Utilization of APC residues from sewage sludge incineration process as activator of alkali-activated slag/glass powder material

In this paper, the soluble salts from the air pollution control (APC) residues of a sewage sludge incinerator and solid sodium silicate were used as a hybrid activator to prepare alkali-activated materials (AAMs) using slag and waste glass powder (GP) as the precursors. The effect of the hybrid activator on the mechanical properties and its reaction mechanism was discussed. The experimental results showed that the APC residues obviously decreased the early compressive strength of the AAMs due to its lower activity, but a steady growth of later compressive strength was achieved due to the dense microstructure. The alkali-activated slag and GP/slag suffered from severe drying shrinkage, but the drying shrinkage of the AAMs reduced by 30%–50% when the 20% APC residues were added. In addition, when the APC residues and GP was used, the insufficient aluminum and calcium contents restrained the formation of the C-(A)-S-H gels in the alkali-activated GP/slag, and the N-(C)-A-S-H gels were formed until the available Ca was exhausted. Some crystalline materials including the ettringite, hydrotalcite, albite and Friedel's salts were detected in the alkali-activated slag/GP after the incorporation of the APC residues in addition to the N–S–H gels.