Study on Compressive Strength of Geopolymer Mortar Based on Fly Ash and GGBFS with Various Molar Variations

The high production and demand for portland cement in the world can trigger even greater emissions produced by the cement industry which are expected to continue to increase. This can happen because the cement production process produces CO2 gas emissions into the air which are equivalent to the amount of portland cement produced, thus triggering the greenhouse effect. Therefore, the application of geopolymers into cement and concrete contributes greatly to reducing CO2 emissions and the greenhouse effect. This research examines the mechanical properties and morphological characteristics of geopolymer mortar based on fly ash and GGBFS with various variations of NaOH molarity which was cured at room temperature (25 °C) for 28 days. In addition to mortar, the fly ash used was also tested for microstructural characteristics. In this research, 165 samples were made in the form of geopolymer mortar with composition variations between fly ash and GGBFS at various NaOH molarity. Mechanical test that carried out was in the form of mortar compressive strength test. In addition, microstructural characteristics was also tested on fly ash and mortar with the highest compressive strength. The results of the mechanical mortar test showed that the highest compressive strength was 92 MPa that was obtained from FG19 mortar (fly ash 10%, GGBFS 90%) with NaOH molarity of 10 and 12 M. The results of the characteristic research of fly ash showed that fly ash was classified as class C and had a crystalline structure. The microstructural characteristics test results of the FG19 mortar with 12 M variation showed that the mortar had cracks and voids. However, the Al, Si, Na, and K elements were evenly distributed so that the mortar mixed homogeneously.