Optimization design and microstructure analysis of ultra-high performance cement-based composites

Good workability and mechanical properties are both important for ultra-high performance cement-based composites (UHPCC). To achieve this goal, UHPCC was produced through a cost-effective approach of substituting cement with mineral admixtures. Based on Modified Andreasen and Andersen grading (MAA) model and orthogonal experimental design, key factors were identified and analyzed. The effect of the sand-to-binder ratio on bulk packing density was examined, while the impact of water-to-binder ratio and sand-to-binder ratio on the workability and mechanical properties of UHPCC was systematically studied. Additionally, X-CT was utilized to quantitatively analyze the steel fiber distribution and mesoscopic pore structure of UHPCC. Results indicated that the sand-to-binder ratio had the significant effect on bulk density, with the optimal ratio being 1.25. The suitable fluidity of UHPCC was between 245–255mm, with an optimal water-to-binder ratio of 0.18. The compressive and flexural strength of the mortar prepared with the optimal parameters were 167.5 MPa and 41.2 MPa, respectively.