Absorption capacity of superabsorbent polymer in cement pastes: a robustness test

The aim of this study is to investigate how the absorption capacity of a superabsorbent polymer (SAP) in cement paste is influenced by a number of variables: cement type, water-to-cement ratio (w/c), additive, dry SAP particle size, mixing time, and temperature. By means of air void analysis of hardened cement paste, the absorption capacity and the specific surface of SAP voids are obtained. Parallel to the direct measurement of specific surface, this parameter is also derived from dry SAP particle size and absorption capacity. The results show that for the specific type of SAP examined the largest variation in absorption capacity is observed when changing the cement type. Prolonged mixing time can increase the absorption capacity of SAP up to 20%. The influence of a superplasticizer on the absorption capacity of SAP is statistically significant, whereas w/c ratio or dry SAP size has no apparent relation with absorption capacity. A temperature either higher or lower than 20 °C can lead to notably higher absorption capacity of SAP. Prediction of specific surface of SAP voids based on measured absorption capacity and calculation seems promising, as it agrees with the specific surface measured directly by air void analysis. During the preparation of differently sized SAP, it was realized that the order of rinsing and sieving influences the registered size distribution of SAP particles.