Properties of High-Density Ultrahigh-Performance Concrete Containing Hematite Powder as a Partial Replacement of Sand

Ultrahigh-performance concrete (UHPC) is a smart material used in engineering structures that are subjected to high flexural, shear, impact, and dynamic loadings to ensure safety against explosions and other accidental loads. However, in order for UHPC to be used in structural members in nuclear power plants, it needs to provide radiation shielding due to its high density in addition to being structurally sound. In this study, an attempt was made to develop high-density ultrahigh-performance concrete (HDUHPC) using hematite powder as a partial replacement for sand. The effect of hematite powder content on the microstructure, density, and mechanical properties of HDUHPC was studied using six mixtures that incorporated 0%-50% hematite powder by volume (partially replacing the sand). The test results indicated that as the dry density of the HDUHPC increased with increasing hematite powder content, the mechanical properties of the HDUHPC were uncompromised; in fact, the mechanical properties improved slightly due to densification of the microstructure of the HDUHPC with the inclusion of very fine particles of hematite powder. In addition, the effect of varying dosages of steel fibers on the mechanical properties of the HDUHPC was examined by considering three different dosages of steel fibers (2%, 4% and 6% by weight) in the concrete mixture. The results showed significant improvements in the mechanical properties at higher fiber contents. Correlations between fiber content and different mechanical properties of the HDUHPC mixtures were obtained with high degrees of fitting.