Effects of NaHCO3 As the Activator and the In-Situ Carbonate Seeding on the Properties of High-Dosage Ca(OH)2 + Slag (HCHS) Cement

This study investigated the effects of the addition of NaHCO3 (5, 10, and 15% molar amount of Ca(OH)(2)) on the setting time, compressive strength, drying shrinkage, and hydration process of high-dosage Ca(OH)(2) + Slag (HCHS) cement. The results indicated that the NaHCO3 addition could significantly increase the 1-day compressive strength of HCHS cement from almost 0 to 10 MPa and decrease the drying shrinkage of HCHS cement up to 46.1% compared to it without NaHCO3. But the addition of NaHCO3 above 5% would result in accelerated setting, increased porosity, and decreased strength in the later stages. NaHCO3 played an in-situ carbonate seeding effect, forming CaCO3 crystals through the initial reaction of Ca(OH)(2), and the activator that increased solution alkalinity promoted the formation of hydration products. These could contribute to the HCHS cement with high early compressive strength, good volume stability and certain porosity, suitable for further carbon capture.