Daily production of municipal sewage sludge coming from wastewater treatment plants is becoming a global issue and requires efficient material and energy recovery. Limited applications of sewage sludge (SS) as raw material and decreasing amount of land in which SS is traditionally used as a soil conditioner represents a severe environmental problem in our society. The presence of heavy metals in the sludge further limits its suitability for usage as fertilizers. In the context of a circular economy, incineration with fluidized bed technologies, along with use of by-products such as ash for construction materials, is under investigation in different countries. Incineration of sewage sludge, along with coal, is an optimum way to utilize the organic content of the sludge, maintaining high combustion efficiency with low flue-gas emissions. Moreover, the application of incinerated sewage sludge ash (ISSA) in the cement industry also resolves the problem of SS and ISSA disposal. Pozzolanic properties indicate ISSA's high potential for exploitation as a supplementary cementing material. However, the application of ISSA in the cement manufacturing process requires careful control since the content of the raw material differs remarkably, determined by the method of SS production and incineration technique. In this work, a detailed thermo-chemical analysis of the ISSA produced from fluidized bed combustion of Kazakhstan’s municipal sewage sludge is performed and compared with the ISSA obtained from furnace incineration. The effect of SS combustion temperature on the ISSA’s pozzolanic activity is determined using TGA/DTA analysis and the Frattini test. Different amounts of SSA (5% - 35%) were utilized to evaluate the pozzolanic activity of mortar mixtures. Compressive strengths of Portland cement and ISSA mortars with 5-35 %wt ISSA were quantified and characterized chemically and physically through Fourier transform infrared spectroscopy and scanning electron microscopy analyses. It was found that the ISSA was capable of cementitious material at a content of up to 15%.