Capillary Pressure Monitoring in Plastic Concrete for Controlling Early-Age Shrinkage Cracking

Cracking of concrete in its plastic stage is mainly caused by the buildup of a capillary pressure in the pore water of the material. Evaporation leads to the loss of water and, eventually, the solid particles at the surface can no longer be covered by a plane water film. The curved water surface between these particles leads to contracting forces and, possibly, to cracking. If the capillary pressure as the driving force for plastic shrinkage cracking is monitored by appropriate technical means, it would be possible to evaluate the cracking risk on site and to control curing measures accordingly. The measured capillary pressure captures the influences of the material composition, environmental conditions, and member's geometry. Therefore, it is a direct indicator for the early-age cracking risk. A newly developed wireless sensor system for on-site capillary pressure measurement is presented. Possible fields of application are the control of curing measures, the evaluation of their efficiency, and the characterization of concrete compositions with respect to their vulnerability to plastic shrinkage cracking.