Effect of silica fume on the characterization of the geopolymer materials

International Journal of Advanced Structural Engineering, Aug 2013

The influence of silica fume (SF) addition on properties of geopolymer materials produced from alkaline activation of alumino-silicates metakaolin and waste concrete produced from demolition works has been studied through the measurement of compressive strength, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM) analysis. Alumino-silicate materials are coarse aggregate included waste concrete and fired kaolin (metakaolin) at 800°C for 3 h, both passing a sieve of 90 μm. Mix specimens containing silica fume were prepared at water/binder ratios in a range of 0.30 under water curing. The used activators are an equal mix of sodium hydroxide and silicate in the ratio of 3:3 wt.%. The control geopolymer mix is composed of metakaolin and waste concrete in an equal mix (50:50, wt.%). Waste concrete was partially replaced by silica fume by 1 to 10 wt.%. The results indicated that compressive strengths of geopolymer mixes incorporating SF increased up to 7% substitution and then decreased up to 10% but still higher than that of the control mix. Results indicated that compressive strengths of geopolymer mixes incorporating SF increases up to 7% substitution and then decreases up to 10% but still higher than the control mix, where 7% SF-digested calcium hydroxide (CH) crystals, decreased the orientation of CH crystals, reduced the crystal size of CH gathered at the interface, and improved the interface more effectively.

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Effect of silica fume on the characterization of the geopolymer materials

Hisham M Khater 0 0 Housing and Building National Research Centre (HBNRC) , 87 El-Tahreer St., Dokki, Giza, P.O. Box 1770, Cairo, Egypt The influence of silica fume (SF) addition on properties of geopolymer materials produced from alkaline activation of alumino-silicates metakaolin and waste concrete produced from demolition works has been studied through the measurement of compressive strength, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM) analysis. Alumino-silicate materials are coarse aggregate included waste concrete and fired kaolin (metakaolin) at 800C for 3 h, both passing a sieve of 90 m. Mix specimens containing silica fume were prepared at water/binder ratios in a range of 0.30 under water curing. The used activators are an equal mix of sodium hydroxide and silicate in the ratio of 3:3 wt.%. The control geopolymer mix is composed of metakaolin and waste concrete in an equal mix (50:50, wt.%). Waste concrete was partially replaced by silica fume by 1 to 10 wt.%. The results indicated that compressive strengths of geopolymer mixes incorporating SF increased up to 7% substitution and then decreased up to 10% but still higher than that of the control mix. Results indicated that compressive strengths of geopolymer mixes incorporating SF increases up to 7% substitution and then decreases up to 10% but still higher than the control mix, where 7% SF-digested calcium hydroxide (CH) crystals, decreased the orientation of CH crystals, reduced the crystal size of CH gathered at the interface, and improved the interface more effectively. - Introduction Silica fume (SF) known as micro-silica is a by-product of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys. Because of its extreme fineness and high silica content, silica fume is a highly effective pozzolanic material. Silica fume is used in concrete to improve its properties like compressive strength, bond strength, and abrasion resistance; it reduces permeability and therefore helps in protecting the reinforcing steel from corrosion. Silica fume has been used as a high pozzolanic reactive cementitious material to make high-performance concrete in the severe conditions (Kohno 1989; Gautefall 1986). This mineral admixture has highly been used in severe environmental conditions despite its several mixing and curing problems because of its acceptable early-age strength development (Cheng-Yi and Feldman 1985; Grutzeck et al. 1983). The hydration mechanism and properties of secondary C-S-H made by pozzolanic reaction have been studied by many investigators (Cheng-Yi and Feldman 1985). However, CSH formed by silica fume-calcium hydroxide reaction might be different with respectto the amount of molecular water, C/S ratio, and density (Cohen and Bentur 1988). Moreover, because of its rather different characteristics, pozzolanic gel has a high potential to contribute in reactions with other internal or external ions such as Al, Cl, and alkalies (Maage 1989; Sellevold and Nilsen 1987). On the other hand, the search for a new environmentally friendly construction material that will match the durability of ancient concrete has provoked interest into the study of alkali-activated cementitious systems over the past decades. Alkali-activated cements refer to any system that uses an alkali activator to initiate a reaction or a series of reactions that will produce a material that possesses cementitious property (Yip et al. 2005). Alkali-activated cement, alkali-activated slag and fly ash, and geopolymers are all considered to be alkaliactivated cementitious systems; however, it is expected that the structures of these materials are vastly different and result from different chemical mechanistic paths. It is commonly acknowledged that calcium silicate hydrate (CSH) is the major binding phase in Portland cement (Taylor 1964) and alkali-activated slags (Richardson and Cabrera 2000); however, the binding property of geopolymers is generally assumed to be the result of the formation of a three-dimensional amorphous aluminosilicate network (van Jaarsveld and van Deventer 1999a; Davidovits 1991; Phair and van Deventer 2002; Lee and van Deventer 2002). The production of geopolymeric precursors is carried out by calcinations of aluminosilicates, natural clay materials. Their source can be also some industrial aluminosilicate waste materials. The result of the hardening mechanism is a three-dimensional zeolitic framework, unlike traditional hydraulic binders in which hardening is the result of the hydration of calcium aluminates and silicates (Davidovits 1991; Phair and van Deventer 2002; Lee and van Deventer 2002; Davidovits 1993); this circumstance is a cause of significant differences in the quality and variety of the engineering properties of the composites based on geopolymer and current cements. As a means of converting waste materials to useful p (...truncated)


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Hisham M Khater. Effect of silica fume on the characterization of the geopolymer materials, International Journal of Advanced Structural Engineering, 2013, pp. 12, Volume 5, Issue 1, DOI: 10.1186/2008-6695-5-12