Defect dynamics of cement mortar under repeated loading, studied by electrical resistivity measurement

Defect dynamics, as studied by electrical resistivity measurement during repeated compression of cement mortar in the elastic regime, are characterized by defect generation, defect healing and defect aggravation. Defect generation dominates in the first compressive loading and in tensile loading in any loading cycle. Defect healing dominates in all subsequent compressive loading cycles and in tensile unloading in any cycle. Defect aggravation dominates during compressive unloading in any cycle and occurs during tensile loading in any cycle. Both the interface between sand and cement and that between silica fume and cement contribute to the defect dynamics, particularly the defect healing. The defect dynamics give similar effects to the longitudinal and transverse resistivities. Upon uniaxial compression, the resistivity decreases (except for the first cycle); upon uniaxial tension, the resistivity increases.