Porosity, gas permeability, carbonation and their interaction in high-volume fly ash concrete

Abstract

This paper describes the results of research into porosity, gas permeability and carbonation of high-volume fly ash (FA) concrete, including a literature review and comparison between models and experimental results. Four mixtures were made, each with a different FA replacement level—0, 35, 50 and 67 %—but with the same water-to-cementitious materials ratio. A vacuum saturation technique and a gas permeation experiment indicate that both porosity and gas permeability increase with increasing FA content. A reduction is noticed between 1 and 3 months for the FA mixtures owing to the pozzolanic reaction. No existing models seem to predict the porosity and gas permeability correctly for all mixtures. Carbonation tests show that the carbonation depth is considerably higher for the 50 and 67% FA mixtures at all ages compared to the ordinary Portland cement concrete. The Jiang model overestimates the carbonation depth for high-volume FA concrete significantly, while the Atiş models predict the depth rather well. Carbonation seems to have a negative effect on gas permeability, especially for the 50 and 67% mixtures.