The engineering properties and microstructure of sodium carbonate activated fly ash/ slag blended mortars with silica fume

Highly concentrated and corrosive alkaline activators are often used for activating polycondensation reactions of aluminosilicate minerals in geopolymers at elevated temperatures. This study investigated the interaction between Pulverised Fuel Ash (PFA), Ground Granulated Blast Furnace Slag (GGBS) and Silica Fume (SF) activated with small dosages of low alkalinity sodium carbonate and sodium silicate. Tests were inclusive of assessments on the consistency and setting behaviours, mechanical strengths and microstructure properties. Results were compared with Ordinary Portland Cement (OPC) mortars and sodium hydroxide activated geopolymer mortars which were established through an existing study. The mechanical strength of sodium carbonate activated geopolymer was found to be comparable with that of the sodium hydroxide activated geopolymer. Geopolymer mortars with 4% of silica fume exhibited the highest mechanical strength. The sodium carbonate activated binder system comprised largely of an interconnected calcium carbonate crystals framework and C-A-S-H gels.