Recycling of steel slag powder in green ultra-high strength concrete (UHSC) mortar at various curing conditions

The large quantity of steel slag deposit has caused great environmental pressure. This study aims to recycle steel slag as binder in the production of green ultra-high strength concrete (UHSC) subjected to different curing regimes (i.e. standard and steam curing). The fresh behaviors, mechanical properties, microstructure and ecological value of the UHSC are explicitly assessed with the help of the Funk and Dinger particle packing model. The results show that the inclusion of steel slag powder (SSP) increases the workability (up to about 13%) and wet packing density of UHSC. The use of SSP results in a decrease of early compressive strength, because the SSP inhibits cement hydration at early stage. The steam curing can minimize this negative impact of SSP on the early compressive strength (>120 MPa). Besides, the increase of SSP dosage results in a reduction in the flexural strength for both early and later ages, but steam curing reduces the decline ratio. The high temperature curing not only promotes the hydration process of both cement and SSP, but also accelerates the pozzolanic reaction of silica fume, resulting in a lower porosity (4.78%) of UHSC with SSP. Finally, the ecological assessment shows that the recycling SSP as a replacement of cement in the UHSC system can reduce energy consumption and carbon emissions. Therefore, the results in this study indicate the feasibility of utilizing SSP in the fabrication of sustainable UHSC products with excellent performance.