Conceptual design and performance evaluation of two-stage ultra-low binder ultra-high performance concrete

This study proposes a novel concept of two-stage ultra-high performance concrete (TS-UHPC), towards ultra-low binder consumption. The effects of grout and coarse aggregate are investigated and their compatibility is evaluated. Results show that TS-UHPC has a low binder amount (down to 364 kg/m3) and high binder efficiency (up to 0.417 MPa·m3/kg), possessing excellent compressive strength of up to 151.8 MPa at 91 days. Microstructural analysis reveals that grout with a sand-to-powder ratio of 1.0 shows a higher hydration degree, denser structure, and increased later strength. Coarser basalt aggregate tends to slightly lower compressive and splitting tensile strength, 14% and 12% reduction with the maximum size from 8 mm to 25 mm, respectively. The TS-UHPC has an excellent interfacial transition zone that induces a water-permeable porosity of 0.91%–1.32%. New formulas are proposed to describe correlation between compressive and splitting tensile strength of TS-UHPC, and to predict strength of TS-UHPC by grout.