Carbonated Ladle Slag Fines for Carbon Uptake and Sand Substitute

The possibility of using a carbonated ladle slag as a fine aggregate in concrete was investigated. The slag was treated with carbon dioxide to reduce the free lime content while binding gaseous CO2 into solid carbonates. The treatment took place with either a high concentration of CO2 at 500 kPa for 2 hours or with a low concentration of CO2 at atmospheric pressure for 56 days. It was found that CO2 uptake by the slag particles between 300 and 600 µm and by the slag particles smaller than 75 µm were about 4.2 and 15.6% of their mass, respectively. The extractable CaO contents were estimated by titration and were found to be significantly reduced by carbonation treatment. The carbonated ladle slag was used as a fine aggregate in zero-slump press-formed compact mortar samples and compared to similar samples containing a control river sand. The 28-day strengths of the mortars made with the carbonated slag sand were comparable to the strengths of the normal river sand mortars. The use of carbonated ladle slag as a fine aggregate in concrete is shown to be a novel way of sequestering CO2 in a beneficial manner.