Monitoring of Corrosion in Reinforced E-Waste Concrete Subjected to Chloride-Laden Environment Using Embedded Piezo Sensor
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors- Clarify the Introduction's Scope and Objectives: The introduction provides a good overview of corrosion in reinforced concrete and the relevance of E-waste, but it could better articulate the specific research gap. Consider explicitly stating why existing corrosion monitoring methods (e.g., HCP, EIS) are inadequate for E-waste concrete and how the EMI technique addresses this gap. A concise statement of the study’s objectives at the end of the introduction would guide readers effectively.
- Enhance Methodology Description: The methodology section is detailed but lacks clarity in some areas. For instance, the preparation of the E-waste material (PCB) is briefly mentioned. Provide more details on the cleaning and cutting process, including the size range of PCB pieces used as aggregates. Additionally, specify the rationale for choosing a 15% replacement level and whether other percentages were considered or tested.
- Improve Figure Captions and Quality: Figures (e.g., Figures 1, 5–10) are critical for understanding the experimental setup and results, but their captions are minimal. Enhance captions to describe what each subfigure represents and highlight key observations (e.g., specific trends in conductance plots). Ensure figures are high-resolution and legible, as some text in the current figures appears small or blurry.
- Strengthen Quantitative Analysis: The quantitative analysis using RMSD is insightful, but the discussion of Figure 12 (RMSD for E-waste concrete) is missing from the document. Include a detailed explanation of Figure 12, similar to Figure 11, to compare RMSD trends between CC and E-waste concrete. Discuss whether the steeper RMSD rise in E-waste concrete correlates with specific material properties (e.g., lower specific gravity).
- Address Statistical Validation: The study uses RMSD as a statistical parameter but does not discuss the statistical significance of the results. Consider incorporating statistical tests (e.g., t-tests or ANOVA) to validate differences in corrosion behavior between CC and E-waste concrete. This would strengthen the reliability of conclusions drawn from the data.
- Expand Discussion on E-Waste Concrete Durability: The conclusion notes that E-waste concrete has reduced corrosion resistance, but the discussion could explore why this occurs. Hypothesize whether the PCB’s chemical composition, porosity, or interfacial bonding with cement contributes to accelerated corrosion. Referencing prior studies on E-waste concrete’s durability would contextualize these findings.
- Refine Terminology and Consistency: Some terms, such as “chloride chloride-laden environment” (Page 3), contain typographical errors. Ensure consistent use of terms like “E-waste concrete” (sometimes written as “Ewaste”) and “CC” (defined but occasionally unclear in context). A thorough proofreading pass would improve professionalism and readability.
- Include Practical Implications: The study highlights EMI’s effectiveness for SHM, but it could better address practical applications. Discuss how this technique could be implemented in real-world infrastructure projects, including cost considerations, scalability, and integration with existing monitoring systems. This would appeal to practitioners and policymakers.
- Acknowledge Limitations: The manuscript does not explicitly address limitations. Mention potential constraints, such as the accelerated corrosion test’s applicability to natural conditions, the limited sample size (12 samples), or the focus on only one E-waste type (PCB). Suggesting future research directions, like testing other E-waste materials or long-term exposure, would enhance the study’s scope.
- Strengthen References and Contextualization: The reference list is limited and could be expanded to include more recent studies on EMI-based SHM or E-waste concrete. For example, cite additional works on piezoelectric sensors or sustainable aggregates to provide a broader context. Ensure all cited references are correctly formatted and accessible, as some DOIs may need verification.
In summary, the manuscript presents a promising study on corrosion monitoring in E-waste concrete using EMI, but it can be improved by enhancing clarity, expanding discussions, and addressing methodological and statistical rigor. Implementing these suggestions will make the paper more robust, accessible, and impactful for both academic and practical audiences.
Author Response
Reviewer #1
COMMENT
- Clarify the Introduction's Scope and Objectives: The introduction provides a good overview of corrosion in reinforced concrete and the relevance of E-waste, but it could better articulate the specific research gap. Consider explicitly stating why existing corrosion monitoring methods (e.g., HCP, EIS) are inadequate for E-waste concrete and how the EMI technique addresses this gap. A concise statement of the study’s objectives at the end of the introduction would guide readers effectively.
RESPONSE
The authors thank the reviewer for the thoughtful and constructive feedback. As per the suggestion of the reviewer, a concise statement of the related to the existing corrosion monitoring methods are mentioned in the revised manuscript and duly highlighted on Page No: 3 and Line Nos: 93 to 100; the same has been shown below for ready reference:
Half-Cell Potential is limited by its inability to detect internal or early-stage corrosion and is mainly effective on exposed surfaces. It provides only intermittent data and may cause surface damage. GPT and LPR require direct contact with concrete and are less effective at early-stage corrosion detection. LPR, in particular, may not detect all corrosion types and has limited resolution, offering only numeric values. Both techniques can potentially damage the structure during testing and focus solely on corrosion rates, lacking comprehensive structural health monitoring capabilities.
A concise statement of the objective of the study is mentioned at the end of the introduction section in the revised manuscript and duly highlighted on Page No: 3 and Line Nos: 115 to 119.
COMMENT
2. Enhance Methodology Description: The methodology section is detailed but lacks clarity in some areas. For instance, the preparation of the E-waste material (PCB) is briefly mentioned. Provide more details on the cleaning and cutting process, including the size range of PCB pieces used as aggregates. Additionally, specify the rationale for choosing a 15% replacement level and whether other percentages were considered or tested.
RESPONSE
The authors thank the reviewer for the thoughtful and constructive feedback. As per the suggestion of the reviewer, a brief description on the cleaning and cutting process, including the size range of PCB pieces used as aggregates are mentioned in the revised manuscript and duly highlighted on Page No: 5 and Line Nos: 187 to 209; the same has been shown below for ready reference:
The E-waste utilized in this study consisted of non-metallic fractions of printed circuit boards (PCBs) which is recovered from end-of-life electronic devices such as computers and mobile phones. The source of the E-waste was the E-waste Collection Bank established on the college campus, an institutional initiative aimed at promoting sustainable electronic waste management and raising environmental awareness. From the variety of components collected, only PCBs were selected for use in the experimental study owing to their structural compatibility with coarse aggregates and absence of metallic hazards after processing. The remaining E-waste, including metallic parts and components unsuitable for concrete applications, was donated to an E-waste recycling agency.
Initially, the electronics components including resistors, capacitors, integrated circuits (ICs), and soldered metallic pathways were manually removed using mechanical tools such as pliers, scrapers, and de-soldering irons from the PCBs. After removal, the bare PCBs were subjected to a multi-stage cleaning procedure designed to remove surface contaminants, adhesives, and chemical residues. The cleaned PCBs were air-dried and then oven-dried at 105 ± 5°C for 24 hours to remove any residual moisture. The fully dried PCBs were then mechanically shredded into angular fragments resembling coarse aggregate. The shredded material was passed through a series of IS sieves, and only particles falling within the 4.75 mm to 12.5 mm size range were retained. This size was selected to match the gradation and physical behavior of conventional coarse aggregates, ensuring good packing density, interlock, and uniform distribution within the concrete mix.
In this study, 15% of E-waste is considered based on the suggested literature As replacing 15% of aggregates serves the purpose of sustainability, the highest amount of waste is included in the concrete matrix without compromising the strength of the concrete [27].
COMMENT
3. Improve Figure Captions and Quality: Figures (e.g., Figures 1, 5–10) are critical for understanding the experimental setup and results, but their captions are minimal. Enhance captions to describe what each subfigure represents and highlight key observations (e.g., specific trends in conductance plots). Ensure figures are high-resolution and legible, as some text in the current figures appears small or blurry.
RESPONSE
We thanks the reviewer for the valuable suggestion regarding the figures. As per the suggestion of the reviewer the quality of Figure 1, 5-10 are improved, the captions are properly marked with same resolution and the highlights of key observations from each figure are mentioned in the revised manuscript and duly highlighted.
COMMENT
4. Strengthen Quantitative Analysis: The quantitative analysis using RMSD is insightful, but the discussion of Figure 12 (RMSD for E-waste concrete) is missing from the document. Include a detailed explanation of Figure 12, similar to Figure 11, to compare RMSD trends between CC and E-waste concrete. Discuss whether the steeper RMSD rise in E-waste concrete correlates with specific material properties (e.g., lower specific gravity).
RESPONSE
The authors apologies for this mistake. The discussion about Figure 12 is added in the revised manuscript and duly highlighted on Page No: 12 and Line Nos: 356 to 376. Further, a detailed comparative analysis between the RMSD trends of CC and E-waste concrete is added in the revised manuscript and duly highlighted on Page No: 12 and Line Nos: 377 to 398.
COMMENT
5. Address Statistical Validation: The study uses RMSD as a statistical parameter but does not discuss the statistical significance of the results. Consider incorporating statistical tests (e.g., t-tests or ANOVA) to validate differences in corrosion behavior between CC and E-waste concrete. This would strengthen the reliability of conclusions drawn from the data.
RESPONSE
We thank the reviewer for the valuable suggestion. The authors used RMSD as a statistical parameter because it is one of established robust statistical parameter as suggested by the various researchers in the field of structural health monitoring (SHM). Hence, in this study the author provides a detailed description analysis of EMI signatures based on RMSD. Regarding the statistical tests such as (t-tests or ANOVA), the author will covers these tests in the future work of this study.
COMMENT
6. Expand Discussion on E-Waste Concrete Durability: The conclusion notes that E-waste concrete has reduced corrosion resistance, but the discussion could explore why this occurs. Hypothesize whether the PCB’s chemical composition, porosity, or interfacial bonding with cement contributes to accelerated corrosion. Referencing prior studies on E-waste concrete’s durability would contextualize these findings.
RESPONSE
The authors thank the reviewer for the valuable suggestion. The discussion on E-waste concrete durability is mentioned in the revised manuscript and duly highlighted in the results and discission section.
COMMENT
7. Refine Terminology and Consistency: Some terms, such as “chloride chloride-laden environment” (Page 3), contain typographical errors. Ensure consistent use of terms like “E-waste concrete” (sometimes written as “Ewaste”) and “CC” (defined but occasionally unclear in context). A thorough proofreading pass would improve professionalism and readability.
RESPONSE
The authors thank the reviewer for the valuable suggestion. The authors thoroughly proofread the paper and remove the problems related to the terminology and consistency.
COMMENT
8. Include Practical Implications: The study highlights EMI’s effectiveness for SHM, but it could better address practical applications. Discuss how this technique could be implemented in real-world infrastructure projects, including cost considerations, scalability, and integration with existing monitoring systems. This would appeal to practitioners and policymakers.
RESPONSE
Thank you for the insightful suggestion. As per the suggestion of the reviewer, the practical implications of this study are mentioned in the revised manuscript and duly highlighted on Page No: 15 and Line Nos: 440 to 445.
COMMENT
9. Acknowledge Limitations: The manuscript does not explicitly address limitations. Mention potential constraints, such as the accelerated corrosion test’s applicability to natural conditions, the limited sample size (12 samples), or the focus on only one E-waste type (PCB). Suggesting future research directions, like testing other E-waste materials or long-term exposure, would enhance the study’s scope.
RESPONSE
Thank you for the insightful suggestion. As per the suggestion of the reviewer, the limitations of this study are mentioned in the revised manuscript and duly highlighted on Page No: 15 to 16 and Line Nos: 446 to 458.
COMMENT
10. Strengthen References and Contextualization: The reference list is limited and could be expanded to include more recent studies on EMI-based SHM or E-waste concrete. For example, cite additional works on piezoelectric sensors or sustainable aggregates to provide a broader context. Ensure all cited references are correctly formatted and accessible, as some DOIs may need verification.
RESPONSE
Thank you for the insightful suggestion. As per the suggestion of the reviewer, the latest studies on EMI-based SHM and E-waste concrete are added in the reference section and cited properly in the text as the guidelines of the journal.
COMMENT
In summary, the manuscript presents a promising study on corrosion monitoring in E-waste concrete using EMI, but it can be improved by enhancing clarity, expanding discussions, and addressing methodological and statistical rigor. Implementing these suggestions will make the paper more robust, accessible, and impactful for both academic and practical audiences.
RESPONSE
Thank you for the insightful feedback and constructive summary. In response, the authors have revised the manuscript to enhance clarity and expand key discussions. The methodology section now includes detailed steps for E-waste (PCB) preparation and the rationale for the 15% replacement level, supported by prior literature. The authors have also added a paragraph discussing study limitations and future research directions. Figure captions and resolution have been improved, and practical applications of EMI in real-world SHM have been addressed, highlighting scalability and integration. These revisions aim to strengthen the paper’s clarity, rigor, and broader impact.
Reviewer 2 Report
Comments and Suggestions for Authors1) Line 50, the citation shall revise in format
2) Line 56, the sentense of "inadequate compaction" shall be rewrited to "inadequate density"
3) Line 82, to provide references, the literature study on E-waste concrete is inadequate, the E-waste aggregate to be reviewed,
4) Line 83, the references to be provided, the problem statement to be restated
5) Line 84, shall provide references on the methods of evaluating the corrosion behaviour of reinforced waste
6) Section 2.1.; the methodology to be justified, the references shall be provided, the proposed sizes to be verified
7) Line 133 to Line 148; a reference shall be verifying the statement on PZT sensor in EMI
8) Section 2.3.; To provide refrences, to validate the methods, sizes and the mixture design
9) Line 216, Line 217, Shall provide refrencess
10) Section 2.5, the method to be elaborated, a reference to be provided, to be validated throughout a standard of testing ..
11) A time-table shall be provided to describe the testing age, frequency applied, and severity index...
Author Response
Reviewer #2
COMMENT
1) Line 50, the citation shall revise in format
RESPONSE
The authors thank the reviewer for pointing out the formatting issue. As per the suggestion of the reviewer, the citation in Line 50 has been revised and duly highlighted on Page No: 2 and Line No: 50
COMMENT
2) Line 56, the sentense of "inadequate compaction" shall be rewrited to "inadequate density"
RESPONSE
The authors thank the reviewer for the comment. As per the suggestion of the reviewer, the phrase "inadequate compaction" has been revised to "inadequate density" in the revised manuscript and duly highlighted on Page No: 2 and Line No: 56.
COMMENT
3) Line 82, to provide references, the literature study on E-waste concrete is inadequate, the E-waste aggregate to be reviewed,
RESPONSE
The authors thank the reviewer for the comment. As per the suggestion of the reviewer, latest references on E-waste concrete are added in the revised manuscript and duly highlighted on Page No: 2 and Line No: 81, Page No: 2 and Line Nos: 81 to 90.
COMMENT
4) Line 83, the references to be provided, the problem statement to be restated
RESPONSE
The authors thank the reviewer for the comment. The problem statement is restated in the revised manuscript and duly highlighted on Page No: 3 and Line No: 101 to 114.
COMMENT
5) Line 84, shall provide references on the methods of evaluating the corrosion behaviour of reinforced waste
RESPONSE
The authors thank the reviewer for the comment. The reference on the methods of evaluating the corrosion behaviour of reinforced concrete is mentioned in the revised manuscript and duly highlighted on Page No: 2 and Line No: 8.
COMMENT
6) Section 2.1.; the methodology to be justified, the references shall be provided, the proposed sizes to be verified
RESPONSE
The authors thank the reviewer for the comment. The reference is mentioned in the revised manuscript and duly highlighted on Page No: 3 and Line No: 135.
COMMENT
7) Line 133 to Line 148; a reference shall be verifying the statement on PZT sensor in EMI
RESPONSE
The authors thank the reviewer for the comment. The reference is mentioned in the revised manuscript and duly highlighted on Page No: 4 and Line No: 146.
COMMENT
8) Section 2.3.; To provide refrences, to validate the methods, sizes and the mixture design
RESPONSE
The authors thank the reviewer for the comment. The reference is mentioned in the revised manuscript and duly highlighted on Page No: 6 and Line No: 223.
COMMENT
9) Line 216, Line 217, Shall provide refrencess
RESPONSE
The authors thank the reviewer for the comment. The reference is mentioned in the revised manuscript and duly highlighted on Page No: 6 and Line No: 251 and 252.
COMMENT
10) Section 2.5, the method to be elaborated, a reference to be provided, to be validated throughout a standard of testing.
RESPONSE
The authors thank the reviewer for the comment. The reference is mentioned in the revised manuscript and duly highlighted on Page No: 7 and Line No: 273.
COMMENT
11) A time-table shall be provided to describe the testing age, frequency applied, and severity index...
RESPONSE
The authors thank the reviewer for the comment. The table related to the testing age, frequency applied, and severity index is mentioned in the revised manuscript and duly highlighted on Page No: 4 and Line No: 150, Page No: 7 and Line No: 274, Page No: 11 and Line No: 340.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe paper presents an interesting study on the application of the Electro-Mechanical Impedance (EMI) technique for corrosion monitoring in reinforced concrete modified with a 15% addition of E-waste (PCB). The scope of the work encompasses a 60-day accelerated corrosion exposure test in an NaCl solution, during which alterations in EMI signatures were monitored in specimens with and without the incorporation of waste. The rationale underpinning this approach is twofold: firstly, to identify sustainable construction materials and secondly, to develop non-destructive, real-time methods for Structural Health Monitoring (SHM).
Notwithstanding the valuable conclusions to which the paper arrives at, there are a few additions that are required.
- E-waste composition: The article does not provide any information regarding the metallic composition of the printed circuit board (PCB) material that was utilised. The presence of metals that are more noble than iron (e.g., copper) has the potential to create galvanic cells, thereby significantly accelerating the corrosion of the steel reinforcement. This is a pivotal, albeit frequently disregarded, corrosion mechanism within the system. It is recommended that the authors include an analysis of the waste's composition and incorporate it into the discussion of degradation mechanisms.
- Selection of methodology: The authors correctly identify the limitations of classical electrochemical methods (e.g. EIS, LPR) with regard to online monitoring. They argue cogently that the EMI technique is the preferred option due to its non-destructive nature and sensitivity to structural changes. However, there is a paucity of validation of the EMI results through parallel, reference electrochemical measurements. A comparison of the RMSD trends with, for instance, the polarization resistance from LPR would significantly strengthen the credibility of the novel methodology.
- The evaluation of effectiveness: The effectiveness of the EMI technique was primarily evaluated by correlating its signals with visual changes, such as cracking and rust. Whilst the approach taken here is correct, it lacks a quantitative reference. It would be beneficial to consider whether the final mass loss of the reinforcing bar correlates with the cumulative changes in the RMSD index, which would allow for a more objective evaluation of the technique's effectiveness.
Author Response
Reviewer #3
The paper presents an interesting study on the application of the Electro-Mechanical Impedance (EMI) technique for corrosion monitoring in reinforced concrete modified with a 15% addition of E-waste (PCB). The scope of the work encompasses a 60-day accelerated corrosion exposure test in an NaCl solution, during which alterations in EMI signatures were monitored in specimens with and without the incorporation of waste. The rationale underpinning this approach is twofold: firstly, to identify sustainable construction materials and secondly, to develop non-destructive, real-time methods for Structural Health Monitoring (SHM).
Notwithstanding the valuable conclusions to which the paper arrives at, there are a few additions that are required.
COMMENT
1. E-waste composition: The article does not provide any information regarding the metallic composition of the printed circuit board (PCB) material that was utilised. The presence of metals that are more noble than iron (e.g., copper) has the potential to create galvanic cells, thereby significantly accelerating the corrosion of the steel reinforcement. This is a pivotal, albeit frequently disregarded, corrosion mechanism within the system. It is recommended that the authors include an analysis of the waste's composition and incorporate it into the discussion of degradation mechanisms.
RESPONSE
Thank you for highlighting this important point regarding the potential impact of metallic components in printed circuit boards on corrosion behavior. As per the suggestion of the reviewer, the suggested information is mentioned in the revised manuscript and duly highlighted on Page No: 5 and Line Nos: 185 to 194.
COMMENT
2. Selection of methodology: The authors correctly identify the limitations of classical electrochemical methods (e.g. EIS, LPR) with regard to online monitoring. They argue cogently that the EMI technique is the preferred option due to its non-destructive nature and sensitivity to structural changes. However, there is a paucity of validation of the EMI results through parallel, reference electrochemical measurements. A comparison of the RMSD trends with, for instance, the polarization resistance from LPR would significantly strengthen the credibility of the novel methodology.
RESPONSE
The authors thank the reviewer for the thoughtful and constructive feedback. As per the suggestion of the reviewer, a concise statement of the related to the existing corrosion monitoring methods and its limitations are mentioned in the revised manuscript and duly highlighted on Page No: 2 to 3 and Line No: 90 to 104. The authors have only calculated the RMSD trends. Hence, the results of the polarization resistance from LPR are not available.
COMMENT
3. The evaluation of effectiveness: The effectiveness of the EMI technique was primarily evaluated by correlating its signals with visual changes, such as cracking and rust. Whilst the approach taken here is correct, it lacks a quantitative reference. It would be beneficial to consider whether the final mass loss of the reinforcing bar correlates with the cumulative changes in the RMSD index, which would allow for a more objective evaluation of the technique's effectiveness.
RESPONSE
The authors thank the reviewer for the insightful comment. As per the suggestion of the reviewer, a Table on final mass loss of the reinforcing bar is added in the revised manuscript and duly highlighted on Page No: 14 to 15 and Line No: 411 to 425. The authors separately discussed the detailed RMSD index and the mass loss technique in this study.
Reviewer 4 Report
Comments and Suggestions for AuthorsThe article is overall well structured and deals with a current and interesting topic: the combination of environmental sustainability (through the use of E-waste in concrete) and advanced structural monitoring techniques (SHM via EMI).
Among the positive aspects:
- the use of integrated piezoelectric sensors (EPS) for real-time corrosion monitoring is technically relevant, quite innovative and well illustrated.
- the reuse of PCBs as aggregates in concrete is consistent with the objectives of sustainability and e-waste reduction.
- the experimental methodology appears clear, with a detailed description of materials and mix design, a well-defined immersion and corrosion acceleration protocol, a correct use of EMI analysis and RMSD for quantification.
- the results appear consistent and documented. For example, the differentiation between traditional and E-waste concrete is well documented both qualitatively (images, EMI signal trend) and quantitatively (RMSD).
At the same time, there are several aspects that should be improved:
- the concepts of corrosion and sustainability are repeated several times, especially during the introduction. An editing to make the initial part more concise would help to maintain the focus.
- other possible effects of E-waste on pH, porosity, absorption or on the phase transition of corrosion compounds are not addressed.
- a chemical or morphological characterization seems to be missing, which instead assumes a certain importance for this kind of studies: it would be desirable, for example, to include a SEM/EDS or XRD characterization to better understand the corrosion products and the role of PCBs in the penetration of chloride ions.
- the discussion of the results partly lacks a critical connection with the most advanced scientific literature. For example, the nature of the interaction between PCBs and concrete in terms of chemical-physical aspects that influence corrosion is not thoroughly analyzed.
- lack of comparison experiental and numerical/analytical results/tendency: e.g. the results are effectively presented through graphs and RMSD, but a comparative table between CC and E-waste is missing (e.g. corrosion onset time, maximum RMSD, percentage variation in parameters).
- the limitations of the methodology were not discussed (e.g. long-term reliability of PZT, effect of sensor confinement, scaling of results to real dimensions).
- the artificial acceleration of corrosion could generate conditions not entirely representative of the real environment: this was not discussed.
- it is convenient to introduce the nomenclature to make the reading more direct.
- There are small errors to be corrected in the text (eg. "Exposoure" on the x-axis of fig 11B) so a rereading is recommended
Author Response
Reviewer #4
COMMENT
The article is overall well-structured and deals with a current and interesting topic: the combination of environmental sustainability (through the use of E-waste in concrete) and advanced structural monitoring techniques (SHM via EMI).
Among the positive aspects:
- the use of integrated piezoelectric sensors (EPS) for real-time corrosion monitoring is technically relevant, quite innovative and well illustrated.
- the reuse of PCBs as aggregates in concrete is consistent with the objectives of sustainability and e-waste reduction.
- the experimental methodology appears clear, with a detailed description of materials and mix design, a well-defined immersion and corrosion acceleration protocol, a correct use of EMI analysis and RMSD for quantification.
- the results appear consistent and documented. For example, the differentiation between traditional and E-waste concrete is well documented both qualitatively (images, EMI signal trend) and quantitatively (RMSD).
RESPONSE
Thank you for the encouraging feedback. The authors are pleased that the manuscript’s relevance, clear methodology, and integration of sustainability with structural health monitoring using EPS sensors were well received. Your appreciation of the documented results and experimental clarity is sincerely valued.
COMMENT
1. The concepts of corrosion and sustainability are repeated several times, especially during the introduction. An editing to make the initial part more concise would help to maintain the focus.
RESPONSE
The authors thank the reviewer for the comment. As per the suggestion of the reviewer, repeated concepts and statement is deleted in the revised manuscript.
COMMENT
2. Other possible effects of E-waste on pH, porosity, absorption or on the phase transition of corrosion compounds are not addressed.
RESPONSE
Thank you for this valuable observation. While the current study primarily focuses on corrosion monitoring using EMI and compares the corrosion behavior between conventional and E-waste concrete, we acknowledge that E-waste may influence other critical factors such as pH variation, porosity, water absorption, and even the phase formation of corrosion products. These aspects were not directly investigated in this work, but we recognize their importance in understanding the durability performance of E-waste concrete. A note has been added in the discussion section to highlight this limitation and suggest it as a direction for future research.
COMMENT
3. A chemical or morphological characterization seems to be missing, which instead assumes a certain importance for this kind of studies: it would be desirable, for example, to include a SEM/EDS or XRD characterization to better understand the corrosion products and the role of PCBs in the penetration of chloride ions.
RESPONSE
Thank you for this insightful suggestion. We agree that incorporating chemical or morphological characterization, such as SEM/EDS or XRD analysis, would provide valuable insights into the nature of corrosion products and the influence of PCB particles on chloride ion penetration. While such analyses were beyond the scope of the current study, we acknowledge their significance and have added a note in the revised manuscript recommending them as an important avenue for future work to deepen the understanding of corrosion mechanisms in E-waste concrete.
COMMENT
4. The discussion of the results partly lacks a critical connection with the most advanced scientific literature. For example, the nature of the interaction between PCBs and concrete in terms of chemical-physical aspects that influence corrosion is not thoroughly analyzed.
RESPONSE
Thank you for your thoughtful comment. We acknowledge that a deeper critical connection with recent scientific literature, particularly regarding the chemical and physical interactions between PCBs and the cementitious matrix, would enhance the depth of the discussion. In response, we have revised the discussion section to incorporate relevant findings from recent studies. These include the potential effects of PCB surface properties, porosity, and inert nature on chloride ingress and interfacial bonding, which may contribute to corrosion susceptibility. This added context helps explain the observed corrosion behavior and positions our findings within the broader research landscape.
COMMENT
- Lack of comparison experimental and numerical/analytical results/tendency: e.g. the results are effectively presented through graphs and RMSD, but a comparative table between CC and E-waste is missing (e.g. corrosion onset time, maximum RMSD, percentage variation in parameters).
RESPONSE:
The authors thank the reviewer for the comment. As per the suggestion of the reviewer, a comparative analysis between the CC and E-waste concrete is added in the revised manuscript and duly highlighted on Page No: 12 to 13 and Line No: 377 to 398.
COMMENT
- The limitations of the methodology were not discussed (e.g. long-term reliability of PZT, effect of sensor confinement, scaling of results to real dimensions).
RESPONSE:
As per the suggestion of the reviewer, the limitation of the methodology are added in the revised manuscript and duly highlighted on Page No: 15 to 16 and Line No: 446 to 456.
COMMENT
- The artificial acceleration of corrosion could generate conditions not entirely representative of the real environment: this was not discussed.
RESPONSE:
The authors thank the reviewer for the comment. As per the suggestion of the reviewer, a discussion on the artificial accelerated corrosion is added in the revised manuscript and duly highlighted on Page No: 15 and Line No: 446 to 448
COMMENT
- It is convenient to introduce the nomenclature to make the reading more direct.
RESPONSE:
The authors thank the reviewer for the comment. The full form of all the abbreviations are included in the body of the manuscript.
COMMENT
- There are small errors to be corrected in the text (eg. "Exposoure" on the x-axis of fig 11B) so a rereading is recommended
RESPONSE:
The authors thank the reviewer for the comment. The small errors are corrected in the revised manuscript.
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsIn response to question 2, the authors stated that they were unable to relate their EMI measurements to LPR measurements. What about the comment regarding EIS measurements, which contain the word ‘impedance’ in their name, just like the EMI method?
These comments should be included in the text of the article.
Author Response
COMMENT 1. In response to question 2, the authors stated that they were unable to relate their EMI measurements to LPR measurements. What about the comment regarding EIS measurements, which contain the word ‘impedance’ in their name, just like the EMI method?
These comments should be included in the text of the article
RESPONSE 1: The authors thank the reviewer for the comment. In EIS measurement, the Electrochemical impedance represents the resistance and reactance of an electrochemical system to a small AC voltage over a range of frequencies. It reflects the electrochemical processes at the electrode–electrolyte interface, such as corrosion rate, charge transfer resistance, double-layer capacitance, and diffusion phenomena. However, the Electromechanical impedance is the mechanical-electrical coupling response of a piezoelectric sensor bonded to a structure, measured across frequencies. It indicates changes in structural stiffness, mass, or damping, and is sensitive to cracks, delamination, or other physical damages affecting mechanical impedance. EIS and EMI are analogous in using frequency-dependent impedance to monitor system health, and can complement each other in hybrid electro-chemo-mechanical monitoring systems.
EIS requires an electrolyte environment and has slower, more complex measurements, making it less suitable for real-time or in-situ monitoring. In contrast, EMI offers a more efficient and reliable alternative due to its exceptional sensitivity to structural changes and ability to provide real-time data and non-destructive evaluation without any labor-intensive work. This information is mentioned in the revised manuscript and duly highlighted on Page No: 3 and Line Nos: 101 to 108.
Reviewer 4 Report
Comments and Suggestions for Authors...
Author Response
Thank you, for reviewing the manuscript.
