Strength and setting times of Metakaolin-Cement-Based geopolymer pastes

Abstract

The objective of this research is, in a first time, to synthesize geopolymer materials from two types of activator concentrated solutions prepared respectively with two different bases (NaOH and KOH). These solutions have been mixed thereafter with a kaolin previously heated under 550°C in order to obtain geopolymers samples, while optimizing the Si/Al ratio. Secondly, the influence of the partial substitution of metakaolin by a Portland cement has been studied in order to reduce the curing time of geo-polymer pastes. Thereafter, mechanical properties of the specimens at hardened state, notably the compressive strengths and the resistances on traction are investigated. The results showed that the use of the activator solution containing KOH during the preparation of the activator solution increases the solubility between KOH and silica gel. However, the solution based on sodium hydroxide (NaOH) promotes obtaining better mechanical resistances in the geopolymer materials. Otherwise, the partial substitution of metakaolin by Portland cement (PC) reduces the setting time of pastes and improves the mechanical resistances of hardened specimens but to a certain percentage before inverse effect appears. Finally, recommendations and perspectives are proposed in relation with the used raw materials and the mechanical performances of the geo-polymers materials found