High calcium fly ash geopolymer mortar containing Portland cement for use as repair material

High calcium fly ash geopolymer mortar containing Portland cement for use as repair material

Construction and Building Materials 98 (2015) 482–488 Contents lists available at ScienceDirect Construction and Building Materials journal homepage...

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Construction and Building Materials 98 (2015) 482–488

Contents lists available at ScienceDirect

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

High calcium fly ash geopolymer mortar containing Portland cement for use as repair material Tanakorn Phoo-ngernkham a, Vanchai Sata b, Sakonwan Hanjitsuwan c, Charoenchai Ridtirud d, Shigemitsu Hatanaka e, Prinya Chindaprasirt b,⇑ a Research Center for Advances in Civil Engineering and Construction Materials, Program in Civil Engineering, Faculty of Engineering and Architecture, Rajamangala University of Technology Isan, Nakhon Ratchasima 30000, Thailand b Sustainable Infrastructure Research and Development Center, Dept. of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand c Program of Civil Technology, Faculty of Industrial Technology, Lampang Rajabhat University, Lampang 52100, Thailand d Dept. of Civil Engineering, Faculty of Engineering, Rajamangala University of Technology Isan, Khon Kaen Campus, Khon Kaen 40000, Thailand e Dept. of Architecture, Faculty of Engineering, Mie University, Mie 514-8504, Japan

h i g h l i g h t s  FA geopolymer mortars (GPM) containing PC could be used as alternative repair material (RM).  GPM gave sufficiently high slant bond and bending strengths compared with RM.  The interface zone of concrete and GPM was more homogeneous and denser than that of concrete and RM.

a r t i c l e

i n f o

Article history: Received 6 June 2015 Received in revised form 23 August 2015 Accepted 27 August 2015

Keywords: Geopolymer High calcium fly ash Portland cement Shear bond strength Bending stress Repair material

a b s t r a c t This article investigated the utilization of high calcium fly ash geopolymer mortars (GPM) containing ordinary Portland cement (PC) for use as Portland cement concrete (PCC) repair material. The shear bond strength of PCC substrate and repair binder and bending strength of notched concrete beam filled with repair binder were used to evaluate the performances of GPM and commercial repair binders (RM). Test results indicated that the use of GPM gave sufficiently high shear bond and bending strengths compared with the use of RM suggesting that it could be used as an alternative product for concrete repair works. In addition, the results from scanning electron microscopy of fracture surfaces indicated that the interface zone of concrete and GPM was more homogeneous and denser than that of concrete and RM. The GPM with 14 M NaOH solution and 10% PC was the optimum mixture for improving the shear bond and bending strengths. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Geopolymer is made from silica and alumina source materials activated with high alkali solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium silicate and potassium silicate [1]. A number of supplementary cementitious materials such as ground granulated blast furnace slag, metakaolin and fly ash are commonly used source materials in geopolymer for their availability and favorable mechanical properties [2–6]. Several researchers [7–10] reported that high calcium fly ash is also a suitable source material for making good geopolymer. The high calcium fly ash geopolymer mixture can be cured at room ⇑ Corresponding author. E-mail address: [email protected] (P. Chindaprasirt). http://dx.doi.org/10.1016/j.conbuildmat.2015.08.139 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

temperature as a result of the reaction of calcium in the system. However, the geopolymerization of high calcium fly ash without additives is still slow at ambient condition [10,11], therefore, low strength is normally obtained. The use of Portland cement to enhance the strength of high calcium fly ash geopolymer is very attractive [8,12–14]. In addition to the formation of calcium silicate hydrate, the heat from the reaction of Portland cement and water can assist the geopolymerization process and enhances the strength development [15]. High calcium geopolymer mortar with compressive strength of 65 MPa has been fabricated with the addition of Portland cement cured at 25 °C ambient temperature [8]. The commercial repair materials with good mechanical property and bonding strength are widely used for repair work in concrete. However, the costs of these products are rather expensive. Alternative repair material with comparable properties but less

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expensive is, therefore, a subject of interest. A number of researchers [9,16–19] have tried to utilize geopolymer as a repair material by testing slant shear, pull-out and direct shear. Hu et al. [16] studied the bond strength between mortar substrate and geopolymer in sandwich specimens and reported that geopolymer exhibited higher bonding strength than that of comparable Portland cement mixture. Pacheco-Torgal et al. [17] determined the bond strength between concrete substrate and geopolymer mortar produced from tungsten mine waste containing calcium hydroxide and found that the geopolymeric binders had very high bond strength even at early ages compared with that of commercial repair products. In addition, Songpiriyakij et al. [18] also tested the bond strength between rebar and concrete substrate by using geopolymer paste as the bonding agent, and reported that the bond strengths of rice husk ash and silica fume geopolymer pastes were approximately 1.5 times higher than those of comparable repair epoxies. Therefore, the bond strengths of geopolymer materials are sufficiently high and should be used as an alternative bonding material for repair works. The objective of this research is, therefore, to investigate the utilization of high calcium fly ash geopolymer mortars containing ordinary Portland cement as additive for use as a repair binder. The obtained knowledge would be very beneficial to the understanding and to the future application of geopolymer products as an alternative repair material. 2. Experimental details and testing analysis 2.1. Materials 2.1.1. Geopolymer mortars The geopolymer mortar (GPM) was made from high calcium fly ash (HFA) from Mae Moh power plant in northern Thailand and local river sand with specific gravity of 2.63 and fineness modulus of 1.80. Sodium hydroxide solution (NaOH) and sodium silicate solution (13.89% Na2O, 32.15% SiO2, and 46.04% H2O) were used as liquid activators. Four levels of HFA replacement by ordinary Portland cement (PC) of 0%, 5%, 10%, and 15% by weight and three NaOH concentrations of 6, 10, and 14 M (molar) were investigated. The chemical composition and physical properties of HFA and PC are shown in Tables 1 and 2, respectively. The mix proportions and strengths of GPM are shown in Table 3. For the mixing of mortars, NaOH and Na2SiO3 solutions were mixed together prior to the start of mixing. The HFA, PC and sand were dry mixed until a homogenous mass was obtained. The prepared liquid solution was then added and the mixing was done for 5 min. The setting time of mortar was also tested in accordance with ASTM C807 [20]. As shown in Table 4, the setting time of GPM was dependent on NaOH concentration and PC content. The final setting times ranged between 12 and 130 min and this could be used advantageously in adjusting the setting of repair material. 2.1.2. Ordinary Portland cement concrete The mix proportions and strengths of ordinary Portland cement concrete (PCC) are shown in Table 5. The local river sand with specific gravity of 2.61 and fineness modulus of 2.40 was used as fine aggregate. While, crushed limestone with specific gravity of 2.71 and fineness modulus of 6.05 was used as coarse aggregate. The PCC was used for preparing two types of specimen viz., slant shear test specimens and bending test specimens. For the slant shear specimens, the fresh PCC was cast in 50  50  125 mm prism molds. They were cured in water for 28 days and then wrapped with vinyl sheet to protect moisture loss and cured for another 60 days. This long curing period was chosen to provide advanced hydration as in the old concretes in the construction field based on the previous research [21]. The PCC prisms were cut in the middle section with the interface line at 45° to the vertical (see Fig. 1) to provide the PCC substrate for the slant shear specimens. For the preparation of specimens for bending stress, the PCC was cast in 75  75  300 mm long beams. They were cured similarly to the slant shear specimens. A notch with height to beam depth (a0/d) ratio of 0.4 and notch width to notch height (w0/a0) ratio of 0.4 was cut in the middle of beam (see Fig. 2).

Table 2 Physical properties of materials. Materials

Specific gravity

Median particle size, d50 (lm)

Blaine fineness (cm2/g)

HFA PC

2.61 3.16

8.5 14.6

4300 3600

2.1.3. Commercial repair material products Five available commercial repair material products (RM) were also tested. This was done so that the performance of GPM could be compared with those of commercial products. RM1 is general purpose non-shrink grout mortar; RM2 is high performance repair and finishing mortar; RM3 is fiber-reinforced non-shrink mortar; RM4 is multi-purpose non-shrink grout; and RM5 is polymer modified repair mortar. The amount of water in these products directly influences the compressive and flexural strengths including the bond adhesion; therefore, the recommended water/binder (W/B) ratios were strictly used. The obtained strengths of these repair materials are summarized in Table 6. 2.2. Testing and analysis 2.2.1. Shear bond strength between PCC substrate and GPM or RM The shear bond strength was evaluated using the slant shear test of PCC substrate and GPM or RM as described in ASTM C882 [22] with stiffer slant shear angle of 45°. The slant shear angle of 45° is officially used for standard evaluation of epoxy bond with concrete [23] and was also used successfully in testing shear bond of concrete and geopolymer [6]. For casting of the specimens, the GPM was placed in two equal layers into a 50  50  125 mm prism mold, half-filled with slant PCC substrate. Each layer was tamped 25 times and vibrated for 45 s. The samples were covered with vinyl sheet and kept in the 25 °C controlled room. The specimens (as shown in Fig. 1) were tested in a constant loading rate of 0.30 MPa/s. The shear bond strength was the ratio of maximum load at failure and the bond area. The reported results of shear bond strength were the average of five samples. 2.2.2. Bending stress of PCC notched beam with filled GPM or RM This test used the same type of specimens as in the test of fracture characteristics as shown in Fig. 2. For casting of specimens, the GPM or RM was mixed and filled in the notch to act as repair materials. The samples were covered with vinyl sheet to protect moisture loss and kept in the 25 °C controlled room until the testing age of 28 days. The specimens were tested by three point bending with deflection control using loading rate of 0.05 mm/min [24]. The reported results were the average of five samples. 2.2.3. Interface zone between PCC substrate and GPM or RM The samples between PCC substrate and repair materials were broken and analysed by the scanning electron microscopy (SEM). The samples were cut, then coated with a layer of gold approximately 20–25 Å thick using a blazer sputtering coater. After that, they were placed on a brass stub sample holder with double stick carbon tape. A JEOL JSM-700IF scanning electron microscopy was used to study interface zone between PCC substrate and GPM or RM.

3. Results and discussion 3.1. Shear bond strength between PCC substrate and GPM or RM The results of 45° slant shear load carrying capacity of PCC substrate and GPM or RM are shown in Fig. 3. The shear bond strengths increased with the increased PC content and NaOH concentration. The noticeable increase in shear bond strength was due to the increase in the reaction products. This is in line with the previous report [25]on the improved strength of fly ash based geopolymers with increased calcium content which the additional C–S–H and C–A–S–H gel co-existed with N–A–S–H gel of GPM. The increase in reaction products at the interface transition zone between PCC substrate and GPM enhanced the strength at contact

Table 1 Chemical composition of HFA and PC (by weight). Materials

SiO2

Al2O3

Fe2O3

CaO

MgO

K2O

Na2O

SO3

LOI

HFA PC

29.32 20.80

12.96 4.70

15.64 3.40

25.79 65.30

2.94 1.50

2.93 0.40

2.83 0.10

7.29 2.70

0.30 0.90

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Table 3 Mix proportions and strengths of GPM. Mix symbol

HFA (g)

PC (g)

Sand (g)

NaOH (g)

Na2SiO3 (g)

Properties of GPM

6M

10 M

14 M

fc (MPa)

ft (MPa)

6M0PC 6M5PC 6M10PC 6M15PC

100 95 90 85

– 5 10 15

100 100 100 100

20 20 20 20

– – – –

– – – –

40 40 40 40

38.5 40.2 45.3 48.2

2.91 3.79 4.77 4.93

10M0PC 10M5PC 10M10PC 10M15PC

100 95 90 85

– 5 10 15

100 100 100 100

– – – –

20 20 20 20

– – – –

40 40 40 40

50.5 56.7 60.4 64.1

6.22 6.85 7.17 7.32

14M0PC 14M5PC 14M10PC 14M15PC

100 95 90 85

– 5 10 15

100 100 100 100

– – – –

– – – –

20 20 20 20

40 40 40 40

56.0 58.5 63.3 62.0

7.07 8.51 8.96 7.49

fc = compressive strength at the age of 28 days (50  50  50 mm3 cube specimen). ft = flexural strength at the age of 28 days (75  75  300 mm3 rectangular specimen).

Table 4 Setting time of GPM. Symbols

6 M NaOH

10 M NaOH

14 M NaOH

Initial (min)

Final (min)

Initial (min)

Final (min)

Initial (min)

Final (min)

21 14 12 7

50 25 19 12

47 30 15 10

88 45 30 20

80 65 23 18

130 105 40 25

GPM or RM 45o

PCC substrate

zone [17]. However, the GPM with high 15% PC content and high 14 M NaOH exhibited a slight decrease in the shear bond strength. The drop in strength at high NaOH concentration was also reported by Somna et al. [10]. At high NaOH concentration, the dissolution silica and alumina was accelerated but polycondensation was hindered [26]. An excess hydroxide ion caused aluminosilicate gel precipitation at the early stage and resulted in lower strength geopolymers [27]. In addition, the dissolution of calcium was suppressed at high NaOH concentration resulting in less hydration products. According to Fig. 3, the results of 45° slant shear load carrying capacity of PCC substrate and RM were between 11.8 and 26.2 MPa with the average of 17.9 MPa comparing with those of 14.2–24.2 MPa for GPM with the average of 20.0 MPa. The mixes with 10 M and 14 M NaOH exhibited significantly higher shear bond strengths than the average of RM. This indicated that the GPM containing PC as additive can be used as an alternative repair material.

Fig. 1. Test set up of slant shear specimens.

b=75 mm

w0

Proportions

495

15 mm

l=270 mm

300 mm Fig. 2. Test set up of bending stress of PCC notched beam with filled GPM or RM specimens.

Table 6 Properties of RM.

Table 5 Mix proportions and strengths of PCC. PC (kg/m3)

PCC

aa00

3.2. Bending stress of PCC notched beam with filled GPM or RM

Components

d=75 mm

GPM or RM

15 mm

The bending stresses of PCC notched beams filled with GPM or RM are shown in Fig. 4. The bending stress of PCC notched beam

125 mm

0PC 5PC 10PC 15PC

Load

Aggregates (kg/m3) Fine

Coarse

510

938

Water (kg/m3)

238

Properties of PCC fc (MPa)

ft (MPa)

35.9

8.5

fc = compressive strength at the age of 28 days (100 mm in diameter and 200 mm in length specimen). ft = flexural strength at the age of 28 days (40  40  160 mm3 rectangular specimen).

Repair materials

Water/binder ratios

fc at 28 days (MPa)

ft at 28 days (MPa)

RM1 RM2 RM3 RM4 RM5

0.15 0.25 0.15 0.14 0.17

62.0 48.3 60.0 70.0 42.6

8.2 11.0 5.5 7.8 8.5

Remark: Water/binder ratios of RMs were based on the recommendation of manufacturer.

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Shear bond strength (MPa)

35 30

6M NaOH

10M NaOH

14M NaOH

RM

25 20 15 10 5

485

tions and high PC contents. This was due to the increase in reaction products with associated improvements of strength and bonding capacity of GPM which led to overall improvement in the bending stresses of PCC notched beams. According to Fig. 4, the notched beam filled with GPM at 10% PC and 14 M NaOH gave excellent bending stress of 3.1 MPa representing 85% improvement from the base line. The good performance with high NaOH concentration mixes could be attributed to the interaction between the NaOH and PCC substrate at the transition zone. The results of bending stress test confirmed the suitability of GPM containing PC as additive as an alternative repair material.

RM1 RM2 RM3 RM4 RM5

14M0PC 14M5PC 14M10PC 14M15PC

10M0PC 10M5PC 10M10PC 10M15PC

6M0PC 6M5PC 6M10PC 6M15PC

0

Fig. 3. Shear bond strength of GPM or RM with interface line at 45° to the vertical.

6M NaOH

10M NaOH

14M NaOH

14M0PC 14M5PC 14M10PC 14M15PC

PCC

10M0PC 10M5PC 10M10PC 10M15PC

Bending stress (MPa)

3.5

6M0PC 6M5PC 6M10PC 6M15PC

4.0 RM

3.0 2.5 2.0 1.5 1.0 0.5 RM1 RM2 RM3 RM4 RM5

Base line

0.0

Fig. 4. Bending stress of PCC notched beam with filled GPM or RM as repair materials.

without filled materials (base line) was 1.7 MPa, while those with filled materials were increased as expected. For the use of RM materials, the bending stresses were 2.1–2.8 MPa with the average of 2.3 MPa representing an average improvement of 36% from the base line. For the GPM, the bending stresses were 1.7–3.1 MPa. With the exception of mixes with low NaOH concentration (6 M) and PC content of 0% and 5%, all other mixes produced sufficiently high bending stresses especially mixes with high NaOH concentra-

3.3. Failure mode and interface zone between PCC substrate and GPM or RM The failure patterns of the slant shear prisms are shown in Figs. 5 and 6. Two failure patterns could be identified. The first was the failure in the GPM from which the cracks were formed in the GPM and the interface while the PCC substrate remained relatively intact. This occurred with the low NaOH concentration and without PC and low PC content (6M0PC and 6M5PC mixes) geopolymer mortars. For other mixes with relatively high strengths, high NaOH and high PC such as 10M10PC and 14M10PC mixes, the slant shear bond prisms failed in the monolithic mode where cracks were formed in both sections of GPM and PCC substrate. This indicated the relatively high resistance to cracking of GPM and the high bonding between the two surfaces. Thus cracks went through the slant plane resulted in monolithic type of failure. For the RM, two types of failure modes were observed. The first type, cracks were formed in the RM and the interface while the PCC substrate remained relatively intact. These were observed with the prisms with RM2, RM3 and RM5 as shown in Fig. 6. The results were in line with the low shear bond strengths of the prisms with RM2, RM3 and RM5 (Fig. 3). For the prisms with RM1 and RM4, the failures occurred in the monolithic mode as shown in Fig. 6a and d. This again indicated the relatively high resistance to cracking of RM1 and RM4 and the high bonding between the two surfaces. The results were in line with the high shear bond strengths of the prisms with RM1 and RM4 (Fig. 3). The SEM results of some of the fracture interfaces between PCC substrate and GPM or RM are shown in Fig. 7. The fracture surface of mortar with low NaOH concentration and without PC (6M0PC) as shown in Fig. 7a showed the relatively plane fracture surface between the PCC substrate and GPM indicating the clean separation of the two surfaces and the low bonding. This result corresponded to a low bending stress and low shear bond strength of

Fig. 5. Fracture surface between PCC substrate and GPM.

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Fig. 6. Fracture surface between PCC substrate and RM.

Fig. 7. SEM of interface zone between PCC substrate and GPM or RM.

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the mix with low NaOH and without PC mortar (6M0PC). The fracture interfacial zone of the mix with high NaOH and high PC mortar (10M10PC) as shown in Fig. 7b indicated that the bonding surface was still intact. The cracks passed through the PCC substrate and GPM interface, and there was no significant gap between the two bonding surfaces. For the 14M10PC mix as shown in Fig. 7c, the SEM showed a highly irregular or rugged fracture surface with no visible plane fracture surface indicating the good bonding between the two surfaces. The results confirmed the increase in shear bond strength and bending stress with high NaOH and high PC mortar and the associated monolithic failure mode as shown in Fig. 5d and e. The increase in bonding has been reported by Pacheco-Torgal et al. [17]. Also, Shi et al. [28] reported the high tensile strength ratio indicating the better bonding of alkali activated binder than that of conventional Portland cement. Furthermore, it has been reported that when recycled concrete is used, the cementing property is activated both by the alkali activation and by the calcium hydroxide presented in the residual paste [29]. Generally, geopolymer is rich in Si4+ and Al3+ ions, therefore, it can react with Ca(OH)2 at the surface of PCC substrate leading to increased strength development at the contact zone. Moreover, the increase in Ca2+ ion balanced the negative charge of Al3+ ions, which resulted in the increase in reaction products at the interface transition zone between PCC substrate and geopolymer matrix leading to a dense interface zone and high strength geopolymer. For the prism with RM1 (high shear bond and high bending strengths), the SEM result as shown in Fig. 7d indicated that the bonding surface was relatively dense with only a small gap. For the prism with RM2 (high shear bond and high bending strengths) as shown in Fig. 7e, a noticeable gap existed at the interface indicating a relatively low bonding. This corresponded well with the failure mode which cracks were formed in the RM and the interface while the PCC substrate remained relatively intact. For the prism with RM4 (high shear bond and high bending strengths), the SEM result as shown in Fig. 7f indicated that only a small gap was observed at the interface. The SEM results of RM1 and RM4 indicated the good bonding and strength of repair material and corresponded well with the monolithic failure mode. The results indicated that the performances of GPM containing PC with high NaOH concentrations as a repair material was at least equal to those of commercially available ones according to the slant shear bond test and beam notch filled bending test.

4. Conclusion The GPM with high NaOH concentration containing PC as additive material gave good performances in the shear bond strength prism test and bending stress of PCC notched beam test. The highest shear bond strength of 24.2 MPa was obtained with 14 M NaOH geopolymer with 10% Portland cement (14M10PC mix). The bending stresses of PCC notched beams with filled GPM were enhanced as expected. The GPM mix with 14 M NaOH and 10% PC gave excellent bending stress of 3.1 MPa. However, with high NaOH concentration (14 M) and high PC (15%), slight decreases in shear bond strength and bending stress were observed. The performance of GPM was found to be comparable to those of the commercial repair materials. The average shear bond strength of RM was 17.9 MPa, while that of GPM was slightly higher at 20.0 MPa. The average improvement of bending stresses of PCC notched beam with filled GPM or RM were 44% and 36%, respectively. In addition, the interface zones between PCC substrate and GPM containing PC as additive were dense and homogenous at contact zone due to the increase in reaction products. The results confirmed the finding of high bending stress and high shear bond strength of mixes with

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high NaOH and high PC. This indicates the suitability of GPM containing PC as additive for use as an alternative repair material. Acknowledgements This work was financially supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission, through the Advanced Functional Materials Cluster of Khon Kaen University; and KhonKaen University and the Thailand Research Fund (TRF) under the TRF-Senior Research Scholar Contract No. RTA5780004. The authors also would like to acknowledge Dr. Akihiro Maegawa (Mie Prefecture Industrial Research Institute, Japan) for the help with SEM analysis. References [1] J. Davidovits, Geopolymers – inorganic polymeric new materials, J. Therm. Anal. 37 (8) (1991) 1633–1656. [2] F. Pacheco-Torgal, J.A. Labrincha, C. Leonelli, A. Palomo, P. Chindaprasirt, Handbook of Alkali-Activated Cements Mortars and Concretes, Wood Head Publishing Limited – Elsevier Science and Technology, 2014. [3] P.D. Silva, K. Sagoe-Crenstil, V. Sirivivatnanon, Kinetics of geopolymerization: role of Al2O3 and SiO2, Cem. Concr. Res. 37 (4) (2007) 512–518. [4] S. Kumar, R. Kumar, S.P. Mehrotra, Influence of granulated blast furnace slag on the reaction, structure and properties of fly ash based geopolymer, J. Mater. Sci. 45 (3) (2010) 607–615. [5] P. Sukmak, S. Horpibulsuk, S.L. Shen, Strength development in clay–fly ash geopolymer, Constr. Build. Mater. 40 (2013) 566–574. [6] T. Phoo-ngernkham, A. Maegawa, N. Mishima, S. Hatanaka, P. Chindaprasirt, Effects of sodium hydroxide and sodium silicate solutions on compressive and shear bond strengths of FA–GBFS geopolymer, Constr. Build. Mater. 91 (2015) 1–8. [7] P. Chindaprasirt, T. Chareerat, S. Hatanaka, T. Cao, High strength geopolymer using fine high calcium fly ash, J. Mater. Civ. Eng. 23 (3) (2011) 264–270. [8] S. Pangdaeng, T. Phoo-ngernkham, V. Sata, P. Chindaprasirt, Influence of curing conditions on properties of high calcium fly ash geopolymer containing Portland cement as additive, Mater. Des. 53 (2014) 269–274. [9] T. Phoo-ngernkham, P. Chindaprasirt, V. Sata, S. Hanjitsuwan, S. Hatanaka, The effect of adding nano-SiO2 and nano-Al2O3 on properties of high calcium fly ash geopolymer cured at ambient temperature, Mater. Des. 55 (2014) 58–65. [10] K. Somna, C. Jaturapitakkul, P. Kajitvichyanukul, P. Chindaprasirt, NaOHactivated ground fly ash geopolymer cured at ambient temperature, Fuel 90 (6) (2011) 2118–2124. [11] D. Panias, I.P. Giannopoulou, T. Perraki, Effect of synthesis parameters on the mechanical properties of fly ash-based geopolymers, Colloids Surf., A 301 (1– 3) (2007) 246–254. [12] H.M. Abdalla, B.L. Karihaloo, Determination of size-independent specific fracture energy of concrete from three-point bend and wedge splitting tests, Mag. Conc. Res. 55 (2) (2003) 133–141. [13] P. Nath, P.K. Sarker, Use of OPC to improve setting and early strength properties of low calcium fly ash geopolymer concrete cured at room temperature, Cement Concr. Compos. 55 (2015) 205–214. [14] T. Phoo-ngernkham, P. Chindaprasirt, V. Sata, S. Pangdaeng, T. Sinsiri, Properties of high calcium fly ash geopolymer pastes containing Portland cement as additive, Int. J. Miner. Metall. Mater. 20 (2) (2013) 214–220. [15] T. Suwan, M. Fan, Influence of OPC replacement and manufacturing procedures on the properties of self-cured geopolymer, Constr. Build. Mater. 73 (2014) 551–561. [16] S. Hu, H. Wang, G. Zhang, Q. Ding, Bonding and abrasion resistance of geopolymeric repair material made with steel slag, Cement Concr. Compos. 30 (3) (2008) 239–244. [17] F. Pacheco-Torgal, J.P. Castro-Gomes, S. Jalali, Adhesion characterization of tungsten mine waste geopolymeric binder. Influence of OPC concrete substrate surface treatment, Constr. Build. Mater. 22 (3) (2008) 154–161. [18] S. Songpiriyakij, T. Pulngern, P. Pungpremtrakul, C. Jaturapitakkul, Anchorage of steel bars in concrete by geopolymer paste, Mater. Des. 32 (5) (2011) 3021– 3028. [19] C. Suksiripattanapong, S. Horpibulsuk, P. Chanprasert, P. Sukmak, A. Arulrajah, Compressive strength development in geopolymer masonsy units manufactured from water treatment sludge, Constr. Build. Mater. 82 (2015) 20–30. [20] ASTM C807, Standard Test Method for Time of Setting of Hydraulic Cement Mortar by Modified Vicat Needle, vol. 04.01, Annual Book of ASTM Standard, 2003. [21] K.E. Hassan, J.J. Brooks, L. Al-Alawi, Compatibility of repair mortars with concrete in a hot–dry environment, Cement Concr. Compos. 23 (1) (2001) 93– 101. [22] ASTM C882, Standard Test Method for Bond Strength of Epoxy-Resin Systems used With Concrete by Slant Shear, vol. 04.02, Annual Book of ASTM Standard, 2005.

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