Combined GPR and Self-Potential Techniques for Monitoring Steel Rebar Corrosion in Reinforced Concrete Structures: A Laboratory Study

Round 1

Reviewer 1 Report

This study focuses on the use of NDT geophysical techniques for the monitoring of steel rebar corrosion in reinforced concrete.  The paper is interesting and provide an exemplary research on data integration and fusion from different non-destructive testing methods. The novelty is quite clear - although the Authors should attempt to make it clearer across the paper - specifically at the introduction level. There is plenty of studies regarding the rebar corrosion with GPR; hence it is important to put focus on this point to clearly distinguish this paper out of the existing literature. Methodology and experimental program is interesting and well described. 

It is required that the presentation of data and results is improved. More specifically, pictures and labels must be increased, as they are not readable for most of the graph and figures. 

It is also clear that the referencing has gone through some formatting issues - which need full revision. 

Apart from that, the paper proves to be valid and can well contribute to the existing literature. 

 

Sincerely.

 

 

Author Response

Dear Reviewer,

you can find below our replied on your comments and suggestions:

This study focuses on the use of NDT geophysical techniques for the monitoring of steel rebar corrosion in reinforced concrete.  The paper is interesting and provide an exemplary research on data integration and fusion from different non-destructive testing methods. The novelty is quite clear - although the Authors should attempt to make it clearer across the paper - specifically at the introduction level. There is plenty of studies regarding the rebar corrosion with GPR; hence it is important to put focus on this point to clearly distinguish this paper out of the existing literature. Methodology and experimental program is interesting and well described.

Authors: Thanks so much for your positive comments. We have implemented the introduction highlighting our contributions on monitor corrosion. Moreover, we have revised the entire paper.

 

It is required that the presentation of data and results is improved. More specifically, pictures and labels must be increased, as they are not readable for most of the graph and figures.

Authors: We have revised all the images and we improved the data description.

 

It is also clear that the referencing has gone through some formatting issues - which need full revision.

Authors: We did a revision of all the cited references.

 

Apart from that, the paper proves to be valid and can well contribute to the existing literature.

Authors: Thank you very much for your positive comments.

Reviewer 2 Report

The paper presents a study on the use of NDT geophysical techniques for monitoring steel rebar corrosion in reinforced concrete structures. The methodology employed in the study is sound, and the results are coherent, providing valuable insights into the performance of these techniques.

One concern with the paper is that the title mentions the more general NDT, while the paper mainly focuses on the use of GPR. To address this, the Authors may consider revising the title to better reflect the primary focus of the study. For example, a more suitable title could be "GPR-based NDT techniques for monitoring steel rebar corrosion in reinforced concrete structures." This revision would accurately convey the primary focus of the study, thereby enabling readers to better understand the paper's objectives and contributions.

Additionally, some pictures in the paper are unclear, as they are too small for details, labels or axes to be discerned. It would be helpful to provide larger and more detailed images, with clear labelling and captions, to enhance the readability of the paper.

Furthermore, the referencing style throughout the manuscript must be revised, as it is not consistent. The Authors should use a single referencing style to ensure consistency and accuracy. At present, some references are missing, and an error message appears in their place. Therefore, the Authors should ensure that all references are properly cited and included in the reference list, and that all in-text citations correspond to a complete and accurate reference entry.

Finally, the English language and style need improving. The Authors should consider proofreading the paper to correct any grammatical errors and improve the clarity of the language.

Author Response

Dear Reviewer,

you can find below our replied on your comments and suggestions:

The paper presents a study on the use of NDT geophysical techniques for monitoring steel rebar corrosion in reinforced concrete structures. The methodology employed in the study is sound, and the results are coherent, providing valuable insights into the performance of these techniques. One concern with the paper is that the title mentions the more general NDT, while the paper mainly focuses on the use of GPR. To address this, the Authors may consider revising the title to better reflect the primary focus of the study. For example, a more suitable title could be "GPR-based NDT techniques for monitoring steel rebar corrosion in reinforced concrete structures."

Authors: Thank you very much for your suggestion. We agree to change the title.

 

This revision would accurately convey the primary focus of the study, thereby enabling readers to better understand the paper's objectives and contributions. Additionally, some pictures in the paper are unclear, as they are too small for details, labels or axes to be discerned. It would be helpful to provide larger and more detailed images, with clear labelling and captions, to enhance the readability of the paper.

Authors: We have arranged all the images of the article.

 

Furthermore, the referencing style throughout the manuscript must be revised, as it is not consistent. The Authors should use a single referencing style to ensure consistency and accuracy. At present, some references are missing, and an error message appears in their place. Therefore, the Authors should ensure that all references are properly cited and included in the reference list, and that all in-text citations correspond to a complete and accurate reference entry.

Authors: We made a revision of all the cited references.

 

Finally, the English language and style need improving. The Authors should consider proofreading the paper to correct any grammatical errors and improve the clarity of the language.

Authors: We asked to mother tongue to check our manuscript.

Reviewer 3 Report

This paper is focus on the NDT monitoring of rebar corrosion process. Lab tests were conducted with NaCl solution and accelerated by DC power. GPR and self-potential voltage were adopted to monitor the corrosion process. Hilbert method was used to process the GPR signal, and the amplitude on at rebar was extracted and compared with time, which proved that GPR is suitable for monitoring rebar corrosion. However, obvious errors were existing in content, especially for references format. So, I think the authors should revise it before publication.

Comments:

(1)   Errors of type setting should be avoided, i.e., Line 127-128,  “2Nmm2”, “22%.water”; line 164, “…n.60 radargrams…”. Table names were hidden for Table.1.

(2)   In. Fig.6, what are the axis names and units for the processed Hilbert transform signal? What are the filter parameters?

(3). What are the GPR sample parameters?

(4) From section 3.1, the author supposed the GPR EM wave velocity in concrete is 0.1m/ns, due to 0.6 ns corresponding to 0.3m depth. Why the velocity doesn’t change along with the change of moisture content of slab?

(5) Why not use the amplitude of A-scan trace at rebar area or B-scan feature to present the corrosion process? And why not use the maximum amplitude position to locate the rebar area instead of using 0.6 ns?

(6) According to the author’s result, how can we determine the corrosion status of rebar with GPR ?

Author Response

Dear Reviewer,

you can find below our replied on your comments and suggestions:

This paper is focus on the NDT monitoring of rebar corrosion process. Lab tests were conducted with NaCl solution and accelerated by DC power. GPR and self-potential voltage were adopted to monitor the corrosion process. Hilbert method was used to process the GPR signal, and the amplitude on at rebar was extracted and compared with time, which proved that GPR is suitable for monitoring rebar corrosion. However, obvious errors were existing in content, especially for references format. So, I think the authors should revise it before publication.

Authors: Thank you very much for your suggestions and we revised the manuscript following the reviewer’s comments.

 

Comments:

(1)   Errors of type setting should be avoided, i.e., Line 127-128, “2Nmm2”, “22%.water”; line 164, “…n.60 radargrams…”. Table names were hidden for Table.1.

Authors: Thank you very much for your detailed corrections. We have replaced them and we depict a new table 1.

 

(2)   In. Fig.6, what are the axis names and units for the processed Hilbert transform signal? What are the filter parameters?

Authors: The Hilbert transform was applied using the Reflex software where the Envelope filter is available. This option doesn’t need filter parameters. Moreover, we improved the figure 6. 

 

(3). What are the GPR sample parameters?

Authors: thank you very much for your advice. We added a new paragraph about and a new table (table 2), where we summarize the used GPR sample parameters.

 

(4) From section 3.1, the author supposed the GPR EM wave velocity in concrete is 0.1m/ns, due to 0.6 ns corresponding to 0.3m depth. Why the velocity doesn’t change along with the change of moisture content of slab?

Authors: We estimated the Vem of about 0.1 m/ns, because we have the rebar at 3cm (0.03 m) and we found it at 0.6ns looking the A-Scan data set. We were able to use the same Vem during all the experimental phases because the samples were immersed in the water (at 1 cm from the bottom) for 10 days before to start the experimental phases. In order to check the Vem variations due to water content variations, we made several GPR acquisitions. Finally, when the Vem starts to be constant for some days, we started the described experimental phases.

 

(5) Why not use the amplitude of A-scan trace at rebar area or B-scan feature to present the corrosion process? And why not use the maximum amplitude position to locate the rebar area instead of using 0.6 ns?

Authors: Several papers used the Amplitude, trying to detect the corrosion. During the first phase of our project, we tried to make the same approach, but the results were far from our expectations. Therefore, we tried to improve our work introducing the Hilbert approach which definitely highlights the rebar corrosion, how you can see in our manuscript.

 

(6) According to the author’s result, how can we determine the corrosion status of rebar with GPR ?

Authors: From our point of view, it is so hard to define the rebar corrosion with a characterization approach (a single investigation). In order to detect the rebar corrosion, it is necessary to use a monitoring approach. The GPR detects the variation of the EM signals due to corrosion, that is a dynamic phenomenon. This should be the new vision that with our paper we would like to highlight.

Reviewer 4 Report

The steel rebar corrosion is an interesting topic with great practical value. However, the paper only implemented a very simple case with one rebar in the concrete slab sample. To make it more sound as a journal paper quality, the author needs to:

(1) investigate the real scenarios and real parameters, such as the depth of the buried rebar, the number of rebar in concrete, and read more GPR related rebar corrosion detection for pavement and highways studies.

(2) mimic at least one of the real reinforce concrete structural components, such as pavement, slab, beams, columns, etc., and redo the experiment. Then collect the results to see how it can show the corrosion of rebars vs the GPR scans.

Otherwise, this paper can only be considered as a conference paper.

Author Response

Dear Reviewer,

you can find below our replied on your comments and suggestions:

The steel rebar corrosion is an interesting topic with great practical value. However, the paper only implemented a very simple case with one rebar in the concrete slab sample. To make it more sound as a journal paper quality, the author needs to:

(1) investigate the real scenarios and real parameters, such as the depth of the buried rebar, the number of rebar in concrete, and read more GPR related rebar corrosion detection for pavement and highways studies.

(2) mimic at least one of the real reinforce concrete structural components, such as pavement, slab, beams, columns, etc., and redo the experiment. Then collect the results to see how it can show the corrosion of rebars vs the GPR scans.

Otherwise, this paper can only be considered as a conference paper.

Authors: There are several works on rebar corrosion which is a practical problem and it is still debated on useful methods to detect it without any excavation (indirect approach). On the use of GPR there are several papers (from our point of view they are few compared with the importance of the problem) and all of them made experiments in the lab with one or more rebars in the concrete samples. We think that a scientific approach needs to start in controlled context when the studied phenomena is so complex. The laboratory approach is common when you have to apply new methods on a complex context, and GPR method is so new on rebar corrosion. Therefore, before to apply GPR on real case, from our point of view it is necessary to make several laboratory experiments in controlled conditions, in order to know what you are looking with it. Our paper would like to make a new point of view of the GPR data on rebar corrosion introducing the Hilbert transform approach (it is the first time that this filter was used for rebar corrosion). Moreover, we know that we used only one rebar in our experiments, but we think that the rebar corrosion is a complex phenomenon to detect and starting from a simple case it should be the best scientific method.

Finally, even if you think that our paper is a conference one, we have to tell you that we already made it and we were honoured to receive the best award conference paper and we were invited to write this paper.

Round 2

Reviewer 3 Report

The authors had addressed most of the previous issues, however, a few minor errors should be revised before publication.

(1) Table names should be at the top of table. And the parameters of Table.2 are not GPR sample information, which should include sample frequency, sample points for each trace...

(2) The top of rebar in Fig.2(b) should consider the phase of Ricker wave, maybe the right rebar top should locate at the black area of hyperbolic due to inverse phase of rebar.

 

Author Response

Dear Reviewer,

you can find below our replied on your comments and suggestions:

Comments and Suggestions for Authors

The authors had addressed most of the previous issues, however, a few minor errors should be revised before publication.

(1) Table names should be at the top of table. And the parameters of Table.2 are not GPR sample information, which should include sample frequency, sample points for each trace...

Authors: Thank you very much for your suggestions and we add more information in the table 2.

 

(2) The top of rebar in Fig.2(b) should consider the phase of Ricker wave, maybe the right rebar top should locate at the black area of hyperbolic due to inverse phase of rebar.

Authors: Thank you very much for your suggestions and we think that you are talking about figure 6b. Therefore, we check it and we have to inform you that we did a mistake on the figure.

 

Reviewer 4 Report

Authors did not address the comments directly, i.e., without adding any extra work or data to improve the paper quality. Authors can read some similar journal papers for reference, such as:

 

(1) Solla, M.; Lagüela, S.; Fernández, N.; Garrido, I. Assessing Rebar Corrosion through the Combination of Nondestructive GPR and IRT Methodologies. Remote Sens. 2019, 11, 1705. https://doi.org/10.3390/rs11141705

(2) Liu, Hai, et al. "Detection of early-stage rebar corrosion using a polarimetric ground penetrating radar system." Construction and Building Materials 317 (2022): 125768.

(3) Zatar, Wael, Tu T. Nguyen, and Hai Nguyen. "Environmental effects on condition assessments of concrete structures with ground penetrating radar." Journal of Applied Geophysics 203 (2022): 104713.

(4) Lai, Wai-Lok, et al. "Measurement of accelerated steel corrosion in concrete using ground-penetrating radar and a modified half-cell potential method." Journal of Infrastructure Systems 19.2 (2013): 205-220.

 

Author Response

Dear Reviewer,

you can find below our replied on your comments and suggestions:

 

Comments and Suggestions for Authors

Authors did not address the comments directly, i.e., without adding any extra work or data to improve the paper quality.

Authors: I’m sorry if we didn’t add useful information following your previous comments, but you asked us to make a new work. We agree that it is important to apply this kind of analysis on real cases and it will be our next aim. Actually, we are still far from this approach on real scenarios, as the suggested papers show. Moreover, we thank you to suggest us the four papers on rebar corrosion and GPR. They are already in our list, but we decided to make our references chapter with some of them, because our paper is not a review on GPR and rebar corrosion. Anyway, we add them in our reference list.