Effect of superplasticizers on properties of one-part Ca(OH)2/Na2SO4 activated geopolymer pastes

Abstract

This paper investigates the effect of three different superplasticizers (SPs), Naphthalene (N), Melamine (M) and Polycarboxylate (PC), on the properties of one-part fly ash/slag geopolymer pastes activated by Ca(OH)2/Na2SO4 powder combination. The flowability, setting time, and compressive strength of the achieved geopolymer pastes were assessed. It was found that the superplasticizers significantly improved the flowability, retarded the setting time, and increased the compressive strength of the one-part Ca(OH)2/Na2SO4 geopolymer pastes. The most recommended superplasticizer was found to be polycarboxylate.The use of polycarboxylate SP for decreasing the water content (i.e. w/b) in Ca(OH)2/Na2SO4 geopolymer pastes has resulted in reducing the porosity and enhancing the compactness of the aluminosilicate gel, therefore, improved the compressive strength. It was found that the excessive use of polycarboxylate (i.e. 3%) for additional water reduction in Ca(OH)2/Na2SO4 geopolymer pastes had an adverse effect; it extended the induction period and delayed the participation of reaction products, thus significantly prolonged the setting time.Furthermore, a comparison between the achieved Ca(OH)2/Na2SO4 geopolymer pastes and the conventional Na2SiO3-anhydrous one-part geopolymer pastes was carried out. It was found that Ca(OH)2/Na2SO4 geopolymer exhibited significantly lower compressive strength, higher flowability and considerably longer setting time compared to Na2SiO3 geopolymer. Hence, such binder can be implemented as a green non-structural material.