Carbon sequestration efficiency of recycled sand in pilot-scale industrial carbonization tank and natural carbonation situation

To advance the industrial application of carbonation sequestration, this study employed a pilot-scale industrial carbonation tank to investigate how different interlayer positions determine the carbonation efficiency of recycled sand. The experimental variables included intrinsic factors (particle size: coarse, medium, and fine recycled sand, denoted as CRS, MRS, and FRS). External factors included CO₂ concentrations of 100 % and 25 % (to simulate cement plant gas emission) and different carbonation durations. The carbonation efficiencies were also compared with a low-cost alternative method of natural carbonation (NC). The results indicated that finer recycled sand exhibited poorer interlayer permeability, resulting in greater differences in carbonation levels between layers. The layers closer to the air inlet showed better carbonation degree. The finer the recycled sand was, the greater the carbon sequestration capacity it had. CRS achieved a higher carbonation rate as to its own carbon sequestration capacity because of the better particle connectivity. FRS achieved a carbon sequestration capacity of 0.0994 g/g after a 28 days NC, which was regarded as a fully carbonated degree. In the pilot-scale carbonation tank, FRS can sequestrate CO₂ over 0.0709 g/g, cover the carbon emission generated during transportation and crushing stages according to LCA analysis. The introduction of industrial carbonation can significantly optimize the life cycle assessment (LCA) carbon footprint of recycled concrete containing carbon-treated recycled sand.