The Effect of Natrium Hydroxide Molarity Variation and Alkali Ratio on the Compressive Strength of Geopolymer Paste and Mortar

Abstract

Geopolymers have great potential to replace conventional cementitious materials and are classified as green materials. Their main constituents are silica (Si) and aluminum (Al), which can be found in the fly ash material from industrial processes of the PLTU. The parameters that affect the strength of the concrete are influenced by the molarity of natrium hydroxide and the ratio of alkalis (NaOH/Na2SiO3). This study examined the characteristics of the geopolymer paste and mortar specimens. Furthermore, mixture composition was carried out using the weight ratio method. The mortar produced consists of 65% fine aggregate and 35% paste, while the pasta contains 60% fly ash and 40% alkaline solution. The molarities of NaOH used were 8M, 10M, 12M, and 14M with a base ratio of 1.5, 2, and 2.5 Na2SiO3/NaOH. The curing of specimens was carried out with the humid temperature method. The results showed that the highest compressive strength of geopolymer paste and mortar was obtained at 12M NaOH molarity with an alkaline ratio of 2.5, namely 12.59 MPa and 21.75 MPa at 28 days, respectively. NaOH of more than 12M can cause a decrease, while the base ratio of 2.5 has the highest strength. The results also showed that the higher the molarity of NaOH and the greater the alkaline ratios, the longer the setting time.