Carbon Accounting for Permeable Pavement Based on the Full Life Cycle Approach and Its Application

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

(1) Please provide the full name of the abbreviation, for example, "RF" in Section 2.6, " IPCC, ELCD, and CPCD" in Section 2.5.

(2) What is the core innovation point of this paper? Has this topic (carbon accounting of permeable pavement) been discussed in other studies? It should be added into the Introduction Section. It was only mentioned that "Recent research demonstrates that permeable pavement offers ecological and carbon reduction benefits during the usage phase".

(3) In Equation (2), what is the meaning of "+" in "+0.01α".

(4) How did you determine the LCA period of 11.3 years?

(5) In Figure 4(b), "suctio" should be "suction".

(6) Where are the tables such as "Table A6. and Table A7."?

Author Response

Comment 1: Please provide the full name of the abbreviation, for example, "RF" in Section 2.6, " IPCC, ELCD, and CPCD" in Section 2.5.

Response1: Thank you for your suggestion. In response to your feedback, we have added the full names of IPCC, ELCD, and CPCD in Section 2.5 and the introduction of RF in Section 2.6:

“This platform integrates various databases including Ecoinvent, the Intergovernmental Panel on Climate Change (IPCC), the European Reference Life-Cycle Database (ELCD), and China Products Carbon Footprint Factors Database (CPCD), leveraging artificial intelligence and big data analysis.” (lines 225-228, page 7)

“The variation of surface albedo influences the radiative forcing (RF), which is quantified as the rate of energy change per unit area.” (lines 249-250, page 7)

Comment 2: What is the core innovation point of this paper? Has this topic (carbon accounting of permeable pavement) been discussed in other studies? It should be added into the Introduction Section. It was only mentioned that "Recent research demonstrates that permeable pavement offers ecological and carbon reduction benefits during the usage phase".

Response 2: Thank you for your comments that helped us improve the standardization and quality of the manuscript.

First, the core innovation of this study is to comprehensively assess the carbon emission and reduction benefits of permeable pavements throughout their entire life cycle. Compared with the existing literature, our study further assessed the priority of different carbon reduction optimization measures by comparing the effects before and after implementing carbon reduction measures at various stages through sensitivity analysis. This approach provides more practical guidance for the implementation of carbon reduction strategies for permeable pavements.

Second, thank you very much for your insightful comments on the background literature. We have supplemented the discussion of related studies in the Introduction section to illustrate the progress and shortcomings of current studies in carbon accounting for permeable pavements.

“LCA is one of the most common and effective methods [1] used in carbon accounting studies for permeable pavement. It can quantitatively analyze both direct carbon emissions during the pavement process, such as energy consumption during use, and indirect carbon emissions, including those associated with material transport and equipment use [2]. Several studies have highlighted the significant reduction in carbon emissions during the permeable pavement and use phases by comparing the LCA results of permeable pavement with those of conventional asphalt and concrete pavement [3]. With proper design and maintenance, permeable pavement can effectively reduce long-term environmental burdens. Further research has also explored the use of alternative materials, such as industrial by-products or recycled materials in permeable pavement, which not only reduce initial carbon emissions but also enhance the overall environmental performance of the pavement.” (lines 52-60, page 2)

1. Zhu, L.; Li, J.; Xiao, F. Carbon emission quantification and reduction in pavement use phase: A review. Journal of Traffic and Transportation Engineering (English Edition) 2024, 11, 69-91.
2. Zhang, O.; Takaffoli, M.; Ertz, M.; Addar, W. Environmental impacts of recycled plastic drainage systems: An LCA case study. Environments 2023, 10.
3. Luo, M.; Wasko, S.; Booth, B. Comparative life cycle assessment of permeable pavement and conventional pavement. Water 2024, 16, 435-460  

Comment 3: Equation (2), what is the meaning of "+" in "+0.01α".

Repsonse 3：We sincerely appreciate your valuable feedback. In Equation (2), the symbol "+" indicates an increase in albedo (?) by 0.01. This notation highlights that the increment is in the positive direction, indicating an increase in the albedo value. This representation is used to illustrate that our model accounts for the effect of a 0.01 increase in albedo.

Comment 4: How did you determine the LCA period of 11.3 years？

Response 4: Thank you for raising this question. The LCA period of 11.3 years for permeable pavement in this study was determined by averaging the service life durations from three relevant studies, which reported service lives of 9, 10, and 15 years, respectively. By taking the average of these durations, we arrived at "11.3 years" as the LCA period for this study. Details of the reference studies can be found in Table S1 of the Supplementary Material.

Comment 5: In Figure 4(b), "suctio" should be "suction".

Response 5: We apologize for this oversight and appreciate your attention to the details of the manuscript. The spelling error in Figure 4(b) has been corrected, and the corrected figure now appears as Figure 5(b) following the addition of a new Figure 2, which was included to explain the structure of the permeable pavement.

Comment 6: Where are the tables such as "Table A6. and Table A7."?

Response 6: Thank you for your question. Tables A6 and A7 are located in the Supplementary Material. After careful review and consideration, we have reformatted the Supplementary Material to make it easier for readers to quickly find the information they need. All tables and figures in the Appendix are now labeled as "Table Sx" and "Figure Sx."

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript calculates the environmental benefits that a specific permeable pavement product can bring. This manuscript is more like a survey and calculation report with weak research-oriented content. My comments are as follows:

(1) Without line numbers, it is hard to accurately locate the content of the article;

(2) The abstract is not rigorous enough. Firstly, the abstract does not clearly state the specific environmental benefits of the permeable pavement but simply lists the LCA calculation results. Secondly, the numbers in the abstract do not have universal applicability and are limited to the research object in the article. Furthermore, as readers, we would prefer to see in the abstract the energy-saving and emission-reducing advantages of permeable pavement compared to traditional asphalt and cement pavements. Typically, 'Permeable pavement showcased substantial potential for carbon emission reduction, with an estimated total reduction of 853.10 tCO2eq.' What is the reduction in carbon emissions mentioned in this sentence compared to, and what is the unit of comparison? Is it one ton of pavement materials? Is it one cubic meter of pavement materials? It is puzzling and cannot provide readers with valuable reference information.

(3) LCA is not rigorous enough and lacks consideration and analysis of the usage stage.

(4) How economical is permeable pavement compared to traditional asphalt pavement and cement pavement? We cannot only consider environmental protection when ignore the economic analysis in practical applications.

(5) I think ignoring the pavement material and its performance and only making an LCA of the pavement product is not very meaningful. Because permeable pavement involves many raw materials, and the LCA results will vary greatly depending on the different raw materials used. Meanwhile, depending on the different usage scenarios, the design methods and raw materials involved in permeable pavement will also vary greatly in terms of durability performance, significantly affecting the final LCA results. So, I think this manuscript leans toward an LCA calculation report rather than a research paper.

Author Response

Comments:

Overview

This manuscript calculates the environmental benefits that a specific permeable pavement product can bring. This manuscript is more like a survey and calculation report with weak research-oriented content. My comments are as follows:

We are very grateful to the reviewer for their constructive comments and recognition of the study. Your feedback is crucial for enhancing the quality of the manuscript. We acknowledge your concern that the manuscript may appear more like a survey and calculation report. In our revisions, we have emphasized the research-oriented aspects by elaborating on the methodology and highlighting the innovative contributions of the study, such as the comprehensive life cycle assessment and the sensitivity analysis of carbon reduction strategies. We sincerely hope that this revision adequately addresses your concerns and demonstrates the research significance of our work.

Comment 1: Without line numbers, it is hard to accurately locate the content of the article.

Response 1: Thank you for your attention to the details of the manuscript. In the revised version of the manuscript, we have added line numbers to make it easier to accurately locate and reference specific content.

Comment 2: The abstract is not rigorous enough. Firstly, the abstract does not clearly state the specific environmental benefits of the permeable pavement but simply lists the LCA calculation results. Secondly, the numbers in the abstract do not have universal applicability and are limited to the research object in the article. Furthermore, as readers, we would prefer to see in the abstract the energy-saving and emission-reducing advantages of permeable pavement compared to traditional asphalt and cement pavements. Typically, 'Permeable pavement showcased substantial potential for carbon emission reduction, with an estimated total reduction of 853.10 tCO₂' What is the reduction in carbon emissions mentioned in this sentence compared to, and what is the unit of comparison? Is it one ton of pavement materials? Is it one cubic meter of pavement materials? It is puzzling and cannot provide readers with valuable reference information.

Response 2: Thank you again for your careful review and valuable comments. Based on your suggestions, we have revised the manuscript accordingly.

First of all, in the revised version of the manuscript, we have clearly stated the specific benefits of permeable pavements in the Abstract. We have emphasized how permeable pavements achieve significant carbon reduction by enhancing groundwater recharge and mitigating the urban heat island effect. These pavements have a greatly lower carbon footprint compared to conventional asphalt and concrete pavements.

“Compared to traditional pavements, permeable pavement showcased substantial potential for carbon reduction, primarily during the use phase, by enhancing groundwater recharge and mitigating the urban heat island effect, which is critical in reducing the carbon footprint. The estimated total carbon reduction was 853.10 tCO₂eq.” (lines 19-22, page 1)

Second, we recognize that the figures in the abstract are not universally applicable and the results are specific to the particular case studied in this research. While most life cycle assessment (LCA) studies are localized, they remain important for understanding underlying mechanisms and contributions. Our findings are particularly relevant in specific application contexts, especially in studies with similar compositional structures and application scenarios, providing some theoretical references. Additionally, our exploration of carbon reduction potential per unit area offers valuable reference information for related fields, helping us to better understand the relative advantages and practical benefits of permeable pavements.

“Based on this study, the area set for permeable pavement in Guanggang Park is 64,065 m², so the unit carbon reduction is 13.32 kg CO₂eq/m².” (lines 332-333, page 10)

Finally, regarding your mention of "Permeable pavements show significant carbon reduction potential, with an estimated total reduction of 853.10 tCO₂eq". The reduction in carbon emissions refers to a comparison with conventional impervious pavement, with the primary reduction occurring during the use phase. Permeable pavements contribute to carbon emission reductions by enhancing pavement albedo of the pavement to mitigate the heat island effect and by serving as mechanisms for rainwater collection, adsorption and purification, which promote groundwater recharge. This groundwater reclamation gradually offsets the carbon emissions associated with the use of pumps to extract an equivalent amount of groundwater. It is important to note that the reduction of "853.10 tCO₂eq" is based on 64,065 m² of permeable paving and is not a comparison of a single unit.

Comment 3: LCA is not rigorous enough and lacks consideration and analysis of the usage stage.

Response 3: Thank you for your suggestions. We acknowledge the importance of considering carbon emissions during the use phase of permeable paving, particularly from rolling resistance, which is a key focus in many studies. However, the application scenario of permeable pavement in this study is a park walkway, where rolling resistance is not a major source of carbon emission during the use phase. Therefore, we exclude it from the system boundary, as explained in the system boundary setting:

“Numerous studies have indicated that permeable pavement generates carbon emissions due to rolling resistance during the usage phase [1-4]. However, the carbon emissions from this aspect were not taken into account in this study. Because the permeable pavement at Guanggang Park is mostly used for pedestrian walkways and has little to do with the rolling resistance of automobiles.” (lines 110-115, page 3)

1. Batouli, M.; Bienvenu, M.; Mostafavi, A., Putting sustainability theory into roadway design practice: Implementation of LCA and LCCA analysis for pavement type selection in real world decision making. Transportation Research Part D: Transport and Environment 2017, 52, 289-302.
2. Pettinari, M. Al-Qadi, I. L.; Ozer, H.; Nielsen, E., Optimised durable pavement rolling resistance. Road Materials and Pavement Design 2023, 24 (sup1), 279-289.
3. Trupia, L.; Parry, T.; Neves, L. C.; Lo Presti, D., Rolling resistance contribution to a road pavement life cycle carbon footprint analysis. The International Journal of Life Cycle Assessment 2017, 22 (6), 972-985.
4. Anthonissen, J.; Van den bergh, W.; Braet, J., Review and environmental impact assessment of green technologies for base courses in bituminous pavements. Environmental Impact Assessment Review 2016, 60, 139-147.

In our study, the use and maintenance phases occur practically simultaneously, so we primarily considered the costs incurred during the maintenance process. The use benefits of permeable pavement and the maintenance process are closely related in practical applications. Our focus is on analyzing the carbon reduction benefits of permeable pavement during the use phase, particularly through mechanisms such as enhancing groundwater recharge and mitigating the urban heat island effect. We have analyzed and calculated these emission reduction benefits in detail in the manuscript.

“In this study, the carbon reduction resulted in the usage phase consisting of two components. The first component involved the carbon reduction attributed to groundwater collection by permeable pavement. Based on the CEIC database for 2020, the annual precipitation in Guangzhou reached an average of 1,890.30 mm. The estimated average rainfall collection is 73,317.87 t/yr., considering an 11.3-year service life, culminating in a total of 828,492 m³ over the life cycle. The carbon emission factor for groundwater pumping, according to the Energy Expert platform, showed that 1 m³ of groundwater extraction produced 0.68 kg of carbon dioxide emissions. As a result, the water resources recovered in this study by using permeable pavement are equivalent to mitigating a 563.37 tCO₂eq carbon footprint. The second component pertained to the carbon reduction achieved by permeable pavement compared to conventional pavement, factoring in changes in pavement albedo. Drawing from prior research, it was determined that permeable pavement reduced carbon emissions by 4.5 tCO₂eq per unit area. Considering the cumulative findings from prior studies, the carbon emission reduction attributed to permeable pavement amounted to 4.56 kgCO₂eq. The total emission reduction reached 289,730.10 tCO₂eq, equivalent to approximately 289.73 tCO₂eq. The combined carbon reduction from both components totaled 853.10 tCO₂eq. Based on this study, the area set for permeable pavement in Guanggang Park is 64,065 m², so the unit carbon reduction is 13.32 kg CO₂eq/m². The net emissions over the lifecycle amounted to 6,213.07 tCO₂eq, with the reduction in carbon emission during the usage phase constituting 12.07% of the total emissions.” (lines 316-335, page 10).

Comment 4: How economical is permeable pavement compared to traditional asphalt pavement and cement pavement? We cannot only consider environmental protection when ignore the economic analysis in practical applications.

Response 4: Thank you for your careful review of our study and your valuable comments. We agree with your point about the importance of economic analysis. In this study, we primarily focused on carbon emission accounting over the entire life cycle of permeable pavements and did not analyzed the economic impacts in detail, which is indeed a shortcoming of this study.

We understand that in the construction and maintenance of infrastructure, economic feasibility is as important as environmental protection, and therefore a comprehensive cost-benefit analysis (CBA) is needed. This analysis should include not only the initial investment cost, but also factors such as return on investment, human resource inputs, and inflation. Although permeable paving may incur higher initial costs, its long-term maintenance costs are lower, and its ecological benefits, such as enhanced groundwater recharge and mitigation of the urban heat island effect, can lead to significant economic returns. Future studies will explore the cost-benefit analysis of permeable pavements versus traditional asphalt and concrete pavements in greater depth to provide a more comprehensive perspective and assess their economics and sustainability in different application scenarios.

“Additionally, the economic impacts of different pavement types were not comprehensively considered, leaving a gap in evaluating the overall cost implications.” (lines 438-440, page 13)

“Future studies will delve into the cost-benefit analysis of permeable pavements versus traditional asphalt and cement pavements to provide a more comprehensive perspective to assess their economics and sustainability in different application scenarios.” (lines 443-445, page 13)

Comment 5: I think ignoring the pavement material and its performance and only making an LCA of the pavement product is not very meaningful. Because permeable pavement involves many raw materials, and the LCA results will vary greatly depending on the different raw materials used. Meanwhile, depending on the different usage scenarios, the design methods and raw materials involved in permeable pavement will also vary greatly in terms of durability performance, significantly affecting the final LCA results. So, I think this manuscript leans toward an LCA calculation report rather than a research paper.

Response 5: Thank you again for your detailed review. We understand your concern about the impact of raw materials and application scenarios on LCA results and agree with that "LCA results can vary significantly across raw materials and application scenarios".

Indeed, any LCA study has limitations in material selection. In this study, our material selection was based on the characteristics of the study site, the availability of materials, and those commonly used at this stage. While these choices may affect the generalizability of the study, our primary goal is to explore the carbon reduction potential of permeable paving, which underscores its broader significance and wide application.

“Surface layers, bedding layers, and grass-roots levels make up the structure of permeable pavement, and each is essential to its operation. Permeable pavement structural design takes into account a number of aspects, such as pavement location and usage [5]. Guangzhou city, characterized by a maritime subtropical monsoon climate with substantial annual precipitation, placing pressure on road surface drainage within Guanggang Park. Therefore, the choice of suitable permeable surface layer materials becomes imperative. Compressive strength and material sustainability are crucial factors to take into account, given Guanggang Park's aesthetic and load-bearing requirements. Because of its performance qualities and adaptability, permeable concrete is the best material for surface layers [6-8]. Permeable concrete offers high water permeability coefficients [9, 10] and efficient heat dissipation capabilities [11, 12]. P.O42.5 cement, a general-purpose permeable concrete binder, and crushed stone that met the requirements of GB/T 1468 for Construction Pebbles and Crushed Stone, the secondary standard, were used in this study. Water was provided on-site through a piped water supply. Besides surface materials, the base and bedding materials must also facilitate permeability to allow rainwater infiltration and groundwater recharge or recycling through drains [13, 14].” (lines 123-138, page 4)

5. Shen, P.; Zheng, H.; Lu, J.; Poon, C. S., Utilization of municipal solid waste incineration bottom ash (IBA) aggregates in high-strength pervious concrete. Resources, Conservation and Recycling 2021, 174, 105736.
6. Adresi, M.; Yamani, A.; Karimaei Tabarestani, M.; Rooholamini, H., A comprehensive review on pervious concrete. Construction and Building Materials 2023, 407, 133308.
7. Deo, O.; Neithalath, N., Compressive behavior of pervious concretes and a quantification of the influence of random pore structure features. Materials Science and Engineering: A 2010, 528 (1), 402-412.
8. Kaplan, G.; Gulcan, A.; Cagdas, B.; Bayraktar, O. Y., The impact of recycled coarse aggregates obtained from waste concretes on lightweight pervious concrete properties. Environmental Science and Pollution Research 2021, 28 (14), 17369-17394.
9. Moretti, L.; Di Mascio, P.; Fusco, C. Porous Concrete for Pedestrian Pavements Water [Online], 2019.
10. Wu, H.; Sun, B.; Liu, Z.; Yin, J., Laboratory-simulated investigation on thermal behaviours of permeable concrete pavements. Road Materials and Pavement Design 2017, 18 (sup3), 97-108.
11. Seifeddine, K.; Amziane, S.; Toussaint, E., Experimental investigation of physical characteristics to improve the cooling effect of permeable pavements. Construction and Building Materials 2022, 345, 128342.
12. Chen, J.; Chu, R.; Wang, H.; Zhang, L.; Chen, X.; Du, Y., Alleviating urban heat island effect using high-conductivity permeable concrete pavement. Journal of Cleaner Production 2019, 237, 117722.
13. Choi, Y.-J.; Ahn, D.; Nguyen, T. H.; Ahn, J. Assessment of Field Compaction of Aggregate Base Materials for Permeable Pavements Based on Plate Load Tests. Sustainability 2018, 10, 3817
14. Muttuvelu, D. V.; Kjems, E. A Systematic Review of Permeable Pavements and Their Unbound Material Properties in Comparison to Traditional Subbase Materials. Infrastructures 2021, 6, 179.

The analytical framework and results provided in this study provide a theoretical reference and baseline data for carbon footprint accounting of permeable paving under similar conditions. Due to its potential for environmental benefits, permeable paving is more in line with the needs of sustainable urban development than traditional paving and can provide an effective solution for optimizing energy and carbon reduction in older communities. Future research will further consider the impact of raw material selection and design methods to enhance the understanding of the environmental benefits of permeable paving in different application scenarios.

“At the same time, the impact of raw material selection and design methods, such as the application of new low-carbon composites [15, 16], will be explored to improve understanding of the environmental benefits of permeable paving in a variety of application scenarios.” (lines 445-448, page 13)

15. Naguib, H. M.; Zaki, E. G.; Abdelsattar, D. E.; Dhmees, A. S.; Azab, M. A.; Elsaeed, S. M.; Kandil, U. F. Exosomal MicroRNAs: An Emerging Important Regulator in Acute Lung Injury. ACS Omega 2023, 8 (9), 8804-8814.
16. Zhang, J.; Feng, C.; Fan, Y.; Yang, J.; Ni, Z.; Hang, Z.; Liu, H. Improved Thermoelectric Properties of Graphene Reinforced Multiphase Cement Composites: Experiments and Modeling. Journal of Sustainable Cement-Based Materials 2024, 1–18.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript entitled “Carbon Accounting for Permeable Pavement Based on the Full Life Cycle Approach and Its Application Research” centered on upgrading facilities in Guangdong, Hongkong, and Macao Greater Bay Area, utilized the Energy Expert platform to assess the carbon footprint of permeable pavement using Life Cycle Assessment. The carbon reduction benefits during operation were estimated. The manuscript needs revision and correction; my comments are listed here:
1. I recommend summerizing the Tiltle to: Carbon Accounting for Permeable Pavement Based on Full Life Cycle Approach and Its Application.
2. Indicate the exact types of permeable pavement, uses, and materials.
3. Highlight the novelty of your work compared with recent literature.
4: I recommend promoting the introduction by including the following citations focusing on reducing carbon in improved applicable construction composites:
https://pubs.acs.org/doi/10.1021/acsomega.3c00086
https://www.tandfonline.com/doi/full/10.1080/21650373.2024.2302095
5: The figures suffer from the low resolution. Please increase the clarity.
6: The conclusion is very detailed. Revise and summarize to give the main findings only with direct meaning.

Author Response

Comments Overview:The manuscript entitled “Carbon Accounting for Permeable Pavement Based on the Full Life Cycle Approach and Its Application Research” centered on upgrading facilities in Guangdong, Hongkong, and Macao Greater Bay Area, utilized the Energy Expert platform to assess the carbon footprint of permeable pavement using Life Cycle Assessment. The carbon reduction benefits during operation were estimated. The manuscript needs revision and correction; my comments are listed here:

We sincerely thank the reviewers for their constructive comments and valuable insights, which are essential for enhancing the quality of our manuscript. We have carefully considered each suggestion and made the necessary revisions. We hope that these changes effectively address your comments and improve the overall clarity and rigor of the study.

Comment 1: I recommend summarizing the Title to: Carbon Accounting for Permeable Pavement Based on Full Life Cycle Approach and Its Application.

Response 1: Thank you for suggesting a change to the title of the manuscript. After careful consideration, we agree that the original title does not fully convey the innovative aspects of our study. Therefore, we have changed the title from "Carbon Accounting for Permeable Pavement Based on the Full Life Cycle Approach and Its Application Research" to "Carbon Accounting for Permeable Pavement Based on the Full Life Cycle Approach and Its Application". We believe this new title more accurately reflects the core work and innovation of our research, allowing readers from various fields to quickly understand the study's focus.

Comment 2: Indicate the exact types of permeable pavement, uses, and materials.

Response 2: Thank you for your question. In this study, the permeable primarily consists of permeable concrete pavement, used mainly in park settings. Based on your suggestion, we have detailed the specific materials for each layer of permeable pavement in Table 1. These materials were selected based on their performance characteristics and suitability for the park's climate and aesthetic requirements. We hope this provides clarity regarding the types, uses, and materials involved in our study.

Table 1. Material information of each layer of permeable concrete.

Material(layer)	Thickness (mm)/ length (m)	Density (kg/m3)	Weight (kg)
Cement (top layer)	N/A	2.88×103	1.95×106
Water (top layer)	N/A	1.00×103	7.33×105
Cementitious material (top layer)	N/A	N/A	8.20×103
Gravel (topping)	N/A	2.10×103	8.46×106
Grading gravel (bedding)	150	2.10×103	2.02×107
Graded gravel (base layer)	150	2.20×103	2.11×107
PVC Drainage Pipe	1.49×103	1.40×103	6.36×103

* The top layer comprises a mixture of various materials, thus no specific thickness value is available, expressed as N/A.

Comment 3: Highlight the novelty of your work compared with recent literature.

Response 3: Thank you for pointing out the need to highlight the novelty of our work. Our study offers a comprehensive carbon footprint analysis of permeable pavement across its full life cycle, addressing a gap in the existing literature, which often focuses on specific phases. We evaluate emission reduction benefits during the use phase, particularly through enhanced groundwater recharge and mitigating the urban heat island effect—areas that have been underexplored in prior studies. Additionally, our extensive sensitivity and scenario analysis identifies key factors impacting carbon emissions, enabling a comparison of carbon reduction measures before and after implementation. By offering practical recommendations for urban planning and infrastructure projects, particularly in the renovation of aging communities, our work not only advances theoretical understanding but also provides actionable insights for optimizing carbon reduction strategies in urban development.

“With an emphasis on the renovation of aging communities, this study offers a comprehensive carbon footprint analysis of permeable pavement across its full life cycle, providing insights that go beyond existing literature, which often focuses on specific phases [1].”(lines 75-78, page 2)

“Most of the existing studies focus on the qualitative study of the environmental benefits of permeable pavement, but this study quantifies the specific emission reduction benefits of permeable pavement in the use phase through LCA method [2, 3].”(lines 78-81, page 2)

1. Zhu, L.; Li, J.; Xiao, F. Carbon Emission Quantification and Reduction in Pavement Use Phase: A Review. Journal of Traffic and Transportation Engineering (English Edition) 2024, 11 (1), 69-91. DOI: 10.1016/j.jtte.2023.09.004.
2. Lu, G.; Wang, Y.; Li, H.; Wang, D.; Oeser, M. The Environmental Impact Evaluation on the Application of Permeable Pavement Based on Life Cycle Analysis. International Journal of Transportation Science and Technology 2019, 8 (4), 351-357.
3. Xie, N.; Akin, M.; Shi, X. Permeable Concrete Pavements: A Review of Environmental Benefits and Durability. Journal of Cleaner Production 2019, 210, 1605-1621

Comment 4: I recommend promoting the introduction by including the following citations focusing on reducing carbon in improved applicable construction composites:
https://pubs.acs.org/doi/10.1021/acsomega.3c00086
https://www.tandfonline.com/doi/full/10.1080/21650373.2024.2302095

Response 4: Thank you for your insightful suggestion to enhance the introduction with relevant citations on reducing carbon in improved applicable construction composites. We have made revisions to the Conclusions section to reflect this. Specifically, we have incorporated the suggested references to emphasize the importance of raw material selection and innovative design methods, such as the application of new low-carbon composites, in advancing the environmental benefits of permeable paving across various application scenarios.

“At the same time, the impact of raw material selection and design methods, such as the application of new low-carbon composites, will be explored to improve understanding of the environmental benefits of permeable paving in a variety of application scenarios [4, 5].” (lines 445-448, page 13)

1. Naguib, H. M.; Zaki, E. G.; Abdelsattar, D. E.; Dhmees, A. S.; Azab, M. A.; Elsaeed, S. M.; Kandil, U. F. Exosomal MicroRNAs: An Emerging Important Regulator in Acute Lung Injury. ACS Omega 2023, 8 (9), 8804-8814.
2. Zhang, J.; Feng, C.; Fan, Y.; Yang, J.; Ni, Z.; Hang, Z.; Liu, H. Improved Thermoelectric Properties of Graphene Reinforced Multiphase Cement Composites: Experiments and Modeling. Journal of Sustainable Cement-Based Materials 2024, 1–18.

Comment 5: The figures suffer from the low resolution. Please increase the clarity.

Response 5: Thank you for your suggestion regarding the resolution of the figures. We have addressed this issue in the revised version of the manuscript by enhancing the clarity and resolution of all images to ensure they are easily readable and visually clear.

Comment 6: The conclusion is very detailed. Revise and summarize to give the main findings only with direct meaning.

Response 6: Thank you for your valuable suggestions. We agree that the conclusion section is too detailed and should be revised and summarized. In the revised version of the manuscript, we have focused on the main findings:

“This study evaluated the carbon emission reduction benefits of permeable pavement using the LCA method throughout its lifespan. The total carbon emissions were found to be 7,066.21 tCO₂eq, with the production phase, including transportation, contributing the most at 47.01%, followed by the maintenance phase at 26.56%, the end-of-life phase at 24.67%, and the construction phase at only 1.72%. Permeable pavement showed considerable potential for energy savings and carbon reduction, achieving a net carbon reduction of 853.10 tCO₂eq. Sensitivity analysis identified diesel energy usage in maintenance, and the production and transportation of cement raw materials as the most impactful factors on the carbon footprint. Implementing specific carbon reduction measures, such as substituting coal gangue for cement clinker, using manual instead of machine sweeping, and recycling all discarded materials, could significantly lower emissions. Thus, replacing traditional pavement with permeable pavement not only reduces the carbon footprint but also supports sustainable urban planning and development. Implementing specific carbon reduction measures, such as substituting coal gangue for cement clinker, using manual instead of machine sweeping, and recycling all discarded materials, could significantly lower emissions. Thus, replacing traditional pavement with permeable pavement not only reduces the carbon footprint but also supports sustainable urban planning and development.

However, this study has some limitations. Data were obtained from various literature and databases, necessitating updates and enhancements to ensure accuracy and reliability. The usage phase may have uncertainties as not all potential carbon emission reduction benefits were taken into account. Additionally, the economic impacts of different pavement types were not comprehensively considered, leaving a gap in evaluating the overall cost implications. Despite these constraints, this study highlights the benefits of carbon reduction and provides practical solutions for using permeable pavement in retrofitting aging communities, offering insights into sustainable development in the GBA. Future studies will delve into the cost-benefit analysis of permeable pavements versus traditional asphalt and cement pavements to provide a more comprehensive perspective to assess their economics and sustainability in different application scenarios. At the same time, the impact of raw material selection and design methods, such as the application of new low-carbon composites [6, 7], will be explored to improve understanding of the environmental benefits of permeable paving in a variety of application scenarios.” (lines 421-448, page 13)

1. Naguib, H. M.; Zaki, E. G.; Abdelsattar, D. E.; Dhmees, A. S.; Azab, M. A.; Elsaeed, S. M.; Kandil, U. F. Exosomal MicroRNAs: An Emerging Important Regulator in Acute Lung Injury. ACS Omega 2023, 8 (9), 8804-8814.
2. Zhang, J.; Feng, C.; Fan, Y.; Yang, J.; Ni, Z.; Hang, Z.; Liu, H. Improved Thermoelectric Properties of Graphene Reinforced Multiphase Cement Composites: Experiments and Modeling. Journal of Sustainable Cement-Based Materials 2024, 1–18.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Most of my comments have been addressed.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have satisfactorily addressed all comments and recommendations. In my opinion, the current version can be accepted now for publication.