Development of Ca2+-based, ion-responsive superabsorbent hydrogel for cement applications: Self-healing and compressive strength.

Superabsorbent polymers (SAPs) are broadly applied in cement and concrete. However, the increased macrovoids resulting from the absorption/desorption of SAPs, remarkably reduced the resulting mechanical properties. In this study, we prepared superabsorbent CaAlg hydrogels by crosslinking Ca2+ and sodium alginate (NaAlg). The ion-responsive behavior of CaAlg was measured, and results showed at lower the Ca2+ concentrations, higher swelling potentials were observed, which was consistent with what was expected with the formation of a less dense network. This interesting dependence on Ca2+ concentration likely avoids the formation of large macro-pores during the mixing process of cement and results in increased swelling when cracks occur and water enters the crevices. The results of compressive strength measurements demonstrated that the addition of 0.5 wt% CaAlg resulted in a negligible reduction (0.014%) in compressive strength due to the limited swelling capacity in pore solution. Interestingly, in the sodium silicate self-healing system, in addition to the widely reported self-sealing effects upon adsorption of additional water, CaAlg also accelerates the precipitation of calcium silicate hydrates (CSH) by providing Ca2+, which makes the healing process more efficient.