A 1D numerical model for simulating early age hydration and related mechanical properties

The heat that liberates during early age cement hydration causes a semi-adiabatic temperature rise of hardening concrete, while starting to develop its physical and mechanical properties. In fact, the heat generated by the hardening mixture depends on the cement properties and its hardening conditions like for instance the type of binders, quality of aggregates, water-to-cement ratio, type of formwork etc. A simple 1D numerical model can be formulated to simulate the time evolution of the aforementioned reaction and determine the corresponding “degree of hydration”. The present paper proposes a detailed description of a numerical procedure that is capable of simulating the time evolution of a concrete’s early age temperature development under semi-adiabatic conditions. In this numerical procedure, the differential heat equation takes into account the heat that liberates to the environment through the formwork or concrete’s surface. This is done by considering the Arrhenius Principle and assuming a pre-defined shape of the adiabatic hydration curve of the concrete mixture. Hence, an indirect identification procedure of the aforementioned adiabatic curve is ideally carried out, as the simulated temperature evolution in semi-adiabatic conditions is brought to match the temperature measurements on a hardening concrete sample. This modelling procedure, enabling various boundary conditions, ranging from semi-adiabatic to isothermal, can be used to calculate the degree of hydration of a real in-situ cast concrete. As a matter of fact, the degree of hydration, which represents the evolution of the microstructure formation, can be correlated to the development of the relevant concrete mechanical properties, such as compressive strength and elastic modulus. The present paper shows several examples of how this model can be used in lab and practical conditions. Finally, it is worth highlighting that this work results from the SUPERCONCRETE Project (H2020-MSCA-RISE-2014 – n. 645704), funded by the European Union as part of the H2020 Programme