Transport due to Diffusion, Drying, and Wicking in Concrete Containing a Shrinkage-Reducing Admixture

Shrinkage-reducing admixtures (SRAs) influence moisture and ionic transport in concrete by altering the properties of the pore solution (the surface tension, viscosity, and contact angle). This paper reports measurements of water vapor desorption isotherms in cementitious systems with different SRA contents. In addition, isothermal drying and wicking experiments were performed for concrete with different SRA contents. Similar pore size distributions and pore volumes were measured for plain concrete and concrete containing SRA. Less water was lost during isothermal drying for systems with SRA. Further, there was a reduction in chloride ion penetration for concrete with a higher SRA content during wicking. The transport processes are described quantitatively using a modified moisture-ion transport model. The viscosity of the pore fluid, the capillary pressure, and the ionic diffusion coefficients are considered as a function of SRA concentration. The simulation results are comparable to the experimentally measured data, which sheds light on the feasibility of predicting the moisture loss and chloride migration in concrete containing SRA.