Effect of Coal Gasification Slag on Mass Transfer Resistance of Concrete

Coal gasification slag (CGS) is discharged as a by-product of the integrated coal gasification combined cycle, which is a new generation technology that improves power generation efficiency compared to conventional coal thermal power generations and reduces carbon-dioxide emissions. The CGS has been attracted as a fine aggregate in concrete and was established as a new fine aggregate by Japanese Industrial Standards (JIS) in 2020. On the other hand, the properties of the concrete using CGS as a fine aggregate have not been clarified yet, and research on the contribution of CGS to the resistance of concrete is insufficient, although it has been suggested that CGS may have a reactivity similar to mineral admixtures. This paper has conducted a series of concrete experiments using CGS as a fine aggregate to explore the mass transfer resistance of concrete based on carbonation resistance and surface air permeability. Two mixture proportions with a water-to-cement ratio of 0.55 were prepared using CGS from the Nakoso power plant (CGSC) and the conventional crushed sand (NC) as fine aggregate. The unit water contents for the CGSC and NC were optimized to get the target slump and air content, and they were 162 and 172 kg/m3, respectively. All the concrete specimens were cured under the condition of two curing methods; 7d-sealed, where the specimens were stored at 20 ± 2 ºC and 60 ± 5%RH after sealing for 7 days, and 28d-water, where they were stored at 20 ± 2 ºC and 60 ± 5%RH after curing in water at 20 ± 2 ºC for 28 days. As a result, CGSC showed better carbonation resistance, especially in 28d-water curing, and an equal or lower surface air permeability than NC.