A comparative study on mechanical properties and environmental impact of UHPC with belite cement and portland cement

Developing an eco-friendly UHPC with Belite cement (BC) is a great challenge because the mechanical strength of concrete with BC develops much more slowly than Ordinary Portland cement (alite-rich cement, OPC). However, BC has a lower CO2 footprint than OPC due to a lower calcined temperature and less limestone demand, making it green cement. Besides, concrete with BC has better long-age performance. In this study, the utilization of BC in UHPC was compared to that of OPC. Three curing regimes were used for the designed UHPC. The compressive and flexural strengths of UHPC-BC are lower than of UHPC-OPC at one day but higher after 28 and 90 days of standard curing. After heat curing, the mechanical strength development of UHPC-BC improves noticeably and exceeds UHPC-OPC. UHPC-BC has a higher flexural strength to compressive strength ratio (ff/fcu), and there are more C-S-H, less CH and lower pore coarsening of UHPC-BC paste than UHPC-OPC, especially after heat curing. UHPC-BC has lower environmental impact indices at long age than UHPC-OPC. At 90 days of autoclaved curing, the compressive of UHPC-BC reaches up to 197.5 MPa with the embodied carbon content of 934.37 kg/m3, which is much lower than most UHPCs.

Automated summary

Developing an eco-friendly UHPC with Belite cement is a challenge due to slower mechanical strength development compared to Ordinary Portland cement. However, BC has a lower CO2 footprint and better long-term performance. Comparing with OPC, UHPC-BC shows lower strength at early ages but higher strength after 28 and 90 days of curing. The mechanical strength of UHPC-BC improves significantly after heat curing and exceeds UHPC-OPC. UHPC-BC has a higher flexural strength to compressive strength ratio and lower environmental impact indices at long age.