Electrically-induced shape changes in cement-based materials

The electromechanical behavior of hardened portland cement paste has been investigated as a function of measurement frequency and DC electrical bias using an interferometric technique. Large field induced shape changes on the order of 100 A have been found in millimeter thick specimens exposed to moisture. In addition, strong hysteresis effects were found on cycling a large AC field. Dry samples were found to exhibit no field-induced deformations. The mechanism underlying this anomalous behavior is believed to be an electro-osmotically induced swelling of the pore structures. Evidence in support of this hypothesis was found by corresponding investigations of porous silica gels.