Matthew Krafcik

Improved Concrete Materials with Hydrogel-Based Internal Curing Agents

This research article will describe the design and use of polyelectrolyte hydrogel particles as internal curing agents in concrete and present new results on relevant hydrogel-ion interactions. When incorporated into concrete, hydrogel particles release their stored water to fuel the curing reaction, resulting in reduced volumetric shrinkage and cracking and thus increasing concrete service life. The hydrogel’s swelling performance and mechanical properties are strongly sensitive to multivalent cations that are naturally present in concrete mixtures, including calcium and aluminum. Model poly(acrylic acid(AA)-acrylamide(AM))-based hydrogel particles with different chemical compositions (AA:AM monomer ratio) were synthesized and immersed in sodium, calcium, and aluminum salt solutions. The presence of multivalent cations resulted in decreased swelling capacity and altered swelling kinetics to the point where some hydrogel compositions displayed rapid deswelling behavior and the formation of a mechanically stiff shell. Interestingly, when incorporated into mortar, hydrogel particles reduced mixture shrinkage while encouraging the formation of specific inorganic phases (calcium hydroxide and calcium silicate hydrate) within the void space previously occupied by the swollen particle.

Synthesis and Characterization of Superabsorbent Polymer Hydrogels Used as Internal Curing Agents: Impact of Particle Shape on Mortar Compressive Strength

Superabsorbent polymer hydrogels have proven to be effective internal curing agents for high-performance concrete because of their ability to absorb and release large amounts of water during hydration and thus mitigate autogenous shrinkage. In this study, the impact of hydrogel particle shape on the microstructure and compressive strength of internally cured mortar was experimentally determined. Inverse suspension polymerization was used to synthesize spherical poly(sodium-acrylate acrylamide) hydrogel particles, while solution polymerization was used to create similarly sized angular particles with identical chemical composition. The hydrogels were characterized with swelling tests in water and cement pore solution. Particle shape did not impact the swelling behavior, and micrographs confirmed that the particles maintained their shape during mixing and placement. Despite the introduction of spherical- and angular-shaped voids from the swollen hydrogel particles, there were no significant differences observed between the compressive strengths of the control mortar and the mortars containing either the spherical or angular hydrogel particles.