How to Measure the Absorption and Desorption Curves of Superabsorbent Polymers in the Presence of Calcium Ions

Abstract

The absorption and desorption curve of superabsorbent polymers (SAP), which reflects key information of the maximum absorbency and retention capacity, is crucial for the mix designs of internally cured concretes. In this paper, the effect of amount of Ca²⁺ on the absorption and desorption curve of SAP is studied. Results show that the proportion between amount of Ca²⁺ and SAP mass has a notable influence on the absorption and desorption curve of SAP, whether in tap water or mimicked pore solution of cement paste. Considering the important effect of amount of Ca²⁺, it is suggested that researchers need to determine the relationship between the retention capacity and the ratio of amount of Ca²⁺ to SAP mass in advance before formal measurement using classic tea bag method or filtration method. Furthermore, from the view of the ion exchange equilibrium between SAP and Ca²⁺, we discussed the mechanism that amount of Ca²⁺, concentration of Ca²⁺, SAP type, alkalinity, etc. have decisive effect on the absorption and desorption curve.