Effect of geopolymer paste on compressive strength, water absorption and porosity

Abstract

This paper presents the effect of geopolymer paste on the compressive strength, water absorption and porosity. Fly ash is a waste materials produced by combustion of coal at power plant. Fly ash were mixed with alkaline activators that are sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions. The alkaline activator was prepared 24 hours prior to use with the ratio of the mixture of NaOH/Na2SiO3 is 2.5 to 1. The mixture are placed in cylinder mould, compacted and kept in the mould for 24 hours until it hardened and and cured at 60 °C in the oven for 24 hours. The sample were then left for 7, 14 and 28 days before it be tested. It was observed that the fly ash geopolymer paste sample had a optimum results. The compressive strength value for 28 days was 53.92 MPa and the value of water absorption were 0.003 % and porosity were 1.829 %. The pore size decreases and the structures became denser. The porosity and permeability also decreased hence the strength potentially improved.