Abstract
Depths of carbonation on specimens of concretes aged for up to 10 years are compared. Both good and poor curing conditions, with either indoor or outdoor exposure are considered. It is demonstrated that the carbonation depth is related systematically to the standard cube strength in dense concretes containing up to and including 40% replacement of Portland cement by pulverized fuel ash (PFA) or up to and including 60% by ground granulated blast furnace slag (GGBFS) or ground pelletized blast furnace slag (GPBFS). The main implications of these findings to methods of specifying concrete (BS 5328: 1981) are that designed mixes may give higher rates of carbonation for low-heat Portland blast furnace cement, but not for other permitted cement replacements, and that prescribed mixes will usually give higher rates if Portland cement is partially replaced by any permitted quantity of cement replacement. Depths of carbonation in concrete containing porous aggregate are more closely related to total water/cement ratio than to standard cube strength. This is probably a result of a closer relationship between total water/cement ratio and pore structure, which controls the rate of carbonation. A comparison has been made between concretes containing porous aggregate and those containing cement replacements by introducing an efficiency factor (k) for cement replacements similar but not always identical to the cementing efficiency factor.
MST/690
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