The Comparison of the Properties of Geopolymer Paste and Ordinary Portland Cement Mortar Produced Using Polycarboxylate Based Admixture

Abstract

Chemical admixtures are generally used in ready mixed concrete production to improve and enhance the concrete properties. Polycarboxylate based superplasticizers are classified as third generation plasticizing admixtures which increase fluidity and workability without decreasing compressive strength. Geopolymers having many superior properties are alternative materials to ordinary Portland cement concrete. Geopolymers are environmentally friendly and sustainable materials because they can be synthesized from waste materials such as fly ash. In this experimental study, geopolymer pastes were produced by using fly ash, 10 M sodium hydroxide, sodium silicate solution and plasticizer. Cement mortars were produced according to TS EN 196-1 standard. Polycarboxylate based plasticizers synthesized at laboratory conditions were used at 1% by weight in both ordinary Portland cement mortar and geopolymer paste. Geopolymer samples were aged for 7 and 28 days at laboratory conditions while cement mortars were aged in water bath. The fluidity values of fresh mixtures were determined. The flexural strength and compressive strength tests were conducted at the ages of 7 and 28 days. The plasticizers had positive effects on cement mortars but unfavorable results on geopolymer. The use of plasticizer increased the fluidity and the strength values in mortars, on the contrary, admixtures caused decrease in the values of geopolymer samples. The highest compressive strength was obtained as 38.3 MPa for mortar sample aged for 28 days and was 15.3 MPa for geopolymer samples.