Use of Superabsorbent Polymers in Concrete

Throughout the life of concrete, water has central importance: (1) it is an essential ingredient in the mixing, curing, and hardening of concrete; (2) its exchange with the surroundings causes hardened concrete to shrink, swell, and possibly crack; (3) its presence in hardened concrete influences strength and creep; and (4) it plays a central role in deterioration caused by frost action or alkali-silica reactions. This article gives an overview of some of the opportunities offered by the use of superabsorbent polymers (SAPs) for achieving that control. SAPs are polymeric materials that have the ability to absorb a large amount of liquid from the surroundings and retain in within their structure. SAPs are mainly developed for absorption of aqueous solutions and, in extreme cases, they may have a water uptake if 5000 times their own weight. SAPs belong to a group of so-called "smart materials" which are materials that, in a controlled way, significantly change their properties in response to an external stimulus. When SAPs are exposed to water, they swell, and when subsequently subjected to drying, they reversibly shrink. These key properties can actively be used in relation to concrete.