Investigation on compressive strength development and drying shrinkage of ambient cured powder-activated geopolymer concretes

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1 Australian Journal of Civil Engineering ISSN: (Print) (Online) Journal homepage: Investigation on compressive strength development and drying shrinkage of ambient cured powder-activated geopolymer concretes Kamal Neupane, Paul Kidd, Des Chalmers, Daksh Baweja & Rijun Shrestha To cite this article: Kamal Neupane, Paul Kidd, Des Chalmers, Daksh Baweja & Rijun Shrestha (2016) Investigation on compressive strength development and drying shrinkage of ambient cured powder-activated geopolymer concretes, Australian Journal of Civil Engineering, 14:1, 72-83, DOI: / To link to this article: Published online: 10 May Submit your article to this journal Article views: 841 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 18 December 2017, At: 14:37

2 Australian Journal of Civil Engineering, 2016 VOL. 14, NO. 1, Investigation on compressive strength development and drying shrinkage of ambient cured powder-activated geopolymer concretes Kamal Neupane a, Paul Kidd b, Des Chalmers b, Daksh Baweja a and Rijun Shrestha a a Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW, Australia; b Cement Australia Pty. Limited, Darra, Queensland, Australia ABSTRACT Geopolymer is an inorganic polymer binding material, generally formed by the reaction between aluminosilicate materials and alkali activator solution. Previous researches on geopolymer concrete around the world suggested that geopolymer concrete possess superior mechanical and durability properties over ordinary Portland cement (OPC) concrete, such as higher indirect tensile strength and resistance to sulphate attack. Generally, fly ash-based geopolymer concrete was cured in elevated temperature for higher early age strength because of their longer setting time in ambient temperature. Published engineering properties of geopolymer concrete cured at ambient temperature are not abundant. In this research, two types of powder-activated geopolymer binders were used as binding material. A detailed study of compressive strength and drying shrinkage of different grades (40, 50, 65 and 80 MPa) of geopolymer and OPC concrete with different workability levels (normal-workable and super-workable) were carried out. All the concrete specimens were cured at standard laboratory temperature. The compressive strength development of geopolymer concrete in early age was relatively lower than OPC concrete; however, the later age strength was significantly higher. The drying shrinkage of geopolymer concrete was similar to OPC concrete of same grade and complied with Australian Standard 1379; however, it was higher than estimated values from Australian Standard The drying shrinkage results of this study were higher than drying shrinkage of accelerated cured geopolymer concretes in previous investigations. Super workable concrete exhibited higher drying shrinkage than normal workable concrete of same grade. 1. Introduction Geopolymer is generally formed by the chemical reaction between an aluminosilicate source material such as fly ash, metakaolin and blast furnace slag with alkaline solution (activators). In this process, aluminium and oxygen atoms create a tetrahedral chain of SiO 4 and AlO 4 to shared oxygen atoms alternatively (Davidovits 1991). The silica and alumina in the source material are activated by alkaline solution to form the geopolymer network (geopolymerisation process) that binds the aggregates and inert materials. A combination of sodium silicate and sodium hydroxide was commonly used as an alkali activator (liquid) in previous researches (Diaz-Loya, Allouche, and Vaidya 2011; Fernandez-Jimenez, Palomo, and Lopez-Hombrados 2006; Hardjito and Rangan 2005). The early investigations of geopolymer binders were carried out using aluminosilicate materials of geological origins such as clay, kaolin and metakaolin. Nowadays, there is more focus on the utilisation of industrial by-product such as fly ash and blast furnace ARTICLE HISTORY Received 24 May 2015 Accepted 1 March 2016 KEYWORDS Powder-activated; normalworkable; super-workable; drying shrinkage slag as an aluminosilicate source material for geopolymers (Heath et al. 2013). During the last two decades, research has been done around the world to evaluate the chemical, microstructural and engineering characteristics of geopolymer binders and concrete (Diaz-Loya, Allouche, and Vaidya 2011; Hardjito and Rangan 2005; Lecomte et al. 2006; Silva, Sagoe-Crenstil, and Sirivivatnanon 2007). The major reasons for the rising interest on geopolymer binders are some of its key advantages over ordinary Portland cement (OPC), environmental benefits and superior engineering and durability properties (Provis 2013). Industrial by-products, such as fly ash and blast furnace, can be utilised as a source material for geopolymer binder, providing proper management of waste material and significantly reduced greenhouse gas emission in the production process. Previous investigations showed that concrete from geopolymer binder possessed superior engineering properties, such as higher compressive, tensile and flexural strengths and durability in sulphate and acidic environments than OPC CONTACT Kamal Neupane 2016 Engineers Australia Kamal.Neupane-1@student.uts.edu.au

3 Australian Journal of Civil Engineering 73 concrete (Bakharev 2005; Fernandez-Jimenez, Palomo, and Lopez-Hombrados 2006; Raijiwala and Patil 2011; Wallah and Rangan 2006). Most of the past research in geopolymer binders was carried out by curing of geopolymer mortar and concrete at elevated temperature (accelerated curing) because of significantly lower early age strength of fly ash or metakaolin-based geopolymer in ambient curing condition (Fernandez-Jimenez, Palomo, and Lopez- Hombrados 2006; Hardjito and Rangan 2005; Puertas et al. 2000; Rovnaník 2010). The engineering properties of ambient temperature cured geopolymer concrete are still not common. Albitar et al. (2015) investigated the mechanical properties and drying shrinkage of fly ash alone and fly ash with granulated lead smelter slag-based geopolymer concrete in ambient curing conditions. Addition of blast furnace slag (as a source of calcium) can play a significant role to reduce the setting time and increase early as well as later age strength of fly ash or metakaolin-based geopolymer concrete cured in ambient temperature. Thus it can set and harden in ambient condition (Nath and Sarker 2012; Parthiban et al. 2013). This effect has been justified by the coexistence of geopolymeric gel and calcium silicate hydrate (C-S-H) in slag fly ash-based geopolymer paste where C-S-H gel is responsible for developing early age strength (Oh et al. 2010; Yip, Lukey, and van Deventer 2005). It was also suggested that the presence of calcium compound increases the dissolution of fly ash in alkaline medium and accelerates the geopolymerisation process, which results in higher early and later age strength (Catalfamo et al. 1997; Diaz, Allouche, and Eklund 2010; Temuujin, Van Riessen, and Williams 2009). Wallah and Rangan (2006) recorded significantly low drying shrinkage of accelerated cured fly ash-based geopolymer concrete which was around 100 microstrain of shrinkage for 1 year of drying period. The lower shrinkage values of accelerated cured concrete can be justified by the evaporation of most of the water from micropores during the elevated temperature curing. Hence, less water remained inside to contribute post-curing drying shrinkage (Davidovits 1999). Fernandez-Jimenez, Palomo, and Lopez-Hombrados (2006) also measured significantly lower (around 200 microstrains) drying shrinakage of fly ash-based geopolymer concrete up to 90 days of age. In their work, geopolymer concrete samples were cured at 85 C for 20 h. Tempest (2010) also heat cured fly ash-based geopolymer samples for 48 h before taking the initial measurement for shrinkage. He found significantly less drying shrinkage of geopolymer concrete; around 120 microstrain compared to 510 microstrain shrinkage of ambient temperature cured OPC concrete at 56 days. Collins and Sanjayan (1999) reported a relatively higher amount of drying shrinkage (around 1500 microstrain) of ambient cured alkali activated slag concrete when compared to OPC concrete (around 700 microstrain) of same grade. Douglas, Bilodeau and Malhotra (1992) also reported a higher drying shrinkage of alkali activated slag concrete (average 890 microstrain at 224 days) under ambient conditions. On the other hand, Albitar et al. (2015) reported significantly lower (less than 100 microstrain) drying shrinkage of fly ash alone and fly ash with granulated lead smelter slag-based geopolymer concrete under ambient curing conditions. In recent decades, the use of self-compacting concrete (SCC) in the construction industry is spreading globally because of its technical and economic benefits over normal-workable concrete (Domone 2006). Superworkable concrete is very similar to SCC in fresh and hardened concrete properties which generally contains higher amount of sand, and binder in concrete mix than normal-workable concrete to develop a high level of workability (CIA 2005). The amount of water required for this workability can be as high as 200 L/m 3 (EFNARC 2002); hence significantly higher water/binder ratio than normal workable concrete is required. These factors can contribute to an increase in drying shrinkage of super workable concrete. Some of the past investigations showed that drying shrinkage of SCC were different than normal-workable concrete because of significant difference in ingredient proportions: sand, coarse aggregate, water content and amount of binder (Bonen and Shah 2005; Leemann and Lura 2014; Maghsoudi and Dahooei 2006). In their study, the paste volume was a dominating factor to increase the shrinkage of SCC. Cattaneo (2009) suggested that smaller maximum size of aggregate and higher proportions of sand may be the reasons for higher drying shrinkage of SCC because they contribute to increase total surface area of aggregates. This paper reports the results of an investigation of compressive strength development of geopolymer concretes from two types of powder-activated geopolymer binders (Geopolymer 1 and Geopolymer 2) at standard laboratory temperature (ambient) curing at various ages (up to 90 days). The investigation was done for concretes of two workability levels: normal-workable and super-workable concretes of four strength grades (40, 50, 65 and 80 MPa) from geopolymer binders and OPC (control). In addition, drying shrinkage of geopolymer as well as OPC concretes of each grade was investigated, and the result was compared with calculated values based on Australian Standard-3600 (2009). All the experimental work of this research was carried out in Darra Laboratory, Queensland. 2. Experimental details 2.1. Materials Two types of powder-activated geopolymers, Geopolymer 1 (general purpose) and Geopolymer 2 (high early strength), recently developed by Cement

4 74 K. Neupane et al. Australia were used as binding materials. In these binders, activators (powder form), Class F fly ash and ground granulated blast furnace slag (GGBFS) were blended together in fixed proportions. The activator was the combination of sodium silicate and sodium hydroxide blended in powder form. The activator/source material ratio was around 0.25 for both binders. The silicate modulus (SiO 2 /Na 2 O) of activators was 4.5 and 4.05 for Geopolymer 1 and Geopolymer 2, respectively. The concentration of sodium hydroxide in binders changed with the water/binder ratio of concrete. For example, the concentration was around 8 M (molarity) in Grade 40 MPa concrete (water/binder ratio 0.45), whereas it was as high as 13 M in 80 MPa concrete (water/binder ratio 0.26). Geopolymer 1 contained 70% fly ash and 30% GGBFS by weight, whereas Geopolymer 2 contained 40% of fly ash and 60% of GGBFS by weight. Table 1 shows the chemical compositions of low calcium fly ash and GGBFS used. The silica content in the fly ash and GGBFS was 52.7 and 33.5% by weight, whereas the alumina content was 26 and 13.9%, respectively. OPC (type GP) was selected to produce control concrete for comparison. This GP cement complied with Australian Standard-3972 (2010). The chemical compositions of Portland cement are presented in Table 1. Crushed river course aggregates maximum sizes of 10 and 20 mm collected in bed of Mary River, Queensland, were used for production of concrete for this study. The majority of aggregate rock type was greywacke which is a type of sedimentary rocks. A combination of medium and fine river sand was used as fine aggregate in the concrete mixes from same source. The particle size distribution of fine and coarse aggregates is shown in Figure 1. Table 1. Chemical compositions of fly ash, GGBFS and OPC (type GP). Two types of chemical admixtures were used in OPC (control) concrete while mixing; normal water reducer (type WR) and high-range water reducer (type HWR). No chemical admixtures were used in geopolymer concretes of both workability levels Mix compositions of concretes The mix proportions of normal-workable concretes were based on the BRE mix design method (Teychenné et al. 1997). Based on preliminary studies, the binder content and water content were reduced up to 30% for geopolymer concrete. The mix design of superworkable concrete was based on mix design guidelines suggested by Concrete Institute of Australia (CIA 2005) and European Project Group (EPG 2005). The mix compositions, normal-workable and super-workable concretes, of different grades are presented in Tables 2 and 3, respectively. The mix compositions are based on surface saturated and dry condition of aggregates, with the excess moisture absorbed in aggregates taken into account when adding water to the concrete batch Mixing and testing of fresh concrete properties From each OPC and geopolymers binders, normalworkable concretes of four strength grades, 40, 50, 65 and 80 MPa, were produced. In addition, super-workable concretes of same strength grades were produced from OPC and Geopolymer 2 binder. Both OPC and geopolymer concretes were mixed in the same way in a rotating pan mixer of 65 L capacity according to LOI CaO SiO 2 Al 2 O 3 Fe 2 O 3 MgO SO 3 Na 2 O K 2 O Others Fly ash GGBFS GP Note: Others: SrO, TiO 2, Mn 2 O 3 and P 2 O 5 ; LOI: loss of ignition Percentage Passing Fine Sand Coarse Sand 10mm aggregate 20mm aggregate Sieve size (mm) Figure 1. Particles size distribution of coarse and fine aggregates.

5 Australian Journal of Civil Engineering 75 Australian Standard (1994). Both normal-workable and super-workable geopolymer concretes were mixed without addition of any chemical admixtures. In case of OPC normal-workable concretes, Grade 40 and 50 MPa concretes were prepared with addition of normal water reducing admixture, and Grade 65 and 80 MPa concretes were prepared with high-range water reducing admixture. All super-workable OPC concretes were produced with addition of high-range water reducing admixture. The workability of normal-workable concrete was assessed by the slump test. For super-workable concrete, workability was determined by slump flow (spread) and T 500 (time to reach 500-mm circle) Casting, curing and testing of concrete specimens For each concrete mix, adequate numbers of 100 mm by 200 mm cylinders were cast to determine compressive strength. A minimum five specimens for 7 and 28 days and minimum three specimens for any other ages were tested for compression. Concrete mixing and casting of specimens were carried out at standard laboratory temperature (23 C). After casting, both OPC and geopolymer concrete cylinders were left in standard laboratory temperature for 24 h. The concrete prisms for drying shrinkage measurement were prepared according to Australian Standard (1992). After levelling the top surface, shrinkage moulds were covered by a plastic tray to prevent the moisture loss and kept at 23 C for 24 h until demoulding. A preliminary investigation into different moist curing methods of geopolymer concretes in Darra Laboratory showed that sealed cured cylinders developed around 10% higher compressive strength than immersed cured cylinders at 28th day. Wrapping the cylinders by plastic sheet is effective to prevent the moisture loss from concrete with no possibility of leaching of activators. Unlike the hydration of Portland cement, water is a by-product of the geopolymerisation process (Davidovits 1999). Therefore, initial moisture available in concrete may be sufficient for further geopolymerisation process. Geopolymer concrete cylinders were wrapped with plastic sheet immediately after the demoulding as shown in Figure 2. A small amount of water was sprayed prior to sealing the cylinders. The sealed cylinders were stored in the laboratory condition (23 C) until testing. OPC concrete cylinders were moist cured in lime saturated water at 23 C until testing according to Australian Standard (2000). The compressive strengths of concretes of different grades and workability levels were tested according to Australian Standard (1999) at 1, 3, 7, 28, 56 and 90 days. The initial curing (first 7 days after demoulding) of shrinkage prism from geopolymer concrete was also carried out by sealing. The prisms were made saturated by immersing in water for 2 3 min prior to sealing. In the case of OPC concrete, shrinkage prisms were cured by submerging in lime-saturated water in the similar way to the cylinders for 7 days. After the initial curing, both OPC and geopolymer concrete prisms were taken out from curing for initial readings and then stored in a room having standard temperature of 23 C and 50% relative humidity according to Australian Standard (1992). Subsequent drying shrinkage readings were taken on 7, 14, 21, 28, 56 and 112 days from the initial reading. 3. Results and discussion In this experiment, the amount of water required in concrete mixes was based on comparable workability of concretes of different grades (average 120 mm slump for normal-workable concretes and mm spread for super workable concretes). Concretes of different grades and workability levels were produced with the similar types (same source and grading) of aggregates. Therefore, it was assumed aggregate type was not a factor in the variation of results in fresh concrete and engineering properties of concretes of different grades Fresh concrete properties-workability As shown in Table 2, the slump of geopolymer concrete mixes ranged from 100 to 160 mm. The average water content in geopolymer concretes with Geopolymer 1 and Geopolymer 2 was 112 and 121 kg/m 3, respectively. OPC concrete exhibited an average slump of 100 mm and average water content was 166 kg/m 3 using water reducing admixtures. In average, normal-workable concrete from geopolymer binders required around 30% less water than OPC concrete of same grade for the comparable workability, although geopolymer concretes were prepared without addition of any chemical admixtures. The lower water demand in geopolymer concrete is due to high proportion of fly ash in binder as well as the propensity of geopolymer to produce water as a by-product. The replacement of 20 25% of Portland cement by fly ash improves workability of concrete for the same amount of water because of its round-shaped particles (Siddique 2008). Thus, when the fly ash supplement is around 50% of binder, the workability of concrete will be significantly increased. Fly ash itself is spherical and can be dispersed easily in alkaline environment without addition of any admixtures (Chindaprasirt, Chareerat, and Sirivivatnanon 2007). The difference in fly ash content (30%) between Geopolymer 1 and Geopolymer 2 binder may be responsible for lower water demand in concrete from Geopolymer 1 than Geopolymer 2 for the same workability. In case of super-workable concretes, concrete from Geopolymer 2 binder required slightly less amount of water (around 7%) than OPC concrete for the comparable workability.

6 76 K. Neupane et al. Table 2. Mix compositions of normal-workable concretes of different grades. Binder type Concrete grade (MPa) Binder content (kg/m 3 ) Aggregate (kg/m 3 ) Coarse 20 mm 10 mm sand Fine sand Water content (kg/m 3 ) Slump (mm) Chemical admixtures (L/m 3 ) OPC WR 1.12 OPC WR 1.38 OPC HWR 1.75 OPC HWR 2.50 Geopolymer Geopolymer Geopolymer Geopolymer Geopolymer Geopolymer Geopolymer Geopolymer Table 3. Mix compositions of super-workable concretes of different grades. Binder ID Concrete grade (MPa) Binder content (kg/m 3 ) 3.2. Compressive strength development Aggregates (kg/m 3 ) Coarse 10 mm sand Fine sand Compressive strength development of Grade 65 MPa concretes from different binders and workability levels is shown in Figure 3. Compressive strength development trends in concrete of other grades were also similar to 65 MPa. In both geopolymer and OPC concretes, compressive strength increased with time at a decreasing rate. For the same strength grade, geopolymer concrete exhibited relatively lower early age (1 3 days) compressive strength than OPC concrete. However, the later age (from 28 to 90 days) strength development was significantly higher in geopolymer concrete than in OPC concrete of same grade. Albitar et al. (2014) also reported Spread (mm) T500 (s) Water content (kg/m 3 ) Chemical admixtures (L/m 3 ) OPC HWR 1.95 OPC HWR 2.1 OPC HWR 2.6 OPC HWR 3.1 Geopolymer Geopolymer Geopolymer Geopolymer a lower early age compressive strength of fly ash-based geopolymer concrete at ambient conditions; however, there was a significant growth of strength in later age. The compressive strength results of all grades of concretes at 3, 28 and 90 days are presented in Table 4. The average sample standard deviations of 28-day compressive strength of geopolymer concretes and OPC concretes were 0.91 and 1.14 MPa respectively. It can be seen from Table 4 that the amount of binder required for the same 28-day compressive strength was significantly lower in geopolymer concrete compared to OPC concrete. In Grade 50 concrete, 295 kg/m 3 Geopolymer 2 binder and 395 kg/m 3 Portland cement Figure 2. Sealed geopolymer concrete specimens (a) cylinders and (b) shrinkage prisms.

7 Australian Journal of Civil Engineering 77 developed 63.5 and 62.0 MPa of 28-day compressive strength, respectively. Geopolymer 2 needs slightly less amount of binder than Geopolymer 1 for the same 28-day compressive strength. In Grade 65 concrete, there was a difference of 9 MPa in 28-day compressive strength of Geopolymer 2 and Geopolymer 1 concrete which was due to the difference in GGBFS content in those binders. In geopolymer concrete, the ratio of compressive strength at day 3 to day 28 (3 days age factor) was significantly lower than OPC concrete in 40 and 50 MPa grade concretes. However, this value was almost similar to OPC regarding high-strength concretes (65 and 80 MPa). The average growth in compressive strength from 28 to 90 days in geopolymer concretes was 17%, whereas the average growth in OPC concrete was 6% for the same period Drying shrinkage The increment of drying shrinkage with respect to time is plotted in Figures 4 7 for 40, 50, 65 and 80 MPa concretes, respectively. Each data points represent the average value of drying shrinkage of six numbers of test specimens. Estimated value of drying shrinkage according to Australian Standard-3600 (2009) for each grade of concretes is also plotted in those figures for comparison. The results of drying shrinkage of 40, 50, 65 and 80 MPa concretes showed that normal workable geopolymer concrete exhibited similar or slightly higher drying shrinkage than OPC concrete of same strength grades at standard temperature curing. Among the normal workable concretes, Geopolymer 1 concrete showed higher drying shrinkage for all grades despite having lower water content and water/binder ratios for all strength grades. In all cases, super workable concretes exhibited higher drying shrinkage than normal Table 4. Summary of compressive strength of different grades of concretes. workable concretes of same grades. For all grades, the measured drying shrinkage of geopolymer as well as OPC concretes of both workability levels were higher than estimated drying shrinkage of concrete according to Australian Standard-3600 (2009). There was a common pattern of decreasing drying shrinkages with the increase in concrete strength grades. This pattern is applicable in all types of concrete of different binders and workability. The rate of increase in drying shrinkage with age was similar in concretes of all grades, higher at early ages and gradually decreasing with time. This experiment found a relatively higher amount of drying shrinkage values in normal workable concretes than measured in some previous published papers for OPC concretes (Al-Attar 2008; Shah, Karaguler, and Sarigaphuti 1992). This may be due to different types of aggregates used and other factors of concrete mix design such as cement type and water/binder ratio. Several previous investigations suggested that aggregate properties (shrinkage and water absorptions) are also major factors influencing drying shrinkage of concrete (Hansen and Nielsen 1965; Hyodo et al. 2013). The drying shrinkage would be different if different types of aggregates, such as limestone, basalt and andesite, were used which usually give drying shrinkage than sandstone aggregate. A detailed investigation into drying shrinkage of concrete from Greywacke sandstone aggregate by Mackechnie (2006) showed an average 800 microstrain of drying shrinkage at 56th day for concretes having water/binder ratio which is similar to drying shrinkage results of the 40 MPa grade concretes of this study. Since, all the concretes were produced from aggregates of same source, the effect of aggregate types was assumed not to be a factor in the variation of the drying shrinkage results for concretes of different grades in this study. Concrete grade (MPa) Concrete ID Binder content (kg/m 3 ) w/b ratio Notes: N = normal-workable concrete, SW = super-workable concrete. Compressive strength (MPa) 3-day 28-day 90-day Growth from 28 to 90 days (%) 40 OPC N Geopolymer 1 N Geopolymer 2 N OPC SW Geopolymer 2 SW OPC N Geopolymer 1 N Geopolymer 2 N OPC SW Geopolymer 2 SW OPC N Geopolymer 1 N Geopolymer 2 N OPC SW Geopolymer 2 SW OPC N Geopolymer 1 N Geopolymer 2 N OPC SW Geopolymer 2 SW

8 78 K. Neupane et al. Figure 3. Compressive strength development 65 MPa grade concretes. Figure 4. Increment of drying shrinkage of 40 MPa concretes. Figure 5. Increment of drying shrinkage of 50 MPa concretes. In this study, super-workable concrete contained higher amount of water, higher amount of binder, higher water/binder ratio and higher proportions of sand than normal-workable concrete of the same grade. The higher values of drying shrinkage in super-workable concrete may be due to the combined effects of all these factors. Australian Standard-1379 (2007) has specified the 56th day drying shrinkage of normal class concrete (50 MPa or less) should be less than 1000 microstrains. Figures 4 7 show that none of the grades of geopolymer concretes exceeded this limit. Drying shrinkage in geopolymer concrete is therefore within the acceptable limits suggested in current code of practice. In previous research, the amount of binder (paste volume) of concrete mix was found as the major factor to increase the drying shrinkage of concrete rather than

9 Australian Journal of Civil Engineering 79 Figure 6. Increment of drying shrinkage of 65 MPa concretes. Table 5. Drying shrinkage of OPC and Geopolymer 2 normal workable concretes. Concrete grades (MPa) OPC N Geopolymer 2 N Binder content (kg/m 3 ) Water/cement ratio Water content (kg/m 3 ) Age (day) Drying shrinkage (microstrain) Figure 7. Increment of drying shrinkage of 80 MPa concrete. Figure 8. Relation of drying shrinkage and water/binder ratio.

10 80 K. Neupane et al. Figure 9. Relation of drying shrinkage and binder content. water/binder ratio (Bissonnette, Pierre, and Pigeon 1999; Leemann and Lura 2014). In addition, water content was also considered as an important factor to increase drying shrinkage of concrete (CCAA 2002; Neville 1995). For a comparison, the drying shrinkage results of OPC and Geopolymer 2 normal-workable concretes of different grades at 56th day are presented in Table 5. Data points in this table show that drying shrinkage of both concretes decreased with the increase in the amount of binder (paste volume) of concrete mix and concrete strength grades. There was no direct relationship between drying shrinkage and water content of the concrete mix. For example, in normal workable concrete from Geopolymer 2, there was a decrease in drying shrinkage from 65 to 80 MPa grades despite increase in total water content and binder content. In all concretes, drying shrinkage was gradually increasing with the increase in water/binder ratios regardless of the water contents. Similar patterns of results can be found in other concretes of this study (Geopolymer 1 normal-workable and OPC and Geopolymer 2 super-workable concretes). The relationship between drying shrinkage and water/binder ratio of concretes from all three binders is plotted in Figure 8, where all concretes show the increase in drying shrinkage with the increase of water/binder ratio with only one exceptional data point (Geopolymer 2 super workable concrete). Among all, drying shrinkages of normal workable concretes from Geopolymer 2 and OPC displayed almost linear relationships of drying shrinkage with the water/binder ratio. The relationship of drying shrinkage and binder content of concretes from all three binders and both workability levels is plotted in Figure 9. In Figure 9, all types of concretes showed the general decrease in drying shrinkage with the increase in binder content with only one exceptional data point (Geopolymer 2 super workable concrete). According to Australian Standard (2009), the basic drying shrinkage strain of concrete (OPC based) decreases with the increase in concrete strength grades with following relationship. Basic drying shrinkage strain (ε csd.b )=( f c ) ε csd.b (1) ε csd.b = final basic drying shrinkage strain depends on the quality of local aggregates ( microstrains); f c = characteristic 28 days compressive strength of concrete (MPa). Generally speaking, concrete strength increases with the increase in binder content of concrete due to the decrease in water/binder ratio. From the results of mix design and testing of concretes of different grades, it was learned that this phenomenon is applicable for both geopolymer and OPC concrete. Therefore, the drying shrinkage of concrete should decrease with the increase in binder content of concrete (both geopolymer and OPC) which supports the results of this experiment. The relationship between water content and drying shrinkage of different types of concretes of this study appeared random and did not exhibit a discernible trend. 4. Conclusions Geopolymer and OPC concretes of four different grades and two workability levels were investigated for their fresh concrete properties, compressive strength development and drying shrinkage at standard laboratory temperature curing (ambient) conditions. Concrete with geopolymer binders required significantly less water and binder for the same workability and 28-day compressive strength when compared to OPC (control) concrete. Both normal and super-workable concretes of geopolymer binders can be produced without addition of any chemical admixtures. Compressive strength development in medium grade (40 and 50 MPa) geopolymer concrete was relatively lower at early age (1 3 days) compared to the control concrete of this study. However, OPC concretes with GP

11 Australian Journal of Civil Engineering 81 cement only (no supplementary cementitious materials added) are not common in field; generally GP cement is replaced by 20 40% of fly ash or slag or combination of both. Therefore, comparing against the early age strength results of OPC concretes with 25% fly ash or slag (data available in Darra Laboratory), geopolymer concrete can attain same level of early age compressive strength to OPC concrete. High-strength (65 and 80 MPa grades) geopolymer concretes exhibited early age strength equal to control concrete of same grade. The later age growth in compressive strength was significantly higher in geopolymer concrete compared to OPC concrete of same grade which ranged from 15 to 20% for 28- to 90-day period. The drying shrinkage results of geopolymer normal workable concretes were similar to OPC concrete of same grades. The drying shrinkage results of geopolymer concretes of this study were significantly higher than drying shrinkage of accelerated cured geopolymer concretes reported in previous investigations. Super workable concretes from both OPC and geopolymer binders exhibited higher drying shrinkage than normal workable concretes of same grades at all ages. The higher drying shrinkage of super workable concretes was due to the higher water/binder ratio, higher water content and higher proportions of fine aggregates in the concrete mixes. The drying shrinkage of geopolymer concretes of all grades measured in this study was less than 1000 microstrain for both workability levels of concretes at 56th day, hence complied with Australian Standard Contrary to some previous suggestions, drying shrinkage of concretes of all four grades from different binders was found to decrease with the increase in binder content and concrete strength grades. A clear trend exhibited between drying shrinkage and water/ binder ratio of concrete; drying shrinkage decreases with the decrease in water/binder ratio. The effect of water content in drying shrinkage, however, was not consistent, and a clear relationship between the two parameters could not be seen. Acknowledgement The authors would like to express sincere acknowledgement to Cement Australia Pty. Ltd. Queensland for the financial and material support and laboratory facility in this research. Disclosure statement No potential conflict of interest was reported by the authors. Notes on contributors Kamal Neupane is a research student in University Of Technology Sydney. He has completed bachelor s degree in civil engineering from Tribhuvan University, Nepal and master s degree in structural engineering from University of Technology Sydney, NSW. His current research is in engineering properties of geopolymer concrete. Paul Kidd is a product performance manager in Cement Australia Pty. Ltd. Darra, Australia. He has done master s in industrial chemistry from Newcastle University. He is one of core member of development team of powder-activated geopolymer in Cement Australia, Pty. Ltd. Darra. Des Chalmers is the group product manager in Cement Australia Pty. Ltd. Darra, Australia. He has done master s in applied chemistry from Queensland University of Technology. He is the leader of development team of powder-activated geopolymer in Cement Australia, Pty. Ltd. Darra. Daksh Baweja is an associate professor at University of Technology Sydney, NSW. He also works as a director for BG&E Material Technology in Sydney. His specialising is in durability of concrete structures. Rijun Shrestha is a lecturer in University of Technology Sydney, NSW. He received his master s degree and PhD from University of Technology Sydney, NSW in structural engineering. His research interest is in concrete and timber structures. References Al-Attar, T. 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