Investigation of drying shrinkage, water absorption and strength properties of metakaolin based geopolymer mortars

Abstract. This paper investigates strength and selected durability properties (drying shrinkage and water absorption) of metakaolin-based geopolymer mortar (GPm). Four geopolymer mixes of different proportions are prepared using metakaolin as precursor with sodium hydroxide and sodium silicate as activators. The ratio of alkaline activator to precursor, the ratio between activators Na2SiO3 to NaOH and the curing temperature, varied (1.2, 1.4), (2, 3), (30, 45, and 60°C) respectively between these mixes to assess their influence on the properties. Geopolymer mortar exhibited significant improvement in shrinkage and compressive strength with values of 482µm/m and 35 MPa compared to ordinary Portland cement-based mortar (OPCm) that shows results equal to 1820µm/m and 15 MPa respectively. A significant disparity in the performance of GPm mixes is observed, which refers to the variation of the ratios and of the oven curing temperature between mixes. Results reveal that the optimum alkaline to binder ratio should be first considered to obtain a dense mortar structure. For a more complete geopolymerization, the increase of alkaline activator content should be coupled with an increase in curing temperature to block any successive dissolution.