Performance of Geopolymer Mortar Using Developed Dry Geopolymer-cement by a Combination of Alkaline Solid Activators

Abstract

This experimental study investigates the possibility of using a combination of solid activators to produce dry powder geopolymer cement. Fly ash (FA) and/or ground granulated blast furnace slag (GGBS) were employed as precursors. Sodium metasilicate pentahydrate (NSP), calcium hydroxide (CH) and sodium carbonate (NC) were used as alkaline solid activators. Meanwhile, the effect of using a combination of solid activators to prepare one-part geopolymer mortars was studied by using three different curing methods and compared with the traditional corrosive alkali solutions that are used as activators in two-part geopolymer mortar, and also compared with Portland cement (PC) mortar mix. Fresh properties were assessed using flowability and setting times, while to evaluate hardened properties of geopolymer mixes, compressive, flexural, splitting tensile strengths, and modulus of elasticity were investigated in addition to scanning electron microscopy (SEM). The test results indicate that the replacement of GGBS by FA increases the flowability and the setting times and decreases the strength and modulus of elasticity of one-part geopolymer mortars. At 28 days, one-part geopolymer mortar achieved compressive, flexural and splitting tensile strengths of 43 MPa, 5.90 MPa and 3.70 MPa, respectively; when the geopolymer precursor was composed of 100% GGBS and activated by a combination of NSP (16%), CH (4%) and NC (4%), while these values are 41 MPa, 5.43 MPa and 4.32 MPa after 28 days, in which the two-part geopolymer mortar with GGBS was activated with sodium silicates (NS) and sodium hydroxide (NH) at (NS/NH ¼ 1.5). Finally, SEM supported these results, as it showed that the mixtures with GGBS had less microcracks comparison with FA and PC mixtures.