Effect of clay fraction on the mechanical properties and microstructural characteristics of waste rock fine-based brick

The disposal of waste rock fine (WRF) from the manufacturing process of crushed aggregates is attracting more and more attention due to the thorny issues related to clay particles. This paper investigated the use of WRF as a substitute for fine aggregate that solidified by phosphogypsum (PG), groundgranulated blast-furnace slag (GGBS), and ordinary Portland cement (OPC) system in manufacturing of baking-free brick. Three kinds of WRF with different clay fraction (i.e., natural WRF, silty WRF, and clayey WRF) were prepared via slurry settlement methods. Thereafter, their mechanical behaviors were compared by unconfined compressive strength (UCS), Xray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests. The results show that natural WRF contains 81.9% silt and 18.1% clay, after settling-based separation process, the strength of solidified silty and clayey WRF samples decreased by 4.1% and 16.5% at 28 days curing period. Micromorphology, compositional, and microstructural analyses indicate that the strength of solidified WRF is governed by both bonding and filling effect, therein, the strength of solidified silty and clayey WRF samples were lower as compared with natural WRF-based modified samples due to the gradation effect. In addition, it was noticed that although clay particles may participate in the secondary pozzolanic reaction to contribute bonding strength, they also possess superior adsorption capability owing to the large specific surface area, which will adsorb on the surface of cementitious materials and thus hinder the hydration reaction. Moreover, water stability, environmental leaching, economic, and greenhouse gas emission results further confirmed the advantage of reusing WRF and industrial by product resources.