Raw sewage sludge was characterized by XRD, FTIR, SEM, and TGA techniques and incinerated in temperature range 650–950°C for 2？h. The effect of incineration temperature on the microstructure and pozzolanic activity of the resultant ash was investigated by techniques mentioned above as well as Chapelle test. It was concluded that incineration of sewage sludge affects the microstructure and pozzolanic activity of the resultant ash. During incineration at temperatures lower than 800°C, amorphous silica captures fixed carbon resulting from incomplete combustion conditions whereas at higher temperatures crystallization of amorphous silica was enhanced. Hydration products formed from hydrothermal treatment of silica fume with lime is amorphous whereas that of sewage sludge ash is fibrous. Hence, incineration of sewage sludge ash must be optimized at 800°C to preserve the pozzolanic activity of the resultant ash. 1. Introduction Sewage is the collection of wastewater effluents from domestic, hospital, commercial, industrial establishments, and rain water. The objective of sewage treatment is to produce treated sewage water and sewage sludge suitable for safe discharge into the environment or reuse . The most common treatment options for sewage sludge include anaerobic digestion, aerobic digestion, and composting. Choice of the treatment method depends on the amount of sludge and other site-specific conditions . Sewage sludge tends to accumulate heavy metals existing in the wastewater. The composition of sewage sludge and its content of heavy metals vary widely depending on the sludge origins and treatment options . In past decades, sewage sludge was primarily disposed to landfills and seawaters . Space limitations on existing landfills and increasing environmental concerns such as groundwater pollution from landfill leachate, odor emission and soil contamination have prompted the investigation of alternative disposal routes . Sewage sludge has been used in agriculture as fertilizer and soil amendment . However heavy metals such as Zn, Cu, Ni, Cd, Pb, Hg, and Cr are principal elements restricting the use of sludge for agricultural purposes . The solidification/stabilization of sewage sludge in cementitious matrix has been evaluated . Sewage sludge adversely affects durability of concrete, mainly due to the organic material which retards setting and heavy metals which interfere with the hardening reactions . Hence, sewage sludge addition in concrete was limited to 10？wt.% and the solidified concrete was recommended for use in certain
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