A simplified mix design procedure for geopolymer cement mortars based on metakaolin and industrial waste products activated with potassium silicate

This paper presents a mix design methodology for geopolymer mortars based on metakaolin and industrial waste products activated using potassium silicate. The work is aimed at enabling performance-based specification and compressive strength prediction to drive forward their adoption as an alternative to Portland cement-based mortars used in fibre reinforced cladding systems. Few studies currently quantify the effects of mix parameters on broad families of geopolymer materials and no standard mix design methodology exists. Resultant mortars must have high strength to create light, thin panels, have high flow to enable effective dispersal of reinforcement fibres and as low an environmental impact as possible to maximise the impact of replacement. For a standard geopolymer mix, the effect of binder composition on mechanical performance and environmental impact is initially studied using ternary contour maps for a range of material blends. Next, the effects of altering mixture parameters such as the liquid/solid, silica/alumina and activator/binder ratios are quantified for three binder compositions identified as having high performance. Finally, correlation analysis is used to identify mix variables strongly correlating with compressive strength and regression analysis of the most deterministic to create a prediction models. Geopolymer mortars have been developed with compressive strengths over 80 and 100 N/mm2 at 7 and 28 days respectively and the methodology presented allows design of such mortars by non-experts. Model predictions of compressive strength is shown to be relatively accurate, with average errors across binder compositions ranging from 2.3-5.8%. Further research expanding the range of materials and mix compositions is ongoing to advance this innovative methodology further.