Performance of Self-Compacted Geopolymer Concrete Containing Fly Ash and Slag as Binders

Geopolymers can replace cement and help reduce the environmental impact of concrete construction, but research is needed to ensure their mechanical properties, durability and practicability. The aim of this investigation is to examine the influence of ground granulated blast furnace slag (slag) content on the performance, at the fresh and hardened states, of fly ash (FA) based self-compacted geopolymer concrete (SCGC). For this purpose, four SCGC mixtures containing 450 kg/m3 of total binder were examined. The alkaline-to-binder ratio was 0.5 for all mixes. FA was substituted with slag at 0%, 30%, 50%, and 100% of the total binder content. The fresh properties in terms of flowability, passing ability, viscosity, and segregation resistance, as well as the mechanical properties in terms of compressive strength and splitting tensile strength, were quantified. The durability behavior of SCGC was also studied to determine sorptivity and long-term free drying shrinkage. The results confirm that slag adversely affects the workability of SCGC mixtures except for the resistance to sieve segregation. Performance of SCGC in hardened states is in general enhanced with slag inclusion but at increased shrinkage strain. Predictions of splitting tensile strength were made using the ACI 318, ACI 363, Eurocode CEB-FIB, and Lee and Lee models. The ACI 363 and Eurocode CEB-FIB models were found to be inaccurate, except for the 30% slag mix. Predicted values obtained from the Lee and Lee model were very close to the actual values of the FA-based SCGC mix. The results of this work could lead to more sustainable concretes using geopolymers instead of OPC