Multiscale Analytical/Numerical Theory of the Diffusivity of Concrete

The ionic diffusivity of a concrete is a function of its microstructure at many length scales, ranging from nanometers to millimeters. The microstructure is largely controlled by the initial concrete mixture proportions and the ultimate curing conditions. Linking a property like ionic diffusivity to the microstructure then requires a multiscale approach. A multiscale microstructural computer model for ionic diffusivity has been previously developed. This model has been developed specifically to compute the chloride diffusivity of concretes with various mixture proportions and projected degrees of hydration. The three key parts of this model were dependent on large-scale supercomputer-magnitude simulations to: (1) determine the total volume of interfacial zones for a given aggregate distribution; (2) simulate the hydrated cement paste microstructure around a typical aggregate; and (3) compute the effect of the aggregates and interfacial zones on the overall diffusivity of the concrete. The key feature of this model is that one can approximately take into account the redistribution of cement paste between interfacial transition zone regions and bulk paste regions, and its important effect on overall concrete diffusivity. In the present article, we review the previously developed model and show how analytical equations can accurately replace the large scale computer simulations of parts (1) and (3). This accomplishment will make the model more usable by those who do not have access to supercomputer computing power.