Compressive strength of geopolymer concrete with fly-ash from Paiton Steam Power Plant and variations of substitution sodium silicate (Na2SiO3) with natural zeolite

Geopolymer concrete is one of the technological innovations of concrete without cement. It was prepared using fine aggregates, coarse aggregates, fly-ash, sodium hydroxide (NaOH), and sodium silicate (Na2SiO3). In the production of geopolymer concrete, sodium silicate and sodium hydroxide serve as an alkaline activator. One of the natural materials that can be used as an alternative material is natural zeolite. Zeolit contains high silica and alumina, that expected to increase the compressive strength of geopolymer concrete. This research aims to develop geopolymer concrete technology by understanding the setting time behaviour and compressive strength by substitution sodium silicate (Na2SiO3) with natural zeolite. The percentage of zeolite that substitute for sodium silicate is 0%, 2.5%, 5%, and 7.5 %. The molarity of NaOH is 12 M. Meanwhile, the ratio of sodium hydroxide and sodium silicate is 1:2.5. Compressive strength testing is carried out on cylindrical specimens 10 cm × 20 cm. The results show that natural zeolite can accelerate the setting time of geopolymer paste. The fastest initial setting time is 48 minutes. Meanwhile, the final setting time is 60 minutes in geopolymer paste with substitution sodium silicate using 7.5 % zeolite. In addition, for compressive strength results, zeolite can increase compressive strength. The highest average of compressive strength results is 46.07 Mpa in substitution of Na2SiO3 with 7.5 % zeolite.