Preparation of high strength autoclaved bricks from hematite tailings

This research investigated the possibility of using hematite tailings as main raw material to prepare high strength autoclaved bricks. From orthogonal test result, it indicated that the optimum formulation was the mixtures of 70% hematite tailings, 15% lime and 15% sand. The optimum autoclave pressure and autoclave time were also observed with 1.2 MPa and 6 h, respectively. The compressive strength, flexural strength, compressive strength of hematite tailings autoclaved bricks after 15 freezing–thawing cycles and the mass loss of it with optimum process condition were 21.2 MPa, 4.21 MPa, 18.36 MPa and 0.72%, respectively. They were well conformed to Autoclaved Lime–sand Brick Standard (GB11945-1999) for MU20 autoclaved bricks. The hydration reaction process of the hematite tailings–lime–sand system was discussed in order to guide the preparation of high strength autoclaved bricks. It was found that hydrogarnet was firstly generated in hydration reaction process, then C–S–H (I) and tobermorite were created, and finally the tobermorite gradually transformed to xonotlite by XRD, DSC, IR and SEM. According to experiment results and hydration reaction process, it was inferred that tobermorite was the significant hydration product, which contributed to the strength of autoclaved bricks.

► The optimum process parameters for preparing autoclaved bricks were investigated.
► The bricks satisfied the requirements in GB11945-1999 for MU20 autoclaved bricks.
► The hydration reaction process of autoclaved brick was discussed.
► Tobermorite was the significant hydration product for the strength of bricks.