Design, preparation and hydration of ecological ultra-high performance concrete (eco-UHPC) with raw waste rock chips

High carbon emissions and high costs have limited the applications of UHPC. The use of environmentally friendly aggregates and fillers can help to address this issue. In this study, an ecological UHPC (eco-UHPC) was designed by using raw waste rock chips (RWRC) with waste rock chips (WRC) and waste rock powder (WRP) to replace quartz sand (QS) and part of the cement to obtain the UHPC with low carbon emissions and low cost. The compressive strength of the eco-UHPC was tested and the microstructure and hydration product were characterized by SEM, XRD and TGA. Calorimetry and MIP tests were carried out to determine the exothermic behavior and pore structure of eco-UHPC. The results showed that the 28-day compressive strength of eco-UHPC with WRC as fine aggregate was 4.3 % higher than that of the sample with QS. For the UHPC sample with WRC as the only aggregate, the addition of 10 wt% WRP slightly increased the compressive strength from 7 d to 56 d by promoting the formation of hydration products and refining the pore structure of UHPC, but the opposite was true for the sample with high content of WRP. In addition, the results of the ecological evaluation showed that the advantages of eco-UHPC produced by RWRC are environmental friendliness and low cost. •Rock powder can replace 30 wt% of cement to produce eco-UHPC.•Waste rock powder increased hydration product and refined pore structure.•Rock chips with 22.5 wt% powder reduced carbon emissions and costs of UHPC.