Recycled geopolymer aggregates as coarse aggregates for Portland cement concrete and geopolymer concrete: Effects on mechanical properties

Abstract

The available literature on recycling of geopolymer concrete is currently limited to application of recycled geopolymer aggregates as coarse aggregates for new geopolymer concrete. This paper highlights an alternative waste management strategy for geopolymer concrete construction and demolition waste by illustrating the suitability of recycled geopolymer aggregates for full or partial replacement of coarse natural aggregates in the widely used Portland cement concrete. The properties of Portland cement concrete and geopolymer concrete made with varying contents of coarse geopolymer recycled aggregates (0%, 20%, 50% and 100% coarse natural aggregates replacement) are investigated and compared with those of Portland cement concrete containing recycled Portland cement concrete aggregates. The results indicate that up to 20% replacement of coarse natural aggregates with recycled geopolymer concrete aggregates results in only insignificant reductions in the modulus of elasticity, flexural strength and volume of permeable voids as well as a moderate reduction in compressive strength of Portland cement concrete. The negative effects of varying amounts of recycled geopolymer concrete aggregates on the properties of Portland cement concrete is however found to be slightly more significant than those caused by same proportions of recycled aggregates produced from Portland cement concrete waste. Furthermore, incorporation of coarse recycled geopolymer concrete aggregates is found to lead to more significant negative effects on properties of Portland cement concrete than geopolymer concrete. These include respectively 21%, 8.3% and 3.4% further reductions in compressive strength, modulus of elasticity and flexural strength of RAGC compared to RAG at 100% coarse aggregate replacement ratio, highlighting a higher compatibility between geopolymer recycled aggregates and geopolymer binder than Portland cement binder.