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Ma

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Materials Science and Engineering A 528 (2011) 7991– 7998

Contents lists available at ScienceDirect

Materials Science and Engineering A

jo ur n al hom epage: www.elsev ier .com/ locate /msea

ffect of nano clay particles on mechanical, thermal and physical behaviours ofaste-glass cement mortars

. Alya,∗, M.S.J. Hashmia, A.G. Olabia, M. Messeiryb, A.I. Hussainc

School of Mechanical Engineering, Dublin City University, Glasnevin, Dublin 9, IrelandDepartment of Engineering Physics, Faculty of Engineering, Cairo University, EgyptDepartment of Pigments & Polymers, National Research Centre, Dokky, Cairo, Egypt

r t i c l e i n f o

rticle history:eceived 9 May 2011eceived in revised form 25 July 2011ccepted 26 July 2011vailable online 3 August 2011

eywords:ano claylass powderement mortar

a b s t r a c t

Worldwide, around 2.6 billion tons of cement is produced annually. This huge size of production consumeslarge amounts of energy and is one of the largest contributors to carbon dioxide (CO2) release. Accordingly,there is a pressing demand to minimise the quantity of cement used in the concrete industry. The mainchallenge to this is to get durable concrete with less cement and within reasonable cost. The economic,environmental and engineering benefits of reusing ground waste-glass powder (WGP) as a partial cementreplacement has been established, but low glass reactivity and the possible alkali–silica reaction (ASR) area drawback. Recent advances in nano-technology have revealed that nano-sized particles such as nanoclay (NC) have a high surface area to volume ratio that provides the potential for tremendous chemicalreactivity, accelerating pozzolanic activity and hindering ASR. This paper presents a laboratory study ofthe properties of NC/WGP cement composites. The microstructure, ASR, fracture energy, compressiveand flexural properties of cement mortars containing WGP as a cement replacement with and withoutNC are investigated and compared with plain matrix. In addition, the hydration of cement compoundswas followed by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and also X-raydiffraction (XRD). The results showed that incorporation of glass powder has a positive effect on themechanical properties of cement mortars after 28 days of hydration. Also, the results revealed that the

mechanical properties of the cement mortars with a hybrid combination of glass powder and NC wereall higher than those of plain mortar and with glass powder after 28 days of hydration. In addition,the DTA/TGA results and XRD analysis showed a reduction in the calcium hydroxide (CH) content inmortars with glass powder and with a hybrid combination of glass powder and NC, which confirms theimprovements of mechanical properties and occurrence of pozzolanic reaction after 28 days of hydration.

. Introduction

Although glass is a highly recyclable material, recycling of colourottle glass causes major problems due to the high cost of clean-

ng and colour sorting. It is widely believed that the storage ofolour bottles is cheaper than recycling them. Therefore, mostolour bottle glass is regarded as a low-value product and is dis-atched to landfill as waste material. Due to the fact that glass isot biodegradable, landfills do not offer an ecological solution. Aotential solution providing a sustainable, ecological and economic

olution to mixed-colour bottle storage would be to reuse colouraste glass in the cement and concrete industries.

∗ Corresponding author. Tel.: +353 863466296; fax: +353 17007563.E-mail address: marwa.aly2@mail.dcu.ie (M. Aly).

921-5093/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.msea.2011.07.058

© 2011 Elsevier B.V. All rights reserved.

The concept of using waste glass in concrete is not new; earlyefforts were conducted in the 1960s to use crushed waste glassas a replacement for aggregate [1]. However, these attempts werenot satisfactory due to the strong reaction between the alkali incement and the reactive silica in glass, namely alkali–silica reac-tion (ASR) [1,2]. In addition to ASR, using waste bottle glass limitsthe size and shape of coarse aggregate, as crushed bottles tend toform flat and elongated shapes, which may negatively affect work-ability and reduce compressive strength. Also, most mixed-colourbottles are of different chemical composition and may be contam-inated by paper, plastic labels, caps and inorganic remaining fromthe original content of the bottles [3]. Furthermore, using wasteglass as an aggregate could decrease slump, air content, fresh unit

weight, tensile and flexural strengths [4].

In the last decade, the reuse of waste glass in the cement andconcrete industries has attracted many researchers due to the highdisposal costs for glass and stricter environmental regulations. Cur-

7992 M. Aly et al. / Materials Science and Engineering A 528 (2011) 7991– 7998

Table 1Chemical composition of waste glass powder and other pozzolans.

Compound Glass [12,13] OPC [15] Slag [3,14] Silica fume [16]

SiO2 63.0–80.5 21.78 11.8–35 92Al2O3 0.8–6.2 6.56 2.0–12 0.7Fe2O3 0.0–3.0 4.13 0.3–22.6 1.2CaO 0.3–12.76 60.12 39.6–47.5 0.3MgO 0.0–8.7 2.08 0.0–7.5 0.2K2O 0.4–6.0 0.42 0.0–0.4 1.8Na2O 1.9–22.0 0.36 0.2–0.3 1.5

rotttsw

ggWetsnrcaaruwaucefia4

pgroaorgmA

nhdchTappcsi

Table 2Physical and chemical properties of Closite® 30B as provided by the manufacture.

Physical properties and chemical properties

Density 1.98 g/cm3

Moisture content <2%Average size 6 �mBasal spacing, d0 0 1 18.5 AColour Off-white

sieving the ground glass to the desired particle size namely 75 �m.Table 3 shows the chemical composition of green WGP used in thiswork. SEM examinations indicate that the ground WGP consists

SO3 0.0–3.50 2.16 0.2–9.0 0.3Others 0.05–3.5 2.39 – 2

ently, several efforts have been made to overcome the limitationf ASR, focussing on reducing the particle size of the waste glasshrough prolonged grinding. The results of this work showed thathe very fine glass powder greatly decreased ASR expansion. Fur-hermore, the results revealed an improvement in compressivetrength, resistance to sulphate attack and chloride ion penetrationith very fine glass powder (less than 100 �m).

Works of Shi et al. [5] and Schwarz et al. [6] indicated that finelyround glass powder (below 100 �m) has a pozzolanic reactivityreater than that of fly ash at low cement replacement (10–20%).hen using up to 50% of waste glass as cement replacement, Chen

t al. [7] found that a particle size less than 75 �m possesses cemen-itious capability and improves compressive strength, resistance ofulphate attack and chloride ion penetration. In another work, Cori-aldesi et al. [8] used sodium–calcium glasses with particle sizeanging from 36 �m to 100 �m, to study the effect of glass parti-le size on ASR. Their results did not detect any deleterious effectt a macroscopic level due to the reaction between cement pastend ground waste glass with particle size up to 100 �m. Also, theiresults showed a strong improvement in the compressive and flex-ral strength of the mortar, due to the positive contribution of theaste glass to the micro-structural properties. Work by Karamberi

nd Moutsatsou [9] indicated that finely ground colour glass culletp to 90 �m was found to increase pozzolanic activity, to improveompressive strength and to cause negligible ASR expansion. Idirt al. [10] showed that the pozzolanic activity increases with glassneness and equivalent or superior compressive strength can bettained when using up to 40% of mixed-colour glass (less than0 �m), compared to their reference specimen without glass.

In fact, the reusing of glass in the concrete industries is accom-anied by two antagonistic behaviours depending on the size of thelass particles: ASR, which causes negative effects, and pozzolaniceaction, which improves the mechanical and physical propertiesf concrete. As the previous works show, the use of waste glasss a cement replacement has shown mixed results over a rangef levels of replacement and particle sizes. In relevance to theequirements of ASTM C618 [11], as shown in Table 1 [3,12–16],lass has the potential to acceptably function as a cement replace-ent; however, proper methods must be developed to control theSR/pozzolanic reaction and increase the glass powder reactivity.

Recent studies have shown that nano-sized particles such asano silica, TiO2 nanoparticles and nano clay (NC) particles have aigh surface area to volume ratio that have the potential for tremen-ous chemical reactivity [17–21]. Nano-particles act as nuclei forement phases, hence promoting cement hydration due to theirigh reactivity. Also they act as a nano-reinforcement, and filler.hus they densify the microstructure and accelerate pozzolanicctivity [18,21,22]. Therefore, using nano-particles to increase theozzolanic activity of waste glass powder (WGP) would be a

romising approach to improving the performance of WGP andontrolling the damaging effect of ASR. The literature review hashown that studies on this subject are very limited. This worknvestigates the hybrid effect of NC particles and WGP on the ASR,

Modifier concentration 90 meqa/100 g clay

a Milli-equivalents per 100 grams.

microstructure, hydration of cement compounds, fracture energy,flexural and compressive properties of cement mortars.

In this study, green WGP with particle obtained from alcoholbottles (5%, 20%, 30 and 50% of total cement weight) and NC par-ticles (2.5 wt%) were used as a partial replacement for cement. Inorder to characterise these developed composites, a series of testswere conducted. These consisted of a study of the ASR, microstruc-ture properties, fracture energy, pozzolanic activity, compressiveand flexural performance. In addition, the hydration of the cementmatrices was followed by differential thermal analysis (DTA), ther-mogravimetric analysis (TGA), and X-ray diffraction (XRD).

2. Materials and methods

Ordinary Portland cement (PC) was used in this study andsupplied by Irish Cement Ltd. The cement was grade 42.5, witha specific gravity of 3.15 g/cm3. Sand with a particle size up to1.18 mm and a specific gravity of 2.65 g/cm3 was obtained froma local supplier in Ireland. The clay used in this study, Closite® 30B,is commercially available from Southern Clay Products Inc., USA.This is an organically modified montmorillonite with quaternaryammonium salt, which has an initial d-space of 18.5 A. The phys-ical and chemical properties of the Closite® 30B provided by themanufacture are listed in Table 2. Scanning electron microscopy(SEM) micrograph of Closite® 30B particles is shown in Fig. 1. It canbe seen that the particles consist mainly of fine ball-milled parti-cles with an irregular microstructure and an average particle sizeof 6 �m.

The WGP used in this study was having particle size up to 75 �mand specific surface (Blaine) of 320 m2/kg. This is accomplished bycrushing and grinding the glass in a ball mill in the laboratory and by

Fig. 1. SEM micrograph of Closite® 30B.

M. Aly et al. / Materials Science and Engineering A 528 (2011) 7991– 7998 7993

Table 3Chemical composition of green waste glass powder used in this work.

Na Al Si K S

10.7 6.65 75.06 4.49 3.1

mautgta

hstmthpTcmwa

Table 4Mixture proportions used in this work.

Batch Binder material Water/binder ratio

Binder/sand ratio

PC (control) 100% PC 0.480 1WGP5 95% PC + 5% WGP 0.482 1WGP20 80% PC + 20% WGP 0.485 1WGP30 70% PC + 30% WGP 0.487 1WGP50 50% PC + 50% WGP 0.489 1NWGP5 92.5% PC + 5% WGP + 2.5% NC 0.510 1NWGP20 77.5% PC + 20% WGP + 2.5% NC 0.515 1

Fig. 2. SEM photographs of ground green waste glass powder.

ainly of fine angular particles with a narrow particle size range,s shown in Fig. 2. Particle size analysis of the WGP was carried outsing a Malvern Mastersizer S (Malvern Ltd., UK). Fig. 3 compareshe particle size distribution of the PC with WGP obtained from therinding process. It shows that in the present technique WGP con-ains about 45% of particles smaller than 10 �m, while PC containsbout 50% of particles smaller than 10 �m.

Organically modified montmorillonite particles have a relativelyigher surface area per unit volume and are difficult to mix at theame time with water, cement and sand. Hence, the microstruc-ure and mechanical properties of cement mortars reinforced with

odified montmorillonite particles are considerably influenced byhe mixing procedure of their constituent materials. Kuo et al. [22]ave successfully used the high-shear mixing technique to incor-orate organo-modified montmorillonite into the cement matrix.herefore, this technique has been chosen to prepare cement–NComposites. Accordingly, mixing was performed as follows. The

odified montmorillonite particles were mixed with total mixingater and stirred vigorously by a high speed shear mixer for 24 h

t room temperature to form a well dispersed suspension solu-

0

20

40

60

80

100

10001001010.1

Cum

ulat

ive

volu

me

[%]

Particle size [µm]

PC WGP

Fig. 3. Particle size distribution of waste glass powder and Portland cement.

NWGP30 67.5% PC + 30% WGP + 2.5% NC 0.517 1NWGP50 47.5% PC + 50% WGP + 2.5% NC 0.519 1

tion. To prepare the cement mortar, the PC, WGP (if applicable)and sand were stirred at high speed for about 3 min. Afterwards,the total suspension solution was added slowly into the mixtureand stirred for 3 min. Then, the well mixed composite was pouredinto moulds. After moulding, the specimens were kept in sealedconditions at a constant temperature of 20 ◦C until curing age wasachieved (28 days). For all specimens the water/binder ratios weretested to reach a flow of 110 ± 5 to permit a medium workabilityof the specimens. Table 4 summarises the mix proportions used inthis work.

3. Experimental techniques

A study of the ASR was performed in accordance with ASTMC1260 [23]. Mortar bars 25 mm × 25 mm × 100 mm in size werecast. Then, the moulds were covered carefully with plastic sheetsand placed in the lab at 22 ◦C for 24 h. After that, the bars wereplaced in water at 80 ◦C for another 24 h to gain a reference length.They were then transferred to a solution of 1 N of NaOH at 80 ◦C.Readings were then taken every day for 14 days.

The DTA/TGA profiles were obtained using Stanton RedcroftDTA/TGA, UK. The samples (24–28 mg) were heated at 10 ◦C/minup to 1000 ◦C. Dry nitrogen gas was circulated within the test cellat a flow rate of 60 cm3/min.

DTA/TGA can be used to determine the amount of the pozzolanicreaction and hydration of blended cement pastes by estimating CHand calcium silicate hydrate (CSH) content [24]. This technique ismore suitable for studying hydration at later stages [25]. Vedalak-shmi [26], as well as Esteves [27], employed TGA/DTA to study thepozzolanic activity of mineral additions such as silica fume, fly ashand slag. Furthermore, the hydration of pozzolanic materials (suchas silica fume, metakaoline, fly ash or slag) by estimating CH contenthas also been investigated in Refs. [28–31].

In the present work, CH exhibits a peak at about 475 ◦C. The areaof this peak was used to determine the amount of CH by the methodapplied by Esteves [27]. Accordingly to calculate the CH content, aseparate test was performed with pure CH to check the enthalpy ofthis compound. Thus, the amount of CH in the system was derivedfrom Eq. (1):

CH (wt%) = k · A (1)

where CH is the wt% of calcium hydroxide in the sample, k is thecalibration constant obtained from the measurement of the pure CH(k = 8.11 × 10−4) and A is the peak area taken from the DTA profilein �V.

When using the TGA technique to estimate the content of CH,the method does not require any calibration procedure. Thus, theCH content was estimated directly from the weight loss measured

from the TGA curve between the initial and final temperatures ofthe corresponding TGA peak [25–27].

In order to study microstructure, SEM was applied to charac-terise the microstructure of composites’ fracture surfaces using a

7994 M. Aly et al. / Materials Science and Engineering A 528 (2011) 7991– 7998

Table 5Mixture proportions for lime test (by weight percent).

Batches Lime WGP NC Sand Water/lime +WGP (or NC)

Smifl

tvo

4wZa2naatwam

lp

tma

dtCccw

4

4

oo

4

omigisNchst

20

25

30

35

6050403020100

Com

pres

sive

stre

ngth

, MPa

Waste glass content, %

Control WGP mortars NC/WGP mortars

highest fracture energy, recording an increase in fracture energy of123% compared to the control specimen. This increase indicates agreater energy adsorption in NC/WGP cement composites.

4

6

8

10

6050403020100

Flex

ure

stre

ngth

, MPa

Control WGP mortars NC/WGP mortars

LWGP 9 18 0 73 85LNC 9 0 18 73 185

EM machine model Hitachi S-3000N VP in secondary electron (SE)ode, operated at around 8 and 15 kV. The samples used for SEM

maging were slices taken from the same specimens used for theexural test.

XRD (Bruker AXS D8 Advance, USA) analysis with Cu-K� radia-ion and a graphite monochromatic with a current of 40 kV and aoltage of 40 mV were used with diffraction intensity in the rangef 10–50◦ (2�-angle range).

For the three-point flexural test, specimens of0 mm × 40 mm × 160 mm size were prepared in accordanceith ASTM C348 [32]. Flexural strength was obtained using the

wick machine. This machine is equipped with a 50 kN load cellnd attached to a computer interface with TestXpert 2 version.1 software for data acquisition. Three point bending tests onotched beams were performed to evaluate the fracture energy inccordance with RILEM 50-FMC [33]. All specimens were testedt room temperature with a cross-head speed of 1 mm/min. Forhe compressive test, specimens of 50 mm × 50 mm × 50 mm sizeere prepared in accordance with ASTM C109 [34]. Both flexural

nd compressive property values were obtained by averaging theeasurements of at least three samples.In order to study the pozzolanic activity of the WGP and NC, a

ime test was conducted following ASTM C593 [35]. The mixtureroportions are given in Table 5.

The water was adjusted to achieve a flow of 75% consistencyhrough a flow table test. The mixture was cast in 50 mm cube

oulds, wrapped in wet burlap, sealed by a plastic bag, and curedt 54 ◦C in an oven.

Compressive strength tests were carried out after curing for 7ays at 54 ◦C and after an additional 21 days curing at 23 ◦C in watero monitor the long-term strength gain. As recommended by ASTM593, a satisfactory pozzolanic material should have a minimumompressive strength of 4.1 MPa when mixed with lime after 7 daysuring at 54 ◦C and after an additional 21 days curing at 23 ◦C inater.

. Results and discussion

.1. Mechanical properties

The results obtained through the present work on the utilisationf WGP/NC as cement replacement on the mechanical propertiesf mortars, can be summarised as follows.

.1.1. Compressive strengthFig. 4 compares the compressive strength of mortars (at 28 days

f hydration) WGP/NC with WGP specimens; apparent improve-ent in compressive strength compared to the control specimen

s reported. The compressive strength increases by increasing thelass content up to 20%, after which it slightly decreases. Evidently,ncorporating NC particles has a positive effect on the compres-ive strength. Moreover, the increases in compressive strength forWG5, NWG30 and NWG50 were 11%, 22% and 8%, respectively

ompared to the control specimen. NCWGP20 samples reveal theighest compressive strength, with a 28% increase in compressivetrength compared to the control specimen. This increase indicateshat the hybrid incorporation of NC particles and finely ground

Fig. 4. 28-Day compressive strength of target mortars.

WGP greatly improves the mechanical performance of the cementmatrix.

4.1.2. Flexural strengthThe flexural strength behaves similarly to the compressive

strength. Fig. 5 shows that the incorporation of WGP improves theflexural strength compared to the control specimen. The additionof NC introduces further improvement to the flexural strength ofWGP mortars. Fig. 5 exhibits the increase in flexural strength formixes NCWGP5, NCWGP20, NCWGP30 and NCWGP50 (5%, 14%,26% and 29%, respectively), compared to the control specimen. MixNCWGP20 revealed the highest flexural strength followed by mixNCWGP30, which confirms the similarity between compressiveand flexural strength.

4.1.3. Fracture energyFig. 6 exhibits the variation of the fracture energy of mortars

versus waste glass content percent for different specimens. It can beseen that the incorporation of WGP has a positive effect on fractureenergy, which increased with increasing glass content. The incor-poration of NC significantly improves the fracture energy of mortarscompared to the control specimen. The increases in fracture energyfor NCWGP5, NCWGP20 and NCWGP30 were 57%, 67% and 82%,respectively, compared to the control specimen. Mix NCWGP50,which contained 50 wt% WGP and 2.5 wt% NC particles, shows the

Waste glass content, %

Fig. 5. 28-Day flexural strength of target mortars.

M. Aly et al. / Materials Science and Engineering A 528 (2011) 7991– 7998 7995

0

200

400

600

6050403020100

Frac

ture

ene

rgy,

N/m

Control WGP mortars NC/WGP mortars

scrzoStpNc

•

•

Tcp

4

ctWt

Waste glass content, %

Fig. 6. 28-Day fracture energy of target mortars.

As the above results show then, the NC/WGP combinationhowed the best results in terms of fracture energy, flexural andompressive strength. It seems that NC behaves not only as a filler toefine microstructure, but also as an activator to accelerate the poz-olanic reaction; this is due to the large and highly reactive surfacef nano particles [19,36,37]. These results are further reinforced byEM micrographs, XRD patterns and DTA/TGA of the cement mor-ars after 28 days of hydration. In fact, the improvements in theroperties of hardened cement composites due to the addition ofC particles can be explained by two mechanisms. The first is thehemical effect, which works on two levels [18]:

accelerating the dissolution of C3S and rapid formation of the CSHphase in the cement paste; andthe pozzolanic reaction of silica with CH generates additional CSHgel in the final stages.

he second mechanism is the physical effect; nano clay particlesan fill the remaining voids in young and partially hydrated cementaste, which leads to a denser and more compact structure.

.2. TGA and DTA

TGA and DTA were carried out on selective specimens of PC (the

ontrol) and mixes WGP20 and NCWGP20 after 28 days of hydra-ion. Figs. 7–9 present the DTA/TGA profiles of the control mix,

GP20 and NCWGP20, respectively. The DTA/TGA curves show theypical reactions occurring in the cement matrix when subjected to

Fig. 7. DTA/TGA profiles for control specimen after 28 days of hydration.

Fig. 8. DTA/TGA profiles for WGP20 specimen after 28 days of hydration.

a progressive temperature increase from room temperature up to1000 ◦C. The DTA/TGA curves of the selective specimens show threemain endothermic peaks. The first peak was observed between 60and 110 ◦C, corresponding to the mass loss on the TGA curve upto 110, which can be attributed to the gradual departure of boundwater in some hydrates like CSH and ettringite [27,28,38,39]. Thesecond endothermic peak was detected at about 475 ◦C and repre-sents a new loss in mass starting around 410 ◦C, that correspondsto the de-hydration of CH; hence, the Portlandite decomposes intofree lime (dehydroxylation) at ≈450–550 ◦C [27,28,40,41]. The thirdpeak was observed at ≈765–785 ◦C, which occurs due to the decom-position of calcium carbonate and escaping of CO2 from the cementmatrix [24,26,27,41].

As Fig. 9 shows, the DTA/TGA profiles of NCWGP20 indicates astrong increase in the first peak, which is related to CSH formation,compared to the control specimen in Fig. 7. Inversely, the secondpeak, which is related to the decomposition of CH, appears consid-erably smaller than the same peak of the control specimen. Thisincrease in CSH at the cost of CH can be attributed to the con-sumption of CH by the pozzolanic reaction. This agrees with theremarkable increase in the compressive strength when WGP and

NC particles were used to replace part of the PC. Also, it should bementioned that the DTA/TGA profiles of WGP20 show an increasein CSH and decrease in the CH peak in comparison to the control

Fig. 9. DTA/TGA profiles for NCWGP specimen after 28 days of hydration.

7996 M. Aly et al. / Materials Science and Engineering A 528 (2011) 7991– 7998

FT

sW

WFrriwcicwoeptr

4

cWtboutcoCcsip

4

at

ig. 10. CH content for control, WGP20 and NCWGP20 specimens as measured byGA and DTA methods.

pecimen, which confirms the increase in compressive strength ofGP20 compared to control specimen.Variations between the CH content of the control specimen,

GP20 and NCWGP20 are shown in Fig. 10. As presented inig. 10, the CH content decreases by adding 20% WGP as a cementeplacement, which indicates consumption of CH in the pozzolaniceaction after 28 days of hydration. The reduction of CH contents much greater when NC particles are loaded in mix NCWGP20,

hich indicates more pozzolanic reaction in terms of the WGPement matrix. As can be seen in Fig. 10, a good correlation is foundn both the TGA and DTA techniques. From the earlier discussion itan be inferred that, when a small quantity of the NC particles isell dispersed in the WGP cement matrix, the hydrated products

f cement deposit on the nanoparticles due to their great surfacenergy, i.e. they act as nucleation sites. Nucleation of hydrationroducts on NC particles further accelerates the pozzolanic reac-ion and hydration process [19,36], which is confirmed by the XRDesults and SEM micrographs.

.3. XRD

XRD analyses were conducted to investigate the mineralogi-al composition of selective specimens of PC (the control), mixes

GP20 and NCWGP20 after 28 days of hydration. For comparison,he peak of CH at 18◦ (2�) and the peak of CSH at 28.6◦ (2�) haveeen selected [19,38]. As shown in Fig. 11, a sharp peak in CH isbserved in the control mix representing the pure hydration prod-ct (CH), which is released from the hydration of cement. Evidently,he intensity of the CH peak is decreased in WGP20 and signifi-antly reduced in mix NCWGP20, which reflects the consumptionf CH by pozzolanic reaction. On the other hand, the intensity of theSH peak significantly increased in mix NCWGP20 compared to theontrol mix, which agrees with the DTA/TGA results in the previousection. Consequently, the XRD results confirm the improvementn the mechanical properties of mixes WGP20 and NCWGP20 com-ared to the control mix.

.4. Scanning electron microscopy (SEM)

SEM was carried out in order to study the influence of WGPnd NC particles on the microstructure of the cement matrix. Addi-ions of glass powder and NC particles were found to influence the

Fig. 11. XRD pattern for control, WGP20 and NCWGP20 specimens.

manner of hydration and resulted in differences in the microstruc-ture of hardened cement systems. Fig. 12 shows the microstructureof selective specimens of the PC control, WGP20 and NCWGP20.Fig. 12(a) presents the typical composition of hydrated mortar inthe control mix. The microstructure of the control specimen dis-played the existence of CSH surrounded by and connected withmany needle-hydrates. When a part of cement was replaced byglass powder, the CSH became relatively dense and fine, as shownin Fig. 12(b). As expected, NCWGP20 (Fig. 12(c)) showed a perfectlydense and compact formation of hydration products. SEM micro-graphs show that the densest mortar structure was observed forthe specimen with a hybrid combination of 20% glass and 2.5% NCparticles, followed by the mix with 20% glass powder (WGP20). Theimprovements in microstructure of NCWGP20 could be attributedto the packing effect of NC particles; due to their great surface area,the NC particles fill the interstitial spaces inside the skeleton of

cement mortar, which leads to increases in toughness and strength[18].

M. Aly et al. / Materials Science and Engineering A 528 (2011) 7991– 7998 7997

4

caE

0

0.04

0.08

0.12

0.16

0.2

NCWGP50NCWG20WGP50WGP20PC control

Expa

nsio

n af

ter 1

6 da

ys [

%]

Also, the LNC mixture exhibits high pozzolanic activity comparedto LWGP, which could be attributed to the smaller particle size andthe higher surface area of NC compared to WGP.

1

2

3

4

5

6

7

Com

pres

sive

stre

ngth

, MPa

LWGP LNC

Fig. 12. SEM micrographs of (a) control, (b) WGP20 and (c) NCWGP20.

.5. Alkali–silica reaction (ASR)

ASR tests were carried out on selective specimens of the PC

ontrol, WGP20, WGP50, NCWGP20 and NCWGP50. The percent-ge expansions in the selected composites are shown in Fig. 13.vidently, NCWGP20 had less expansion compared to the control

Fig. 13. ASR test results for control, WGP20, WGP50, NCWGP20 and NCWGP50specimens.

mix, followed by WGP20. It is clear that all specimens had expan-sions of less than 0.2% and, therefore, according to ASTM C1260, theexpansion was within accepted limits. The expansion tests showedthat the addition of glass powder assisted in hindering the expan-sion compared to the control specimen, which confirms the resultsobtained by Shao et al. [2]. Moreover, the hybrid incorporation ofglass powder and NC greatly reduced the possible ASR. The role ofNC in reducing ASR expansion is therefore in decreasing the amountof CH, which is confirmed by TGA/DTA and XRD results, and hencepreventing formation of a swelling gel [42].

4.6. Activity of ground glass and nano clay with lime

Fig. 14 exhibits the compressive strength of the lime–glass(LWGP) and lime nano clay (LNC) mixtures. It is clear from thisfigure that both LWGP and LNC mixtures satisfied the minimumstrength requirement test at 7 days (4.1 MPa) and attained anincrease in strength after an additional 21 days of curing in water.

0

28-day7-day

Fig. 14. Compressive strength of lime–WGP and NC mixtures.

7 d Eng

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998 M. Aly et al. / Materials Science an

. Conclusions

Green glass powder (5–50% by cement weight) and NC powder2.5% by cement weight) were tested for potential employments cement replacement in cementitious materials. The followingonclusions can be drawn:

Based on flexural and compressive strength, the ASR test andthe CH content of the plain, glass powder, and NC/glass powdercement mortars, it was observed that the replacement of cementby 20 wt% glass powder and 2.5 wt% NC particles is feasible in acementitious system.Compared to the control mix without glass, high fracture energy,flexural and compressive properties can be obtained when usingup to 50% green glass powder as a cement replacement (less75 �m) after 28 days of hydration.Based on the ASR test results, no damaging effect can be detectedat a macroscopic level due to the reaction between glass powderand cement paste with particle size up to 75 �m.DTA/TGA techniques can be used to assess the hydration ofNCWGP cement mortar after 28 days of hydration.The addition of NC particles has great potential to accelerate thepozzolanic reaction. It seems that their nano size allows them toreact more readily with the CH, thereby increasing CSH conver-sion at 28 days of hydration. The hybrid combination of NC andWGP was found to be a very effective way to use ground wasteglass as a high-volume cement replacement and to achieve goodperformance at reasonable cost.

cknowledgements

This work is financed by the Egyptian Ministry of Higher Edu-ation and facilitated by Dublin City University. The authors areeeply indebted to Mr. Christopher Crouch and Mr. Michael May inublin City University for their technical support and cooperation.he authors gratefully acknowledge Southern Clay Products Inc.,SA for their supply of nano clay particles.

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