Influence of Activator and Superplasticizer on Fly Ash-Based Geopolymer Paste and Mortar

Abstract

The cement-based binder is mostly used in concrete. However, the production of CEM-I causes a significant amount of CO2 emission in the environment and requires a lot of energy. According to Portland Cement Association (PCA), on average 927 kg of CO2 is being emitted for every 1000 kg of CEM-I produced in the U.S. Geopolymer is an innovative and environment-friendly building material and an alternative to Portland cement. The use of a geopolymer can decrease CEM-I demand and make the construction industry more sustainable. Fly ash is an industrial by-product generally produced from a coal-based power plant. The geopolymerization reaction of fly ash with an alkaline solution of NaOH and Sodium Silicate can be used as a binder for the production of eco-friendly concrete. It is evident from the literature that geopolymer mortars achieve better strength with lower water content in the mix. However, lower water content also reduces workability. This study aimed to evaluate the influence of activator concentration and commercial superplasticizers’ dose on the workability and compressive strength of fly ash-based geopolymer paste and mortar specimens. PCE-based superplasticizer was used to assess its effect on fly ash-based geopolymer paste and mortars with lowered water content. The result demonstrates the effectiveness of up to 2% dose of PCE admixture in the geopolymer system. The best results were found in the samples containing 12 M activator concentration. Higher activator concentration not only influenced the workability, but also affected other properties of geopolymer mortar. Heat curing was found effective for improving the early strengths of both geopolymer pastes and mortars. However, high temperature may introduce adverse effects in geopolymer pastes by dry shrinkage and swelling.