Washed waste incineration bottom ash as a raw ingredient in cement production: Implications for lab-scale clinker behavior

Abstract

Municipal solid waste incinerator (MSWI) ash has a similar chemical composition to traditional cement kiln feed components, making it a potentially viable replacement for traditional materials in the absence of deleterious components invariably present in ash. This supposition should be confirmed by lab-scale experimentation prior to full-scale implementation. This study explores lab-scale cement manufacturing using varying replacement percentages of unwashed and water-washed MSWI bottom ash. The use of unwashed MSWI ash as a kiln feed is associated with a considerable decrease in tricalcium silicate content. Each replacement percentage of washed bottom ash incorporation resulted in an approximate tricalcium silicate content of 45%, while unwashed bottom ash specimens had tricalcium silicate contents of approximately 35%. Aluminate concentrations in ash-amended clinkers were considerably higher than reference clinkers, which may require additional gypsum to ensure proper setting. The effects of mineralogical differences were reflected in cement reactivity. Unwashed MSWI ash-amended specimens should be monitored for chloride and alkali content. Results of this study highlight the simultaneous impact of washed and unwashed MSWI bottom ash addition as kiln feed on clinker formation, and the special considerations for clinker production and behavior. The addition of MSWI ash as cement kiln feed is beneficial provided it is washed and appropriately controlled below 8% to reduce deleterious phase composition.