Thermo-poro-mechanics Modelling of Gypsum Dehydration

Understanding the behaviour of natural calcium sulphates is important to ensure the sustainable integrity of civil structures. The phase transitions of these minerals are associated with considerable volume variations, creation of porosity with local defects, and water exchanges. Such changes can jeopardise the integrity of structures when the conditions that trigger the phase transitions are encountered. This paper uses advanced poromechanics to investigate the dehydration of gypsum when subjected to heating. The proposed approach includes the fundamental principles of non-equilibrium thermodynamics as well as the coupled multi-physics of thermal, hydraulic, mechanical and chemical (THMC) processes. A novel mathematical formulation is introduced to describe the coupled constitutive relationships in the reversible and dissipative regimes as well as the consequent partial differential equations that describe the THMC processes. The governing equations are integrated numerically using the finite element method. The obtained results show a significant correlation between gypsum dehydration and creation of fluid pathways. The proposed model can be generalised to describe the effects of dehydration in other minerals carrying water in their crystal structures.