Analysis of new damage evolution models for early age concrete

Concrete cone (or breakout) failure mode is the dominant failure for cast-in headed anchors under tension in mature brittle concrete, however, other failure modes such as plug failure has been found experimentally to dominate in early age concrete. Design codes generally assume concrete cone failure and do not cover plug failure. A new model for concrete at early ages is proposed based on continuum damage mechanics which can model both failure modes for cast-in headed anchors in early age concrete. The new damage model combines a modified power law for the onset of damage, an exponential softening law for the post-failure softening stage, and an additional modified power law to reproduce the final stages of fracture. The combined damage law is calibrated with three experimental tests for concrete at two different ages (43 hours and 14 days): uniaxial compression, Brazilian splitting tensile and wedge splitting tests. The new models are applied to investigate anchor pull-out failure to demonstrate that both cone and plug failure modes are produced depending on concrete age. Simulations using the combined damage evolution laws gave the lowest average percent error over the mechanical properties measured in the four tests, when compared with existing damage evolution laws.