Utilization of iron ore tailings as fine aggregate in ultra-high performance concrete

• Iron ore tailings were used as aggregate at different replacement levels to make UHPC.
• The tailings were characterized by techniques like SEM, XRD and nanoindentation.
• The mechanical properties of UHPC mortars and UHPC were measured.
• The pore structure and microstructure of the UHPC matrix were studied.
• The UHPC with tailings content up to 40% showed comparable properties to the control.

Iron ore tailings are a common type of hazardous solid waste in China and have caused serious environmental problems, and the high cost of producing ultra-high performance concrete (UHPC) provides the motivation to look for low-priced raw materials. In this paper, the possibility of using iron ore tailings to replace natural aggregate to prepare UHPC under two different curing regimes was investigated. It was found that 100% replacement of natural aggregate by the tailings significantly decreased the workability and compressive strength of the material. However, when the replacement level was no more than 40%, for 90 days standard cured specimens, the mechanical behavior of the tailings mixes was comparable to that of the control mix, and for specimens that were steam cured for 2 days, the compressive strengths of the tailings mixes decreased by less than 11% while the flexural strengths increased by up to 8% compared to the control mix. In addition, pore structure analysis revealed a coarsening of micro-pore structure with an increase of the tailings content and a good correlation between the porosities and compressive strengths of the UHPC matrices, and microstructure image showed a possibly poor interfacial transition zone around some tailings particles.