Comparison of Sorption Assessment Methods for Superabsorbent Polymers

Abstract

Currently, superabsorbent polymers (SAP) constitute a promising class of chemical admixtures for concrete. However, since their sorption capability and kinetics can differ significantly depending on chemical composition and grading, when choosing a SAP for a particular application it should be pre-tested with respect to its sorption capacity before actual implementation in concrete. Due to the influence that the test liquid ionic composition has on SAP sorption behaviour, they should be tested not only for free water sorption but also for sorption of solutions with chemical compositions as close as possible of those of concrete or mortar pore solutions; furthermore, this should be complemented with the evaluation of sorption behaviour in an environment similar to the one the SAP will experience when in a mortar or concrete. This article focuses two free sorption assessment testing methods, teabag and filtration methods, and two methods that indirectly provide the SAP sorption capacity, slump flow consistence method, using a cementitious mortar, and a new method, plunger penetration consistence method, using a cement paste. It was found that a good agreement exists between the results obtained with the two indirect methods, and that both the direct and indirect methods produced similar sorption trends. Hence, from the results obtained so far, it appears that the plunger penetration method could be a useful complement to the teabag and filtration methods, by providing a simple and quick way of estimating SAP sorption capacity in an environment more similar to that found by the SAP in concrete.