Thermo-hygro-chemical model of concrete: from curing to high temperature behavior

• Published in: Materials and structures 2024-09, Vol.57 (8)
• Main Authors: Sciumè, Giuseppe, Moreira, Murilo Henrique, Dal Pont, Stefano
• Format: Article
• Language: English
• Subjects: Civil Engineering; Engineering Sciences
• ISSN: 1359-5997; 1871-6873
• DOI: 10.1617/s11527-024-02454-3

Concrete is a heterogeneous multiphase material composed of various solid phases that interact both physically and chemically with each other and with the water filling the pores. Among these solid phases, a crucial role is played by the calcium silicate hydrates (C-S-H), which are the primary products of cement hydration and are primarily responsible for the material's physical properties. When concrete is subjected to high temperatures, the chemically bound water in C-S-H is progressively released, leading to a degradation in the strength and durability properties of the concrete. Hence, understanding how the dynamics of C-S-H dehydration and the corresponding evolution of hygro-mechanical properties (e.g. strength, permeability, porosity) are related with the characteristic observed phenomenology of spalling is crucial to assess the resistance of a structure under high temperature. Within this context, multiphysics thermo-hygro-chemical (THC) numerical models now play a pivotal role in predicting and analyzing structures' performance under fire accidents. However, to enhance the reliability of numerical results, properly accounting for the initial hygro-chemical state of the structure just before the accident is of chief importance. This work presents a monolithic fully-coupled unified THC mathematical model enabling the simulation of the full service life of the material: from casting (early-age behavior and curing), through aging, until the eventual occurrence of an accident (high temperature, high pressure, ...). The model provides the evolution of the hydration reaction as a function of time, temperature, and relative humidity, as well as the eventual dehydration occurring at high temperature. The main contribution of this work lies in the proposition of general chemo-physical constitutive relationships that incorporate the influence of the hygro-thermal state of the material as well as that of C-S-H hydration/dehydration in a fully-coupled manner. The evolution of volume fraction of phases and porosity during hydration/dehydration follows Powers' stoechiometric model, while a novel adsorption-desorption model is proposed to properly account for the irreversibility of chemical damage in the porous microstructure. This enables an alternative, simpler approach requiring only a limited number of experiments for the model calibration. The model is firstly benchmarked by simulating the early-age behavior of a concrete sample, and it is then validated aga