New methodology for assessing the environmental burden of cement mortars with partial replacement of coal bottom ash and fly ash

• Coal bottom ash, an industrial byproduct, can be employed as a supplementary cementitious material.
• Bottom ash has higher heavy metal content than fly ash, usually employed in standard cements.
• Environmental effects of the use of residual ashes have not yet been studied.
• A specific procedure to evaluate environmental impact of mortars with bottom ash is proposed.
• The use of environmental assessment parameters allows the integral evaluation of this type of cements.

This paper assess the mechanical an environmental behaviour of cement mortars manufactured with addition of fly ash (FA) and bottom ash (BA), as partial cement replacement (10%, 25% and 35%). The environmental behaviour was studied by leaching tests, which were performed under several temperature (23 °C and 60 °C) and pH (5 and 10) conditions, and ages (1, 2, 4 and 7 days). Then, the accumulated amount of the different constituents leached was analysed. In order to obtain an environmental burden (EB) value of each cement mixture, a new methodology was developed. The EB value obtained is related to the amount leached and the hazardous level of each constituent. Finally, the integral study of compressive strength and EB values of cement mixtures allowed their classification. The results showed that mortars manufactured with ordinary Portland cement (OPC) and with coal BA had similar or even better environmental and mechanical behaviour than mortars with FA. Therefore, the partial replacement of cement by BA might be as suitable or even better as the replacement by FA.