This presentation will describe the synthesis, characterization, and use of superabsorbent polymer hydrogel particles as internal curing agents in cement-based mixtures. When incorporated into cement, the swollen hydrogel particles release their stored water to fuel the hydration reaction, resulting in reduced mixture shrinkage and cracking and thus increasing cement strength and durability. However, the hydrogel’s swelling performance and mechanical properties are strongly sensitive to multivalent cations that are naturally present in the alkaline aqueous phase of cementitious mixtures (including calcium and aluminum ions). To investigate polymer-ion interactions, model poly(acrylic acid-acrylamide)-based hydrogel particles with different chemical compositions were synthesized using solution and suspension polymerization techniques. Upon immersion of the particles in different salt solutions, the presence of multivalent cations significantly decreased the swelling capacity and altered the swelling kinetics to the point where some hydrogel compositions displayed rapid deswelling behavior. In solutions containing aluminum ions, a dense and mechanically stiff outer layer formed at the particle-solution interface and the internal polymer network was effectively destroyed, resulting in a water-filled capsule. It was also discovered that the presence of hydrogel particles of certain compositions encouraged the formation of specific inorganic phases within cement, including calcium hydroxide and calcium silicate hydrate phases. Ongoing work is now focused on optimizing the chemistry of the polymer hydrogels and specifically incorporating silica nanoparticles into the gels to allow for greater control of the cement microstructure.

Swelling and mechanical characterization of poly(acrylic acid)-based hydrogel particles used as internal curing agents in cement

255th National Meeting (2018)

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