High temperature performance of mortars containing fine glass powders

Accepted Manuscript High temperature performance of mortars containing fine glass powders

Zhu Pan, Zhong Tao, Timothy Murphy, Richard Wuhrer PII:

S0959-6526(17)31165-4

DOI:

10.1016/j.jclepro.2017.06.003

Reference:

JCLP 9753

To appear in:

Journal of Cleaner Production

Received Date:

17 January 2017

Revised Date:

01 June 2017

Accepted Date:

01 June 2017

Please cite this article as: Zhu Pan, Zhong Tao, Timothy Murphy, Richard Wuhrer, High temperature performance of mortars containing fine glass powders, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.06.003

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1 2

High temperature performance of mortars containing fine glass powders

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Zhu Pan1, Zhong Tao2, Timothy Murphy3, Richard Wuhrer4

42

Address: Centre for Infrastructure Engineering, Western Sydney University, Penrith, NSW 2751, Australia

43

Tel.: +61 2 47360088

1 Postdoctoral

Research Fellow, Centre for Infrastructure Engineering, Western Sydney University, Penrith, NSW 2751, Australia 2 Professor,

Centre for Infrastructure Engineering, Western Sydney University, Penrith, NSW 2751, Australia

3 Technical

Officer, Advanced Materials Characterisation Facility, Western Sydney University, Parramatta, NSW 2116, Australia 4 Research

Manager, Advanced Materials Characterisation Facility, Western Sydney University, Parramatta, NSW 2116, Australia

Keywords: Elevated temperatures; Compressive strength; Thermal strain; Glass powder; Thermal conductivity

*

Corresponding author. E-mail address: [email protected]

1

ACCEPTED MANUSCRIPT 44

ABSTRACT

45

This paper reports on the high-temperature performance of cementitious materials containing

46

fine glass powders (GP) as a partial replacement for ordinary Portland cement. Various mixes

47

were prepared in which cement was replaced by GP in 3 different proportions, i.e., 5wt%,

48

10wt% and 20wt%. Compressive strength tests were carried out at various temperatures (20,

49

500 and 800 C) for mortars containing GP. To have a fundamental understanding of the

50

material behaviour at elevated temperatures, X-ray diffraction (XRD), scanning electron

51

microscopy (SEM) and thermal strain tests were conducted on the corresponding pastes.

52

Results show two distinct temperature ranges regarding effects of GP on the strength of

53

mortars. At temperatures below 500 C, a mortar mix with 20% GP (Type I) showed the best

54

performance with an average strength loss of 15% compared to 33% strength loss in

55

reference samples. The XRD analysis shows a reduction in the calcium hydroxide (CH)

56

content in mortars with GP. At temperatures below 500 C, the strength loss is believed to be

57

due to the dehydration of CH. Therefore, the low strength loss of mortars with GP is

58

associated with their low CH content. In the temperature range of 500800C, the average

59

strength loss was 56% in the GP mortar and 35% in the reference mortar. The thermal

60

shrinkage of GP paste is higher than the reference paste. This can be attributed to softening of

61

glasses. The higher strength loss of GP mortar is due to the higher thermal incompatibility

62

which arises because the paste shrinks while sand particles expand.

63

1. INTRODUCTION

64

Concrete is one of the most commonly used materials in the construction industry (Lee and

65

Choi, 2013). Aggregates, which account for 60-75% of the total volume of concrete, are

66

mainly produced from naturally occurring rock or sand and gravel mineral deposits (Singh et 2

ACCEPTED MANUSCRIPT 67

al., 2016a). Due to the booming infrastructure development, concrete industry has acquired

68

the credentials of being one of the largest consumers of aggregates (Singh et al., 2016b).

69

However, operations associated with aggregate extraction and processing has led to serious

70

environmental impacts, including increased dust, riverbank erosion and physically disturbed

71

landscapes and habitats, etc. (Singh et al., 2016c). Using waste glasses as aggregates has a

72

potential to mitigate the detrimental effects of the mining activities (Tiwari et al., 2016). As a

73

result, the use of waste glasses in concrete has attracted an increasing research interest. The

74

initial study by Pike et al. (Pike et al., 1960) could be traced back to the 1960s when crushed

75

waste glasses were used as aggregates for making concretes. In this study, all the coarse

76

aggregates were replaced by siliceous glasses and glasses containing lithium and lead. It was

77

found that concrete made with siliceous glasses suffered severe cracking with age. The

78

degree of cracking was found less for concrete containing lithium and lead than for concrete

79

containing siliceous glasses. In a later study, Park et al. (2004) investigated the properties of

80

concrete containing a low amount of recycled glasses. The investigated glasses include amber,

81

emerald green, flint, and mixed glass. If glass replacement percentages were less than 30%,

82

no negative effects were observed in concrete mixes (Park et al., 2004).

83 84

During their service life, some civil engineering structures are at the risk of fire. In this case,

85

the high-temperature performance of building materials is required to evaluate the fire

86

resistance of structural members. The study has been conducted to investigate the

87

compressive strength of concrete made with aggregates replaced with coarse waste glasses

88

and fine waste glasses at elevated temperatures (Terro, 2006). When the aggregates were

89

partially replaced with glasses, an optimum replacement ratio of 10% was reported for the 3

ACCEPTED MANUSCRIPT 90

residual strength of concrete after exposure to 700 C. As the replacement ratio increases, the

91

residual strength decreases. The waste glasses were also used to replace fine aggregates for

92

making self-compacting concrete (SCC) (Ling and Poon, 2014). The replacement of fine

93

aggregate was at ratios of 0%, 25%, 50%, 75% and 100% by weight. After exposure to 800

94

C, the residual strength of SCC was improved by incorporation of waste glasses. Compared

95

to improvement in the residual strength, replacing fine aggregates with recycled glasses has

96

more pronounced effects on the improvement in the residual elastic modulus (Guo et al.,

97

2015). More recently, the fire performance of concrete columns using waste glass as coarse

98

aggregate was investigated (Yu et al., 2016). The columns were submitted to compressive

99

loading and then heated to a target temperature of 800 oC in a gas furnace. When the coarse

100

aggregate was replaced by 13% waste glasses, the column endured longer time in fire, as

101

compared to concrete columns using normal aggregates.

102 103

Using waste glasses as the replacement of coarse and fine aggregates in concrete has been

104

found to improve high-temperature performance and to provide environmental benefits (Ling

105

and Poon, 2014). In a highly alkaline environment, the hydroxyl ions in cement pastes and

106

the reactive forms of silica in aggregates react in the presence of sufficient moisture

107

(Rajabipour et al., 2015). This reaction, namely alkali-silica reaction (ASR), produces a gel

108

which swells with age and thereby leading to cracking in concrete. Depending on the types of

109

glasses, approximately 921% of Na2O presents in the glass. The high alkali content of glass

110

could be a major concern for its use in concrete due to the potential risk of ASR. Previous

111

studies have shown that effects of glass on ASR are size dependent (de Castro and de Brito,

112

2013). Glass particles will facilitate ASR when the particle size is greater than 1.21.5 mm 4

ACCEPTED MANUSCRIPT 113

(Meyer and Xi, 1999). However, glass particles will not cause ASR when the particle size is

114

reduced to 300 µm or finer (Zheng, 2016). In contrast, fine glass particles (less than 100 µm)

115

were found to mitigate ASR (Ling and Poon, 2011). Although there are different explanations

116

proposed for this mitigation effect, it is commonly accepted that fine glass particles favour a

117

relatively rapid pozzolanic reaction over slower ASR (Zheng, 2016). The pozzolanic reaction

118

consumes the portlandite, which reduces the availability of calcium for ASR (Bleszynski and

119

Thomas, 1998). According to the studies mentioned above, incorporation of GP not only

120

modify engineering properties at a macroscopic level but also affects the hydration process

121

(by pozzolanic reaction) and results in differences in the microstructure of hardened cement

122

matrix. Such effects have been studied by using X-ray Diffraction (XRD) and

123

Thermogravimetric analysis (TGA) technique (Aly et al., 2012). The results from the two

124

techniques showed a good match, indicating a decrease in the portlandite phase by replacing

125

cement with GP.

126 127

Portlandite, which forms from the hydration of tricalcium silicate and dicalcium silicate,

128

occupies around 1525% of the volume of ordinary Portland cement paste. When portlandite

129

reaches a temperature in the range of 450550 C, it decomposes abruptly, being transformed

130

into CaO (Sarker et al., 2014). This transformation is accompanied by expansion followed by

131

shrinkage of the ordinary Portland cement (OPC) paste. As a result, cracking followed by

132

decrepitating the concrete surface is believed to be the main reason for the significant loss of

133

strength after 400 C in OPC concrete specimens. Khoury (1992) suggested that calcium

134

hydroxide dehydration could be the “Achilles heel” of concrete in high-temperature

135

applications. 5

ACCEPTED MANUSCRIPT 136 137

The portlandite content should be reduced by using GP as the replacement of cement, due to

138

the consumption of portlandite by the pozzolanic reaction. As a result, cementitious materials

139

containing GP generally retain higher mechanical properties after thermal exposure (Türkmen

140

and Fındık, 2013), in comparison with the ordinary cementitious materials. It is noted that the

141

residual mechanical properties are very important for evaluating serviceability of structural

142

members after the fire. However, to evaluate the fire resistance of structural members, the

143

materials’ properties in fire (tested in a hot state) must be known. For the first time, the

144

current research will present the results (at elevated temperatures) of cementitious materials

145

containing GP. At ambient temperature, the thermal properties of materials are also

146

investigated.

147 148

2. MATERIAL AND METHODS 2.1 Characterisation of materials

(b)

(a)

149

Figure 1 (a) Particle size distribution; (b) Sand grading

150

As specified by ASTM C150, Type I Portland cement was used in the current investigation.

151

Two types of fine glass powders (provided by Potters Australia) were used in this project. 6

ACCEPTED MANUSCRIPT 152

The particle size distribution (PSD) of GPs, along with that of the cement powder is shown in

153

Fig. 1 (a). Although all the materials have the particle size less than 100 µm, the size

154

distribution is different. The cement powder has a continuous gradation, while both GPs have

155

a more uniform gradation. By comparison of two GPs, the average particle size of Glass I

156

was smaller than that of Glass II. The average particle sizes were 45 µm and 60 µm for Glass

157

I and Glass II, respectively. The morphology of the two types of GP is shown in Fig. 2. It was

158

found that GP consists mainly of fine sphere particles with a uniform gradation. The chemical

159

compositions of the cement and GPs were determined by X-ray Fluorescence (XRF) analysis,

160

as shown in Table 1.

161

Table 1 Chemical composition of materials Materials Cement (%) Glass I (%) Glass II (%)

Al2O3 4.9 1.5 0.1

SiO2 18.2 73.7 64.0

CaO 60.7 7.5 -

Fe2O3 2.6 0.1 -

K2O 0.4 0.3 0.1

MgO 1.0 0.2 -

Na2O 0.2 9.1 20.2

SO3 2.2 0.4 0.4

LOI 8.8 0.3 5.2

162 163

It can be seen from Table 1 that Glass I and Glass II present a higher amount of SiO2 and

164

Na2O, as compared to cement. A comparison of the two types of glass powder shows that

165

Glass I presents a higher content of lime and SiO2. According to the specification of ASTM

166

C618, as presented in Table 2, Glass I might be accepted as a cement replacement, while the

167

SiO2 content of Glass II has not reached the minimum requirement in the standard.

168

Table 2 ASTM C 618 requirements for pozzolanic additives ASTM C618 SiO2+Al2O3+Fe2O3, min % SO3, max % Moisture content, max % Loss on ignition, max %

Glass I 75.3 0.4 0.3

70 4 3 10

169

7

Glass II 64.1 0.4 5.2

ACCEPTED MANUSCRIPT

(b)

(a)

170

Figure 2 Photographs of (a) Glass I and (b) Glass II

171

The sand used was locally available river sand. The physical properties of the sand are

172

summarised in Table 3. The sand has a continuous grading, which meets the grading

173

requirement for fine aggregate specified in ASTM C33 (Fig. 1(b)). The mixing water was

174

local tap water. The superplasticiser (SP) used was a polyethylene sulphonate that complied

175

with ASTM C 494. The sand was dried in an oven until there was no loss in weight. The

176

extra mixing water was then added to sand to reach its saturated surface dry condition.

177

Table 3 Physical properties of sand Apparent specific gravity

Bulk specific gravity

2.67

2.51

Water absorption (%) 1.80

Fineness modulus 2.95

Coefficient of uniformity 2.89

178

2.2 Mixing and casting

179

The whole mixing procedure took place in a constant-speed mixer. The dry ingredients were

180

mixed briefly before the water was added. Then the water, together with SP, were added and

181

stirred at 80 rpm for 300 s. The fresh mixture was poured into hollow PVC tubes in three

182

equal layers. Each layer was vibrated for 15–30 s on a vibration table. The tops were sealed

183

with consumer cling-wrap to avoid moisture evaporation and the samples were cured in the

184

moulds for 1 d. Then the samples were cured in lime-saturated water until the testing day or 8

ACCEPTED MANUSCRIPT 185

28 d. Prior to compressive strength tests, the samples were ground to have smooth and

186

parallel top and bottom edges.

187 188

To have a fundamental understanding of the properties, the paste samples were prepared for

189

XRD, Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS),

190

thermal shrinkage and thermal properties measurements. However, the paste samples are

191

normally quite brittle, leading to scattering results for strength tests. To overcome this

192

limitation, mortar samples were prepared for compressive strength tests. The mixture

193

proportions of mortars are summarised in Table 4. In order to avoid effects of superplasticizer

194

on the comparison of different mixes, superplasticizer dosage was kept consistent for all

195

mixes.

196

Table 4 Compositions of mortar mixes Components Cement Sand Water GP I GP II Superplasticizer (L)

Cement 567 1281 252   1.7

Mass of component (kg/m3) 5Glass I 10Glass I 20Glass I 539 510 454 1281 1281 1281 252 252 252 28 57 113    1.7 1.7 1.7

20Glass II 454 1281 252  113 1.7

197

198

2.3 Compressive strength testing

199

Three steady-state test methods are commonly used for measuring the high-temperature

200

strength of cementitious materials. They are residual, unstressed, or stressed test methods. In

201

the current study, compressive strength tests were conducted at 500 and 800 C, using

202

unstressed test method. The tests were carried out in an electric split-tube furnace equipped 9

ACCEPTED MANUSCRIPT 203

with a closed-loop servo-control (1,000 kN) hydraulic pump actuator and a loading frame.

204

The unstressed samples were heated to the target temperature at 4 C/min. The samples have

205

further remained at the target temperature for 1.5 h. This period was found to be sufficient for

206

reaching a steady-state condition in our preliminary tests. Then, the samples were loaded up

207

to failure. The procedures proposed by RILEM (1995) were followed for measuring strength

208

at elevated temperatures. At ambient temperature, the compressive strength tests were carried

209

out by ASTM C39. The compression tests were performed on 60 × 180 mm cylinders. The

210

length/diameter ratio meets the requirement proposed by RILEM (1995).

211

2.4 Thermal strain testing

212

To measure thermal strains, the sample was placed at the centre of the electric furnace. The

213

unstressed sample was heated at a constant heating rate of 4 C/min. The strain was measured

214

by a high-temperature extensometer, with a 100 mm gauge length, mounted on the outside of

215

the furnace. The spring-loaded ceramic rods of the extensometer were steadily fixed on the

216

specimen surface with a static pressure. The relative movement of the two rods recorded the

217

expansion or contraction of the specimen. The procedures proposed by RILEM (1997) were

218

used in this investigation.

219

2.5 Specific heat and thermal conductivity testing

220

The thermal properties of pastes, at ambient temperature, were measured using a

221

commercially available instrumentHot Disk TPS 1500. This thermal analyser is based on

222

transient plane source technique, which meets the requirements of ISO/DIS 22007 standard.

223

In order to measure specific heat and thermal conductivity, a flat source sensor with a radius

224

of 4.868 mm was placed between two halves of Ø 60×25 mm paste samples. The size was 10

ACCEPTED MANUSCRIPT 225

determined in accordance with the requirement for the ratio of the minimum specimen

226

diameter to the maximum aggregate size in RILEM (1997). These two symmetrical samples

227

were prepared by slicing from paste cylinders.

228

2.6 SEM analysis

229

A JEOL 6510LV high-performance scanning electron microscope (SEM) was used to

230

investigate the morphology and microstructures of the pastes. The sample used for SEM

231

imaging was the piece taken from the same specimen used for the strength test. The

232

secondary electron detector was operated at 15 kV. The samples were coated with carbon to

233

make a conductive surface.

234

2.7 XRD testing

235

XRD patterns were obtained using a Bruker D8 Advance Powder Diffractometer. The

236

samples were crushed just before running the tests. Diffraction analyses were made from 5 to

237

60 2θ using copper K radiation. The excitation voltage was 40 kV at 40 mA. Counting time

238

was 5 s, or 1.542 nm per point.

239

2.8 Mini-slump measurements

240

The workability was measured by mini-slump test method which is commonly used for

241

assessing flowability of fresh pastes. The design details of the mini-slump cone can be found

242

in the reported literature (Pan et al., 2015). The fresh paste was poured into the cone sitting

243

firmly on a flat surface. A spatula was used to tamp the cone and smooth the top surface. The

244

cone was then slowly removed in a vertical direction. The diameter of the spread area was

245

measured twice in two perpendicular directions, and the mean value was reported. 11

ACCEPTED MANUSCRIPT 246

3. RESULTS AND DISCUSSION

247

3.1 Environmental impact of GP and OPC mortars

248

It has been reported that a reduction in energy consumption and greenhouse gas emissions

249

(GHGs) could be achieved over a life cycle of a concrete/mortar mix when OPC is partially

250

replaced with GP (Ling and Poon, 2011). To quantify the environmental effects, GHGs and

251

cumulative energy demand of GP and OPC mortars are compared.

252 253

In general, GP is produced by grinding waste glass into fine powders. Jiang et al. (2014) have

254

reported a series of electricity input values required to produce a unit mass of GP with the

255

desired fineness value. Based on these values, 0.25 kW h is determined as the electricity input

256

for producing 1 kg of GP with a size less than 100 µm. The GHGs associated with the

257

required electricity input was estimated as 0.338 kgCO2-e, based on the emission factor of

258

1.35 kgCO2-e/kW h proposed by the Australian National Greenhouse Accounts (NGAs)

259

Factors (DEE, 2016). The energy consumed to obtain 1 kg of GP was estimated as 0.889

260

MJ/kg. The mortars were produced by using locally available materials. Inventory data

261

collected from fine aggregate quarries (Turner and Collins, 2013) and cement manufacturers

262

(McLellan et al., 2011) were used for estimating environmental impacts of producing sand

263

and Portland cement. The environmental impacts of provision and consumption of water for

264

making mortars were estimated based on the data reported by the Water Services Association

265

of Australia (WSAA, 2008). The impact assessment results for all the mortar’s components

266

are presented in Table 5. It can be seen from the table that the largest impact contribution is

267

the production of Portland cement. 12

ACCEPTED MANUSCRIPT 268

Table 5 Environmental impacts of components of mortars

GHGs (kg CO2e/kg) Embodied Energy (MJ/kg)

Portland cement 8.200 5.600

Water

Sand

GP

0.001 0.010

0.014 0.081

0.338 0.889

269 270

The mixture proportions presented in Table 4 were used in the impact calculations of

271

producing 1 m3 of mortar. The calculated GHGs and embodied energy are presented in Fig. 3.

272

As expected, Portland cement is by far the most significant contributor to both GHGs and

273

embodied energy. It contributes 90% of GHGs and 96% of embodied energy for OPC mortar.

274

The use of GP as partial cement replacement in mortar could reduce both GHGs and

275

embodied energy. For GHGs, mortars made with 20% cement replacement with GP has 15%

276

lower GHGs as compared to OPC mortars. As for embodied energy, the energy use for

277

mortars made with 20% cement replacement with GP is approximately 14% lower than that

278

of OPC mortars. In an early study reported by Jiang et al. (2014), the estimate of GHGs due

279

to partial substitution of Portland cement with GP was 19% lower than OPC concrete with a

280

strength of 35 MPa. The use of GP as a partial replacement in concrete also reduces the

281

energy use by 17% for OPC concrete. As can be seen, both the GHGs and embodied energy

282

of GP mortars (in the current study) is higher than those of GP concretes in the previous

283

study. The key factor that led to the differences is the finer GP used in our study. The finer

284

GP requires longer grinding times, resulting in higher electricity consumption. It is worth

285

mentioning that the estimation of environmental impacts (in this study) is a conservative

286

assumption. In real production, GP could be retrieved as a side product (e.g., production of

287

glass beads). In this way, the environmental impacts will be much less than those associated

288

with the products made by grinding glass.

13

ACCEPTED MANUSCRIPT

289

290

291

Figure 3 Environmental impacts of mortars 3.2 Workability

Figure 4 Mini slump test results

292

Mini-slump tests were carried out to assess workability by calculating the area of spread flow.

293

The effect of the percentage of glass powder on the workability of mortars containing Glass I

294

and Glass II is demonstrated in Fig. 4. It seems that the workability decreases with a higher

295

percentage of glass powder. This could be attributed to the large specific surface area of glass

296

powder. A significant amount of mixing water is restrained on the surface of glass powder,

297

which reduces free water content (in the fresh mix) and results in reduced workability. Up to

298

10% replacement of cement with Glass I, the reduction in workability is negligible. At a 20%

299

replacement level, it is observed that the area of mini-slump is reduced to approximately

300

9,000 mm2, which is 85.5% lower than that of the plain cement mortar. At a high replacement 14

ACCEPTED MANUSCRIPT 301

proportion of 20%, incorporation of Glass II also leads to a significant decrease of

302

workability.

303 304

3.3 Compressive strength at ambient temperature

305

Figure 5 Strength activity indexes at different ages

306

ASTM C618 recommends that strength activity index should be determined based on samples

307

prepared with 80% cement plus 20% additive by mass. The index can be calculated as the

308

ratio of the compressive strength of samples with the additives, to the compressive strength of

309

reference

310

(80%OPC+20%Glass I) and 20Glass II (80%OPC+20%Glass II) at different ages up to 28 d.

311

According to ASTM C618 recommendation, a pozzolan may have a minimum strength

312

activity index of 75%. As a result, the activity index of both 20Glass I and 20Glass II at early

313

ages did not satisfy the criteria. As age increases, the activity index of mortars with glass

314

powders has a tendency to increase. At the age of 28 d, the value of activity index of 20Glass

315

I was 79%, which is higher than the ASTM criterion. On the other hand, the value of activity

316

index of 20Glass II at 28 d was 73%, which is slightly lower than the criterion. The different

317

activity indices for these two glass powders could be attributed to their different fineness. In

samples.

Fig.

5

shows

the

strength

15

activity

index

for

20Glass

I

ACCEPTED MANUSCRIPT 318

comparison to Glass II, Glass I possesses a significantly higher amount of fine particles with

319

a grain size smaller than 30 µm. These fine particles, having a high specific surface area,

320

would provide C-S-H with preferential nucleation sites, promoting the hydration and leading

321

to a higher compressive strength, as compared to 20Glass II.

322 Figure 6 Strength development of mortars with ages 323

The effect of age on the strength of mortars containing 0 wt.%, 5 wt.%, 10 wt.% and 20 wt.%

324

glass powder is shown in Fig. 6. It can be seen that in all cases, compressive strength

325

increases with age. The strength of the reference mortars was seen to be greater than those of

326

mortars containing glass powder at an early age. This difference had a tendency to decline

327

with age. For example, at the age of 3 d the compressive strength of 5Glass I was 67% of that

328

of the reference mortar; this value increased to 89% at 7 d and 110% at 28 d. This tendency is

329

an indication of pozzolanic reactivity which can be further confirmed by XRD results. XRD

330

analyses (Fig. 7) were carried out to investigate changes in crystalline phase composition of

331

paste specimens with ages. The portlandite content of pastes may be reflected approximately

332

by the intensity of main diffraction peaks of portlandite such as 18.008o2θ and 34.102o2θ. At

333

3 d, diffraction peak intensities of 18.008o2θ and 34.102o2θ of 5Glass I were almost equal to

334

those of cement paste. This suggests that the 5Glass I and cement paste have a similar amount

335

of portlandite at 3 d. As age increases, the portlandite content of cement is higher than that of 16

ACCEPTED MANUSCRIPT 336

5Glass I. This difference has a tendency to increase with age. For example, in comparison

337

with the reference sample, the intensities of 18.008o2θ and 34.102o2θ of sample 5Glass I at 7

338

d decreased by 63% and 61%, respectively. At 28 d, the value of 18.008o2θ remained almost

339

unchanged, but the value of 34.102o2θ decreased significantly. The results indicate the fast

340

portlandite consumption after 3 d, which is due to the pozzolanic reaction. As age increases,

341

strength development of cement is mainly due to hydration while strength development of

342

5Glass I is a result of both hydration and pozzolanic reaction. At 28 d, the strength of 5Glass

343

I was higher than that of the reference sample.

P P

C A,B

P

C B

C E P P

C

A,B

P

B C

C E

P C A,B

P

C

C

P

B

E P

P

C P

A,B C

C

B

E

P C

P

P

A,B

C B

C

E

P P C A,B E

C

C

17

B

P

ACCEPTED MANUSCRIPT 344 345 346

It is noted that the pozzolanic activity of glass powder at an early age is low, which is similar

347

to other pozzolan additives. Results reported in the previous literature (Qing et al., 2007)

348

show that the pozzolanic reaction between pozzolan additives (e.g. fly ash and silica fume)

349

and portlandite formed during cement hydration begins to occur after 3 d of hydration. At 3 d,

350

the strength of mortars containing glass powders was lower than that of the reference sample.

351

The difference increases as the replacement ratio increases. This is believed to be due to the

352

dilution effect (Luo et al., 2013) that is a consequence of the partial replacement of cement by

353

the same amount of GP. The increase in the content of glass powder leads to a decrease in the

354

content of cement, resulting in a reduction in the cement to water ratio. In return, less cement

355

is associated with less hydrated products and lower compressive strength, as compared to the

356

reference sample.

357 358

As discussed above, the pozzolanic effect leads to an increase in strength while the dilution Figure 7 XRD patterns of pastes at different ages. Peak labels are: A-alite (3CaO.SiO2), B-belite

359

effect leads to(Caa2SiOdecrease in strength. These two opposing processes influence strength 4), C-calcite (CaCO3), E-ettringite (3CaO.Al2O3.3CaSO4.26H2O), P-portlandite (Ca(OH)2)

360

simultaneously when cement was replaced by glass powders. As a result, the efficiency

361

regarding compressive strength is dependent on the percentage of glass powder. At 28 d,

362

replacing 5% of cement by glass powder has an optimum efficiency and leads to a higher

363

compressive strength for 5Glass I as compared to the reference sample without GP.

364 365

3.4 Compressive strength in hot state 18

ACCEPTED MANUSCRIPT 366

Changes in relative compressive strength as a function of glass type, replacement ratio and

367

temperature are presented in Fig. 8. When the specimens were exposed to elevated

368

temperatures, the mortars containing Glass I performed better as compared to mortars

369

containing Glass II. In each temperature range, mortars containing 5% and 20% Glass I

370

replacements maintained a higher percentage value of strength (in the hot state) than mortars

371

containing 20% Glass II replacement. The different high-temperature performances could be

372

attributed to the different compositions and particle sizes of the two types of glass powders.

373

These issues require further study. The change of replacement ratios has little effects on the

374

hot compressive strength. At 500 C, the retained percentage values of hot compressive

375

strength for mortars containing 5% and 20% Glass I replacements were 77% and 85%,

376

respectively. The difference of these values was only 7%, which further reduced to 5% at 800

377

C. In the current research, the maximum standard deviation of hot strength results was 8%.

378

Therefore, the different performance (due to replacement ratio) may be a result of

379

measurement error.

380

Figure 8 (a) Relative change in strength and (b) hot strength at elevated temperatures

381

A close examination of Fig. 8 reveals a difference in performance between reference and GP

382

mortars when they were exposed to temperatures up to 800 C. From the perspective of 19

ACCEPTED MANUSCRIPT 383

performance of mortars containing GP (as compared to the reference), the heating profile

384

could be divided into two ranges as 0500 C and 500800 C. A distinct pattern of better

385

performance and then worse performance was observed in each temperature range. Initially,

386

mortars containing glass powder maintained higher original strength than the reference. For

387

example, at 500 C, the retained hot strength was 85% for 20Glass I but 67% for the

388

reference. After 500 C, the loss in strength of mortars containing GP was faster than that of

389

the reference mortar. In the 500800 C temperature range, the loss was 56% for 20Glass I

390

but only 35% for the reference mortar. The possible mechanisms for these effects will be

391

further discussed later, based on physical and chemical changes (taking placing at elevated

392

temperatures) observed in this research.

393 394

3.5 Thermal strain

395 Figure 9 Thermal strain of pastes 396 397

The variation of the thermal strain of cement paste and cement paste containing glass powder

398

is plotted as a function of temperature in Fig. 9. The data for cement paste reveal a slight

399

expansion up to 350 C. This is generally attributed to an expansion of the unhydrated 20

ACCEPTED MANUSCRIPT 400

particles and portlandite presented in the paste (Piasta, 1984). At around 350 C, a slight

401

shrinkage of cement paste occurs, which may be attributable to dehydration of the different

402

hydrates at various temperatures. Between 600800 oC, a rapid shrinkage occurs. In this

403

temperature range, samples containing glass powders exhibited significantly higher shrinkage,

404

as compared to cement paste. At 800 C, the shrinkage strain for pastes containing GP is

405

nearly 3 times as high as that of the cement paste. The large shrinkage strain was also

406

observed on a cementitious binder with three-dimensional glassy structures (Vickers et al.,

407

2014). This is an indication that the glass particles had gone through the glass transformation

408

from a hard state into a rubber-like state. A comparison of curves in Fig. 9 shows a lower

409

temperature for 20Glass II at the onset of shrinkage, which can be attributed to its high

410

content of Na2O. In glasses, Na2O serves as a network modifier and lowers the temperature

411

for glass transition (Rahier et al., 1996). Regarding various oxides presented in glasses, SiO2

412

has a low expansion coefficient, whereas Na2O has a high expansion coefficient due to its

413

large atomic volumes (Jackson and Mills, 1997). As a result, 20Glass II exhibited a high

414

degree of expansion between 200 and 400 C.

415 416

3.6 Phase changes in a hot state

417

Figure 10(a) shows XRD results of cement pastes exposed up to 800 C. Before thermal

418

exposure, the presence of portlandite can be characterised by main diffraction peaks at crystal

419

faces of 001, 100 and 101. Minor amounts of ettringite were also identified, as evident by the

420

peaks at crystal faces of 100 and 110. Other important peaks are due to calcite and some

421

unhydrated alite/belite. After being exposed to 500 C, notable changes in crystalline phases 21

ACCEPTED MANUSCRIPT 422

were the disappearance of the portlandite and ettringite peaks. Moreover, the broad

423

diffraction peaks were observed between 32 and 34o 2θ, which is a reflection of poorly

424

ordered crystalline phases. Diffraction in this region may correspond to belite and alite as

425

well as other unhydrated phases such as gehlenite and akermanite. In the temperature range

426

of 500 to 800 C, XRD pattern shows little changes in crystalline phases. For a purpose of

427

comparison, XRD patterns for 20Glass I before and after heat exposure are presented in Fig.

428

10(b). It seems that the effects of temperatures on the change of crystalline phases are similar

429

for both cement paste and 20Glass I. G*

(a)

(b)

B

G*

B

G*

G* B

C

B

P P

P C A,B

P A,B

B C

C E

430 431

C

P

P

B C

E

Figure 10 XRD patterns of (a) cement paste and (b) 20Glass I at elevated temperatures. Peak labels are: A-alite (3CaO.SiO2), B-belite (Ca2SiO4), C-calcite (CaCO3), E-ettringite (3CaO.Al2O3.3CaSO4.26H2O), G*-(A, B, G-gehlenite (Ca2Al(AlSiO7)), Ak-akermanite (Ca2Mg(Si2O7)) ), P-portlandite (Ca(OH)2)

432

3.7 Microscopic observations

433

The effects of temperatures on the morphology of cement paste and 20Glass I are presented

434

in Fig. 11 (a)-(f). Fig. 11 (a) shows the cement paste having hexagonal plates of portlandite

435

representing the microstructure of the samples before thermal treatment. After exposure to

436

500 C, hexagonal plates could not be observed in this sample, indicating the decomposition

437

of portlandite. This change in morphology is in good agreement with that of XRD patterns. 22

ACCEPTED MANUSCRIPT 438

Micro-cracks appeared in the cement paste after exposure to 500 C, notably in the area

439

around unhydrated particles. More severe cracking was observed for the samples heated to

440

800 C. The cement paste did not show a significant microstructural change from 500 to 800

441

C. At 800 C the hydrated phases lost their characteristic crystal structure, and irregular and

442

amorphous agglomerates were abundant throughout the sample. SEM image (Fig. 11 (b)) of

443

20Glass I (before exposure) showed that the crystalline phase characterised by large plates

444

similar to the phase seen in the cement paste. Micrometer-sized sphere glass powders were

445

clearly visible throughout the sample. After exposure to 500 C, the platelike crystal

446

disappeared, but intact GP were sometimes found in the sample. An interesting SEM finding

447

(Fig. 11 (f)) was the presence of molten GP at 800 C, suggesting that the glass

448

transformation temperature is lower than 800 C. This provides the evidence for the

449

hypothesis that the softening of GP promotes the shrinkage of mortar at 800 C.

(a)

(b) Portlandite

GP particles

Portlandite (c)

(d)

GP particles Micro-cracks

23

ACCEPTED MANUSCRIPT

(e)

(f) Cracks

GP particles 450

Figure 11 SEM analysis of pastes at 20 C, (a) cement paste, (b) 20Glass I;

451

SEM analysis of pastes after exposure to 500 C, (c) cement paste, (d) 20Glass I;

452

SEM analysis of pastes after exposure to 800 C, (e) cement paste, (f) 20Glass I 3.8 Thermal properties

453 Figure 12 (a) Thermal conductivity of pastes; (b) Specific heat of pastes 454

The variation of thermal conductivity of the cement paste and the pastes containing GP are

455

demonstrated in Fig. 12(a). The thermal conductivity of the cement paste was observed as

456

1.047 W/mK whereas thermal conductivities of 5Glass I, 10Glass I and 20Glass I pastes were

457

found as 1.013, 0.911 and 0.707 W/mK, respectively. These results suggest that glass powder

458

replacement leads to a considerable reduction in thermal conductivity. The reduction for

459

20Glass I was 32% compared to the reference paste. This is similar to the effect of

460

incorporation of silica fume (Xu and Chung, 2000) or natural zeolite (Vejmelková et al., 2015)

461

in cementitious materials, which could be attributed to that both glass powder and silica fume 24

ACCEPTED MANUSCRIPT 462

mainly consist of amorphous silicon dioxide. The measured specific heat results are presented

463

in Fig. 12(b). The incorporation of glass powder reduces the specific heat of cement paste.

464

This effect is pronounced in specimens with high replacements. The specific heat of glasses

465

was reported between 0.71.0 MJ/m3K (Sharp and Ginther, 1951), which is much lower than

466

that of cement paste. It is thus expected that the paste with GP to have lower specific heat.

467 468 469

470

3.9 Strength loss due to chemical and physical changes

Figure 13 XRD pattern for portlandite peak

471

When the cementitious materials are exposed to elevated temperatures, it has been recognised

472

that the strength is governed by the chemical and physical changes taking place

473

simultaneously at high temperatures. From the chemical point of view, strength loss is due to

474

the dissociation of phases such as portlandite (discussed above). From the physical point of

475

view, strength loss is due to thermal incompatibility that arises in mortars because of different

476

movements between the paste and sand particles.

477 25

ACCEPTED MANUSCRIPT 478

Regarding chemical changes at elevated temperatures, the distinct change of XRD patterns is

479

the disappearance of the peak for portlandite, which occurred at 500 C. As this phase

480

transformation leads to strength loss, it would be logical to assume a correlation between the

481

degree of strength loss and the portlandite content in materials. At the same age of 28 d, a

482

comparison of the peaks of portlandite at 18.008o2θ is presented in Fig. 13. It can be seen that

483

the intensity of the portlandite peak is decreased by the incorporation of glass powder. As a

484

result, pastes containing type I glass powder exhibited less strength loss compared to the

485

cement paste at 500 C. As the temperature increased, the XRD patterns showed little

486

changes. On the other hand, the pastes containing GP were found to have larger shrinkage,

487

indicating that the corresponding mortars suffered severe thermal incompatibility, which

488

would explain the higher strength loss at 800 C, as compared to the mortar without GP.

489 490

The introduction of GP reduces strength loss at elevated temperatures up to 500 oC. Although

491

the strength of 20Glass I is lower than that of the reference mix before heating (Fig. 2), the

492

hot strength of 20Glass I is comparable to that of the reference mix (Fig. 8 (b)). Moreover,

493

high temperature resistance of materials depends not only on the strength but also on the

494

thermal properties. The introduction of GP leads to a considerable reduction in thermal

495

conductivity. The reduction for 20Glass I was 32% compared to the reference mix (Fig. 12

496

(a)). The low thermal conductivity indicates slow heat transfer in 20Glass I. For mixes with

497

GP, the time required reaching target temperatures is longer compared to the reference mix.

498

Therefore, results obtained from this study show that GP has a potential to enhance fire

499

resistance of cementitious materials.

500 26

ACCEPTED MANUSCRIPT 501

In this study, the strength of mortars with GP was investigated at elevated temperatures. The

502

strength decrease of mortars was mainly due to the dehydration and destruction of CH and

503

CSH in the matrix. These changes would be expected to have the same influence on both

504

mortar and concrete. Therefore, results obtained from this research would provide useful

505

information to predict the high-temperature performance of GP concrete, which could be

506

used to construct various structural elements. However, concrete may behave slightly

507

different from mortar because of the inclusion of the coarse aggregate. Further research could

508

be conducted to understand the high-temperature performance of GP concrete, and the gained

509

knowledge can be used to assist the fire safety design of structures made with GP concrete.

510 511

4. CONCLUSIONS

512

The effects of temperatures on properties of cementitious materials containing GP have been

513

investigated. Based on the results obtained in the current study, the following conclusions are

514

drawn:

515

1. When cement is partially replaced by GP, strength of mortars is influenced by the

516

dilution (negative) effect and the pozzolanic (positive) effect. The contributions of

517

these two effects are dependent on the replacement ratio. At the age of 28 d, the

518

replacement of cement by 5% is an optimal mix regarding compressive strength.

519

2. The pozzolanic activity increases with age. At 28 d, due to consumption of portlandite

520

by pozzolanic reaction, the portlandite content of pastes containing GP was lower

521

than that of control samples.

522

3. Heating of the samples to 800 C led to similar chemical changes taking place in both

523

control paste and the paste containing of GP. Heating induced the dehydration of 27

ACCEPTED MANUSCRIPT 524

portlandite and ettringite. The unhydrated phases (e.g. gehlenite and akermanite) were

525

also observed.

526

4. The addition of GP had little effects on thermal expansion of pastes below 500 C.

527

Above 500 C, amorphous glass powders experienced glass transformation, and the

528

softening glasses resulted in larger shrinkage, as compared to control samples.

529

5. At temperatures below 500 C, the strength loss was observed to be associated with

530

the dehydration of portlandite. As the addition of GP reduced the portlandite content

531

in samples, the mortars containing of GP performed better than mortars without GP.

532

At temperatures above 500 C, the strength loss of mortars containing GP was higher

533

than that of control mortars. This is attributed to the high movement between cement

534

matrix and sand particles at high temperatures.

535

6. Compared with control samples, the addition of GP decreases thermal conductivity.

536

As a result, the transfer of heat flow within the specimen is slow. Further research

537

could be conducted on elevated temperature behaviour of concrete containing glass

538

powder and fire resistance of structural members made with such concrete.

539

7. The life cycle assessment shows that the use of GP as partial cement replacement

540

could reduce environmental impacts of cementitious materials. The experimental

541

results show that mortars made with 20% cement replacement with GP had higher

542

activity index than the value for pozzolanic materials specified in ASTM C618. Thus,

543

GP is recommended as a pozzolanic material to partially replace Portland cement in

544

concrete.

545

Manufacturing OPC is energy intensive, while the calcination of limestone and combustion

546

of fossil fuels during manufacturing liberates high CO2 emissions. The partial replacement of 28

ACCEPTED MANUSCRIPT 547

cement by GP leads to reduction of cement consumption in construction industry. The life

548

cycle assessment shows that GP mortar has 15% lower CO2 emissions and 14% less energy,

549

as compared to OPC mortar. Therefore, GP contributes to the development of cleaner

550

production of cement-based products. The study also demonstrates that GP contributes not

551

only to pozzolanic activity but also to enhanced fire resistance of cement-based products.

552

This would encourage industrial practitioners to use GP in production of construction and

553

building materials.

554

ACKNOWLEDGMENTS

555

The authors are grateful for the financial support provided by the Western Sydney University

556

through an ECA award. The authors would also like to acknowledge the contributions from

557

the laboratory staff Mr Murray Bolden and Mr Robert Marshall.

558

559

REFERNCES

560 561 562 563 564 565 566 567 568 569 570 571 572 573 574

1995. Compressive strength for service and accident conditions. Mater Struct 28, 410-414. 1997. Recommendations: Part 6-thermal strain. Mater Struct 30, 17-21. Aly, M., Hashmi, M.S.J., Olabi, A.G., Messeiry, M., Abadir, E.F., Hussain, A.I., 2012. Effect of colloidal nano-silica on the mechanical and physical behaviour of waste-glass cement mortar. Materials & Design 33, 127-135. Bleszynski, R.F., Thomas, M.D.A., 1998. Microstructural Studies of Alkali-Silica Reaction in Fly Ash Concrete Immersed in Alkaline Solutions. Advanced Cement Based Materials 7, 66-78. de Castro, S., de Brito, J., 2013. Evaluation of the durability of concrete made with crushed glass aggregates. Journal of Cleaner Production 41, 7-14. Department of Energy Effieiency (DEE), National Greenhouse Accounts (NGA) Factors. Commonwealth of Australia, Canberra; 2016. Guo, M.-Z., Chen, Z., Ling, T.-C., Poon, C.S., 2015. Effects of recycled glass on properties of architectural mortar before and after exposure to elevated temperatures. Journal of Cleaner Production 101, 158-164.

29

ACCEPTED MANUSCRIPT 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621

Jackson, M.J., Mills, B., 1997. Thermal expansion of alumino-alkalisilicate and aluminoborosilicate glasses -- comparison of empirical models. Journal of Materials Science Letters 16, 1264-1266. Jiang, M., Chen, X., Rajabipour, F., Hendrickson, C.T., 2014. Comparative Life Cycle Assessment of Conventional, Glass Powder, and Alkali-Activated Slag Concrete and Mortar. Journal of Infrastructure Systems 20. Khoury, G.A., 1992. Compressive strength of concrete at high temperatures: a reassessment. Magazine of Concrete Research 44, 291-309. Lee, G.C., Choi, H.B., 2013. Study on interfacial transition zone properties of recycled aggregate by micro-hardness test. Construction and Building Materials 40, 455-460. Ling, T.-C., Poon, C.-S., 2011. Properties of architectural mortar prepared with recycled glass with different particle sizes. Materials & Design 32, 2675-2684. Ling, T.-C., Poon, C.-S., 2014. High temperatures properties of barite concrete with cathode ray tube funnel glass. Fire and Materials 38, 279-289. Luo, F.J., He, L., Pan, Z., Duan, W.H., Zhao, X.L., Collins, F., 2013. Effect of very fine particles on workability and strength of concrete made with dune sand. Construction and Building Materials 47, 131-137. McLellan, B.C., Williams, R.P., Lay, J., van Riessen, A., Corder, G.D., 2011. Costs and carbon emissions for geopolymer pastes in comparison to ordinary portland cement. Journal of Cleaner Production 19, 1080-1090. Meyer, C., Xi, Y., 1999. Use of Recycled Glass and Fly Ash for Precast Concrete. Journal of Materials in Civil Engineering 11, 89-90. Pan, Z., He, L., Qiu, L., Korayem, A.H., Li, G., Zhu, J.W., Collins, F., Li, D., Duan, W.H., Wang, M.C., 2015. Mechanical properties and microstructure of a graphene oxide–cement composite. Cement and Concrete Composites 58, 140-147. Park, S.B., Lee, B.C., Kim, J.H., 2004. Studies on mechanical properties of concrete containing waste glass aggregate. Cement and Concrete Research 34, 2181-2189. Piasta, J., 1984. Heat deformations of cement paste phases and the microstructure of cement paste. Mat. Constr. 17, 415-420. Pike, R.G., Hubbard, D., Newman, E.S., 1960. BINARY SILICATE GLASSES IN THE STUDY OF ALKALI-AGGREGATE REACTION. Highway Research Board Bulletin, 39-48. Qing, Y., Zenan, Z., Deyu, K., Rongshen, C., 2007. Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume. Construction and Building Materials 21, 539-545. Rahier, H., Van Mele, B., Wastiels, J., 1996. Low-temperature synthesized aluminosilicate glasses. JOURNAL OF MATERIALS SCIENCE 31, 80-85. Rajabipour, F., Giannini, E., Dunant, C., Ideker, J.H., Thomas, M.D.A., 2015. Alkali–silica reaction: Current understanding of the reaction mechanisms and the knowledge gaps. Cement and Concrete Research 76, 130-146. Sarker, P.K., Kelly, S., Yao, Z., 2014. Effect of fire exposure on cracking, spalling and residual strength of fly ash geopolymer concrete. Materials & Design 63, 584-592. Sharp, D.E., Ginther, L.B., 1951. Effect of Composition and Temperature on the Specific Heat of Glass. Journal of the American Ceramic Society 34, 260-271. Singh, S., Khan, S., Khandelwal, R., Chugh, A., Nagar, R., 2016a. Performance of sustainable concrete containing granite cutting waste. Journal of Cleaner Production 119, 86-98. 30

ACCEPTED MANUSCRIPT 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650

Singh, S., Nagar, R., Agrawal, V., 2016b. Performance of granite cutting waste concrete under adverse exposure conditions. Journal of Cleaner Production 127, 172-182. Singh, S., Nagar, R., Agrawal, V., Rana, A., Tiwari, A., 2016c. Sustainable utilization of granite cutting waste in high strength concrete. Journal of Cleaner Production 116, 223235. Terro, M.J., 2006. Properties of concrete made with recycled crushed glass at elevated temperatures. Building and Environment 41, 633-639. Tiwari, A., Singh, S., Nagar, R., 2016. Feasibility assessment for partial replacement of fine aggregate to attain cleaner production perspective in concrete: A review. Journal of Cleaner Production 135, 490-507. Türkmen, İ., Fındık, S.B., 2013. Several properties of mineral admixtured lightweight mortars at elevated temperatures. Fire and Materials 37, 337-349. Turner, L.K., Collins, F.G., 2013. Carbon dioxide equivalent (CO2-e) emissions: A comparison between geopolymer and OPC cement concrete. Construction and Building Materials 43, 125-130. Vejmelková, E., Koňáková, D., Kulovaná, T., Keppert, M., Žumár, J., Rovnaníková, P., Keršner, Z., Sedlmajer, M., Černý, R., 2015. Engineering properties of concrete containing natural zeolite as supplementary cementitious material: Strength, toughness, durability, and hygrothermal performance. Cement and Concrete Composites 55, 259-267. Vickers, L., Rickard, W.D.A., van Riessen, A., 2014. Strategies to control the high temperature shrinkage of fly ash based geopolymers. Thermochimica Acta 580, 20-27. Water Services Association of Australia (WSAA), Energy Use in the Provision and Consumption of Urban Water in Australia and New Zealand; 2008 Xu, Y., Chung, D.D.L., 2000. Effect of sand addition on the specific heat and thermal conductivity of cement. Cement and Concrete Research 30, 59-61. Yu, X., Tao, Z., Song, T.-Y., Pan, Z., 2016. Performance of concrete made with steel slag and waste glass. Construction and Building Materials 114, 737-746. Zheng, K., 2016. Pozzolanic reaction of glass powder and its role in controlling alkali–silica reaction. Cement and Concrete Composites 67, 30-38.

651

31