Study on preparation and properties of the leather sludge wrap shell aggregate by non-burning method

The leather sludge was used as raw material to prepare non-burning sludge wrap shell aggregate by the non-burning method. The effects of different processes on the cylinder compressive strength, water absorption rate, and frost resistance of the non-burning wrap shell aggregate were discussed, through the research on the wrap shell amount, core component, and curing age of the non-burning wrap shell aggregate. The entropy method was used to determine the best process of sludge wrap shell aggregate, and the solidification effect of the shell wrapping process on sludge heavy metal Cr+6 was evaluated and analyzed. The results show that with the increase of curing age, the cylinder compressive strength of wrap shell aggregate increases first and then stabilizes, the water absorption rate decreases gradually, and the frost resistance is significantly enhanced until the 28d of curing age. The more the wrap shell amount and the less the sludge content in the core component is, the higher the cylinder compressive strength, the lower the water absorption, and the better the frost resistance of the wrap shell aggregate are. The entropy method, finally determined the optimal shell wrapping process to be sludge: cement: slag = 50%: 25%: 25%, the wrap shell amount was 25g/100g, and the curing age was 28d. The composite cementitious system and the shell wrapping process can inhibit and effectively reduce the leaching of heavy metals Cr+6 from the sludge wrap shell aggregate by more than 80%.