Improvements of the Carbonation Resistance of Concrete After Steam Autoclave Curing

Incorporation of mineral admixtures, secondary water curing, and surface treatments were performed to improve the carbonation resistance of concrete after steam autoclave curing. The mineral admixtures used were fly ash, slag, and a mixture of both, and the surface treatments applied were those of organic silicone (OS) water repellent and epoxy resin (ER) coating. Accelerated carbonation experiments were performed on specimens at 28, 90, 180, and 360 d. Experimental results indicated that steam autoclave curing significantly reduces concrete carbonation resistance compared with standard curing. Secondary water curing for one week can replenish water in concrete and further hydrate the residual unhydrated cement particles in concrete, effectively improving the concrete carbonation resistance. The reduction of concrete carbonation depth can reach 81% at 360 d. The incorporation of mineral admixtures cannot improve the early-age carbonation resistance of concrete. However, it can provide several benefits to long-term carbonation resistance. Comparatively, slag behaves better than fly ash, and the maximum improvement ratio by 20 wt.% replacement of slag can reach 36.9% at 360 d. ER coating can substantially improve the carbonation resistance of concrete due to the formation of a compact membrane on the concrete surface, with an average improvement ratio of 77.2%. By contrast, the OS repellent can only improve the hydrophobic properties of the concrete surface, which is not effective enough