Effects of Crushed Glass Cullet Sizes, Casting Methods and Pozzolanic Materials on ASR of Concrete...

7/28/2019 Effects of Crushed Glass Cullet Sizes, Casting Methods and Pozzolanic Materials on ASR of Concrete Blocks

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*Second author: [email protected]; [email protected] Page 1

Original citation:

Lee, G.,Ling, T.-C., Wong, Y.-L., Poon, C.-S. (2011) Effects of crushed glass cullet sizes,casting methods and pozzolanic materials on ASR of concrete blocks. Construction andBuilding Materials; 25 (5): 2611-2618.

http://www.sciencedirect.com/science/article/pii/S0950061810006859

Effects of crushed glass cullet sizes, casting methods and pozzolanic

materials on ASR of concrete blocks

Gerry Lee, Tung-Chai Ling, Yuk-Lung Wong and Chi-Sun Poon*

Department of Civil and Structural EngineeringThe Hong Kong Polytechnic University

Abstract

The aim of this study is to investigate the influence of using different particle sizes ofrecycled glass, casting methods and pozzolanic materials in reducing the expansion due toalkali-silica reaction (ASR) of concrete blocks prepared with the use of crushed glass as fineaggregate. In this work, 2525285mm mortar bar specimens were prepared usingconventional wet-mixed and dry-mixed methods. Except for the control mortar bar, all thespecimens were prepared by completely replacing river sand with different particle sizes ofrecycled glass. In addition, the influence of fly ash (PFA) and metakaolin (MK) content onthe reduction of ASR expansion was also investigated. The flexural strength of the mortar barspecimens before and after they had been exposed to 1 N NaOH solution was determined tocomplement the results of ASR expansion test. SEM was performed to examine themicrostructure as well as nature of the cement binder-glass interfacial zone. The resultsreveal that ASR expansion reduced with reducing particle size of glass used. For the same

given mix proportion, the dry-mixed method resulted in 44% less expansion when comparedwith the wet-mixed method. Both PFA and MK were demonstrated to be able to reduce ASRexpansion of the concrete glass blocks significantly.

Keywords: Recycled glass, particle size distribution, ASR, dry-mixed method, pozzolanicmaterials

1. IntroductionRecently, the use of recycled glass as aggregate in concrete has attracted much researchinterest. It is known that concrete containing glass aggregate has lower water absorption anddrying shrinkage [1-3]. However, the use of glass in concrete may result in expansion due toalkali-silica reaction (ASR) [4-6].

A number of studies have been done by several researchers to study the influence of differentparticle sizes, colours and percentages of glass used in concrete on ASR expansion. Ingeneral, the ASR expansion decreased with decreasing particle size of glass aggregate. Meyeret al. [10] found that there was no deleterious expansion when the particle size of glass wasless than 100m.This phenomenon is related to the large surface area of glass which allowsthe pozzolanic reaction to occur [2]. Byars et al. [7] examined the effect of glass colour onASR reactivity and found that blue glass aggregate appeared to be most reactive, followed by


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amber and then flint glass. Green glass showed the least ASR reactivity. Tapcu et al. [8] alsoreported that the higher content of silica in clear glass caused the concrete to suffer more inASR expansion. Some of the researchers have reported that different glass colours havedifferent pessimum size. Pessimum size refers to the size of the reactive glass aggregate

where the largest ASR expansion may occur. For regular soda lime clear glass, Pyrez glassand fused silica, the pessimum size is found to be at 1.18mm, 150m and 75m, respectively[9]. For the effect of percentage of glass, most of the reported data concluded that ASRexpansion decreased with decreasing percentage of recycled glass used in concrete [4].

Modifying the cementitious system may also reduce the ASR reaction. Several papers havebeen published [7, 11] on the use of suitable pozzolanic materials such as silica fume (SF),fly ash (FA), ground granulated blast furnace slag (GBFS) and metakaolin (MK) in theconcrete mix at appropriate proportions to react with calcium hydroxide to reduce thealkalinity of the cementitious system. Among the mineral additives, SF was found to be themost effective in reducing the expansion [7]. Recently, studies have found that a combinationof mineral additives was more effective than using a single type of mineral additive alone in

reducing ASR expansion [12, 13]. Byars et al. [7] have assessed the effect of cement alkalilevels on glass ASR reactivity. In their work, white cement which had a lower alkali content(Na2O equivalent: 0.17%) appeared to cause less expansion than ordinary Portland cement(Na2O equivalent: 0.62%).

However, not much attention has been paid to assess the effect of different concrete castingmethods on the expansion caused by ASR. It is expected that lower moisture level (wateramount) in dry-mixed concrete could be an effective alternative solution to reduce ASRexpansion. The objective of this study was to determine the ASR expansion of mortar barsprepared with different casting methods (dry-mixed and wet-mixed). The effects of differentparticle sizes of recycled glass were also evaluated. Ways to further reduce the ASRexpansion by using different pozzolanic materials were compared.

2. Experimental details2.1. Materials

Ordinary Portland cement (OPC) complying with BS 12 [14] and ASTM Type I was used asthe principal cementitious material. Fly ash (PFA) and metakaolin (MK) were used aspozzolanic materials. The chemical compositions and physical properties of all thecementitious materials are presented in Table 1. River sand was used as the fine aggregate forthe control mortar bar mixture and its density and fineness modulus were 2,630 kg/m 3 and2.46, respectively. Post-consumer glass bottles with a green color obtained from a local glassrecycling plant were used. The recycled glass bottles were crushed into smaller particle sizes

and used to replace sand in the mortar bar mixtures.

2.2. Preparation of mortar bar specimens

2.2.1. Prepared with different particles size of recycled glass

In this study, four different particles size of recycled fine glass was used as a full replacement(100%) of river sand by mass in all mixes and their gradation curves are shown in Fig. 1. Thefour different particles size of crushed glass used were:


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a) FG-A was un-sieved glass having maximum size of 5 mm with a fineness modulus of3.29.

b) FG-B was sieved glass (2.36mm) with a fineness modulus of 3.03.c) FG-C was sieved glass (1.18 mm) with a fineness modulus of 2.33.

d) FG-D was sieved glass (600 m) with a fineness modulus of 0.43.

Table 1. Chemical composition and physical properties of cementitious materialsCement PFA MK

SiO2 (%) 19.61 56.79 53.20Fe2O3 (%) 3.32 5.31 0.38Al2O3 (%) 7.33 28.21 43.90CaO (%) 63.15


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2.2.2. Prepared by wet-mixed and dry-mixed (casting) method

For each mortar bar mix, a fixed cement to fine aggregate ratio of 1:2.25 was used and theprepared mortars were cast into rectangular prisms of dimensions 2525285 mm. Differentwater contents were used for the production of the wet-mixed and dry-mixed mortar bars.

The mix proportions are presented in Table 2. For the wet-mixed method, the water tocement ratio was kept constant at 0.45 and a superplasticizer- Sulfonated naphthaleneformaldehyde condensate was used to adjust the workability.

Table 2. Mix proportions of wet-mixed and dry-mixed mortar bars (kg/m3)

Mix Notation Cement Sand FG-A FG-B FG-C FG-D W/C (SP, %)

WM-Control 440 990 0 0 0 0 0.45 0WM-A 440 0 990 0 0 0 0.45 1.0WM-B 440 0 0 990 0 0 0.45 1.3

WM-C 440 0 0 0 990 0 0.45 1.5WM-D 440 0 0 0 0 990 0.45 2.1

DM-Control 440 990 0 0 0 0 0.27 0DM-A 440 0 990 0 0 0 0.27 0DM-B 440 0 0 990 0 0 0.28 0

DM-C 440 0 0 0 990 0 0.29 0DM-D 440 0 0 0 0 990 0.34 0

Cement and fine aggregate materials were first placed in a pan mixer and mixed for about 1minute before water was added. The superplasticizer thoroughly mixed with water was addedto the mixer, and the mixing was continued for another 2 minutes. The freshly wet-mixedmaterials were placed into the mortar bar mould in two layers of approximately equal depth.After each layer was filled, a uniform vibration was applied by using a vibrating table.

For the dry-mixed method, the materials were prepared with only sufficient amount of waterto produce a cohesive mix but with zero slump. After mixing the materials in the pan mixer,the materials were placed into the mortar bar moulds in four layers of about equal thickness.A compression force was applied manually by hammering a wood stem on the surface layerto provide an evenly distributed compaction for the first three layers. At fourth layer, theoverfilled materials were subjected to a static compaction load by using a compressionmachine. The load increased at the rate of 600 kN/min for 50 seconds for the first staticcompaction. The excess material was then removed to provide a good surface texture andsecond compaction was applied at the same rate until it reached 500 kN.

After casting, all the wet-mixed and dry-mixed mortar bar specimens were covered with aplastic sheet in the laboratory at 233C and 75% relative humidity. After one day, all thespecimens were demoulded and stored in a water tank at an average temperature of 253 Cuntil the day of testing.

2.2.3. PFA and MK replacement of OPC

Some dry-mixed mortar bar specimens with the inclusion of PFA and MK were also preparedin order to further investigate the effect of admixture content on the ASR expansion. The


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specimens were prepared with four different particle sizes of 100% recycled glass. For eachparticular size of glass, PFA and MK at dosages of 5, 10 and 20% by weight of cement wereadded in the mortar mixtures. The mix proportions of dry-mixed mortar bar prepared withPFA and MK are shown in Tables 3 and 4, respectively.

2.3. Test program

To measure the ASR expansion for a given mix proportion, an accelerated mortar bar testwas carried out on three prism specimens of 2525285 mm in accordance with ASTMC1260 [15]. After 28 days of water curing, the mortar bar specimens were removed from thewater tank and stored in distilled water at 80 oC for another 24 hours at which a zero readingwas taken. The bars were then transferred and immersed in 1 N NaOH ( solution wereprepared by diluting 40 g of sodium hydroxide crystals into 900 mL of distilled water) at 80C until the testing time at 1st, 4th, 7th, 14th and 28th day. The expansion of the mortar bars wasmeasured within 155 seconds after the mortar bars were removed from the 80 C distilledwater or alkali storage condition by using a length comparator.

Before and after the ASR test, the flexural strength test was carried out under a central lineload simply supported over a span of 120 mm with a displacement rate of 0.05 mm/min.After the mechanical testing, selected samples were used to examine the microstructure byScanning Electron Microscopy (SEM), in particular the nature of the binder-glass interfacialzone. The fractured samples with size smaller than 101010 mmwere immersed in acetonefor 4 hours and dried in a vacuum oven in order to eliminate any free water for cementhydration. The samples were then gold coated and analyzed by SEM operated at anaccelerating voltage of 20 kV with a probe current of 70 to 78 A.

3. Results and discussion

3.1. Effect of particle size of recycled glass on ASR expansionThe average ASR expansion results of the mortar bars prepared with different particle sizesof glass are shown in Fig. 2. The results show that in all cases, the ASR expansions of thewet-mixed samples were higher than that of the dry-mixed sample. Regardless of the particlesize of glass, all the ASR expansion of the dry-mixed mortar bars were found to be within thepermissible limit of 0.1% at 14 days. However, the expansion of the wet-mixed mortar barsprepared with FG-A and FG-B were found to be higher than the limit set by ASTM C 1260.It can also be noticed that there was an increase of approximately 8% and 28% respectivelyin average of the expansion when the wet-mixed and dry mixed mortar bars were continuedto be placed in the aggressive ( 1N NaOH alkali solution) for an additional 14 days.

From the figure, it can be clearly observed that the ASR expansion decreased with decreasing

particle size of glass. This might be due to some fine glass containing high content of activesilica can be classified as a reactive aggregate or a pozzolanic material [16]. This is consistentwith the results of Shi et al. [11]. They reported that glass particle with size less than 0.7 mmhad a pozzolanic strength activity index of 74% at 7 days which is nearly achieved theminimum of 75% as specified in ASTM C618 for pozzolanic materials. Also, the figureshows the influence of particle size of glass on the wet-mixed mortar bars was morepronounced than that on the dry-mixed mortar bars.


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0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

contro l un-sieved


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-30

-20

-10

0

10

20

30

40

50

60

control un-sieved


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0

10

20

30

40

50

60

70

control un-sieved


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Fig. 6. SEM image of mortar bars after exposed to rapid environment for 14 days (a) wet-mixed (b) dry-mixed

3.3. Influence of PFA and MK on ASR expansion

Figs. 7 and 8 show the influence of PFA and MK content on the ASR expansion at 14 and 28days, respectively. It can be seen that the ASR expansion noticeably decreased with anincrease in PFA and MK content regardless of the particle sizes of recycled glass used. This

(ai) WM-Control

No crack

observed

(aii)WM-A

Cracksobserved(~8-12m)

(aiii)WM-B


(aiii)WM-C


(aiv)WM-A

Cracksobserved(


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could be due to the pozzolanic reaction led to the formation of C-S-H gel that is able to takeup alkalis and subsequently led to the reduction of ASR expansion [8]. A comparison ofefficiency of PFA and MK on ASR expansion of mortar bars prepared with different particlessizes of glass is also included in Figs. 7 and 8. It is found that when the amount of PFA is at

5%, the ASR expansion at 14 days was reduced to the range of 0.028% to 0.035% regardlessof the particle size of glass used. However, as the amount of PFA was increased to 10% and20%, there was no significant change in ASR expansion. On the other hand, as the amount ofMK increased from 0% to 5%, 10% and 20%, there was a gradual reduction in ASRexpansion by approximately 14.2%, 29.3% and 47.2%, respectively, regardless of the particlesizes of glass used.

Fig. 9 compares the effectiveness of PFA and MK in reducing the ASR expansion at 14 days.It is worth to note that the expansion reduction of mortar bars containing 5% PFA was clearlyhigher than that of the mortar bars containing the same percentage of MK. This indicated thatat a low content of pozzolanic materials used, PFA is found to be more effective than MK inreducing the expansion due to ASR. However, as the PFA and MK contents increased to 20%,

for any given mix proportion, the effectiveness on the reduction of ASR expansion werequite similar.

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

DM-A

DM-A-P5

DM-A-P10

DM-A-P20

DM-B

DM-B-P5

DM-B-P10

DM-B-P20

DM-C

DM-C-P5

DM-C-P10

DM-C-P20

DM-D

DM-D-P5

DM-D-P10

DM-D-P20

ASRE

xpansion(%)

14 days

28 days

Fig. 7. Influence of PFA content on the ASR expansion at 14 and 28 days

Control Control

Control

Control


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0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

DM

-A

DM-A

-M5

DM-A-M10

DM-A-M20

DM

-B

DM-B

-M5

DM-B-M10

DM-B-M20

DM

-C

DM-C

-M5

DM-C-M10

DM-C-M20

DM

-D

DM-D

-M5

DM-D-M10

DM-D-M20

ASRExpansion(%)

14 days

28 days

Fig. 8. Influence of MK content on the ASR expansion at 14 and 28 days

0

10

20

30

40

50

60

70

un-sieved


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additional C-S-H, possibly due to hydration of PFA hydration products. This revealed thatthe particle sizes of glass less than 600m and the use of PFA significantly enhanced thepozzolanic reaction in cement mortar and thus less of the alkali content was available foractivity of ASR.

Fig. 10. SEM images of sample (a) DM-A, (b) DM-D and (c) DM-A-P20

Glass

Glass

(b) DM-D

(a) DM-A

Glass

(a) DM-A-P20


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4. Conclusions

Based on the experimental test results, the following conclusions can be drawn:1. ASR expansion reduced with reducing particle sizes of glass, in particular for glass size

less than 600 m.

2. The dry-mixed method was very efficient in reducing the ASR expansion especially forlarger particle size (highly reactive) glass aggregate. For a given mix proportion, thereduction of expansion is up to about 44% as compared with the wet-mixed method. Itwas understood by the mortar bars made by dry-mixed method had higher porosity whichwas able to accommodate more gel produced due to ASR resulting in lower expansionand cracks.

3. Both PFA and MK can effectively mitigate ASR expansion regardless of the particlesizes of glass used. At low replacement level, PFA was more effective than MK incontrolling ASR. However, at higher replacement percentage, both PFA and MK showedsimilar effectiveness in suppressing ASR expansion.

4. Observation of SEM images confirmed that the use of very fine glass (< 600m) andpozzolanic material had significantly enhanced the pozzolanic reaction and leads to a

lower content of alkali level in preventing activity of ASR.

AcknowledgementThe authors would like to thank the Hong Kong Polytechnic University for funding support.

References

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[11] Shi C, Wu Y, Riefler C, Wang H. Characteristics and pozzolanic reactivity of glasspowders. Cem Concr Res 2005;35(5):987-93.

[12] Schwarz N, Cam H, Neithalath N. Influence of a fine glass powder on the durabilitycharacteristics of concrete and its comparison to fly ash. Cem Concr Compos

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Effects of Crushed Glass Cullet Sizes, Casting Methods and Pozzolanic Materials on ASR of Concrete...

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