Effectiveness of the traditional parameters for specifying carbonation resistance

This paper presents data on carbonation measurements taken from a range of test specimens stored outside but protected from rainfall. A wide range of concretes were tested that were representative of UK ready-mixed concrete production at ages of between 3·5 and 5·7 years. None of the traditional specification parameters (maximum water/cement (w/c) ratio, minimum cement content and compressive strength class) on their own or in combination give a consistent carbonation resistance. When compared at a fixed w/c ratio of 0·55, there was no clear influence of cement content on carbonation resistance. The measured carbonation depths of the Portland cement concretes were too low to show any influence of aggregate type. When extrapolated to 35 years, in a conservative manner, the data provide no grounds for concern with the BS 8500-1 recommendations with respect to carbonation resistance. There is some indication that the BS 8500-1 recommendations with respect to CEM I concretes may be too conservative. The predicted performance of concrete containing 40% or more fly ash indicates that the particular recommendations set out in BS 8500-1:2006 are justified.