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Effect of sodium hydroxide and sodium silicate solutions on strengths of alkali activated high calcium fly ash containing Portland cement

ABSTRACT

In this paper, the mechanical performance of fly ash and Portland cement geopolymer activated with sodium hydroxide and sodium silicate solutions was studied. The Geopolymer Mortars (GM) were made from high calcium Fly Ash (FA) and ordinary Portland Cement (PC) with FA:PC weight ratios of 100:0, 95:5, 90:10, 85:15, and 80:20. The GMs were activated with three combinations of sodium Hydroxide Solution (SH) and sodium Silicate Solution (SS) viz., SH, SH+SS (SH:SS=2) and SS. For all mixes, 10 molar SH, alkali activator liquid/solid binder ratio of 0.60 and curing at ambient temperature of 25oC were used. The result indicated that the compressive and shear bond strengths of GM depended on the alkali activators used and the amount of PC. The use of SH and SHSS resulted in the formation of additional Calcium Silicate Hydrate (CSH) which coexisted with sodium aluminosilicate hydrate (NASH) gel. Whereas, the use of SS resulted in NASH gel with only a small amount of CSH. The increasing of PC content enhanced the compressive and shear bond strengths of GMs due to the formation of additional CSH. The 15% PC mixed with SHSS gave the optimum compressive and shear bond strengths.