Effects of Sodium Silicate Proportion on Strength Development of Calcined Clay Geopolymer Mortar

Geopolymers are derived from the synthesis of reactive alumino silicate source with alkali metal source to produce a binder that has lower carbon footprint compared to the traditional Portland cement. The long-term supply of precursors for geopolymers in the UK will be difficult to secure based on the dominant used materials – PFA, GGBS and white Metakaolin. Iron rich lateritic clay may offer a good alternative due to its low embodied energy and abundance. In this study, seven mixes were designed and tested. The first five mixes were based on varying the molar oxide ratios of the mortar mixes by activating the flash calcined lithomarge clay with different proportions of 54.5% Na2SiO3 solution. The last two mixes were grouts based on different water to
geopolymer solid ratios. The important characteristics of the fresh and hardened mortars that were investigated based on the relevant standards are: strength development, setting times, UPV and rheological properties. The mix that achieved the peak strength of 30 MPa at 28 days cured under sealed
condition has molar oxide ratios - SiO2/Al2O3, Na2O/Al2O3, Na2O/SiO2 and H2O/Na2O of 4.12, 1, 0.24 and 14.1 respectively. The results also showed that a more controllable and consistent rheology was achieved by increasing the water to geopolymer solid ratio of the grout.