Defect dynamics and damage of cement-based materials, studied by electrical resistance measurement

Defect dynamics, as studied by DC electrical resistance measurement during repeated compression of cement paste, mortar and concrete in the elastic re gime, are characterized by defect generation that dominates during the firs t loading, defect healing that dominates during subsequent loading, and def ect aggravation that dominates during subsequent unloading. The interface b etween sand and cement, that between silica fume and cement, and that betwe en coarse aggregate and mortar contribute to the defect dynamics, particula rly the defect healing. Electrical resistance measurement is also effective for monitoring damage, which causes the resistance to increase. Defect gen eration results in an irreversible increase in the baseline resistance as s tress cycling progresses, whereas defect healing results in a reversible de crease in the resistivity upon compression within a stress cycle. Defect ge neration is relatively significant in the early cycles and diminishes upon cycling. As the cumulative damage increases, the extent of defect healing w ithin a cycle also increases. (C) 2001 Kluwer Academic Publishers.