Compressive and flexural behavior of alkali-activated slag-based concrete: Effect of recycled aggregate content

Alkali-activated concrete (AAC) is a more eco-friendly alternative than conventional concrete since its production does not need cement. As a majority of the concrete volume is consumed by aggregates, there is a need to reduce the utilization of natural aggregates thereby reducing the exploitation of natural resources. This paper deals with the effect of recycled concrete aggregate (RA) content on the compressive and flexural behavior of slag-based AAC. The compressive stress-strain behavior (i.e., failure pattern, compressive strength, peak strain, elastic modulus and toughness) and flexural properties were studied. Finally, the carbon emissions and cost effectiveness of AAC with various RA contents were assessed. The results show that all the concrete specimens under both compression and flexure exhibit brittle failure modes due to the poor aggregate-matrix interfacial transition zones. The addition of RA weakens the flexural properties of concrete. However, as the RA content changing from 0% to 100%, the compressive properties of peak strength, elastic modulus and toughness exhibit a first slight increase and then decrease trend. The RA content in AAC can reach 75% to achieve the same compressive strength compared to plain concrete due to the excellent dense structures. Based on the test results in current study and literature, an empirical analytical model is developed to generate the compressive stress-strain curve of AAC with various RA contents.