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Multi-Scale Microstructural Modeling of Concrete Diffusivity: Identification of Significant Variables.


pdf icon Multi-Scale Microstructural Modeling of Concrete Diffusivity: Identification of Significant Variables. (1167 K)
Bentz, D. P.; Garboczi, E. J.; Lagergren, E. S.

Cement, Concrete, and Aggregates, Vol. 20, No. 1, 129-139, June 1998.

Keywords:

concretes; concrete diffusivity; durability; experimental design; interfacial transition zone; microstructure; modeling; performance prediction

Abstract:

The ability to predict the expected chloride diffusivity of a concrete based on its mixture proportions and field-curing conditions would be of great benefit both in predicting service life of the concrete and in developing durability-based design codes. Here, a multi-scale microstructural computer model is applied to computing the chloride diffusivities of concretes with various mixture proportions and projected degrees of hydration. A fractional factorial experimental design has been implemented to study the effects in the model of seven major variables: water-to-cement (W/C) ratio, degree of hydration, aggregate volume fraction, coarse aggregate particle size distribution, fine aggregate particle size distribution, interfacial transition zone thickness, and air content. Based on this experimental design, W/C ratio, degree of hydration, and aggregate volume fraction have been identified as the three major variables influencing concrete diffusivity in the model. Following identification of the significant variables, a response surface design has been executed and least squares regression used to develop a simple equation for predicting chloride ion diffusivity in concrete based on these three parameters. This simple equation essentially summarizes the complicated simulations involved in computing the model response. Finally, simulations have been conducted to examine the extent of the surface layer in cast-in-place concrete, where the local aggregate volume fraction near the surface is less than that to be found in the bulk of the concrete.