Compressive stress-strain relationship of limestone calcined clay cement-based UHPC matrix

Limestone calcined clay cement-based ultra-high performance concrete (LC³-UHPC) was found to possess excellent eco-efficiency and mechanical properties. However, the effect of the substitution rate and the calcined clay to limestone powder ratio on the compressive stress-strain relationship of LC³-UHPC matrix remains unclear. This study tested the uniaxial compressive stress-strain relationships of LC³-UHPC matrix with different mix proportions. DTG, SEM-EDS, and MIP have been performed to investigate the hydration process and microstructures. The results show that LC³-UHPC matrix achieves optimal mechanical performance with a 1:2 calcined clay to limestone powder ratio and a 30 % substitution rate of limestone calcined clay (LC²) for cement in this study, while the typical calcined clay to limestone powder ratio for LC³-based normal concrete is 2:1. With the optimal mix, the 28-day compressive strength of 104 MPa can be achieved without employing any special curing, silica fume or fibers. Furthermore, adding an appropriate amount of LC² (no more than 30 %) to UHPC matrix is found to reduce the nonlinearity of compressive stress-strain relationships, thereby minimizing the plastic deformation of LC³-UHPC matrix. At last, the uniaxial compressive constitutive model proposed by Popovics is used to formulate the compressive stress-strain relationships of LC³-UHPC matrix. It should be noted that the compressive stress-strain relationship of LC³-UHPC matrix is influenced by many factors, such as the chemical composition of raw materials, particle packing density, and the presence of silica fume. Therefore, the optimal mix proportion obtained in this study is not applicable to all scenarios. Nonetheless, this study can provide a reference for the mix proportion design and mechanical performance analysis of LC³-UHPC.