Evaluation of Absorption Capacity and Spacing of Superabsorbent Polymer Particles in Cement Paste

The absorption capacity of superabsorbent polymers (SAP) in a real cement environment is a need-to-know property as a new admixture for concrete. In this study, fundamental stereology techniques were applied to cross sections of cement pastes in which solution-polymerized SAP particles were embedded. Its absorption capacity was estimated from the area fraction and particle size distribution of the SAP in the 2D planes. Further, the representative spacing between the SAP particles was also evaluated using point process statistics. The absorption capacity estimated was greater than that obtained by the tea-bag method using a cement filtrate. The SAP seems to absorb mixing water quickly in the initial short time during mixing. The number density of the SAP particles in the cross sections was also greater than the estimation calculated from the absorption capacity and the particle size distribution of initial dry SAP. This fact suggests that the SAP particles broke away during mixing. The centroids of SAP particles were distributed as to form a regular pattern. A procedure to evaluate the median distance from a given location to the surface of the nearest SAP particle was proposed by combining the mean diameter of swollen SAP profiles and the point process G- and F-functions. The distances between SAP particles were found at most a few mm for the mass fraction of 0.58% against cement.