Alkali-activated binders based on incinerator bottom ash combined with limestone-calcined clay or fly ash

Abstract

This study investigates the feasibility of improving the properties of alkali-activated bottom ash (AABA) binders by incorporating limestone-calcined clay (LC2) or fly ash (FA) with the aim of treating and utilising bottom ash in a large-scale as a potential resource for construction materials. Experimental results revealed that increasing the substitution with LC2 or FA in the AABA binders increased both the compressive strength and the immobilization capacity of heavy metal when compared to the pure AABA binders. Given a Na2O content of 5%, the compressive strength of the AABA binder with 30% bottom ash substituted by FA was almost 200% higher than that of the pure AABA binder. However, further increase in the Na2O dosage did not necessarily lead to higher compressive strength, which was found to be controlled by the volume fraction of air voids and large pores. When greater Na2O dosages were employed, i.e., 6 % and 7 %, LC2 was found to be more useful in improving the properties of AABA binders than FA. Furthermore, the substitution of bottom ash with FA resulted in the formation of N-A-S-H gels, whereas the substitution with LC2 led to the formation of more C-A-S-H gels. Finally, the immobilization capacity appeared to be influenced by many factors, such as hydration products, capillary pores and different types of heavy metals.