Recycled aggregate high calcium fly ash geopolymer concrete with inclusion of OPC and nano-SiO2

In this study, the use of ordinary Portland cement (OPC) and nano-SiO2 (nS) to improve the mechanical and durability properties of recycled aggregate geopolymer concrete (RAGC) was evaluated. The results indicated that the inclusion of OPC enhanced the compressive strength and reduced the water absorption, porosity, as well as the penetration of chloride. Moreover, the concrete with 15% OPC-fly ash blend mixture exhibited the highest compressive strength of 48.7 MPa, which was 38% higher than that of natural aggregate geopolymer concrete (NAGC). It was also found that the addition of nS showed a great potential to strengthen the mechanical properties of RAGC. With 1% nS added, the compressive strength of RAGC was significantly higher than those of NAGC.