Experimental investigations on the effect of concrete quality, exposure conditions and duration of initial moist curing on carbonation rate in concretes exposed to urban, inland environment

This paper reports an investigation on the influence of inland exposure conditions, concrete quality and cover depth on carbonation-induced corrosion initiation of steel in concretes exposed to urban, inland environment. 100 mm concrete cube specimens of were prepared using five types of binder namely plain Portland cement (CEM I 52.5 N, PC), 70/30 PC/FA (fly ash), 50/50 PC/BS (blast furnace slag), 90/10 PC/SF (silica fume) and 60/30/10 PC/BS/SF at three w/b ratios of 0.40, 0.60 and 0.95. For all the concretes, two companion sets of specimens were cast and cured for 7 and 28 days before being exposed to natural indoor, outdoor-sheltered and outdoor-unsheltered environments. Concrete quality was characterized using water sorptivity and oxygen permeability. Carbonation depths were measured at 6-month intervals up to 2 years. The results show that as the quality of the concrete increases the rate of carbonation rate decreases. The results also show that carbonation rate is more sensitive to concrete quality (binder type and w/b ratio) than duration of curing. The indoor-exposed specimens exhibited higher carbonation rates than the corresponding outdoor-exposed concretes. Blended cement concretes showed higher carbonation rate than to the plain PC concretes. An empirical carbonation rate prediction model incorporating both gas permeability and water sorptivity as input parameters is proposed.