Influence of duration of heat curing and extra rest period after heat curing on the strength and transport characteristic of alkali activated class F fly ash geopolymer mortar

Influence of duration of heat curing and extra rest period after heat curing on the strength and transport characteristic of alkali activated class F fly ash geopolymer mortar

Construction and Building Materials 151 (2017) 363–369 Contents lists available at ScienceDirect Construction and Building Materials journal homepag...

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Construction and Building Materials 151 (2017) 363–369

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Influence of duration of heat curing and extra rest period after heat curing on the strength and transport characteristic of alkali activated class F fly ash geopolymer mortar a,⇑ _ S. Ilkentapar , C.D. Atisß a, O. Karahan a, E.B. Görür Avsßarog˘lu b a b

Erciyes University, Civil Engineering Department, Kayseri, Turkey KSU, Vocational School, Kahramanmarasß, Turkey

h i g h l i g h t s  Influence of rest period after heat curing on property of AAFA mortar was evaluated.  Heat and extra rest period of curing increased transport properties value of mortar.  Heat and extra rest period of curing improved mechanical properties of AAFA mortar.  High strength and abrasion resistant fly ash geopolymer mortar mixture was developed.

a r t i c l e

i n f o

Article history: Received 14 December 2016 Received in revised form 18 May 2017 Accepted 7 June 2017

Keywords: Sodium hydroxide Fly ash Geopolymer Heat curing Rest period

a b s t r a c t In the study, the influence of heat curing duration and rest period after heat curing duration on the strength and transport characteristics of alkali activated fly ash (AAFA) mortar were investigated. A local class F type fly ash, CEN reference sand, sodium hydroxide and potable water were used in preparation of cement-less fresh geopolymer mortar mixture. Mixture ratios (in mass basis) were 3, 1, 0.29, and 0.1 for sand, fly ash, water and sodium hydroxide, respectively. Some samples were cured at 75 °C temperature for 4 h, 1, 2, 3 and 7 days; then, they were tested after heat curing period. Additionally, some of the equivalent samples were kept in the laboratory at 23 ± 2 °C temperature with 50 ± 5% relative humidity, until 28 days after their initial heat curing period. Then, they were tested at 28 days for combined curing conditions. The measured properties of AAFA mortar were unit weight, porosity, capillary water absorption, water absorption capacity, flexural-bending and split tension strength, compressive strengths and abrasion resistance. It was observed that the strengths of mortar were significantly increased with the increase in heat curing duration. A significant strength development was also observed after rest period. As a result of the study, high strength and abrasion resistant AAFA geopolymer mortar was produced. However, transport properties of AAFA geopolymer mortar found to be not as good as mechanical properties. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Cement production is not a green process, since it consumes large energy; also sintering of calcareous and clayey materials in cement production is responsible for CO2 emission at about 10% into atmosphere. Equivalent of total CO2 emission of energy consumed for cement production as well as CO2 emission due to disintegrating CaCO3 rock is known to be at about 7% [1,2].

⇑ Corresponding author. _ E-mail address: [email protected] (S. Ilkentapar). http://dx.doi.org/10.1016/j.conbuildmat.2017.06.041 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

Pressure of green peace movements, savings energy and cement cost lead researchers to find a way for manufacturing cheaper cement and binder. One of the way to obtain green and cheaper cementing materials is employing industrial waste and byproducts (for example; ground granulated slag, fly ash, rice husk ash and silica fume) in concrete as a partial replacement of Portland cement [3]. Some researchers [3–5] investigated utilisation of a vast quantity of fly ash as cement substitution in concrete mixture. They partially substituted Class F type fly ash with cement and prepared high volume fly ash concrete mixture with proper water content.

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They reported that high volume fly ash can be utilized in concrete without imparting the mechanical and durability properties of concrete. A researcher [3] added fly ash in concrete up to 70% instead of cement, other [4] replaced fly ash with cement up to 80% by weight; similarly, another [5] prepared a concrete mixture containing 80% fly ash as a partial replacement of cement and used lime saturated water in the mixture. It may be commented that, they [3–5] targeted to utilize fly ash in concrete as much amount as possible instead of cement. Currently, that aim was come into reality by activating fly ash in alkali medium to form a geopolymeric binding materials. Geopolymerization is chemical reaction similar to organic polymeric chain; in final product it forms alumina-silica chain that has binding property. Geopolymeric reaction takes place between glassy silica and alumina in a high pH strong alkaline catalysing medium. The reaction is also named as alkali activation, that convert glassy compositions of source matter into a solid compound matter with a robust binding property [6–9]. Fly ash is a waste of coal consuming thermal power plant supplying electricity. Currently fly ash is also called as by-product due to its pozzolanic property. In its content, it has an abundant amount aluminous and siliceous matter in amorphous phase, hence, it is considered a proper geopolymeric source material [10]. Studies have shown that, molar concentration of alkali activation materials have a significant role in the geopolymeric reaction. Strong alkaline medium, with high pH value, dissolves the glassy phase of ingredients of fly ash to form geopolymer precursors and, at the end of reaction geopolymer formed with aluminasilicate chain [11–14]. As mentioned before that geopolymerization is a chemical reaction and process that take place in time, and reaction of geopolymerization for a fly ash-based mixture is low at ambient temperature, thus, temperature of curing medium and curing period are prominent parameters that influence the reaction kinetics [8,11,13–19]. A literature survey has been made on fly ash based geopolymer. This is presented in the following. Olivia and Nikraz [20] designed the mixture of fly ash based geopolymer concrete to optimize the properties of mixture using Taguchi method. As a result of their study, they achieved compressive strength value of 60 MPa. In their study, they used sodium hydroxide and sodium silicate solution as the activator, 14 Molar NaOH solutions and 1.5–2.5 ratio of sodium silicate to NaOH were used; fresh geopolymer concrete samples were cured at 75 °C for 24 h. Ryu et al. [21] reported from their laboratory study that they obtained 45 MPa maximum compressive strength developments from AAFA geopolymer concrete. Sodium hydroxide and sodium silicate were the activators used in the preparation of mixtures. The mixtures prepared were cured at 60 °C for 24 h, then, the samples were de-moulded from their mould and stored in laboratory condition until testing day of 56th day. Vora and Dave [22] investigated strength properties of concrete containing class type F fly ash as the geopolymeric source material in the mixture. Alkali activation was made with the combination of sodium hydroxide and sodium silicate solution. The highest value for compressive strength achieved was about 40 MPa. De Vargas [23] investigated the influence of combination NaOH and Ca(OH)2 mixture as activator on strength development of fly ash geopolymer system. He cured geopolymer specimens at 80 C for 24 h, after heat curing, specimens were kept in laboratory condition until testing time at 7, 28 and 91 days. One mixture has shown strength reduction after 7 days, compressive strength of another mixture continuously increased up to 91 days; however, strength was neither increased nor decreased in another mixture.

The highest compressive strength they reported from their laboratory study was in the order of 30 MPa. Skvara et al. [24] activated brown coal class F type fly ash with sodium hydroxide plus sodium silicate solution. Samples prepared were cured at 80 °C for 12 h and developed 40 MPa compressive strength at 28 days. They observed that strength developments were continued up to four years and significant increase was reported. Compressive strength value for geopolymeric concrete made with fly ash in the order of 25 MPa was reported in the literature by Somna et al. [10]. Even less compressive strength than 10 MPa of AAFA geopolymer was also reported by Swanepoel and Strydom [7]. Rownanik [25] investigated the influence of curing temperature on the development of hardened properties of metakaolin based geopolymer. Sodium hydroxide and sodium silicate used together as the activator. Specimens produced were cured for 1, 2, 3 and 4 h at different temperature, after heat curing, samples were stored in laboratory condition until testing at 1, 3, 7 and 28 days. Increasing heat curing time increased the compressive strength. They reported that when temperature of heat curing was higher than 50 °C, duration of curing time at ambient temperature did not significantly influenced the compressive strength. However, duration of curing at ambient temperature influenced compressive strength considerably at lower temperature (lower than 50 °C). Moreover, that influence was marked particularly at lower heat curing duration (lower than 4 h). Published materials on the influence of heat curing period longer than 24 h found to be scanty. Also, after heat curing period, influence of rest period duration on the strength and transport properties of fly ash geopolymer mortar needs more study. Therefore, this study focused on influence of heat curing time up to 7 days, and rest period after heat curing on strength and transport properties of class F type fly ash based geopolymer.

2. Properties of materials used and methods 2.1. Fly ash Low lime F type fly ash was employed in this laboratory study. It was provided from ISKEN Company a thermal power plant established at a south city in Turkey. According to ASTM C618 [26] standard specification current fly ash is categorized as low lime and class F type fly ash due to its chemical composition presented in Table 1. Specific weight of fly ash used was 2.39. The residue of fly ash on 45 mm sieve was 12%. Pozzolanic activity index of current ash was obtained according to ASTM C618 [26] specification and it was 78.2 and 93.8%, for 28 and 90 days, respectively. 2.2. Standard sand The sand used in the preparation of mortar mixes was complied with Rilem Cembureau Standard and TS EN 196-1 [27] standard. Size distribution of current sand used was carried out by sieve analysis described in relevant standard [27]. The results of sieve analysis and specification of standard were given in Table 2 confirming that grading of sand used was complied with the limits of standard. 2.3. Activator In the experimental study, the alkali activator used was sodium hydroxide, its purity was higher than 97%. The chemical

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Table 1 Oxide components of fly ash used (%). Oxide

SiO2

Al2O3

Fe2O3

CaO

SO3

Na2O

Free CaO

Cl

LOI

Fly Ash

61.81

19.54

7.01

1.77

0.31

2.43

0.07

0.04

2.20

Table 2 Grading of sand used and standard specification. Sieve Size (mm) Remaining on sieve (%) Standard Limits (%)

0.08 99 99 ± 1

0.16 87 87 ± 5

0.5 72 67 ± 5

1.0 34 33 ± 5

1.6 6 7±5

2.0 0 0

Table 4 Mortar mixture composition for three cell prism mould with 160  40  40 mm size (g).

Table 3 Chemical ingredient of alkali activator. NaOH (%)

Na2CO3 (%)

Cl (%)

Al (%)

Fe (%)

SO4 (%)

97

1

0.01

0.002

0.002

0.01

ingredients of NaOH (obtained from Zülfikarlar Group Akça Chemical) are summarized in Table 3.

2.4. Water Clean and potable water was used for the mixture of AAFA geopolymer mortar.

2.5. Experimental program Mortars prepared in this experimental study were made with class F type fly ash, standard sand, water and sodium hydroxide. Mixture ratios in mass basis were 3, 1, 0.29, and 0.1 for sand, fly ash, water and sodium hydroxide, respectively. The weights of materials, needed to prepare three cell prism samples having dimensions of 160  40  40 (length; depth and height) mm, were presented in Table 4. After preparing fresh fly ash geopolymer mortar mixture, prismatic specimens were cast using 160  40  40 mm size three cell moulds. Then, specimens were placed in an oven with 75 °C temperature; some specimens were cured for 4 h in oven. Some specimens were cured 1, 2, 3 and 7 days in oven. After oven curing period, specimens were taken out of their mould, then, testing measurements were carried out without cooling down the specimens. After each oven curing period (at 75 °C), some of the specimens taken out of their mould were left in laboratory condition at 23 ± 2 °C temperature with 50 ± 5% relative humidity, for a rest period until 28 days. After rest period, testing measurements were carried out at 28 days. Compressive, flexural tensile and split tensile strength tests were performed on AAFA geopolymer mortar. Prismatic specimens with 40  40  160 mm size were used in the measurement of flexural tensile strength. Flexural tensile strength testing was carried out according to TS EN 1015-11 [28] standard, three point loading test set up was used. After flexural tensile test for a prism specimen, two broken pieces of halved prismatic part were obtained. These two pieces were used in compression test, using an apparatus with 40  40 mm sized compression plate. Split strength tests were conducted using prism samples with 40  40  160 mm size; loading was applied over its 160 mm length. Split tensile strength and flexural tensile strength results were average of three specimens. However, compressive strength result was average of six specimens, since 6 broken pieces obtained from flexural tensile testing were utilized for compression test.

Standard Sand

Fly Ash

NaOH

Water

1350

450

80

130

After oven curing and rest period of curing, tests were also made for transport properties, including water absorption, porosity, and capillary water sorptivity test. Transport property testing were carried out using 40  40  160 mm size prismatic specimens in accordance with ASTM C642 [29] and ASTM C1585 [30] standard, respectively. Cubic specimens with 70 mm side were utilized in the measurements of horizontal Bohme abrasion value of AAFA geopolymer mortar, testing was carried out according to TS 2824 EN 1338 standard [31]. Water absorption measurements were carried out after immediately taking the specimens from their mould. Three specimens were used for transport property and abrasion value and unit weight measurements.

3. Results and discussions 3.1. Unit weight, water absorption and porosity Transport properties obtained from AAFA geopolymer mortar after heat curing and combined heat curing with extra rest period curing were presented in Table 5. Comparison between curing with and without extra rest period after heat curing duration shows that there is not much difference on unit weight measurements. Unit weight of hardened geopolymer mixture was found to be between 2137 and 2187 kg/m3. Water absorption measurements were carried out after immediately taking the specimens from their mould. Water absorption value of mortar specimen was increased by the increase of heat curing duration. Shorter heat curing duration results with lower water absorption value. This could be attributed to the amount of water in the specimens. While heat curing duration increases, the amount of water in the sample was evaporated more by heat curing, then, evacuated volume of water absorbed more water when compared to short heat curing duration. A comparison was made between heat curing and extra rest period after heat curing period, extra rest period of curing after heat curing results with higher value of water absorption. This could be explained by the water present in the specimens. After heat curing, the remaining water could be evaporated in the laboratory environment within extra rest period of curing time. Therefore, left volume gets empty which could cause more water absorption during absorption testing. The relative difference between heat curing and extra rest period curing for absorption value decreases with the increase in heat curing duration. For

2137 2143 2161 2170 2187 1.4 2.3 4.7 5.4 5.6 2179 2166 2162 2161 2159

2.9 4.9 9.8 11.0 11.4

K6 K7 K8 K9 K10

4h 1d 2d 3d 7d

+28 d +27 d +26 d +25 d +21 d

9.1 8.5 7.6 7.6 7.5

Porosity (%) Absorption (%) Unit Weight (kg/m3) Extra Rest Period Heat Curing Duration Mixture No Porosity (%) Absorption (%) Unit Weight (kg/m3)

4h 1d 2d 3d 7d K1 K2 K3 K4 K5

+0 +0 +0 +0 +0

Heat Curing Duration

Extra Rest Period

example, water absorption value was 1.4% for samples cured for 4 h by heat curing; it was increased to 9.1% after extra rest period of curing. However, water absorption value was 5.6% for samples cured for 7 days by heat curing; it was increased to 7.5% after extra rest period of curing. Porosity results values showed similar development to water absorption value. Similar explanation can be made for porosity values. For example, porosity value was 2.9% for samples cured for 4 h by heat curing. It was increased to 17.9% after extra rest period of curing. However, water absorption value was 11.4% for samples cured for 7 days by heat curing. It was increased to 15.3% after extra rest period of curing. When the heat curing time or extra rest period increase, absorption value increases but with a decelerating rate, then absorption value gets asymptotic to a constant. This is valid for porosity results of the samples. Some more discussions for the transport properties were presented in the following sorptivity section. 3.2. Sorptivity Capillary sorptivity testing results of AAFA geopolymer mortar after heat curing and combined heat curing with extra rest period were presented in Table 6. A close observation and evaluation of capillary sorptivity testing measurements show that increase in heat curing duration results with an increase in initial sorptivity coefficient. Similar observation made for extra rest period curing. Comparison between heat curing and extra rest period after heat curing showed that extra rest period of curing results with higher initial sorptivity coefficient value than for only heat curing condition. These increases could be explained by the amount of water in the specimens. It is known that geopolymeric reaction does not bind water [32,33], water in the mixture during curing time dries out in time. Longer heat curing duration results more water to dry out, and increase the pore volume of mortar which results more water intake and increase the sorptivity coefficient. Similarly, extra rest period of curing after heat curing also provides time for water to be evacuated from the medium, thus, contribute to increase in pore volume resulting with higher sorptivity coefficient. When the curing periods prolonged, initial sorptivity coefficient gets stabilized and become asymptote to a constant value for both curing conditions. After evaluation of water absorption, porosity and initial sorptivity coefficient results, it is commented in this study that measuring these transport properties of hardened AAFA geopolymer mixture at early age can lead to misinterpretation of the results obtained. Transport properties of heat cured AAFA geopolymer mixture should be measured after 28 days or more time after initial curing time. 3.3. Compressive strength

Mixture No

Table 5 Unit weight, water absorption and porosity results of mortars.

17.9 16.7 15.3 15.3 15.3

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Table 7 and Fig. 1 present compressive strength (CS) obtained from AAFA geopolymer mortar after heat curing and combined heat curing and rest period curing. Table 7 shows that increasing heat curing duration from 4 h to 7 days significantly improves the compressive strength development. For instance, four hours heat curing duration developed 4.41 MPa, compressive strength. CS increased from 4.41 MPa to 33.84, 50.50, 63.32, 73.57 MPa value, due to increase in heat curing duration from four hours to 1, 2, 3 and 7 days, respectively. This is attributed to kinetics of geopolymeric chemical reaction; heat curing accelerates the chemical process and longer time allows more reaction between amorphous silica an alumina in the presence of high pH alkali medium. CS of four hours heat cured samples was 4.41 MPa, this value was 168% improved and reached to 11.82 MPa value after extra

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Table 6 Water sorptivity results of mortars. Mixture No

Heat Curing Duration

Extra Rest Period

Initial Sorptivity (mm/sn1/2)

Mixture No

Heat Curing Duration

Extra Rest Period

Initial Sorptivity (mm/sn1/2)

K1 K2 K3 K4 K5

4h 1 day 2 days 3 days 7 days

+0 +0 +0 +0 +0

0,00016 0,00038 0,00047 0,00050 0,00057

K6 K7 K8 K9 K10

4h 1 day 2 days 3 days 7 days

+28 days +27 days +26 days +25 days +21 days

0.00041 0,00043 0,00079 0,00081 0,00083

Table 7 Compressive strength results of AAFA geopolymer mortar mixture. Mixture No

Heat Curing Duration

Extra Rest Period

Compressive Strength

Mixture No

Heat Curing Duration

Extra Rest Period

Compressive Strength

K1 K2 K3 K4 K5

4h 1 day 2 days 3 days 7 days

+0 +0 +0 +0 +0

4.41 33.84 50.50 63.32 73.57

K6 K7 K8 K9 K10

4h 1 day 2 days 3 days 7 days

+28 days +27 days +26 days +25 days +21 days

11.82 45.30 64.78 70.03 75.69

Strength increase in CS during extra curing period after heat curing was attributed to two reasons. One of the reasons is thought to be the accelerating influence of thermal energy deposited in mortar sample during heat curing time. Whilst the thermal energy was dissipating to laboratory environment, geopolymeric reaction took the advantage of this thermal energy after heat curing duration and continued. After cooling down temperature to laboratory environment condition of samples within a few hours, it is thought that geopolymeric reaction was slowed down, however, it is continued within extra rest period of curing, and being as other reason allowed AAFA geopolymer mortar to develop compressive strength. Thus, in total, both reason substantially contributed to strength gain. 3.4. Flexural tensile strength Fig. 1. Effect of extra rest period on compressive strength.

rest period until 28 days. CS of 1 day heat cured samples increased from 33.84 MPa to 45.30 MPa after extra rest period until 28 days, the rate of increase was about 34%. CS of 2 days heat cured samples increased from 50.50 MPa to 64.78 MPa after extra rest period until 28 days, the rate of increase was about 28%. CS of 3 days heat cured samples increased from 63.32 MPa to 70.03 MPa after extra rest period until 28 days, the rate of increase was about 11%. CS of 7 days heat cured samples increased from 73.57 MPa to 75.69 MPa after extra rest period until 28 days, the rate of increase was about 3%. It can be observed from Table 7, Fig. 1 and above discussions that, while heat curing time increases, the rate of increase in compressive strength after extra curing period was decreased from 168% to %34, %28, %11 and 3%, gradually. When the rate of increase in compressive strength is evaluated, while increasing heat curing duration time, the increase in compressive strength (due to extra rest period of curing) significantly decreased. In fact it may be thought that increase was completed for 7 days of heat curing; since the rate of increase was 3% after extra rest period of curing. This deceleration within the increase in CS can be explained by the geopolymeric reaction of fly ash. Increasing heat curing periods consumes geopolymeric source components of fly ash in geopolymeric reaction, thus, in extra rest period of curing time, quantity of consumable components of fly ash into geopolymeric reaction decreases which results with lower increase in compressive strength.

Flexural tension strength (FTS) test results of AAFA mortar were illustrated in Table 8 and Fig. 2. Figures show that increasing heat curing duration result with an increase in FTS of geopolymer mortar mixture as observed for compressive strength values. Table 8 also shows that increasing heat curing duration from four hours to 7 days significantly improves the FTS development. For instance, after four hours heat curing duration AAFA mortar developed 1.45 MPa FTS. Strength increased from 1.45 to 3.87, 5.90, 10.63, 13.83 MPa value, due to increase in heat curing duration from four hours to 1, 2, 3 and 7 days, respectively. FTS of four hours heat cured samples was 1.45 MPa, this value was 234% improved and reached to 4.84 MPa value after extra rest period until 28 days. FTS of 1 day heat cured samples increased from 3.87 MPa to 6.76 MPa after extra rest period until 28 days; the rate of increase was about 75%. FTS of 2 days heat cured samples increased from 5.90 MPa to 9.72 MPa after extra rest period until 28 days; the rate of increase was about 65%. FTS of 3 days heat cured samples increased from 10.63 MPa to 12.00 MPa after extra rest period until 28 days; the rate of increase was about 13%. FTS of 7 days heat cured samples increased from 13.83 MPa to 14.10 MPa after extra rest period until 28 days; the rate of increase was about 2%. Above discussions, Table 8 and Fig. 2 illustrate that, while heat curing increases, the rate of increase in FTS was decreased from % 234, %75, %65, %13 and %2, gradually. Evaluation of rate of strength gain in FTS showed that while increasing heat curing duration, rate of strength gain in FTS due to extra rest period of curing remarkably reduced. Similar explanation made in CS section is valid for strength gain in FTS during extra curing period after heat curing.

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368 Table 8 Flexural strength of AAFA mixture. Mixture No

Heat Curing Duration

Extra Rest Period

Flexural Strength

Mixture No

Heat Curing Duration

Extra Rest Period

Flexural Strength

K1 K2 K3 K4 K5

4h 1 day 2 days 3 days 7 days

+0 +0 +0 +0 +0

1.45 3.87 5.90 10.63 13.83

K6 K7 K8 K9 K10

4h 1 day 2 days 3 days 7 days

+28 days +27 days +26 days +25 days +21 days

4.84 6.76 9.72 12.00 14.10

Fig. 2. Effect of extra rest period on flexural strength.

Fig. 3. Effect of extra rest period on splitting tensile strength.

3.5. Splitting tensile strength Splitting tensile strength (STS) value of fly ash based geopolymer mortar was presented in Table 9 and Fig. 3. Figures show that increasing heat curing duration result with an increase in STS value of geopolymer mortar mixture as observed for compressive and flexural tensile strength cases. Both Fig. 3 and Table 9 show that increasing heat curing duration from four hours to 7 days improves STS development in substantial amount. For instance, four hours heat curing duration developed 0.42 MPa STS. Strength increased from 0.42 to 2.59, 3.64, 4.91, 5.67 MPa value, due to increase in heat curing duration from four hours to 1, 2, 3 and 7 days, respectively. STS of four hours heat cured samples was 0.42 MPa, this value was 288% improved and reached to 1.63 MPa value extra after rest period until 28 days. STS of 1 day heat cured samples increased from 2.59 MPa to 4.25 MPa after extra rest period until 28 days; the rate of increase was about 64%. STS of 2 days heat cured samples increased from 3.64 MPa to 5.63 MPa after extra rest period until 28 days; the rate of increase was about 55%. STS of 3 days heat cured samples increased from 4.91 MPa to 5.72 MPa after extra rest period until 28 days; the rate of increase was about 16%. STS of 7 days heat cured samples increased from 5.67 MPa to 6.06 MPa after extra rest period until 28 days; the rate of increase was about 7%. It can be observed from above discussion that, while heat curing increases; the rate of increase in STS was decreased from %288, % 64, %55, %16 and %7, gradually. Evaluation of the increase in STS

indicates that increasing heat curing time cause a rise in STS within extra rest period of curing duration, however, the rate of rise significantly decreased. Explanation made for CS and FTS is valid for the strength gain in STS within extra rest period of curing time. 3.6. Abrasion resistance The results of Bohme abrasion testing were presented in Table 10. It can be seen from Table 10 that increasing heat curing period with and without rest period results with decrease in the abrasion value. This can be considered as direct influence of strength development with increasing heat curing period. However, a closer observation shows that extra rest period curing results with significantly lower abrasion value. A remarked development was observed in abrasion resistance of AAFA geopolymer mortar after rest period. At about 26% decrease was observed for abrasion of 7 days oven curing combined with rest period curing, in comparison to abrasion of only 7 days of oven curing period. Moreover, 55% decrease was observed for abrasion of 4 h oven curing combined with rest period curing, in comparison to abrasion of only 4 h of oven curing period. From this observation, it can be concluded that AAFA geopolymer mortar can be utilized in the field where abrasion resistance is important i.e. road surface. Similarly, Ramujee and Potharaju [34] also concluded that AAFA geopolymeric concrete was found to be abrasion resistant material than those of Portland cement concrete.

Table 9 Split tensile strength of AAFA mixture. Mixture No

Heat Curing Duration

Extra Rest Period

Splitting Tensile Strength

Mixture No

Heat Curing Duration

Extra Rest Period

Splitting Tensile Strength

K1 K2 K3 K4 K5

4h 1 day 2 days 3 days 7 days

+0 +0 +0 +0 +0

0.42 2.59 3.64 4.91 5.67

K6 K7 K8 K9 K10

4h 1 day 2 days 3 days 7 days

+28 days +27 days +26 days +25 days +21 days

1.63 4.25 5.63 5.72 6.06

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Table 10 Abrasion resistance of AAFA mixtures. Mixture No

Oven Curing Duration

Extra Rest Period

Abrasion (mm3/5000 mm2)

Mixture No

Oven Curing Duration

Extra Rest Period

Abrasion (mm3/5000 mm2)

K1 K2 K3 K4 K5

4h 1 day 2 days 3 days 7 days

+0 +0 +0 +0 +0

5082 3311 2693 2120 2047

K6 K7 K8 K9 K10

4h 1 day 2 days 3 days 7 days

+28 days +27 days +26 days +25 days +21 days

2267 2171 1925 1913 1516

4. Conclusions From this laboratory study, following conclusions were made; 1- Water absorption value of mortar specimen studied was increased with the increase of heat curing duration. Extra rest period of curing after heat curing results with larger value of water absorption. 2- Increase in heat curing time or extra rest period results with an increase in absorption, porosity and sorptivity values but with a decelerating rate, then, these values get asymptotic to a constant value. 3- Compressive, flexural tensile and split tensile strength and abrasion resistance of AAFA geopolymer mortar were significantly increased, while heat curing duration was increased, in general. However, the increase in strength gain rate due to heat curing duration decelerates. 4- Flexural tensile and split tensile strength were increased in extra rest period of curing duration after heat curing but in a decelerating rate. 5- As a result of this study, a high strength and abrasion resistant AAFA geopolymer mortar mixture coded K5 was developed.

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