Effect of moist-curing time at early ages on carbonation resistance of pumping concrete incorporated with fly-ash

Based on accelerated carbonation test, the variation of carbonation resistance of pumping concrete (C30 grade) with moist-curing time at early ages and fly ash content was studied in this paper. Results indicate that the carbonation resistance of the concrete decreased obviously with moist-curing time at early ages reducing and with the cement replacement by fly ash increasing. For example, under conditions of curing schedules with 28, 7, 3, 2 and 1 d moist-curing at early ages and then 0, 21, 25, 26 and 27 d air-curing at (60+5)% RH respectively, the 28-day accelerated carbonation depths of the concrete incorporated with 20% fly ash were 15.6, 20.5, 25.3, 31.5 and 45.9 mm respectively, and thus it can be seen the calculated times when concrete cover (25 mm) was completely carbonated naturally in the air were 98, 57, 38, 24 and 11 years respectively. The results suggest that for the carbonation resistance of the concrete incorporated with 20% fly ash, it is necessary that the moist-curing time at early ages should need 7 days.