Self-healing of Portland and slag cement binder systems incorporating circulating fluidized bed combustion bottom ash

Abstract

The potential of circulating fluidized bed combustion (CFBC) bottom ash, which has high contents of sulfate, free lime, and portlandite, for improving the self-healing capacity of Portland cement (PC) and slag cement binder systems was evaluated. Ordinary and slag cement binders were replaced with 10% and 20% CFBC bottom ash in this investigation. The decrease in permeability observed across successive permeability measurements was used as a measure of crack healing. It was found that using flow parameters from Darcy’s law and Poiseuille flow to classify cracks, instead of measuring the crack width, better related with the self-healing inside various crack sizes. The healing materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results showed that addition of CFBC bottom ash can activate slag and form healing products provided that atmospheric carbonation is prevented. Dense ettringite network was found on the crack surfaces for specimens with the ashes.