The Effect of Gas Solubility on the Secondary Sorption in a Portland Cement Mortar Observed by X-ray CT

Abstract

In this study, we investigate the secondary sorption in an air-entrained Portland cement mortar that is purged with different gases— $$\hbox {CO}_{2}, \hbox {CH}_{4}$$ , or $$\hbox {N}_{2}$$ . By altering the gas phase present in the void space, we are able to evaluate how gas solubility influences the secondary sorption. The rate of water sorption in the presence of different gases in the entrained voids was captured using successive 30 min X-ray micro-computed tomography scans for 24 h after water-specimen contact. The results show the higher the solubility of the gas, the faster the mortar reaches saturation. The air voids in the $$\hbox {CO}_{2}$$ -purged specimen begin to absorb water within 30 min and reach a critical degree of saturation within hours, while the air voids of $$\hbox {N}_{2}$$ and $$\hbox {CH}_{4}$$ -purged specimens show a significantly slower water absorption over 24 h. The high solubility of $$\hbox {CO}_{2}$$ was found to alter the X-ray mass attenuation value of the water as the water becomes $$\hbox {CO}_{2}$$ saturated. These tests reveal the gas type present in the void space significantly influences secondary sorption of Portland cement mortars. The findings of this study have implications on predicting mass transport in cement-based materials used in below ground carbon sequestration structures.