Stress-Strain Behaviour of Fire Exposed Self-compacting Glass Concrete

7/28/2019 Stress-Strain Behaviour of Fire Exposed Self-compacting Glass Concrete

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First author: [email protected]; [email protected] Page 1

Original citation:

Ling, T.-C., Poon, C.-S. (2013) Stress-strain behaviour of fire exposed self-compactingglass concrete. Fire and Materials;37(4): 297-310.http://onlinelibrary.wiley.com/doi/10.1002/fam.2131/full

Stress-strain behaviour of fire exposed self-compacting glass concrete

Tung-Chai Ling1,2, and Chi-Sun Poon1,*1Department of Civil and Structural Engineering, The Hong Kong Polytechnic University

Hung Hom, Kowloon, Hong Kong.2School of Civil Engineering, University of Birmingham, Edgbaston, Birmingham,

United Kingdom

Abstract

Concrete normally suffers from low stiffness and poor strain capacity after exposure to

high temperatures. This study focused on evaluating the effect of recycled glass (RG) onthe residual mechanical properties of self-compacting glass concrete (SCGC) afterexposure to elevated temperatures. RG was used to replace fine aggregate at ratios of 0%,25%, 50%, 75% and 100% by weight. The residual properties were evaluated accordingto compressive strength, elastic modulus, stress-strain behaviour, and strain at pre-loadand peak stress. A comparative assessment of different curing conditions on the SCGCwas also conducted. The results showed that there were significant decreases incompressive strength, elastic modulus and concrete stiffness of the concrete withincreasing temperature. The use of RG had little influence on the elastic modulus atambient temperature; however after exposure to 800C, the mechanical properties of theconcrete were greatly enhanced by incorporating RG.

Keywords: Self-compacting concrete; recycled glass; elevated temperatures; stress-strainbehaviour; elastic modulus

1. Introduction

When concrete is exposed to fire, physical changes and chemical reactions in thecementitious system begin to take place, including evaporation of water from capillariesand voids, dehydration of cement paste and decomposition of aggregates [1-5]. Theseprocesses will be accompanied by significant strength degradation as well as loss ofconcrete stiffness [6, 7]. The loss of stiffness capacity at elevated temperature may berepresented in terms of residual elastic modulus [8]. The major factors influencing the

elastic modulus of concrete at elevated temperatures include the type, volume fractionand size of aggregates used (the stiffer and finer the aggregate, the higher the residualelastic modulus), as well as the test (hot and cold) conditions [9, 10]. However, theduration of high temperature exposure, cement type, water-to-cement ratio and sealing(prevention of moisture loss) have less influence on the residual elastic modulus [11].The original concrete strength and age test apparently also do not greatly affect theresidual elastic modulus [12].


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In the last decade, the use of various types of recycled aggregates as replacements fornatural aggregates in concrete has received much research interest [13-18]. This has beensuggested to be an effective way to reduce the need to dispose of waste glass as well as toconserve natural sand and stones resources. Most of the previous studies of glass-modified concrete focused on studying the effect of glass replacement levels on the

mechanical properties such as compressive strength. They found that the use of recycledglass in concrete had a negative effect on concrete strength and might to deleterious toconcrete due to alkali-silica reaction (ASR) [17-19]. To overcome the limitation, somestudies [20-22] recommended grinding the glass aggregate to very fine glass powderwhich induces pozzolanic reactivity to the glass powder and suppresses the potential ofASR. By nature, crushed glass cullets are largely impermeable which would decrease thedrying shrinkage and the water absorption when it is used in concrete [23, 24].Furthermore, the aesthetic pleasing properties of glass cullet have also promoted its use inconcrete for building and architectural applications [25, 26].

Up to date, there have only been limited studies on the elastic modulus of glass-modified

concrete [17, 26]. No information is available on the elastic modulus and stress-straincurves of glass-modified concrete after exposure to elevated temperatures. Thisinformation is a key parameter for determining the integrity of fire-damaged concrete andhelp make decisions about serviceability and safety of structural members. Also, due tothe wider use of self-compacting concrete in building construction [27, 28], the risk ofexposing it to fire could be assessed.

This study is a further development of our previous work [13] to explore the stress-strainbehaviour of self-compacting glass concrete (SCGC) under high temperatures. SCGCcontaining 0% to 100% recycled glass (RG) for replacing natural fine aggregate wereprepared. The SCGC was cured in water and air for 60 days before being exposed to

elevated temperatures of up to 800

C. The influence of glass content, curing conditions,and exposure temperature on the residual mechanical properties including cylindercompressive strength, elastic modulus, pre-strain, peak strain, and stress-strain curve ofSCGC were investigated.

2. Experimental details2.1. Materials

The materials used to prepare the SCGC mixtures were coarse aggregates, fineaggregates, ordinary Portland cement and fly ash. The total content of SiO2, Al2O3 andFe2O3 of fly ash is more than 70%, which represent a typical composition of class F flyash based on ASTM C 618 [29]. Two different sizes (20/10 mm and 10/5 mm) of crushedgranite with a specific gravity of 2.62 were used as the coarse aggregates. Crushed finestone with a nominal maximum size of 5 mm and a specific gravity of 2.62 was used asthe natural fine aggregate. The crushed fine stone has a water absorption capacity of 0.87.Crushed recycled glass (with a particle gradation close to that of the crushed fine stone)obtained locally from a waste glass recycler was used as the fine aggregate replacement(see Fig. 1). The recycled glass has a specific gravity of 2.49 and almost zero waterabsorption capacity. The gradation curves of the coarse and fine aggregates are shown inFig. 2. ASTM Type I ordinary Portland cement and fly ash complying with ASTM class


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F ash were used as binder materials in the study. The physical properties and chemicalcompositions of the cement and fly ash are presented in Table 1. A superplasticizerADVA 109 with a specific gravity of 1.045, containing no added chloride, was used toachieve the desired workability in the SCGC mixtures.

Fig. 1. Photograph of recycled crushed glass aggregate with particle size less than 5 mm.

0

10

20

30

40

50

60

70

80

90

100

20 10 5 2.36 1.18 0.6 0.3 0.15

Sieve Size (mm)

CumulativePassing(%

)

Recycled glass

Crush ed f ine s tone

10mm agg regate

M ixing rat io of coarse ag gregates

and crush ed f ine ag gregateM ixing rat ios of coars e

aggregates wi th recycled glass

Fig. 2. Sieve analysis of coarse and fine aggregates.


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Table 1: Chemical compositions and physical properties of cement and fly ash.

Chemical composition (%) Cement Fly ash ASTM C618 limit (Class F)

Calcium oxideCaO 63.15 < 3

Silicon dioxide (SiO2) 19.61 56.79

Aluminium oxide (Al2O3) 7.33 28.21Ferric oxide (Fe2O3) 3.32 5.31

SiO2 + Al2O3 + Fe2O3 90.31


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attributed to the impermeable property of RG which improved the workability of themixtures. The fresh properties results summarized in Table 3 show that the slump flow,blocking ratio and segregation ratio of all the SCGC mixtures tested in this study met theEFNARC [30] requirements.

Table 3: Results on fresh SCGC properties.Notation Slump flow diameter (mm) Blocking ratio Segregation ratio (%)

RG0 740 0.81 5.03

RG25 750 0.80 11.32

RG50 775 0.94 13.38

RG75 740 0.86 11.38

RG100 770 0.89 16.08EFNARCLimit

650-800 0.80-1.0 0-15

2.4. Curing condition

After the fresh properties testing, the fresh concrete mixtures were used to cast 30100200 mm cylinder samples without any external vibration. After 4 h of casting, thesamples were covered with a thin plastic sheet in the laboratory at room temperature(233C). One day later, the samples were demoulded, 15 cylinders were stored in awater tank (water curing) at an average temperature of 253C, and 15 other cylinderswere kept in air (air curing) at room temperature of 233C and 755% relativehumidity.

2.5. Heating regimes and spalling

After 60 days of curing, the samples were conveyed to an electrical furnace and heated ata constant rate of 5C per min from room temperature to 300C, 500C, 600C and800C separately. A peak temperature of 800C was chosen to evaluate the effect ofthermal damage and transition of glass aggregate on the stress-strain behaviour of theconcrete. Once the electrical furnace reached the desired temperature, the maximumtemperature was maintained for 4 h in order to ensure uniform heating throughout theconcrete samples. After such heating treatment, the samples were allowed to coolnaturally to room temperature before further mechanical testing. No spalling damage wasobserved for all the water and air cured samples containing RG. This is probably due tothe lower (0.93 W m1 K1) thermal conductivity of RG [31] which decelerates the rate oftemperature rise and reduces the risk of spalling. However, for the water cured samples

prepared with no RG replacement, spalling damage was observed in the 600

C and800C heating treatments.

2.6. Test method

Before and after the heating processes, the cylinder compressive strength and the elasticmodulus (compressive mode) were performed conforming to ASTM C 469 [32]. Threesamples were tested for each heating temperature and each curing condition.


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3. Results and discussion

3.1. Residual compressive strength

Fig. 3 shows the residual compressive strength of the water and air cured samples afterexposure to elevated temperatures. The relative residual strengths (ratio of residualstrength after exposure to elevated temperatures to the initial strength at ambient

temperature) of the SCGC samples are shown in Fig. 4.

0

10

20

30

40

50

60

70

80

Residualcom

pressivestrength(MPa)

R G 0 R G25 R G 50 R G75 R G100

W ater Air W ater Air W ater Air W ater Air W ater Air

20 C 300 C 50 0 C 600 C 800 C

Fig. 3. Residual compressive strength of water and air cured SCGC samples aftersubjected to elevated temperatures.

0 .0

0 .1

0 .2

0 .3

0 .4

0 .5

0 .6

0 .7

0 .8

0 .9

1 .0

Relativeresidualstrength

R G0 R G25 R G50 R G 75 R G100

W ater Air W ater Air Wa ter Air W ater Air

300 C 500 C 600 C 800 C

Fig. 4. Relative residual strength of water and air cured SCGC samples at elevatedtemperatures.


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At ambient temperature, the initial compressive strength of the water and air cured SCGCprepared with different RG content ranged from 47.7-73.2 MPa and 39.1-58.4 MPa,respectively. The strength decreased with increasing RG content. It is believed that thereduction of strength is attributed to the weak bonding at the interface between the RG

aggregates and the cement pastes [24, 25]. Interestingly, the influence of RG on thecylinder compressive strength in this paper was higher than on the cube strength reportedin the literature [33] and this may be an indication of the sensitivity of the cylinderstrength to aggregate mortar bond failure. The water cured samples had higher initialstrength than that of the air cured samples for all RG replacement ratios. As expected, thestrength decreased with increasing exposure temperature. The reduction in compressivestrength with the use of RG was less significant at higher temperatures.

The reduction in concrete strength with increasing temperature can be attributed to thefollowing reasons. Upon first heating, substantial amounts of moisture are driven outfrom the pores close to the concrete surface. Up to 300C, dehydration of ettringite, C-S-

H and calcium carboaluminate hydrates takes place [1-2]. In the temperature range from300C to 500C, there is dehydroxylation of calcium hydroxide [3]. From 500C to600C, in conjunction with dehydroxylation, micro-cracks form in the specimen whichfurther weaken the interfacial transition zone as well as bonding between the aggregateand the cement paste [4]. It is known that the rate of C-S-H decomposition is furtherenhanced when the temperature is further increased to 800C [3]. Therefore, at 800C,the main hydration products of hydrated cement paste and C-S-H are considerablydecomposed and result in a significant drop in concrete strength.

As can be seen in Fig. 4, at each heating temperature, the relative residual strength of thewater cured samples was lower than that of the air cured samples. This means that the

decrease in strength for the water cured samples was much higher than that of air curedsamples, under the same heating condition. The enhancement effect of water curing onconcrete strength also decreased with increasing temperature (see Fig. 5). Nevertheless,in general, the residual strength of the water cured samples remained higher than that ofthe air cured samples for all the tested temperatures.


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0 .8

0 .9

1 .0

1 .1

1 .2

1 .3

1 .4

20 300 5 00 60 0 800

Temperature (C)

R G0 R G25 R G50 R G75 R G100

Fig. 5. Residual strength (water/air) ratio of SCGC samples at elevated temperatures.

3.2. Elastic modulus in compression

3.2.1. Initial elastic modulus

Previous results on the effect of RG content on the elastic modulus of concrete at ambienttemperatures were somewhat limited and tended to be inconsistent. Some data reportedthat the elastic modulus increased with increasing RG content [17], whereas othersreported that it was difficult to identify the differences between the elastic modulus of

concrete prepared with 50% and 100% RG [26]. They further noted that the elasticmodulus of glass-modified concrete was more related to the quality of the materials(cement and coarse aggregate) used for concrete preparation.

The dependence of E (elastic modulus) values on RG content and curing conditions atambient temperatures are shown in Fig. 6. The results show that for both the water and aircured samples, the E values did not vary much with the increasing use of RG in thesamples despite the fact that the compressive strength did show a decreasing trend (Fig5). The results are consistent with those of the previously reported data [26]. This furtherdemonstrated that the elastic modulus of aggregate rather than the bonding strength(between aggregate (RG) and cement paste) is the major factor in determining the E

values of concrete. The relatively higher modulus of the glass aggregate (72 GPa) thanthe granite aggregate (54 GPa) [34] might contribute to the relatively small loss ofmodulus of the concrete. For a given RG content, the E values of the water cured sampleswere slightly higher than that of the air cured samples.

Residualstrengthwater

/Residuals

trengthair


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0

5

10

15

20

25

30

35

0 2 5 50 7 5 1 00

Na tural f ine agg rega te replace d by recycled glass (%)

Elasticmodulus(GPa)

Wate r curing Air curing

Fig. 6. Effect of recycled glass content on elastic modulus of water and air cured samplesat ambient temperature.

3.2.2. Residual elastic modulus

The residual and relative residual elastic modulus of the water and air cured SCGCsamples after exposure to the high temperatures are shown in Figs. 7 and 8, respectively.They are consistent with the results obtained in the residual compressive strength test.The residual elastic modulus for both the water and air cured samples decreased with

increasing exposure temperatures.

Fig. 7 shows that as the heating temperature was increased from 20C to 300C, theelastic modulus dropped significantly (ranging from 15.9 to 19.2 GPa and 14.3 to 17.1GPa, a reduction of about 39-50% and 45-52% for the water and air cured samples,respectively). At 500C, the elastic modulus was further reduced. A further slightreduction in residual elastic modulus was observed after the heating temperature wasincreased from 500C to 600C. At 600C, the elastic modulus of the water and air curedSCGC samples were only 4.0-4.6 GPa and 3.7-4.2 GPa, respectively. It can be noted that,except for the samples containing 100% RG, the residual elastic modulus of the othersamples kept decreasing as the temperature was increased from 600C to 800C.


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0

5

10

15

20

25

30

35

40

Residualelasticmodulus(G

Pa)

R G0 R G25 R G50 R G75 R G100


2 0 C 3 0 0 C 5 0 0 C 6 0 0 C 8 0 0 C

Fig. 7. Residual elastic modulus of water and air cured SCGC samples at elevatedtemperatures.

0 .0

0 .1

0 .2

0 .3

0 .4

0 .5

0 .6

0 .7

Relativeresidualelasticmodulus

R G 0 R G25 R G 50 R G75 R G100

W ater Air W ater Air W ater Air W ater Air

3 0 0 C 5 0 0 C 6 0 0 C 8 0 0 C

Fig. 8. Relative residual elastic modulus of water and air cured SCGC samples atelevated temperatures.


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3.2.2.1. Effect of recycled glass content on residual elastic modulus

From Figs. 7 and 8, two interesting effects of RG content on the residual elastic moduluscan be observed. Firstly, it can be observed that in the heating range of 20C-600C, thehigher the RG content, the higher the reduction in elastic modulus. Second, in the heatingtemperature range of 600C-800C, incorporating RG in the concrete significantly

enhanced the residual elastic modulus. The enhancement was proportional to the RGcontent. This may be because in this temperature range, the RG exhibits a transition glassprocess of melting and re-solidification (after cooling), which could have a pore-fillingeffect to fill up micro-cracks and pores in the concrete matrix, thus increasing the elasticmodulus. This is in agreement with the results in the literature [33], which indicated thatconcrete containing RG after exposure to 800C had a better resistance to waterpenetration, probably due to the transformation process of glass in the heated concretewhich is able to provide a void filling effect and control the progression of cracking.

3.2.2.2. Effect of curing conditions on residual elastic modulus

Fig. 9 shows the effect of curing conditions on the residual elastic modulus after exposure

to the elevated temperatures. In contrast to residual concrete strength (see Fig. 5), theinfluence of water curing had less influence on the E values in the temperature range of20C-600C. However, the enhancement effect of water curing became more dominant at800C, particularly for the samples with higher RG content.

0 .8

0 .9

1 .0

1 .1

1 .2

1 .3

1 .4

1 .5

1 .6

20 300 5 00 6 0 0 80 0Temperature (C)

R G0 R G2 5 R G50 R G7 5 R G1 0 0

Fig. 9. Residual elastic modulus (water/air) ratio of SCGC samples at elevatedtemperatures.

3.3. Relationship between elastic modulus and cylinder compressive strength

The relationship between cylinder compressive strength and elastic modulus at ambienttemperature and after exposure to the elevated temperatures are presented in Figs. 10 and

Residualelasticmoduluswater

/Residual

elasticmodulusair


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11, respectively. For ambient temperature (Fig. 10), the RG content and curing conditionshad a larger influence on the initial compressive strength than on the initial elasticmodulus. This shows that the bond strength and cement hydration are less importantparameters in affecting the E values than is compressive strength.

2 0

3 0

4 0

5 0

6 0

7 0

8 0

0 20 4 0 6 0 8 0 10 0

Re cycled glass co ntent (%)

Initialcompressivestrength

(MPa)

20

30

40

50

60

70

80

InitailEvalue(G

Pa

)

Inital compress ive s trength for water cured SC GC

Initial E value for air cured SCG C

Initial E values for water cured SCG C

Inital compress ive s trength for air cured SCG C

Fig. 10. Comparison of initial elastic modulus and compressive strength at different RGcontent and curing conditions.

Fig. 11 shows a non-linear relationship between the residual compressive strength andresidual E values. This is because as the temperature increased to the range of 300 C-600C, the influence of RG content on compressive strength reduced. Moreover, after800C, the positive effect of the molten glass which acted as a filler became moresignificant. But this contributed more to the residual elastic modulus (change in the y-axis) than to the residual compressive strength (change in the x-axis).

0

2

4

6

8

10

12

14

16

18

20

0 1 0 20 3 0 4 0 50 60

Residual compressive strength (MPa)

Residualelasticmodulus(GPa)

W-RG0

W-RG2 5

W-RG5 0

W-RG7 5

W-RG1 0 0

0

2

4

6

8

10

12

14

16

18

0 1 0 20 3 0 40 5 0 60

Residual compressive strength (MPa)

Residualelasticmodulus(GPa)

A-RG0

A-RG2 5

A-RG5 0

A-RG7 5

A-RG1 0 0

Fig. 11. Relationship between residual elastic modulus and residual compressive strengthobtained from (a) water and (b) air cured SCGC samples.

(a) (b)

300 C

500 C600 C800 C

300 C

500 C

600 C800 C


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3.4. Pre-strain

The pre-strain of the water and air cured SCGC samples are shown in Fig. 12. Pre-strainis defined as the strain corresponding to pre-load stress (at the start of the third loadingand unloading cycle) [35]. As the temperature increased, the pre-strain increased. Thepre-strain attained for the control water cured samples corresponding to 0.5 MPa stress at

300C, 500

C, 600

C and 800

C were two, five, 15 and 25 times the pre-strain obtainedat ambient temperature. The increase of pre-strain can be explained by the presence of

pre-existing cracks due to heating and cooling. It is worth mentioning that the use of RGhad a beneficial effect on the pre-strain attained, particularly at high temperatures. Asignificant decrease of pre-strain at high temperatures was probably due to thetransformation of solid to viscous glass preventing the formation of serious cracks. Asseen in Fig. 13, the control samples without RG experienced serious cracking around theedges of the samples after exposure to 800C. It can be seen that the degree of crackingon the concrete surface decreased consistently with increasing RG content. On the otherhand, only minor micro-cracks were observed on the surface samples incorporated with100% RG.

0 .0

0 .5

1 .0

1 .5

2 .0

2 .5

3 .0

R G0 R G25 R G50 R G75 R G100


20 C 3 0 0 C 5 0 0 C 6 0 0 C 8 0 0 C

Fig. 12. Pre-strain of water and air cured SCGC samples at elevated temperatures.

Pre-strainatpre-loadedstress(m/mm)


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Fig. 13. The photograph of water cured samples containing (a) 0%, (b) 25%, (c) 50%, (d)75% and (e) 100% of RG after exposure to 800C temperature.

3.6. Stress-strain curvesThe influence of RG content on the stress-strain curves of the samples at ambient andelevated temperatures are shown in Figs. 14-17. At the ambient temperature (see Fig. 14),the presence of RG had little influence on the linear part (between ~2% to 40% of itsmaximum stress) of the stress-strain curve. Beyond this, the curves (non-linear) becameflatter with increasing RG content. This can be explained by the weak bonding betweenthe RG and the cement paste in the concrete matrix and more micro-cracks developing atthe glass-cement pastes interfaces. Also, a progressive debonding process occurred at theinterfaces as the stress further increased causing a major increase in the strain capacity.

It is notable that the peak strain of the water cured SCGC samples also varied with the

RG content. The peak strain is defined as the strain attained at the peak stress. Similar tothe pre-strain, the main factor that influenced the peak strain at ambient temperature wasthe aggregate type. The peak strain of the control unheated sample was the highest, whichcan be attributed to the lower elastic modulus value of the crushed fine stone than that ofRG [36]. It can be noticed that the unheated specimens failed soon after they had reachedtheir peak stresses. This phenomenon was more pronounced in the water cured sampleswithout RG replacement. The peak strain decreased as the RG content increased. For the

(a) (b)

(c) (d)

(e)

20 mmMagnificent 3

3mm

W800-RG100

Glass-cement pasteinterfaces

20 mmMagnificent 3

20 mmMagnificent 3

20 mmMagnificent 3

20 mmMagnificent 3


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100% RG sample, the peak strain was reduced by 24% and 30% for the water and aircured samples, respectively.

Fig. 14. Effect of RG content on stress-strain curves of water cured SCGC samples atambient temperature

0

10

20

30

40

50

60

70

0 1 2 3 4 5

Strain (m/mm)

Stress(MPa)

W300-R G0 W300-R G25 W 300-R G50 W300-R G75 W300-R G100

Fig. 15. Effect of RG content on stress-strain curves of water cured SCGC samples attemperature of 300C

Linear portion

Non-linear portion

RG0

RG25RG50

RG75

RG100


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0

5

10

15

20

25

30

0 2 4 6 8 1 0 12 1 4

Strain (m/mm)

Stress(MPa)

W 600-R G 0 W 600-R G 25 W600-R G50 W600-R G 75 W 600-R G 100

Fig. 16. Effect of RG content on stress-strain curves of water cured SCGC samples attemperature of 600C

Fig. 17. Effect of RG content on stress-strain curves of water cured SCGC samples attemperature of 800C.

RG10 0RG75

RG50

RG25

RG0


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For the concrete samples that were exposed to high temperatures, as expected, asignificant gain in strain capacity (deformation) and loss in concrete stiffness wasobserved before fracture occurred. As can be seen in Figs 15 and 16, the peak strainincreased with increased temperature. In the case of the control sample, the peak strain

was increased by 150%, 248% and 386% with respect to that at the ambient temperature300C, 600C and 800C, respectively. It can be noted that the positive influence of RGon peak strain was less significant for SCGC samples after exposure to 600C, probablybecause there were large volume changes in the coarse granite aggregates and crushedfine stone (due to thermal expansion) [37].

However, significant changes in stress-strain relationships were observed after exposureto 800C. Fig. 17 shows that the RG replacement percentages had a significant positiveinfluence on the stress-strain curve. For the linear-portion, as the RG content increased,the slope of the curves increased, indicating that the transition change of the glass at hightemperature had a positive influence on the stress-strain curves. The results also indicate

that at any stress lower than 10MPa (the peak stress of RG100), the water cured RG100sample suffered lower strain than the water cured RG0 sample. Also, the RG100 samplesuffered lower strain than RG25, RG50 and RG75 at any stress level applied.

4. Conclusion

Based on the experimental investigation, the following conclusions can be drawn: The compressive strength decreased with increasing recycled glass (RG) content and

heating temperature. For the same exposure temperature, the residual strength of thewater cured samples reduced more than for the air cured samples.

The use of RG appeared to have no influence on the initial elastic modulus ofconcrete. As compared to the air cured samples, the water cured samples showed a

higher initial elastic modulus. For the heated samples, two distinct effects of RG canbe identified. In the temperature range of 20C-600C, the use of RG decreased theresidual elastic modulus. However, at 800C, a beneficial effect of RG on residualelastic modulus was observed. This is because at this temperature, the transition ofRG from solid to liquid fills the internal cracks, and thus enhances the pore structuresand properties of the heated samples.

The pre-strain and peak strain increased with increasing temperature. The use of RGgreatly reduced the strain capacity especially after exposure to 800C. For 100%replacement of RG, the strain obtained at pre-load was reduced by 89.3% and 82.3%for the water and air cured samples, respectively. As for peak strain, at any stresslevel lower than 10MPa (the peak stress of RG100 at 800C), the water cured RG100

sample suffered a lower strain than that of the water cured RG0 sample. The use of RG had little influence on the linear ascending portion of the stress-strain

curves of the unheated concrete samples. However, with increasing temperature, theshape of the stress-strain curves was significantly changed and a significant decreasein concrete stiffness was observed.


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Acknowledgements

The authors would like to thank The Hong Kong Polytechnic University and SHKProperties Ltd for funding supports.

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Stress-Strain Behaviour of Fire Exposed Self-compacting Glass Concrete

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