SUBCRITICAL CRACK-GROWTH IN THE CEMENT PASTE-STEEL TRANSITION ZONE

The shape of the stress-strain curve for most concretes may be explained in terms of subcritical crack growth in the transition zone between coarse aggregate particles and the cement paste matrix. This paper discusses an investigation of subcritical crack growth in composite double torsion specimens made of steel and cement paste containing silica fume, carbon black, or plain portland cement. At age 7 days, the specimens containing carbon black proved to be less resistant to crack propagation in the transition zone than the other specimens. This result is consistent with the stress-strain behavior of concretes containing carbon black. An examination of the microstructure showed that the carbon black cement paste contained larger and more numerous voids than a comparable silica fume cement paste. © 1990.