Utilization of ultra-fine fraction of gold tailings in autoclaved aerated concrete: Effects of mix design on mechanical properties and microstructure

The ultra-fine fraction of gold tailings is difficult to utilize due to their tiny size, large surface area, and high clay content. This study proposes a novel and energy-efficient approach by directly utilizing the ultra-fine fraction of gold tailings (UGT, 300–12,000 mesh) as a siliceous raw material to replace quartz sand in autoclaved aerated concrete (AAC), thereby eliminating the energy-intensive ball milling process. The effects of key mix design parameters, including the lime-to-cement ratio, calcium-to-silicon molar ratio, water-to-solid ratio, and aluminum paste dosage, on slurry rheology, mechanical properties, and microstructure were systematically investigated. Under the optimal mix proportion, the prepared UGT-AAC achieved a compressive strength of 4.33 MPa and a dry density of 587 kg/m3, meeting the A3.5 and B06 requirements. Microstructural analyses indicate that strength development is governed by a dense pore-wall skeleton formed by tobermorite and calcium silicate hydrate gels, demonstrating the feasibility of high-value utilization of UGT.