A multi physics based modelling approach to predict mechanical and thermo mechanical behaviour of cementitious composite in a multi scale framework

Abstract

Concrete is a heterogeneous material whose constituents (e.g., cement paste, aggregate etc.) range from a characteristic length-scale dimension of a nanometre to a metre. Owing to the heterogeneity of concrete and the contrasting nature of its constituent s (cement paste, aggregate) response at ambient and high temperatures, applying a homogeneous macroscopic model to predict concrete s mechanical and thermo-mechanical performance is questionable. Hence, in this thesis, multiple physical and chemical processes that occur within the concrete constituents at different length scales are considered, and a multi-scale model is developed to study the mechanical and thermo-mechanical behaviour of concrete in a hygral-thermal-chemical-mechanical (HTCM) framework. Firstly, the governing equations of HTCM processes are described at meso-scale, a length-scale where coarse aggregate is explicitly modelled in a binding medium called mortar. After that, a hierarchical homogenization approach is employed, and the evolution of mechanical properties etc., are upscaled (from micro to meso) and used at the meso-scale. The proposed methodology is then used to predict the evolution of mechanical properties (e.g., compressive strength) and time-dependent deformation (e.g., shrinkage and creep) of cement paste, mortar and concrete for a wide variety of factors (e.g., type and content of constituents, different curing conditions, etc.). Like ambient conditions, the developed model is used to simulate thermo-mechanical responses (e.g., in terms of spalling, deformation, residual capacity, etc.) of both plain and reinforced concrete structural elements. Further, the effect of several other meso and macroscopic parameters (e.g., interfacial transition zone, aggregate shape, random configurations of aggregates etc.) on concrete s mechanical and thermo-mechanical behaviour is studied numerically at the meso-scale. Validation of the proposed methodology with the available experimental results at both ambient and high temperatures for a wid...