Utilization of sewage sludge ash in ultra-high performance concrete (UHPC): Microstructure and life-cycle assessment

In this research, an economical and eco-friendly ultra-high performance concrete (UHPC) with compressive strength of more than 120 MPa was prepared with the dosage of sewage sludge ash (SSA) at 8 wt%. The results indicate that the addition of SSA has an adverse influence on the workability of UHPC samples due to its special morphology. Furthermore, the microstructure and phase assemblage of SSA-based UHPC were determined and the results show that SSA inhibits the early hydration of cement clinker, while promotes the precipitation of additional hydration products at later curing ages due to its pozzolanic reaction. The pore structure analysis of SSA-based UHPC determined by mercury intrusion porosimetry indicates that the addition of SSA increases the cumulative pore volume, while decreases the large pore volume of UHPC. Economic and environmental analysis indicates that using SSA-based UHPC greatly reduces the unit cost and the impacts on the environment. [Display omitted] •Eco-friendly UHPC with sewage sludge ash (SSA) was developed.•Replacing OPC or SF with 8 wt% SSA increases mechanical properties of UHPC.•The pozzolanic reaction of SSA increases the Si/Ca ratios of C–S–H gels.•The environmental impact of UHPC was reduced with the addition of SSA.