Optimizing steel fiber content and holding time for enhanced mechanical properties of UHPC prepared via prepressure technology

Abstract

The mechanical properties of concrete are the key indicators for determining the bearing capacity, stability, safety and durability of a structure. The excellent mechanical properties of concrete under strong dynamic loading can reduce or even eliminate damage to the structure. Prepressure technology is more effective in enhancing the compressive strength of concrete. Therefore, this paper uses the prepressure method to design corresponding molds and prepressure processes for samples of different geometric sizes. By setting different steel fiber volume fractions, preloading gradients and continuous preloading times, the axial compressive strength, elastic modulus and compressive strength of cylindrical and cubic samples were tested, and the influences of preloading and holding time on the mechanical properties and the ratio between the compressive strengths of cylindrical and cubic samples were obtained. The results show that the compressive strength at 9 MPa is 50.6 % (SF0), 112.0 % (SF2) and 127.0 % (SF4) greater than that at 0 MPa, and the highest cube compressive strength is 281.1 MPa. The strength growth, mechanical property changes and apparent damage mode of ultra-high performance concrete (UHPC) were revealed via microcomputed tomography(micro-CT), mercury intrusion tests (MIPs) and scanning electron microscopy (SEM). X-ray diffraction (XRD) was used to synchronize the hydration process of the UHPC.