Use of oxyfuel combustion ash for the production of blended cements: A synergetic solution toward reduction of CO2 emissions

In this paper, it is investigated the possibility of reusing ashes, issued by an oxyfuel combustion process aimed at mitigating CO2 emission, as substitutes for natural pozzolan in the production of low-CO2 blended cements. To this end, the oxyfuel plant (a 95 kWth pilot-scale fluidized bed reactor) was operated under controlled conditions by feeding blends of anthracite or lignite and biomass corn stover. Characterization of fly and bottom ashes revealed that the latter showed properties able to make them considerable for obtaining blended cements by mixing them with Portland clinker and natural gypsum. The cements were subjected to pozzolanicity and hydration tests for curing times ranging from 2 to 28 d at 20° and 40 °C. X-ray fluorescence and diffraction, differential thermal–thermogravimetric analyses and scanning electron microscopy were employed as characterization techniques. With reference to a standard blended cement, and with particular eye on the blended cement containing bottom ashes obtained from the lignite–biomass mixture combustion, it was observed a good similarity in the ability of the silico-aluminous fraction to react with Ca(OH)2 produced by Portland clinker hydration, to yield the desired calcium silicate hydrates among the hydration products.