Study on shrinkage and cracking performance of SAP-modified concrete

SAPs (Super Absorbent Polymers) are a group of polymeric materials that have the ability to absorb a significant amount of liquid many times their own weight from the surroundings and to retain the liquid within their structure without dissolving and to desorb it in the dry environment. The shrinkage and cracking performance of SAP-modified concrete was studied by experimental investigation, which express as total cracking area from early-age plastic cracking tests and shrinkage rate (restrained and unrestrained) from shrinkage tests respectively. The effect of SAP on shrinkage and cracking of concrete was compared with that of using pre-soaked ceramsite or perlite. The results show that SAP can effectively improve the cracking and shrinkage of concrete with achieving a 30-50% decrease. SAP particles improve the shrinkage and cracking performance of concrete in three ways as absorption-desorption, some absorbed water being bonded with hydrogen bond of macromolecule and filmforming on SAP particles. The coupling effect of SAP retards the water losing and change the moisture distribution in concrete, and thus reducing the cracking and shrinkage of concrete.