Multi-Scale Microstructural Modeling of Concrete Diffusivity: Identification of Significant Variables.
Multi-Scale Microstructural Modeling of Concrete
Diffusivity: Identification of Significant Variables.
Bentz, D. P.; Garboczi, E. J.; Lagergren, E. S.
Cement, Concrete, and Aggregates, Vol. 20, No. 1,
129-139, June 1998.
concretes; concrete diffusivity; durability;
experimental design; interfacial transition zone;
microstructure; modeling; performance prediction
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.