Mechanical properties and microstructures of hypergolic and calcined coal gangue based geopolymer recycled concrete

Abstract

The geopolymer recycled concrete specimens were produced by using hypergolic or calcined coal gangue, slag, fly ash and recycled aggregate as the raw materials. Five different ratios of recycled coarse aggregate to total coarse aggregate and two types of geopolymer recycled concrete schemes (hypergolic coal gangue and calcined coal gangue respectively) were designed for specimen preparation. The compressive strength and splitting tensile strength of the specimens were studied, and the microstructure of the specimens was analyzed by scanning electron microscopy. It is demonstrated by the mechanical property test that the compressive and splitting tensile strength first drop and then grow with the increased mixing ratio of recycled coarse aggregate when the turning point occurs at the mixing ratio of about 30–50%. The microstructure analysis shows that the key factors affecting the mechanical properties of the recycled concrete include the internal porous structure, micro-cracks and the interface bonding ability between geopolymer and recycled coarse aggregate.