During curing of concrete, hydration and thermal transfer inevitably result in expansion and shrinkage and hence, large tensile stresses in early-age concrete structures. As the mechanical properties of young concrete are still very low, structures are vulnerable in the construction stage to defects induced by crack nucleation, propagation and evolution, severely threatening the integrity, durability and safety of concrete structures and infrastructures like nuclear containment vessels, bridges and tunnel linings, hydraulic and off-shore structures. In order to predict the fracture property of early-age concrete and quantify its adverse effects on structural performances, it is pressing to investigate the computational modeling of early-age cracking in concrete structures under the chemo-thermo-mechanically coupled environment. To the above end, in this work we propose a multi-physically coupled phase-field cohesive zone model within our previously established framework of the unified phase-field theory. The interactions between the crack phase-field with the hydration reaction and thermal transfer are accounted for, and the dependence of the characteristics of crack phase-field evolution, e.g., the strength-based nucleation criterion, the energy-based propagation criterion and the variational principle based crack path chooser, etc., on the hydration degree and/or temperature, are quantified. Moreover, the numerical implementation of the proposed model in the context of the multi-field finite element method is also addressed. Representative numerical examples indicate that, with the couplings among hydration, thermal transfer, mechanical deformations and cracking as well as the competition between thermal expansion and autogenous shrinkage both properly accounted for, the proposed multiphysical phase-field cohesive zone model is able to reproduce the overall cracking process and fracture property quantitatively. Remarkably, the numerical predictions are affected by neither the phase-field length scale nor the mesh discretization, ensuing its promising prospective in fracture control of early-age concrete structures.

2021, 53(5): 1367-1382.
doi: 10.6052/0459-1879-21-020