Carbonation of High Strength Concrete Containing Class F Fly Ash

Abstract

Carbonation is one of the major causes for corrosion of reinforcement, which reduces service life of concrete structures significantly. The performance of fly ash concrete in resisting carbonation varies widely. In this paper, high strength concrete containing fly ash was evaluated against carbonation. A locally sourced class F fly ash was used as 30% and 40% of total binder in concrete. Two series of concrete were designed: one with adjusted water to binder ratio (w/b) and total binder content to account for the inclusion of fly ash and the other series with constant binder content and w/b ratio. Air permeability and carbonation tests were carried out. Early age properties were used along with some selected parameters to predict service life against carbonation with the fib model code. Fly ash concretes with adjusted mix proportions achieved similar 28-day compressive strength and equivalent air permeability and carbonation depth as compared to the control concrete. Fly ash concretes subjected to carbonation achieved similar service life of control concrete of similar strength grade. The results show that, it is necessary to adjust the mixture proportions to account for fly ash in order to achieve equivalent service life as that of the control concrete.