Lightweight ultra-high performance concrete prepared with the waste fraction of sintered shale pottery sand: preparation, mechanical properties, and material selection method

Abstract To address the high construction difficulty and cost resulting from the heavy self-weight of concrete-filled steel tube (CFST) skeletons in the construction of long-span arch bridges, as well as the ineffective utilization of 0–3 mm waste fraction of sintered shale pottery sand —which leads to resource waste and environmental pollution when stockpiled—this study employed an experimental approach combining the close packing and over slurry theories to determine the optimal mix proportion for lightweight ultra-high performance concrete (LUHPC) incorporating 0–3 mm waste fraction of 800/700-grade sintered shale pottery sand. LUHPC exhibited excellent properties. With a volume fraction of 3% straight-round steel fibers, the compressive strength was 147.7 MPa, the tensile strength was 17.4 MPa, and the elastic modulus was 49.9 GPa. All groups achieved a slump flow of at least 220 mm, meeting the requirements for self-compacting. The apparent density ranged from 1.943 to 2.178 g/cm 3 , 22.2%–30.6% lower than that of ultra-high performance concrete (UHPC). Scanning electron microscope (SEM) analysis showed that the waste fraction of 800-grade sintered shale pottery sand provided better internal curing than that of 700-grade sand, thereby improving its mechanical performance. The addition of irregular steel fibers (end-hooked and wavy) enhanced tensile strength, but reduced flow properties and other mechanical properties. Analyses of carbon emissions and economics indicated that LUHPC with the waste fraction of 700- and 800-grade sintered shale pottery sand reduced emissions by 21.0% and 24.1%, and raw material costs by 42.9% and 45.0%, respectively, compared with conventional UHPC. Finally, a method integrating combined weighting and grey relational analysis was proposed to evaluate multiple performance criteria and select the optimal mix proportion, providing decision support for various engineering applications.