"From Baby Diapers to Bridge Decks: Using Polymer Science to Improve Concrete"
Polymer hydrogels have many industrial uses, from injectable drug-delivery and self-healing materials to the superabsorbent particles used in baby diapers and as soil additives. This presentation will describe the design and use of hydrogel particles as internal curing agents in high-performance concrete. These particles release water as the cement cures, preventing self-desiccation and increasing the concrete’s strength, durability, and service life. Since 2012, we have conducted experiments at Purdue using custom synthesized hydrogel particles to determine the relationship between the chemical and physical structures of the hydrogels and their overall internal curing performance. Construction practitioners commonly assume that hydrogel internal curing agents are chemically inert within concrete mixtures. However, our more recent results have shown that instead, the presence of hydrogel particles of certain compositions – including acrylamide-rich particles and composite particles containing silica – encourages the formation of high-strength inorganic phases within the cement microstructure, thus forming a more dense and durable concrete. We have also shown that the presence of multivalent cations that naturally occur in hydrating cement actually decreases the swelling capacity and sorption kinetics of the hydrogel particles to the point where some compositions displayed fast deswelling behavior and the formation of a mechanically stiff outer shell. Ongoing work is now focused on optimizing the chemistry of the polymer hydrogels to tune and control the microstructure of the concrete, with the ultimate goal of designing new concrete mixtures with increased performance and durability.