ANOMALOUS ELECTROMECHANICAL BEHAVIOR OF PORTLAND-CEMENT - ELECTRO-OSMOTICALLY-INDUCED SHAPE CHANGES

The electromechanical behavior of hardened portland cement paste has b een investigated as a function of measurement frequency and de electri cal bias, using an interferometric technique. Large field-induced shap e changes on the order of 100 Angstrom A have been found in millimeter -thick specimens exposed to moisture. In addition, strong hysteresis e ffects were found on cycling a large ac field. Dry samples mere found to exhibit no field-induced deformations. The mechanism underlying thi s anomalous behavior is believed to be an electro-osmotically induced swelling of the pore structures. Evidence in support of this hypothesi s was Pound by corresponding investigations of porous silica gels.