An Experimental and Statistical Study on Rebar Corrosion Considering the Temperature Effect Using Gaussian Process Regression

Round 1

Reviewer 1 Report

The work analyses the effects of temperature on rebar corrosion. To do this, the authors use Gaussian process regression in order to predict the behaviour of different samples in an uncontrolled air environment without forced corrosion. The results are used to generate a Temperature-potential index, which is subsequently applied on rebars with forced corrosion to remove the effects of temperature from the potential. The authors highlight the influence of temperature on the corrosion potential, as well as a different behaviour between samples depending on the diameter.

The manuscript addresses a useful issue, providing a simple methodology to eliminate the effect of temperature on the corrosion potential. However, different parts of the document should be improved to clarify some details.

 

• The quality of the figures should be improved. Some of them are very small.
• Lines 90 – 92: the authors refer to two experimental cases: automatic and manual. How often are measurements taken in the first case? And in the second? How long was this second experiment? The measurement procedure and instruments should be described for repeatability.
• Lines 93 – 95: What criteria was used for the elimination of outliers?
• Line 94: ¿How was the temperature measured? How often?
• An attempt is being made to analyse the influence of temperature but, was humidity in the room also taken into account? Was it measured?
• Line 97: Can be more convenient to represent the diameters without hyphens. In addition, the measurement instrument sensitivity should be included (magnitude and error, and same number of decimal places).
• Line 111: the data was collected during two months. Continuously? How often?
• Section 2.2. It would probably be interesting to indicate how the corrosion potential was measured. It could make reading easier.
• Section 2.3. The procedure used to determine the corrosion rate or corrosion intensity should be described.
• Line 149: where the f(x) follows … where f(x) follows …
• Line 161: the verb was omitted. “The regression model is considered to be reliable”
• Section 2.7. How the TPI was applied to the corrosion potential data? The authors should clarify this issue.
• Line 187: authors should give more indications about the “inflection point”.
• Table 1. The table 1 is confusing. Perhaps it would be convenient to divide the table in two. On the one hand, the relationship between corrosion rate and corrosion level; inn another table, the results obtained for the samples.
• Line 220: ¿ML? Should be previously described.
• Figure 7 and 8: seems to provide the same data. Is everything correct? Seems that both give de GPR fitting for non-corroded potential. Should be better explained. The label in figure 7a and 8a could be confused.
• Line 236. The trend was clearer than in Figure 4. In what sense?
• Lines 242 to 244. The idea is repeated in the previous paragraph. Can be omitted.
• Figure 9. Is the range gap an average value? Authors should indicate this issue.
• Despite the fact that the authors indicated that two experimental cases were carried out, the data used for corrosion rate seems to not have much weight in the results.

Author Response

Respected Reviewer,

Thank you for reviewing our manuscript entitled “An experimental and statistical study on rebar corrosion considering the temperature effect using Gaussian process regression” for possible publication in the journal of “Applied Sciences”. We are thankful to you for your quick and valuable feedbacks to improve the quality of our manuscript for possible publication in the journal. We have revised the manuscript according to your comments and suggestions. The pointwise replies are given here in the word file.

Author Response File: Author Response.pdf

Reviewer 2 Report

I think the paper is interesting and important for corrosion research in concrete. The introduction was very well written providing insights to previous related studies. However, I think there are still a lot of room for improvement on the methodology and discussion sections. Here are some comments and suggestions to improve the quality and readability of the paper.

 

Please be careful with the use of article "the" throughout the paper, and please recheck it.

Line 14, suggestion of terminology "corrosion potential behavior": to either “corrosion behavior” or “corrosion potential”.

Line 31, Does "these aggressive materials" refer to chloride and sulfate? If so, maybe it is better to use the term "aggressive ions" or "aggressive medium" instead of "aggressive materials".

Line 34, terminology: electro-chemical --> electrochemical. "the" can be removed from all methods, i.e., concrete resistivity method, half-cell method, and LPR.

Line 61, "corrosion behavior with pores and humidity". This is a bit unclear. Can the authors explain more clearly what was carried out in this research? Otherwise, I think the sentence should be rephrased.

Line 66, Please delete "are required" or please complete the sentence.

Line 80-82, I think this sentence is a bit unclear. "thermal effects" on which parameter?

Line 109, Terminology: Checking --> measuring?

Line 110, Can the authors explain more in this paragraph, why an uncontrolled air was chosen to remove the temperature effect?

Line 116 - 118: Can the author explain exactly how the experiments were performed?

Line 119: "evaporating a 10% NaCl solution", how do the authors evaporate the NaCl solution here?

Line 125: "The corrosion rate was measured manually", what does the author mean by measured manually? What method was exactly used here? As far as I know, the most manual measurement is by gravimetry method.

Line 196, Terminology inconsistencies: corrosion speed --> corrosion rate. Or is there any reason why the authors use the term speed instead of rate?

Line 199, "the timing in this experiment was faster", just a suggestion: "the duration of experiment was shorter"?

Line 202 - 204,  Please make the sentence more clearer. I think it is also possible to split it into 2 sentences.

Table 1, It is a bit confusing to have the description of corrosion level in the first two columns. As a suggestion, this description can be provided elsewhere, for example, above/below the table.

Line 253, "Two experimental cases were carried out, one that measured the corrosion potential within an uncontrolled air temperature environment, and another that manually measured the corrosion rate."

I think these two types of experiments are not explicitly comparable. Therefore, it would be better to explain why did the authors choose these two cases? Does this mean that the manually measured experiment was performed in a controlled environment? If so, why is it considered a controlled environment? Does it also mean that the uncontrolled air temperature environment was measured automatically instead of manually?

Line 260, "wan not" is supposed to be "was not"

 

Author Response

Respected Reviewer,

Thank you for reviewing our manuscript entitled “An experimental and statistical study on rebar corrosion considering the temperature effect using Gaussian process regression” for possible publication in the journal of “Applied Sciences”. We are thankful to you for your quick and valuable feedbacks to improve the quality of our manuscript for possible publication in the journal. We have revised the manuscript according to your comments and suggestions. The pointwise replies are given here in the word file.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper is focused on the evaluation of the effect of temperature on corrosion of steel in concrete. The subject of the manuscript is rather actual. It can be published after some minor correction:

Line 94: what the authors mean as "non-corroded potential, and corroded potential"? Please comment.

Line 97: Please provide the exact composition of the used steel. 

Figure 2 and 3b are very strange. What do they give to the subject of the manuscript? I think they can be omitted.

Line 121. Copper sulfate cannot be used as an electrode. I guess the authors meant copper–copper(II) sulfate electrode.

Figure 4. The potential fluctuation was only 2-3 mV (based on Fig. 4). For me, it is oppositely too low for steel with such a corrosion attack. Can the authors comment on it?

Author Response

Respected Reviewer,

Thank you for reviewing our manuscript entitled “An experimental and statistical study on rebar corrosion considering the temperature effect using Gaussian process regression” for possible publication in the journal of “Applied Sciences”. We are thankful to you for your quick and valuable feedbacks to improve the quality of our manuscript for possible publication in the journal. We have revised the manuscript according to your comments and suggestions. The pointwise replies are given here in the word file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The work has been improved and all the recommendations made in the previous review have been included and argued.

Author Response

Respected Reviewer,

Thank you for reviewing our manuscript entitled “An experimental and statistical study on rebar corrosion considering the temperature effect using Gaussian process regression” for possible publication in the journal of “Applied Sciences”. We are thankful to you for your quick and valuable feedbacks to improve the quality of our manuscript for possible publication in the journal. We have revised the manuscript according to your comments and suggestions. The pointwise replies are given here in the word file.

Author Response File: Author Response.docx

Reviewer 2 Report

There are some improvement on the clarity and readability of the paper. The authors have decided to focus on one study case, and have improved the quality of images presented in the paper.

There are some minor additions from me as follow:

1. Line 93: Please be careful with space between value and unit, e.g., 3 mV

2. Line 94: ith, th should be subscript or superscript? Or should be uniform with line 150

3. Line 180: A suggestion on the terminology: "lower value of potential" instead of "small value".

4. Line 195: Masmoudi et al. [38] showed experimentally that rebars with different diameters have different thermal characteristics.

It is not so clear to me, which thermal characteristics are of interest. There are many thermal properties that might be affected, e.g., thermal expansion, heat capacity, thermal conductivity, thermal diffusivity, etc.

5. Line 196: In that study the thermal coefficient was decreased as the diameter increased; hence, the larger specimens were less affected by the temperature because of the thermal coefficient.

What does "thermal coefficient" here refer to? Based on reference 38, their study focuses on the thermal expansion coefficient. If this is the same parameter that was investigated, i think the term "thermal expansion coefficient (CTE)" should be used instead of "thermal coefficient". Please comment on this.

7. Line 232: How did the authors calculated the range gap values presented in Figure 6? Is it by substracting the black to red curves and blue to red curves? If so, from which time was it calculated? And why the author didn't use absolute difference values to compare how big the gap is in each case?

8. Figure 6: Can the author describe what information is highlighted by the green square in Figure 6?

9. Line 233: Please start the sentence with a capital letter.

 

Author Response

Respected Reviewer,

Thank you for reviewing our manuscript entitled “An experimental and statistical study on rebar corrosion considering the temperature effect using Gaussian process regression” for possible publication in the journal of “Applied Sciences”. We are thankful to you for your quick and valuable feedbacks to improve the quality of our manuscript for possible publication in the journal. We have revised the manuscript according to your comments and suggestions. The pointwise replies are given here in the pdf file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Some minor comments still exist:

1) Line 129: "copper-copper(II) sulfate solution was used as an electrode". This is incorrect from the fundamental point. This is the electrode of the first kind and the solution cannot be an electrode. Please correct to, for example, "copper-copper(II) sulfate solution setup was used as an electrode"

2) Line 94-95. What was the reason to select 1.5 mV as a statistical interval? Please explain.

3) The discussion about diameter and temperature factor is a bit speculative. As the samples were exposed to the solution from only one side, the active sample area was varying for each type of the rebar, causing the corrosion attack was severe on the samples of greater D. So I will consider it as an experiment design limitation rather than the temperature effect.

4) The concept of corroded and non-corroded potential is still not clear for me. If the samples were exposed above the NaCl solution, evaporation of the salt is not expected. I agree that water will evaporate, however, the salt will remain in the solution. As you kept the relative humidity in the room constant, both samples will be exposed to similar conditions, and the effect of  NaCl, in this case, is not so straightforward. This may explain so small potential fluctuations. Much better will be using a droplet method or a salt spray testing, where the solution containing dissolved NaCl will contact the rebar surface.

5) The corrected parts of the manuscript (in red) are written with numerous grammar mistakes and typos.

Author Response

Respected Reviewer,

Thank you for reviewing our manuscript entitled “An experimental and statistical study on rebar corrosion considering the temperature effect using Gaussian process regression” for possible publication in the journal of “Applied Sciences”. We are thankful to you for your quick and valuable feedbacks to improve the quality of our manuscript for possible publication in the journal. We have revised the manuscript according to your comments and suggestions. The pointwise replies are given here in the word file.

Author Response File: Author Response.pdf