Behavior of Superabsorbent Polymers in Calcium- and Sodium-Rich Solutions

Although superabsorbent polymers, especially polyacrylamides, have been successfully used as internal curing agents in concrete for over a decade, the absorption and desorption behaviors, which are key factors in determining the effectiveness of internal curing, are not yet fully understood. Polyacrylamides tend to deprotonate in a high pH environment, allowing superabsorbency of high pH solutions, but their structure is very sensitive to changes in ionic content and concentration of the surrounding solution. This work is aimed at demonstrating how polyacrylamides with very similar chemical compositions can behave differently as they are exposed to different solutions. In parallel, two solutions with the same pH can cause the same polyacrylamide to swell differently. Spontaneous swelling and deswelling behavior in saturated conditions is observed under significant changes in the ion concentration of the surrounding solution. The polyacrylamides used in this work also show strong ion filtration behavior, as observed through analyses of the surrounding pores' solution.