Effect of Seasonal Characteristics of Temperature and Relative Humidity on Chloride Diffusion Process in Concrete: A Preliminary Theoretical Study

Round 1

Reviewer 1 Report

This paper presents a theoretical approach to chloride diffusion in concrete that accounts for the effect of seasonal variations (temperature and humidity) on the chloride diffusivity. Although the approach has merits, there are simplifying assumptions in the approach that mislead to some of the conclusions. Specific comments that should be addressed are listed below:

Page 2, line 54, line 68 - the authors state that chloride transport is a very complex process, yet their approach assumes that chloride ingress is governed by diffusion only and not by other transport mechanisms. Chloride convection becomes critical when there is fluctuation of the concrete relative humidity in the concrete cover.  Eq. (3) assumes that D_a is constant over the depth of the concrete cover. Chloride binding affects the chloride diffusivity along the concrete depth. Furthermore, by implying D_a is space-independent, it is also assumed that the humidity profile is constant over the concrete cover, which is not a realistic assumption unless the concrete is saturated (where h = 100%). In fact only the external few mm (convection zone) are affected by fluctuations in relative humidity; the inner concrete usually remains saturated. Therefore, different transport mechanisms govern chloride ingress along the depth of the concrete depending on the concrete saturation level. At what depth is the chloride content of Fig. 3 calculated? Also, what is the value of C_s for the numerical solution? The same for both cities? Use the same scale in the y-axis to compare the norm error of chloride profiles for Beijing and Urumqi in Fig. 4. What is the correlation coefficient R² for the results presented in Fig. 5 for both Beijing and Urumqi? What is the value of R² chosen as acceptable for the seasonal correction coefficients presented in Fig. 6? The argument that the seasonal correction coefficient is completely independent for D might be misleading, since the authors already assume D as space and time independent in the solution. Why is the depth of the convection zone Dx = 0 in the results presented in Fig. 11? If humidity variation is to be accounted for in the calculation of chloride profiles, this parameter needs to be taken into account. Otherwise, there is an implicit assumption that the concrete is saturated, and therefore D should not be modified for humidity variations. The validation presented in Fig. 11 is misleading as the finite element solution is modelling the same process solved by the analytical solution provided in Eq. (19), so both solutions should be equal. In fact, Eq. (19) already accounts for the seasonal correction coefficient calculated from a regression analysis between Eq. (3) and the FE solution. Page 12, line 304 - the authors argue that their approach improves the accuracy of the calculated chloride profiles. While different theoretical solutions might differ in complexity and therefore account for different physical phenomena, their accuracy can only be established by comparing to actual field chloride profiles.

Author Response

Thanks a lot for your comments and suggestions on this paper. We have revised the paper according to your comments. Please check the uploaded file.

Thank your again for reviewing our paper.

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Reviewer 2 Report

The authors describe an interesting theoretical model for chloride diffusion in concrete that could take into account seasonal effects while being computationally efficient.

The article is well-written and scientifically sound. The purely proof-of-concept nature of the work is correctly pointed out.

I only have a few comments:

Is "chloride environment" a technical jargon? Otherwise I feel it might be better to use the expression "chloride-rich environment" or similar Line 268: correct "chlorine" as "chloride".

Author Response

Thanks a lot for your comments on this paper. We have revised the paper according to your opinions. Please check the uploaded file.

Thank you again for reviewing our paper.

Author Response File: Author Response.pdf