Based on accelerated carbonation test, the variation of the carbonation resistance of ordinary concrete (C40 grade) with early age wet curing time, clinker and CaO content was studied. Results indicate that the carbonation coefficient and the accelerated carbonation depth of the concrete increased obviously with a reduction in the wet curing time at early ages, the clinker or CaO content in binder and the compressive strength at 28 d age. For example, in conditions of curing schedules with 28, 7, 3, 2 and 1 d wet curing at 20 °C with above 95% RH at early ages and then 0, 21, 25, 26 and 27 d air curing at 20 °C with 60% RH, respectively, carbonation coefficients of the concrete incorporated with 15% fly-ash and 25% slag were 1.83, 2.71, 3.61, 4.67 and 5.50 mm/a0.5 respectively, and thus it can be seen that the calculated times when concrete cover (25 mm) was completely carbonated naturally in now atmosphere (0.04% CO2) were 191, 104, 52, 31 and 20 years respectively. It is possible to predict the potential carbonation coefficient of the concrete from its clinker or CaO content in binder and from its compressive strength at 28 d age in conditions of the certain wet curing time at early ages.
Effects of Carbonation on the Properties of Concrete