Microstructural modelling to relate transport properties to chemically and mechanically induced change in microstructure (PhD)

Microstructural models are used for investigating the evolution of the microstructure as well as for predicting transport in and mechanical properties of concrete. These models are applied to simulate interactions between particles at the microscale and make it possible to predict the hydration of cement-based materials, structural formation and the development of strength. Microstructural models allow for assessing factors that affect hydration, the probability of cracking and the effect of alkalis, gypsum and additives on the rate of hydration. Cement hydration, structural formation and the chemical evolution of cement-based materials in contact with porewater are mutually dependent phenomena. Existing microstructural models have paid relatively little attention to the modelling of the chemical evolution of cement-based materials in contact with porewater. The present research proposal intends to integrate chemical interactions between a cementitious solid phase and an aqueous phase, which are not in thermodynamic equilibrium with each other, in microstructural models.

The main goals of the proposed Ph.D. thesis are:

• To simulate the microstructural changes of concrete due to chemical degradation processes such as carbonation,  decalcification and sulphate attack, and
• To link the effect of microstructural transformations to changes in (macroscopic) transport properties (e.g. permeability or pore diffusion coefficient).

 To achieve these objectives, it is intended to integrate a geochemical module into the existing model HYMOSTRUC, which has been developed at the Technical University of Delft, The Netherlands. This will allow to model chemical degradation processes as a function of invasive pore water composition for time periods beyond the period of cement hydration (i.e. the current time period of HYMOSTRUC).

Research proposed as part of work package 1 will be based on the existing microstructural model HYMOSTRUC. This model for cement hydration and virtual microstructures allows simulating the degree of hydration as a function of (i) particle size distribution, (ii) chemical composition of the cement, (iii) the water/cement ratio and (iv) the reaction temperature.

The current R&D proposal plans to implement a general geochemical module in HYMOSTRUC. Together with the transport module, which was recently integrated in the HYMOSTRUC code, this will allow to couple microstructural changes with geochemical degradation processes.

Next, the new microstructural model will be used to characterize the pore structure in terms of pore size distribution, connectivity, surface area, hydraulic radius and total porosity. These properties are linked to (macroscale) transport properties by empirical or physical models. Alternatively, permeability is simulated outside HYMOSTRUC, by exporting respective geometry at the specific time and link it to a dedicated modelling tool.