Defect dynamics, as studied by DC electrical resistance measurement during repeated compression of cement paste, mortar and concrete in the elastic regime, are characterized by defect generation that dominates during the first loading, defect healing that dominates during subsequent loading, and defect aggravation that dominates during subsequent unloading. The interface between sand and cement, that between silica fume and cement, and that between coarse aggregate and mortar contribute to the defect dynamics, particularly the defect healing. Electrical resistance measurement is also effective for monitoring damage, which causes the resistance to increase. Defect generation results in an irreversible increase in the baseline resistance as stress cycling progresses, whereas defect healing results in a reversible decrease in the resistivity upon compression within a stress cycle. Defect generation is relatively significant in the early cycles and diminishes upon cycling. As the cumulative damage increases, the extent of defect healing within a cycle also increases.