Effect of aggregate properties on the mechanical and absorption characteristics of geopolymer mortar

Even though aggregate constitutes major volume in geopolymer concrete, only limited study related to this parameter has been reported. This paper presents the summary of study carried out to understand the influence of aggregate content and grading on the mechanical and absorption characteristics of geopolymer mortar. Three types of aggregates, namely, natural river sand, crushed limestone, and combined sand-limestone were used in geopolymer mortar. Fly ash was used as source material. Effectiveness of aggregates was evaluated in terms of the workability, fresh unit weight, absorption and strength of geopolymer mortar. The alkaline activator is a mix of 12 molarity of NaOH solution with Na2SiO3 in ratio of 1:2.5. The experiments were performed on geopolymer mortar cubes under curing temperatures of 90 °C with curing period of 24 h. Test results indicate that geopolymer mortar including natural sand shows better flowability compared to other aggregates, moreover, coarse grading of sand caused higher flow. The highest compressive and splitting tensile strength was obtained in crushed limestone. The combined sand-limestone shows the lowest water absorption and sorptivity compared with other types of aggregates.