The effect of adding nano-SiO 2 and nano-Al 2 O 3 on properties of high calcium fly ash geopolymer cured at ambient temperature Tanakorn Phoo-ngernkham a , Prinya Chindaprasirt a,⇑ , Vanchai Sata a , Sakonwan Hanjitsuwan b , Shigemitsu Hatanaka c a Sustainable Infrastructure Research and Development Center, Dept. of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand b Program of Civil Technology, Faculty of Industrial Technology, Lampang Rajabhat University, Lampang 52100, Thailand c Dept. of Architecture, Faculty of Engineering, Mie University, Mie 514-8504, Japan article info Article history: Received 10 August 2013 Accepted 21 September 2013 Available online 29 September 2013 Keywords: Geopolymer Nano-SiO 2 Nano-Al 2 O 3 Compressive strength Flexural strength Shear bond strength abstract This article presents the effect of adding nano-SiO 2 and nano-Al 2 O 3 on the properties of high calcium fly ash geopolymer pastes. Nano-particles were added to fly ash at the dosages of 0%, 1%, 2%, and 3% by weight. The sodium hydroxide concentration of 10 molars, sodium silicate to sodium hydroxide weight ratio of 2.0, the alkaline liquid/binder ratio of 0.60 and curing at ambient temperature of 23 °C were used in all mixtures. The results showed that the use of nano-SiO 2 as additive to fly ash results in the decrease of the setting time, while the addition of nano-Al 2 O 3 results in only a slight reduction in setting time. Adding 1–2% nano-particles could improve compressive strength, flexural strength, and elastic modulus of pastes due to the formation of additional calcium silicate hydrate (CSH) or calcium aluminosilicate hydrate (CASH) and sodium aluminosilicate hydrate (NASH) or geopolymer gel in geopolymer matrix. In addition, the additions of both nano-SiO 2 and nano-Al 2 O 3 enhances the shear bond strength between concrete substrate and geopolymer. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction At present, geopolymer is getting more attention as an alterna- tive binder to normal cement binders for applications in concrete industry [1,2]. It is made from rich silica and alumina source mate- rials such as fly ash, calcined kaolin, and blast furnace slag. In Thai- land, the major source of fly ash is Mae Moh power station in the north. Approximately 3 million tons is produced annually and it is used mainly as supplementary cementitious materials to replace of Portland cement in construction industry. Many researchers have shown that it can also be used as starting material for making good geopolymer [3,4]. Geopolymeric reaction relies on the activation with alkali solu- tions and temperature curing at 40–75 °C [3,5]. The obtained geo- polymer paste possesses similarly strength and appearance to normal Portland cement paste. However, when fly ash geopolymer material is cured at ambient temperature of around 25 °C, the strength development is rather slow and low strength is obtained [6]. Many researchers have tried to improve the strength develop- ment of fly ash geopolymers [7,8]. Khater et al. [9] and Riahi and Nazari [10] reported that the compressive strength of geopolymer depends on the type of starting material and its fineness. The fine particles induce higher leaching of silica and alumina in the alkali environment and leads to a higher strength geopolymer [3]. Recently, nanoparticle is receiving more attention as an alterna- tive binder used for the improvement of nanostructure of building materials [9]. Nano-SiO 2 and nano-Al 2 O 3 are most commonly used [11] to enhance compressive and tensile strengths of concrete by additional pozzolanic and filler effects [12]. The nano-SiO 2 particle belongs to highly pozzolanic materials because it consists essen- tially of SiO 2 in amorphous form with a high specific surface, there- fore, exhibits great pozzolanic activity [13]. This research aims to study the properties and application of geopolymer paste made from high calcium fly ash containing nano-SiO 2 and nano-Al 2 O 3 . The obtained results should be very beneficial to the understand- ing and to the future applications of the materials. 2. Experimental details and testing analysis 2.1. Materials The materials used in this study were high calcium fly ash (FA) from Mae Moh power plant in northern Thailand, nano-SiO 2 (S), and nano-Al 2 O 3 (A). The liquid portions in the mixture were 10 M sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3 ) with 13.89% Na 2 O, 32.15% SiO 2 , and 46.04% H 2 O. The chemical composition and physical properties of FA are shown in Tables 1 and 2. The FA had specific gravity, Blaine 0261-3069/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2013.09.049 ⇑ Corresponding author. Tel.: +66 4320 2355; fax: +66 4320 2355x12. E-mail address: prinya@kku.ac.th (P. Chindaprasirt). Materials and Design 55 (2014) 58–65 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes