Potential for the liquid carbonation curing of Portland cement using sodium bicarbonate solutions

Potential for the liquid carbonation curing of Portland cement (PC) using NaHCO3 solutions was investigated. The PC paste samples were sealed-cured or immersed in a 0%, 1%, 3%, 5%, or 10% NaHCO3 solution after undergoing one day of initial curing. The characterization and quantification of the samples and NaHCO3 solutions at various curing ages were performed using X-ray diffractometry, thermogravimetry, 29Si nuclear magnetic resonance spectroscopy, inductively coupled plasma mass spectrometry, and compressive strength measurements. The test results revealed that the use of NaHCO3 solution as a carbonation curing medium partially carbonated the hydrates, resulting in the formation of calcium carbonate and CO2-bearing AFm phases. In addition, the NaHCO3 solution enhanced the reaction degree of clinkers. The carbonation rate further increased at higher NaHCO3 concentrations. Inductively coupled plasma mass spectrometry results indicated that Ca leaching from the PC samples rarely occurred because of the high Na concentration in the NaHCO3 solution and the presence of stable CaCO3 in the samples. The compressive strengths of the samples cured in the NaHCO3 solution were higher than those of the samples sealed-cured samples at later stages.