Dr.-Ing. Tao Wu
A phase-field approach to fracture coupled with diffusion
A variety of durability problems in cement and concrete are the results of the interaction of diffusion processes combined with chemical reactions, such as the attack of chloride ions. Crack have large impact on increasing the diffusivity of cementitious materials since they provide low-resistance pathways for chloride ions, such that the attack process of chloride ions is accelerated. Hence, the study of the transport of chloride ions in cracked concrete is crucial to determine the durability and the service life of concrete structures.
Phase-field modeling is a very powerful and reliable tool to predict cracking phenomena. It is able to simulate complicated fracture processes, including crack initiation, propagation, merging and branching in a unified framework without the need for ad-hoc criteria and on a fixed mesh. The objective of this project is to develop phase-field modeling coupled with diffusion for describing the effect of cracking on diffusivity of cementitious materials. The proposed model satisfies the consistency of the second law of thermodynamics. The analysis starts from the cement paste. An anisotropic diffusivity tensor is defined as a function of the phase-field parameter, accounting for the evidence that diffusivity is related to the availability of connected paths for the ion migration and therefore is expected to increase parallel to the crack plane. The brazilian test is used to calibrate the local relationship between phase-field parameter and diffusivity through the comparison between numerical and experimental data.
The calibrated relationship between phase-field parameter and diffusivity is then upscaled to the mesostructure of concrete, which is comprised by cement paste and aggregates. The mesostructure of concrete is obtained by CT-Scan.
Publications within the framework of the RTG:
Publications in peer-reviewed scientific journals:
T. Wu, A. Carpiuc-Prisacari, M. Poncelet and L. De Lorenzis. Phase-field simulation of interactive mixed-mode fracture tests on cement mortar with full-field displacement boundary conditions, Engineering Fracture Mechnics,182: 658-688, 2017.
V. Rheinheimer, Y.P. Wu, T. Wu, K. Celik, J.Y. Wang, L. De Lorenzis, P. Wriggers, M.H. Zhang and P.J.M. Monteiro. Multi-scale study of high-strength low-thermal-conductivity cement composites containing cenospheres. Cement and Concrete Composites, 80:91-103, 2017.
T. Wu and L. De Lorenzis. A phase-field approach to fracture coupled with diffusion. Computer Methods in Applied Mechanics and Engineering, 312:196-223, 2016.
P. Carrara, T. Wu, R. Kruse and L. De Lorenzis. Towards multiscale modeling of the interaction between transport and fracture in concrete. RILEM Letters 1, S. 94-101, 2016.