Mechanical, environmental and economic performance of sustainable Grade 45 concrete with ultrahigh-volume Limestone-Calcined Clay (LCC)

Low-grade calcined clay mixed with limestone powder (Limestone-Calcined Clay, LCC) is a new kind of cement replacement material in the face of the inadequate availability of conventional pozzolans such as fly ash. Because of the high water demand and likely insufficient strength gain of LCC, the information on using more than 50% of LCC in the binder is extremely limited, which hinders using LCC in a higher replacement level to develop greener concrete. This study attempts to address this knowledge gap by producing Grade 45 structural concrete with ultrahigh-volume LCC (UHV-LCC). UHV-LCC mortar mixes with various LCC/binder ratios (50-80%) and water/binder ratios (0.3-0.4) were firstly examined to determine the cementing efficiency factor of LCC. Four Grade 45 UHV-LCC concrete mixes with different LCC/binder ratios (50%, 60%, 70% and 80%) were then designed and demonstrated. With the judicious choice of water/binder ratio, UHV-LCC concrete achieved compressive strength of 33-37 MPa at 3 days, 47-51 MPa at 7 days, 56-58 MPa at 28 days, and 62-64 MPa at 90 days. The flexural strength of UHV-LCC concrete was 2-10% higher than that of plain Portland cement concrete with identical compressive strength class. Additionally, UHV-LCC concrete showed 36.8-44.4% lower total embodied carbon than plain Portland cement concrete, and a higher LCC/binder ratio resulted in lower embodied carbon in Grade 45 concrete. A 5-D representation was used to evaluate different concrete mixes by comprehensively considering the mechanical, environmental, and economic performance. Our findings are useful for the mix design of sustainable concrete with LCC.