Effect of superabsorbent polymers on the properties of cement paste particle under different relative humidities

This study investigated the adsorption-desorption kinetics of polyacrylic acid sodium salt (AA) and polyacrylic acid-acrylamide copolymer (AM) under different relative humidities by the static water vapour adsorption experiment. TG and SEM-EDS were used to study the effect of Superabsorbent polymers (SAP) on the hydration degree of cement without mixing water. The results show that the adsorption capacity of AA is higher than that of AM, and the desorption capacity of AA is worse than that of AM. At 97%RH, AA and AM can absorb 233.2% and 210.5% of water vapour from the environment. Compared with cement without SAP, the addition of AA can increase the hydration degree of cement by 17.05%-53.58% (one-element system) and 14.21%-30.29% (binary system); the addition of AM can increase the hydration degree of cement by 8.82%-20.13% (one-element system) and 4.79%- 9.15% (binary system). The degree of cement hydration on the surface of SAP particles is higher than that of other parts. It was found that needle-like products exist on both the surface of SAP particles and cement particles and the calcium content is similar to the TG results. Calcium hydroxide and calcium element content are ranked as AA particle surface cement > AM particle surface cement > AA cement added > AM cement added > pure cement.