically inaccordance with these requirements, except for Na2O content

Fig. 3. Compressive and flexural strength.

Fig. 4. Activity index at 28 and 90 days.

Table 3Required grading requirements in ASTM C 1567 and grading for CEN sand used.

Grading requirements ASTM C 1567 CEN sand

Retained on sieve size Mass (%) Retained on sieve size Mass (%)

2.36 mm (No. 8) 10 2,00 mm 01.18 mm (No. 16) 25 1.60 mm 70.60 mm (No. 30) 25 1.00 mm 260.30 mm (No. 50) 25 0.50 mm 340.15 mm (No. 100) 15 0.16 mm 20


(17%), far above the limit (5%) imposed in the standard for fly ash.This corroborates Shao et al [12] who observed general accordancewith ASTM C 618 [33] but not meeting the optional requirementfor the alkali content, causing concern due to potential ASR.

Initial setting time (Table 1) was marginally shorter for WGP10(10 and 20 min) for paste with 10% and 20% cement replacement

with WGP, respectively, compared to control paste. Final settingtime was similar for all types of mortar.

Total CaO was determined but, as free CaO was unknown,soundness testing was carried out with results well under standardlimits, as can be seen in Table 1.

SEM observations (Fig. 2) indicate that WGP particles seemmore angular, denser and more prismatically shaped comparedto cement and naturally much larger than spherical silica fumeparticles. Fineness obtained through laser particle size distribution,is similar for WGP and cement (Fig. 2).

3.2. Strength and activity index

Mechanical and durability related properties for WGP werecompared to those of CTL and SF mortar for the present study aswell as to results by other authors.

Strength for WGP mortar was lower than control at 7 and 28days, decreasing with replacement dosage but at 90 days generally

Fig. 5. Expansion vs. time due to ASR.

Fig. 6. Final expansion of mortar after 14 days in 1 N NaOH.


attaining CTL although under SF levels. WGP20 gained significantstrength between 28 and 90 days showing pozzolanic reaction tak-ing place in this period. Idir et al [26] for fine glass with particle sizerange under 41 lm and mean particle size of 7.8 lm obtained sim-ilar results concluding that the general trend is for replacement ofcement by glass to lead to a decrease in compressive strength [26].

Strength activity indexes obtained were higher than 90% at 90days of curing for 10% and 20% replacement by fine glass powder,confirming results obtained by Jin et al [25]. Shao et al [12], usedhigher replacement (30%) by fine glass powder (<38 lm) in con-crete and obtained concrete strength activity indexes higher than90% at 90 days. Shi et al, for 25% replacement and coarser material(<100 lm) obtained strength activity values around 74% at 28 days,with which the results of the present study for 20% replacementseem to be in accordance.

3.3. Alkali silica reaction

Results obtained for ASR expansion respecting control mortarindicated potential deleterious expansion according to ASTM1567 (higher than 0.10% after 14 days in NaOH). Results for both

SF and WGP were effective in reducing ASR expansion. Increasingglass powder content led to lower expansion despite the high alkalicontent. Frederico and Chidiac [4] reported results on ASR expan-sion relating to particle size of glass and cement replacement dos-age including work by Jin et al [25] and Shao et al [12] with whichpresent results are in accordance.

ASR results in the present study also confirm findings by Sch-warz et al [20] where expansion for 10% and 20% replacement withglass powder was slightly higher, presumably due to use of coarserglass particles. Sacanni and Bizigoni [21], where fine aggregate wasalso replaced by glass particles, obtained ASR expansion similar tovalues in the present study.

Therefore ASR testing confirmed that glass powder assisted inhindering expansion compared to control specimens, confirmingconclusions by other authors [20–22].

The possible explanations for this phenomenon according toTaha and Nounu [22] is that available reactive silica in glass pow-der as an amorphous material will dissolve very quickly during thepozzolanic reaction and react with other chemicals to form themineral phases of concrete. Therefore, the dissolved reactive silicaof glass powder will be accommodated in the crystals of concrete

Fig. 7. Chloride diffusion coefficient for each mortar type.

Fig. 8. Linear regression for absorption by capillarity during 4 h 30 min on test cores.


minerals and not available for the ASR which occurs in later stages.With the presence of other chemicals the dissolved reactive silicaof glass powder will not be able to form ASR gel during the pozzo-lanic reaction, or even a gel having a swelling property likewise theASR gel. Otherwise, if there was any chance to form ASR gel duringthe pozzolanic reaction from the reactive silica of glass powder onecan envisage that any existing ASR expansion would be noticeable.If any ASR could occur during the pozzolanic reaction stage, theproduced expansion would vanish and accommodate within theplasticity of fresh concrete. On the other hand, in the first 4 weeksof the pozzolanic reaction and hydration process, most of the alka-lis would have been consumed in order to catalyse the pozzolanicreaction and act as chemical activators to compensate for the lowercalcium content in the glass powder. Therefore, in later age, therewould not be enough free alkali to interact with the reactive silicain the pore solution of the concrete to induce ASR, as illustrated inFig. 13.

Additions with low CaO content act as ASR inhibitors, whereasthose with more than 10% CaO content act as ASR promoters [27]and therefore WGP proved once again to inhibit ASR.

3.4. Chloride diffusion, absorption by capillarity, carbonation andsulphate attack

CTH rapid method results show that using WGP as a partial ce-ment replacement drastically enhances resistance to chloride pen-etration compared to control mortar specially for 20% replacementdosage (on average, CTL Dns is about double compared to WGP20)and even compared to 10% SF mortar. Samples of silica fume andWGP10 have very similar diffusion coefficients. Results obtainedin the present study, confirm values by other authors [16,19,20],where performance of glass powder mortar is better than controlmortar regarding chloride penetration. Only Jain and Neithalath

Fig. 9. Sorptivity of each mortar type.

Fig. 10. Carbonation depth results after 2 months curing followed by 4 months in the chamber.


[13] carried out the NT Build 492 [43] test as in the present studyand obtained similar improvement to WGP 20 at 56 days.

Absorption by capillarity and sorptivity proved to be similar forWGP and CTL mortar and a little lower for SF mortar. This situationmay be explained by similar fineness of both WGP and cement (seeFig. 9). Much finer SF particles physically fill capillary pores reduc-ing capillary absorption. Other authors, such as Taha and Nounu[23] also showed similar results for concrete with cement replace-ment materials, but following BS 1881.

Carbonation depth for all blended cement mixtures was greaterthan for the Portland cement mixture. It was found that carbon-ation increased along with the increase in WGP content, which isconsistent with the trend observed in concrete for various pozzola-nic materials and probably due to CH reduction. WGP10 carbon-ated almost half of SF10 mortar, albeit pore refinement due to

silica fume. This may be explained by higher SF reactivity and thusfurther CH reduction, compared to WGP. When WGP replacementis doubled, carbonation depth is similar to SF. Although a less reac-tive material, higher WGP replacement and less cement in the mix-ture, both contribute to CH reduction levelling out intense CHreduction in SF mortar.

Sulphate expansion at 26 weeks should be under 0.10% accord-ing to the Portuguese standard E-462 and therefore Portland ce-ment used is not sulphate resistant. Blended Portland cementwith 10% replacement with WGP showed an impressive resistanceto sulphate attack, far higher than SF marginally within the limit of0.10%. The pozzolanic activity of WGP and SF binds portlandite(CH) released in the hydration of calcium silicates (C3S and C2S),so CH is no longer available for reaction with sulphates, inaccordance with [28,29]. This prevents the formation of gypsum.

Fig. 11. Expansion during 26 weeks due to sulphate.

CTL 562 days 2500 times enlarged CTL 562 days 5000 times enlarged CTL 562 days 10000 times enlarged CT L 562 days 20000 times enlarged

WGP10 562 days 2500 times enlarged WGP10 562 days 5000 times enlarged WGP10 562 days 10000 times enlarged WGP 562 days 20000 times enlarged

Fig. 12. SEM on 562 days old mortar.


Pozzolanic reaction produces a secondary C–S–H that also de-creases the capillary porosity of mortar and enhances significantlythe paste–aggregate interface [28].

3.5. Scanning electron microscopy

Regarding SEM observations, glass particles seem to be thor-oughly encapsulated and dispersed into to the hydrated productsof a dense and mature gel with needle shaped ettringite crystals(see WGP10 10,000 and 20,000 times enlarged, Fig. 12). CH layeredcrystals were observed in the CTL mortar (see CTL 5000 times en-larged, Fig. 12) and CSH gel filling the hydrated structure. CSH gel

in WGP10 was found to contain more calcium as well as more alka-lis compared to CTL mortar. These findings are in accordance withSobolev et al [30] who suggested that the main difference betweenglass containing mortar and reference Portland cement is related tothe decrease in size and the amount of CH, caused by consumptionof CH as a result of the pozzolanic reaction involving glass grains.More alkalis found in the gel of WGP10 compared to CTL also con-firm findings by Shayan and Xu [17] who proposed that the pozzo-lanic reaction of glass powder with cement causes the binding ofalkalis in the paste, making it unavailable for ASR [17] and thereforein accordance with the mechanism proposed by Taha and Nounu[22] explaining lower expansion due ASR when glass is used.

Table 4Requirements in standards.

European Standards

Fly ash (NP EN 450-1) Silica fume(NP EN13263-1)

Slag (NP EN 15167-1) GP Remarks

Chemical requirements Cl 60.10% 60.3% 60.10% <0005 OKSO4 63.0% 62.0% 62.5% – OKSO3 – – 62.0% <0.05Free CaO 62.5% 61.0% 8.70% Only the total content of CaO

is known but soundness is OKReactive CaO 610% –SiO2 P25% P85% 70% OKSiO2 + Al2O3 + Fe2O3 P70% 71.82% OKCaO + MgO + SiO2 P67.0% OKNaO2eq 65.0% 17% KO, but OK in ASR testingLOI Class A 6 5% 64.0% 63.0% 0.92%

Class B 2–7% OKClass C 4–9%

Pozzolanicity – – Positive OK

Physical requirements Activity index P75% at 28 days P100% at28 days old

P45% at 7 days and P75%at days

KO Almost OK for 28 days, and okfor 90 days

P85% at 90 daysStart setting time 6120 min plus start time of

the paste-setting reference62 times the start time ofthe paste-setting reference

OK

Soundness 610 mm 610 mm OK

Fig. 13. Model illustrates the consumption of alkali in the pozzolanic reaction in thefirst 4 weeks [22].


4. Conclusions

This study aimed to evaluate use of glass powder in cementbased materials. An experimental study on the mechanical anddurability properties of mortar containing waste glass powder ascement replacement provided the following results:

In terms of physical and chemical characteristics, glass can beconsidered a pozzolanic-cementitious material according torequirements in ASTM C 618 [33] as well as in European stan-dards [38–40], if the alkali content is disregarded;Attractive strength activity indexes were obtained at 90 days ofcuring in WGP containing mortar, with significant increasebetween 28 and 90 days which means pozzolanic activityoccurred;In spite of high alkali content in WGP, ASR expansion was dras-tically reduced. The explanation of this phenomenon can bereferred to the consumption of the alkali in the structure ofthe C–S–H gel during the pozzolanic reaction which occurs ear-lier than ASR, therefore not leaving enough alkali to induce ASR;

Higher resistance to chloride penetration was obtained for WGPcontaining mortar, increasing with dosage replacement;Sorptivity of glass mixes was equivalent to control due to theeffect of similar particle size distribution;Carbonation depth for all blended cement mixtures was greaterthan for the Portland cement mixture, increasing with replace-ment dosage in the trend for pozzolanic materials;WGP10 mortar showed a remarkable resistance to sulphateattack, far higher than SF;SEM observations may help explaining these findings as glassparticles seem to be completely encapsulated and dispersedinto dense and matured gel.Although soda lime glass presents a high alkali content, use ofground waste glass as cement replacement in mortar, improvedresistance to ASR and chloride penetration with replacementdosage and greatly improved sulfate resistance without com-promising strength. Therefore this waste material can success-fully enhance durability and further contribute to sustainabilityin construction

5. Future developments

Future research comprising use of glass powder is underway,including use in self-compacting concrete, taking advantage of in-creased workability provided by this waste material.

Acknowledgement

The authors would like to thank Mr. Oliveira from the glassindustry, LEMC, LABEST and to FCT under Project PTDC/ECM/098117/2008.

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