Study on workability and mechanical strength of low cement ultra-high performance concrete with ultrafine quartz powder as alternative material under high temperature curing

High CO2 emission has been a key issue that needs to be addressed for the widespread use of ultrahigh performance concrete (UHPC). In this study, low cement UHPC was prepared by using ultrafine quartz powder (UQP) as a replacement material for cement, and the effects of UQP on workability and mechanical strength were investigated. The TG, XRD, MIP, and SEM methods were used to study the effects of UQP on hydration products and pore structure of UHPC. Results showed that the addition of UQP reduced the fluidity, shortened the setting time, and increased the drying shrinkage of UHPC. Under high temperature curing, when the amount of cement replaced by UQP was 15%, the maximum compressive strength of UHPC at 7 d reached 147.9 MPa. Meanwhile, the compressive strength of UHPC at 7 d was still as high as 132.8 MPa when the amount of cement replaced by UQP was 75 %. Under high temperature curing, Ca(OH)2 in UHPC reacted with UQP to produce more C-S-H resulting in a decrease in total porosity and an increase in gel pores of UHPC. Under the simultaneous guarantee of mechanical properties and sustainability of UHPC, the replacement of cement by UQP for the preparation of UHPC can reduce the consumption of cement to 188 kg/m3.