Mechanical Properties and Durability Aspects of Alkali-activated Fly Ash Mortars With and Without Addition of Blast Furnace Slag
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The production of ordinary Portland cement (OPC) is associated with large emissions of greenhouse gasses. Alkali-activated materials (AAMs), including the subset named geopolymers, are alternative binders with lower associated emissions. AAMs and OPC have a fundamentally different chemistry, making studies on the durability properties of the binder types relevant. In this thesis, mechanical properties and durability aspects of AAMs and geopolymers have been studied. Researched properties were compressive strength, porosity, fire resistance, chemical resistance, and autogenous shrinkage. The binders studied were alkali-activated blast furnace slag-fly ash (AASFA) blends, fly ash (FA) geopolymers and OPC. Through the comparison of AASFA blends produced with two different SiO2/Na2O ratios (1.27 versus 3.31), the effect of alkalinity in these blends was researched. The results revealed that lowered alkalinity yields a binder with poor mechanical properties, reaching only 1.4 MPa in 28 days. In contrast, high alkalinity yielded 87 MPa, which clearly demonstrated its importance. The results further showed that the FA geopolymer had superb fire resistance up to 1000 °C.However, OPC was the only binder to maintain its original geometry after exposure to 1200 °C. All other binders were partially or completely deformed. Lastly, the FA geopolymer had very low autogenous shrinkage when compared to OPC. In conclusion, the study has shown that AAMs and geopolymers may serve as suitable alternatives to OPC in regard to certain durability concerns.However, AAMs still face some problems compared to OPC, in particular in the production phase.