The Effect of Surface Properties of Steel Sections on Bond Strength in Soil-Cement Mix

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper investigates the impact of hot-rolled steel surface roughness on the bond strength of cemented soil, demonstrating certain innovative aspects and practical significance. Through systematic experimental design and data analysis, the study explores the bond performance between steel and cemented soil under different surface treatment conditions, providing references for relevant engineering designs. However, there is still room for improvement in the comprehensiveness of the experimental design, the depth of data analysis, and the clarity of the text. Specific comments are as follows:
(1) The paper should further elaborate on the mechanism by which hot-rolled steel surface roughness affects the bond strength of cemented soil and how the microstructure changes. It is recommended to add SEM testing.
(2) The experimental design covers different surface treatments and cemented soil mixture ratios. However, the sample size appears insufficient in some aspects, especially for samples with higher roughness (such as R06, R09, and R10 in the R series), which may limit the representativeness of the results. It is suggested to increase the sample size to enhance the reliability of the findings.
(3) The experiment did not consider the effect of cement content on bond strength. Cement content is one of the key factors affecting the performance of cemented soil. It is recommended to add experimental groups with different cement contents to more comprehensively evaluate their impact on bond strength.
(4) The paper employs the Kolmogorov–Smirnov test and the Wilcoxon rank-sum test to analyze the data but lacks a detailed discussion on the distribution characteristics of the data. It is suggested to supplement the results of normality tests for the data and explain in the discussion why nonparametric tests were chosen.
(5) Although a correlation analysis was conducted between roughness and bond strength, it only considered the Ra parameter. It is recommended to supplement the correlation analysis with Rq and Rz parameters to more comprehensively assess the impact of surface roughness.
(6) The paper mentions that the correlation coefficient R² significantly decreases after excluding certain high-roughness samples. This indicates that these high-roughness samples have a considerable influence on the results. It is suggested to further analyze the possible reasons for these outlier samples in the discussion, such as differences in material batches.

Author Response

The response is provided in the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article is well written, with appropriate methodology and consistent discussion of the results based on statistical analysis. Some points require minor corrections:

- Fix the caption for Table 5 and insert the coefficient of variation values

- Insert the caption for Figure 4b in the graph

- The COV values of the models were very low. This is not statistically significant

- The discussion of the results should be presented separately from the conclusions of the study, which should be in a single item.

Author Response

The response is provided in the attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I appreciate the authors' interest in the journal Applied Sciences. However, the manuscript presents numerous language, organization, and content deficiencies. Furthermore, the roughness effect is the central focus of the manuscript and was an aspect that was neglected during the methodological development. My comments will help you improve the article for resubmission.

1. Using the term "natural roughness" is incorrect when referring to steel bars. The authors must specify the full dimensions of the bars (30×4 mm). What is the thickness? The sieve size is never indicated.
2. Despite the justification provided by the authors (lines 120–127), I believe that samples R09 and R10 should be excluded from the study. These are clearly outlier data, which are typically recommended to be discarded in any experimental methodology. The authors admit this in the discussion (lines 206–212).
3. Tables 2–4 should include error margins or standard deviations for each measurement. It is not acceptable to perform only a single roughness measurement per sample. The samples have a large surface area; therefore, a single roughness measurement does not represent the entire surface. This is clearly evident in Figure 3(a), where samples P07 and P02 were sanded completely irregularly and carelessly. A single roughness measurement on these samples may have been aligned with the sanding marks (which is a flawed practice), and thus does not reflect an accurate measurement.
4. Line 134: "A sample view is shown in the figure." The authors forgot to include the figure. The methodology used for the pull-out tests is never described.
5. Why did the authors use the Kolmogorov–Smirnov (K-S) test instead of other non-parametric tests? This should be explicitly stated in the manuscript.
6. Sections 2, 3, and 4 need to be restructured and reorganized. Section 2 should contain all experimental details. Experimental procedures should not be included within the results section. In the results section, tables should be unified, table titles should be corrected (see Table 5), and Figures 4, 5, and 6 should be described more thoroughly.
7. Section 4 should be the Discussion of Results. The authors do not explain, justify, or compare their findings in depth with existing literature. At a minimum, the results must be discussed concerning previous studies and the working hypotheses. The findings and their implications should be addressed in the broadest possible context, and the limitations of the work should be highlighted. Future research directions may also be mentioned. This section may be combined with the Results.
8. The authors should be more precise in their expressions, such as "0.2–0.6 Ra". Ra is a parameter that has units. The authors should include a correlation analysis using other roughness parameters, as each parameter represents different characteristics of the same surface.
9. Finally, the authors must separate the conclusions from the discussion, as this is part of the journal's formatting requirements.

Author Response

The response is provided in the attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No more comments.

Author Response

Once again, we thank you for all your valuable comments, which in our opinion have allowed us to improve the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

I thank the authors for the revision. The manuscript has been substantially improved. However, several aspects still need further improvement, which I describe below:

1. Specify which sample each curve corresponds to in Figure 6 (b) force–displacement curves.
2. The units of the X-axis are missing in Figure 3—grain size distribution curve of the prepared soil mixture.
3. The authors should provide a more detailed discussion of the failure mechanisms observed. In the literature review presented in the introduction, adhesion was never mentioned as a mechanism. For example, they stated in Line 72: “Two failure modes were identified: splitting (sample fracture) and bar slippage.” In fact, the authors affirmed in Line 255: “adhesion determines bond strength.” However, in Figure 6, this mechanism alone is not observed. Indeed, the authors indicated in Line 168: “The failure mode for all samples was slip at the steel–soil–cement mix interface.” Slip is different from adhesion. Failure does not necessarily occur through a single mechanism; however, the authors cannot contradict themselves within the manuscript. They should discuss in greater depth and detail the failure mechanisms for the three types of samples. If they have higher-magnification images clearly showing the failure types, this would help support the discussion.
4. The authors should be more precise in their expressions, such as “10 Ra” or “1000 Ra.” Ra is a parameter that has units. Lines 282–283: “The study requires testing for roughness values of 10 Ra and higher, up to 1000 Ra – a value corresponding to the grain diameter of the sand fraction.”
5. The authors changed the title to “The effect of surface properties of steel sections on bond strength in soil–cement mix”; however, I still believe that the content presented in the manuscript does not correspond to the title. Surface properties involve more than just roughness. A more complete characterization of topography and aspects such as hardness or surface chemical characterization should be included. The previous title, “The impact of hot-rolled steel roughness on bond strength in cemented soil,” was more appropriate, informing the reader that only roughness was evaluated in the study. That said, I acknowledge that the description of roughness measurement and the analysis of the results were improved; however, I still consider that the discussion about the roughness parameters selected should be expanded (why they were chosen, why they are correlated, what each represents, and why only Ra was selected for the rest of the comparison). Since roughness is the central aspect of the manuscript, dedicating only a few lines (Lines 213–219) to this discussion is insufficient. The literature indicates that these three parameters are related, meaning that this result was foreseeable, so the discussion provided by the authors in Lines 213–219 is not entirely justified.
6. I recommend that the authors carry out a unidirectional sanding process for future work. As I mentioned earlier, Figure 3(a) clearly shows that samples P07 and P02 were sanded completely irregularly and without care. Therefore, several roughness profile measurements on these samples may have been aligned with the sanding marks (which is an incorrect practice), and thus do not represent an accurate measurement.

Author Response

The response to the comments is provided in the attached file.

Author Response File: Author Response.pdf