Altering the Crosslinking Density of Polyacrylamide Hydrogels to Increase Swelling Capacity and Promote Calcium Hydroxide Growth in Cement Voids

Polyacrylamide (PAM) superabsorbent polymer microspheres were synthesized for use as internal curing agents in low water-to-cement ratio mixtures. An increase in PAM swelling capacity in pore solutions was achieved by reducing the crosslinking density during synthesis: 5.1 g/g swelling was observed for 2 wt.% crosslinker and 20.6 g/g for 0.5 wt.% crosslinker. Capillary micromechanical experiments showed that a reduction in crosslinking density decreased the PAM elastic modulus from 1100 ± 310 kPa to 110 ± 15 kPa. Yet all PAM maintained mechanical integrity when mixed with cement and cured under a compressive load. SEM analysis showed hydrated product formation within cement voids left behind by dehydrated PAM. PAM with reduced crosslinking densities resulted in a 26 ± 7.3% increase in hydrated product formation within these voids. Cement paste density and compressive strength was not compromised by the addition of PAM.