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The final menu selection of the VCCTL is provided to calculate an estimated chloride ion diffusion coefficient for a concrete (optionally containing silica fume), based on knowledge of its mixture proportions and the achieved degree of hydration. The equations used in this prediction have been presented previously [12] and are also incorporated into a prototype Computer Integrated Knowledge System (CIKS) for predicting the service life of steel-reinforced concrete exposed to chloride ions [13], available separately from the VCCTL. To use Menu Selection 18, the user supplies the following four inputs for the concrete of interest: the w/c ratio, the silica fume content (mass fraction of cement basis), the volume fraction of aggregates, and the degree of hydration of the cement. Recommended ranges of applicability for each of these parameters are provided on the fill-in form and the user should extrapolate beyond these ranges only with extreme caution. Upon submittal, the estimated value of the diffusion coefficient, D, in SI units, is returned along with the 90 % confidence limits for D and some instructions on methodologies to lower the D value, if necessary.
Figure 22: Form to specify inputs for predicting chloride ion diffusivity of a concrete based on mixture parameters.