The impact of iron tailings on the properties and microstructure of mortar under coupled freeze-thaw and sulfate attack environments

Abstract

The construction industry extensively consumes river sand (RS), and its over-exploitation has led to significant environmental and economic challenges, which have become global issues. Therefore, there is an urgent need to find alternatives to RS. In this study, river sand was partially replaced with iron tailings (IOT) at varying substitution rates (0 %, 25 %, 50 %, 75 %, and 100 %). The mix ratios for the iron tailings-modified mortar (IOTM) were designed to account for the different water absorption rates of IOT and RS. The basic properties of IOTM and its durability under combined freeze-thaw and sulfate (FT-S) attack conditions were subsequently investigated. Microscopic characterization of IOTM was performed using Mercury Intrusion Porosimetry, X-ray Diffraction, and Scanning Electron Microscopy. The results indicated that: (1) The consistency of IOTM after adjusting the mix ratio was in the range of 70–90 mm, which was in accordance with the design specification. The specimen with 50 % IOT substitution rate (IOT50) had the best impermeability and mechanical properties. (2) Compared to the specimen with 0 % IOT substitution rate (IOT0), IOT50 showed less appearance damage, mass loss, and strength loss under FT-S coupling environment. With the number of cycles increased, the degree of destruction and the rate of destruction of the specimens increased significantly. (3) Under the FT-S coupling environment, gypsum and ettringite are generated within the IOTM, leading to the development of pores and cracks. IOT50 has the best pore distribution, hydration reaction and densification at different IOT substitution rates. This study provides valuable insights into the mix ratio design of IOTM and its potential application in bank protection structures in regions with hot summers and cold winters.