Hydration characteristics investigation of iron tailings blended ultra high performance concrete: The effects of mechanical activation and iron tailings content

Abstract

The large consumption of energy-intensive material cement is an urgent problem restricting the development of ultra high performance concrete (UHPC) and the exploration for high-quality cement substitutes has attracted extensive attention from society. In this study, the screened iron ore tailings (IOT) from the tailings dam were selected to improve the grinding efficiency. The optimal grinding time is determined through the pozzolanic activity index test. The effects of IOT substitution on the compressive strength, hydration characteristics, and microstructure of UHPC under the optimal mechanical activation time were studied, substituting cement for 10, 20, and 30% wt%. The results demonstrated that the mineral phases in IOT were decreased by mechanical activation and the optimal grinding time was 3.5 h. The pozzolanic activity index (28d) reached 74.5% and meet the Chinese National Standard GB/T 2847–2005, which revealed that the mechanical activated IOT was appropriate as a kind of supplementary cementitious material. The addition of IOT in UHPC does not transform the type of hydration products, differing only in amounts. The reasonable addition of IOT (not exceed 20%) can make up for the compressive strength loss caused by cement reduction. The current study provides an innovative method for utilizing IOT in the UHPC application, which would alleviate the problem of excessive cement consumption in UHPC and reduce the greenhouse effect.