Effect of activated water treatment sludge on carbonation of mortar

Activated water treatment sludge (AWTS) is a newly developed environmentally friendly blending material that contains 12CaO7Al2O₃ and C2S as cementitious minerals. In order to evaluation service performance of AWTS blended cement, carbonation characteristic and microstructure of mortar incorporating 20 wt. % AWTS was studied in present paper. Increasing with carbonated time prolonging under standard test condition, carbonation performance of mortar specimens achieved quality index of class T-IV of Chinese construction code JGJ/T 193-2009. Compressive strength of carbonated mortar had a little rise compared to controlled mortar cured at standard condition for 28 days. Portlandite reacts with carbon dioxide to form calcite and, calcite reacts with aluminate minerals to form monocarboaluminate. This was confirmed by SEM observation. AWTS has no disadvantageous effect on carbonation of Portland cement. More aluminate in the blended cement resulted in monocarboaluminate type AFm formation. ATWS can be employed as blending material for modern cement industry.