A Handy Model for Simulating the Hydration Phenomena in Concrete: General Formulation and Application to Recycled-Aggregate Concrete

Concrete mechanical properties are strictly controlled by the physical and chemical phenomena induced by the hydration reactions developing during the setting and hardening phases. Hence, modelling such phenomena is instrumental in predicting the time evolution of the relevant mechanical properties and their possible correlations with both the mix constituents and the actual curing conditions. Particularly, heat transfer due to the exothermal hydration reaction of cement is the key physical phenomenon occurring during concrete hardening. This paper presents a consistent theoretical formulation to model the heat-flow occurring in hardening concrete mixes. The model is based on the Fourier equation of heat transfer: an adiabatic hydration curve is assumed to describe the heat source deriving by the hydration reaction and the well-known Arrhenius approach is adopted to describe the relationship between reaction kinetics in ideal adiabatic conditions and in the actual temperature field developed inside the concrete sample. A Finite-Difference numerical solution is presented as a further relevant contribution. The model is formulated under the simplified assumption of 1D heat flow and the proposed numerical solution is particularly suitable to be implemented into a common spreadsheet, this being - in the authors' opinion – a very attractive feature. Temperature measurements obtained for the samples of two different mixes, cured under both adiabatic and semi-adiabatic conditions, are considered for validating the proposed model. Finally, the application of the proposed model to simulate the hydration processes occurring in Recycled Aggregates Concrete (RAC) allows to clarify the role that some key parameters play on the mechanical properties of RAC. It is an attempt to introduce a more fundamental approach in the analysis of RAC’s mechanical properties, that are often investigated under a merely empirical perspective