Multi-cale model for concrete

Deterioration of concrete structures by chemical and/or thermal processes is one main cause of reduced life-span expectation of civil infrastructure such as, e.g., buildings, tunnels, and bridges. Concrete can undergo significant damage because of swelling in consequence of internal chemical reaction and/or phase change of the capillary water (freezing, evaporation). E.g., evaporation of the capillary water as observed during tunnel fire accidents leads to spalling of the concrete lining. Such deterioration processes may cause the collapse of the entire structure. In the course of the proposed research project, an analysis tool for quantification of the deterioration of concrete and of the load-carrying capacity of damaged concrete structures will be developed. Hereby, the realistic description of the deterioration process in consequence of chemical and thermal loading is of central importance. As regards mechanical modeling of concrete, a material model for concrete subjected to local, large triaxial stress states was recently developed at the Institute for Strength of Materials (IFF) at Vienna University of Technology (FWF-P11337-ÖPY:"Numerical modeling of concrete under local, large triaxial pressure"). The underlying macroscopic formulation of this model, however, does not allow simulation of chemical reactions and/or phase- change processes in concrete. In the course of the proposed research project, the macroscopic formulation will be extended towards consideration of several scales of observation (hydrates scale, cement-matrix scale, aggregate scale). The so-obtained multi-scale material model for concrete allows to simulate chemical and phase-change processes at the scale of their occurence. Continuum micromechanics will be employed to shift the determined material response from lower scales towards the macroscale. Accordingly, all findings at lower scales will be incorporated into the developed (macroscopic) material model for concrete. Financial support via the TUWP18 project "Einsatz numerischer Berechnungsverfahren zur Ermittlung der Sicherheit im Tunnelbau" (recommended project by the "Rat für Forschung und Technologieentwicklung") allows to considerably improve the research facilities at the laboratory of the IFF within the year 2002 (no financial support for personnel is provided by the TUWP18 project). These facilities will be intensely used throughout the proposed research project. Theoretical findings will be continuously assessed by means of respective experimental work. The multi-scale material model for concrete will allow simulation of the effect of seasonal or artificial freezinghawing, fire load, chemical shrinkage, and other chemical attacks. In the course of the proposed research project, this model will be employed for the assessment of the stability of shallow tunnels under fire load.