Multi-scale study of the effect of superabsorbent polymers on microporosity, dimensional stability, and durability of cementitious materials

Abstract

As internal curing agents, superabsorbent polymers (SAPs) help enhance the degree of hydration of cement particles. In the meantime, however, they affect the dimensional stability and durability of the mixtures that benefit from them. This critical aspect, which is influenced by the type, size, and dosage of SAPs, motivated the current study. To obtain holistic assessments and side-by-side comparisons, six high-performance mortar mixtures were developed based on a control mixture. The referenced mixtures contained two types, two sizes, and two dosages of SAPs. Initially, the performance characteristics of the SAP powders were determined, in terms of water absorption and desorption. Autogenous shrinkage tests were then performed to evaluate how SAPs contribute to controlling this type of shrinkage over time. The microstructures of the developed mixtures were then analyzed using mercury intrusion porosimetry, paired with scanning electron microscope images, providing fundamental insights into to the role of SAPs in both short and long terms. To correlate the findings to the mechanical properties of the developed mixtures, a set of compressive strength and abrasion resistance tests were performed. The results were then complemented with the data obtained from the rapid chloride migration tests. This study’s outcome showed that SAP particles can effectively reduce the development of autogenous shrinkage-induced strains. Additionally, the inclusion of SAPs was found to alter microstructural characteristics, increasing the density of the binding gel, while introducing capillary pores. This was confirmed through enhanced abrasion resistance and reduced chloride resistivity.