13 14Experimental work has demonstrated that cracks can be healed in ordinary cementitious 15 materials in the presence of water. The primary healing mechanisms are hydration of the 16 unreacted nuclei of cement particles and the long-term formation of calcite. A mathematical 17 model for simulating early-age autogenous healing of ordinary cement-based materials is 18proposed, which employs a coupled thermo-hygro-chemical (THC)

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The paper presents an overview of a finite element approach for the analysis of the thermohygro-mechanical-hydration behaviour of concrete structures. The thermo-hygro component considers the mass balance equation of moisture as well as the enthalpy balance equation, and uses two primary variables, namely the capillary pressure and temperature. Heat of hydration is simulated using the approach of Schlinder and Folliard. The basic mechanical model simulates directional cracking, rough crack closure and crushing using a plastic-damage-contact approach. Hydration dependency is introduced into the mechanical constitutive model. The material data from the Concrack benchmark (CEOS.fr,2013) are considered with the model. This includes data on adiabatic temperature changes during curing, changing elastic properties during curing, shrinkage and creep. The model, as implemented in the finite element program LUSAS, is used to analyse the Concrack benchmark beam RL1. Particular attention is paid to crack openings and the difference between predicted crack openings from analyses with and without time dependent effects. It is concluded that ignoring time dependent effects can result in a significant underestimate of crack openings in the working load range.

An overview of a recently developed thermo-hygro-mechanical-hydration model (THMH) model for concrete is presented. The coupled flow aspect of the model solves a mass balance equation for moisture and an enthalpy balance equation for heat transport. A key assumption used to simplify the moisture flow component of the model is that the gas pressure is assumed to remain constant at atmospheric pressure. The model simulates early age concrete behaviour and therefore a hydration component is included in the formulation. This uses the approach of Schindler & Folliard, which was based on a comprehensive range of data and gives good predictions for a range of cement types. The mechanical component of the model simulates the dependence of the strength and stiffness properties of the model on the degree of hydration. Furthermore, the plastic-damage-contact model of Jefferson and Mihai; which simulates cracking, crushing and crack closure; has been extended to include hydration dependent behaviour. The hydration sub-model is also linked to a new creep model. The paper includes an example of the analysis of beam RL1 from the Concrack benchmark programme. The focus of the work from this benchmark is the accurate prediction of crack widths in reinforced concrete elements and reference is made to a recent study that explored the accuracy of the present model in this context. A critique of the model is presented which concludes that the moisture flow component of the model would be greatly improved by including coupling between the flow parameters and mechanical damage.