Carbonation Resistance of Portland Blast Furnace Slag Cement Type B Concrete Internally Cured by Using Roof-Tile Waste Aggregate

Abstract

Internal curing is a method in which a portion of the aggregate is replaced by a porous material having a high water absorption to supply curing water inside the concrete. The use of roof-tile waste aggregate as an internal curing material has been investigated, and its effect on reducing the autogenous shrinkage and increasing the compressive strength of ultra-high strength concrete has been reported. The purpose of this study was to evaluate the effects of roof-tile waste aggregate on the carbonation resistance of Portland blast furnace slag cement type B concrete. Six types of concrete with water-to-cement ratios of 0.50 and 0.35 were prepared with different replacement ratios of roof-tile waste coarse aggregates and fine aggregates. Concrete specimens were cured under sealed condition at 20 ℃ for 7 days before exposing to the air (20 ℃, 60%R.H.). The accelerated carbonation resistance, air permeability, and pore structure of concrete near the exposed surface were investigated. From the investigations, no densification of the pore structure by roof-tile waste aggregate was observed. It was found that roof-tile waste aggregate did not improve the carbonation resistance with a water-to-cement ratio of 0.50. When the water-to-cement ratio was 0.35, carbonation did not proceed enough to measure the carbonation depth and no difference was observed in the use of roof-tile waste aggregate. On the other hand, the use of roof-tile waste aggregate reduced permeability, regardless of the water-to-cement ratio. Therefore, the relationship between carbonation resistance and air permeability was different depending on the presence or absence of roof-tile waste aggregate. It is because the surface water content of concrete with roof-tile waste aggregate is higher than that without roof-tile waste aggregate, allowing more water to be stored inside the concrete and consequently increasing its impermeability.