Utilization of iron tailings as substitute in autoclaved aerated concrete: physico-mechanical and microstructure of hydration products

• The appropriate preparation conditions of the B05, A2.5 grade AAC blocks from iron tailings were determined.
• The mineral composition and transformation of iron tailing AAC during the process were investigated.
• Characterization of the AAC blocks, including environmental safe were examined.

Based on the background that a large amount of iron tailings was stockpiled in China, the most appropriate preparation conditions of producing autoclaved aerated concrete (AAC) with iron tailing was studied. The slurry properties were tested to evaluate the effects of the raw material factors on gas forming character. The compressive and specific strengths were measured to assess the feasibility of producing B05, A2.5 AAC blocks. The analysis of morphology, mineral components and thermal property were carried out in order to determine the mineral composition of iron tailing AAC blocks. Leaching toxicity was determined to ensure the environmental safety of iron tailing AAC blocks. The results shows that under the following conditions, cement 8%, quicklime 21%–27%, 20 min ball milled siliceous 62%–68% (with 40%–60% substituted by iron tailings), gypsum 3%, ratio of water to raw material (W/R) 0.6, aluminum (Al) powder 0.14% and at 1.4 MPa steam pressure maintaining for 8 h, the bulk density can be between 490 and 525 kg/m3, compressive strength higher than 2.5 MPa and specific strength higher than 4700 N m/kg. The main minerals in the AAC were dough-like CSH gel, flake-like tobermorite and long-strip anhydrate besides quartz and other residual minerals from the iron tailings. The compressive strength is mainly attributed to the interconnected microstructure constituted of CSH gel and tobermorite. The thermal analysis also proved the existing of the main minerals.