A new multi-axial failure criterion for concrete

In this paper, a new failure criterion for the concrete is developed. Cement, sand, aggregates and water are mixed together and, after the setting, the cement paste binds aggregates and hardens to form concrete. Experimentally, pores of different sizes are diffused in the hardened cement paste and micro stresses arise in the neighborhood of the small pores when the concrete is loaded. The main idea of the proposed fail- ure criterion is based on the assumption that the macroscopic concrete failure occurs when the maximum ten- sile stress, around the small pores reaches the local hardened cement paste tensile strength. The proposed model explains many experimental phenomena as, for example, the different compression and tensile strengths, the different crack geometries in the tension and compression failures and the experimental failure contours under biaxial stress. 1 INRODUCTION of calcium silicate hydrates, the structure of the hardened cement paste. When concrete is loaded, The research of a failure criterion for concrete under high stress concentrations take place at microscopic multi-axial stresses is a very important task because level around these small cavities: they produce mi- of its numerous civil engineering applications. cro cracks that propagate across the hardened ce- Nowadays, several concrete failure tests under mul- ment paste till they become visible at macroscopic tiaxial stresses are available and many theoretical level. failure criteria have been proposed. These criteria, on the other hand, have been formulated, as a rule, by modifying failure conditions concerning other materials, (e.g. the Coulomb criterion) to the con- crete. Among all the criteria available in literature, the Rankine criterion (Van Mier, 1997, Jiràsek & Bazant, 2001, McClintock & Argon, 1966) seems to have a physical basis for the concrete. According to this criterion, in fact, concrete fails in brittle manner Figure 1.