Asbestos-cement wastes as supplementary precursors of NaOH-activated binders

Abstract

The need to remove, eliminate the hazard, and correctly dispose of asbestos-cement artifacts found in buildings or incorrectly in the environment is considered a global problem. Processes of inerting asbestos-cement waste (ACW) and application thereof are research priorities. In this sense, this article proposes the production of alkali-activated binders (AAB) with partial metakaolin replacement by heat-treated asbestos-cement wastes (ACWT) as a sustainable alternative for the ACW disposal. To produce AAB, metakaolin, ACWT, and liquid sodium silicate were used. Through the statistical mixture design (SMD), the mineralogical phases formation, the compressive strength, and the skeletal density of the mixtures were evaluated. In addition, an indirect method to determine the unreacted sodium content based on the electrical conductivity and the mass of efflorescent material of the pastes was proposed. The results showed that the presence of ACWT can promote the formation of new alkali-activation products, although it does not significantly influence mechanical strength and efflorescence formation. The paste with the lowest efflorescence mass and lowest electrical conductivity presented higher compressive strength, equal to 61.3 MPa. The determination of electrical conductivity is an accurate method for quantifying unreacted sodium. The incorporation of ACWT in the geopolymer matrices increased the sustainable character of this binder.