Environmental Impact Comparison Analysis between a Traditional Hot Mixed Asphalt (HMA) and with the Addition of Recycled Post-Consumer Polyethylene Terephthalate (RPET) through the Life Cycle Assessment (LCA) Methodology
Round 1
Reviewer 1 Report
This study is a cradle-to-built Life Cycle Assessment (LCA) for road pavement with several scenarios (pavements structure of Hot Mixed Asphalt (HMA) with recycled post-consumer Polyethylene Terephthalate (RPET) addition in micronized and flake form). There are a few limitations of the study, in case we consider the circularity of PET, then RPET has different uses (i.e. bottle-to-bottle recycling), and those can be more environmentally friendlier than RPET use in road pavements. Also, the usage phase and end-of-life impacts (RPET will slowly leak into the environment in the user phase, etc. The authors need to add this discussion into the discussion section as a limitation of the study. If RPET keeps using it for road making, then there need to be new fossil fuel extractions to produce PET (these points need to be discussed).
The overall manuscript is at the moment results in graphical form. The authors need to discuss the results.
Methods:
Life cycle inventory data need to be provided with references (Add a table with values and references).
Discussion: Can not find any adequate discussion. Pelase discusses your results with other studies. Also the limitations of the study.
See the example indicating the LCA limitations
Kamalakkannan, et al., 2022. Life Cycle Assessment of Selected Single-Use Plastic Products towards Evidence-Based Policy Recommendations in Sri Lanka. Sustainability, 14(21), p.14170.
Few more papers on LCA
Gravina, R. J., & Xie, T. (2022). Toward the development of sustainable concrete with crumb rubber: Design-oriented models, life-cycle-assessment and a site application. Construction and Building Materials, 315 doi:10.1016/j.conbuildmat.2021.125565
Yao, L., Leng, Z., Lan, J., Chen, R., & Jiang, J. (2022). Environmental and economic assessment of collective recycling waste plastic and reclaimed asphalt pavement into pavement construction: A case study in hong kong. Journal of Cleaner Production, 336 doi:10.1016/j.jclepro.2022.130405
Conclusion:
Need to revise a lot. Please point out the important findings with numbers (i.e. how much GWP is reduced by RPET). Also, point out some directions on limitations and then recommendations for further studies to use the LCA approach to make decisions.
Supplementary
All the text of the supplementary material should be in English. Please revise it. Also, Life cycle inventory information should be given including the references.
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments:
1. Writing style to quoting the papers should be improved. Below sentences show the quoting at the start of the sentence which was not pretty good in research writing.
In [10] it was performed a cradle-to-gate LCA to compare the envi- 50
ronmental performance of two pavement alternatives from Brazil and Switzerland using 51
practical rates of Reclaimed Asphalt Pavement (RAP), showing that RAP recycling can 52
improve the environmental performance of such pavements, reducing the Binder percent- 53
age and minimizing its environmental burden.
[11] performed a comparative LCA of the 54
use of recycled plastic in the production of asphalt mixes, using primary data.
In [16] it was performed the LCA of asphalt pave- 64
ments with recycled post-consumer polyethylene (RP) introduced via dry process, con- 65
cluding that RP pavements are environmentally beneficial relative to HMA when savings 66
in pavement thickness of 12.5% or extension of maintenance cycles by 7% are achieved.
Section 2.1.3 is not clear. The authors did not mention clearly how the procedure and the analysis on pavement structures are performed.
2. The explanation on the life cycle inventory needs to be improve. I did not see the link between the life cycle inventory with other contents in the manuscript.
3. At which section, the methods for below findings are explained?
The variant pavement structures for the HMA + RPET mixes were considered with 260
and without a subbase course in the design software procedure to evaluate the sensitivity 261
of such mixes to a variance in layer stiffness. The analyses resulted in a thicker HMA 262
+RPET layer for the FU without a subbase. Nevertheless, both structures presented an 263
average similar performance for the environmental impact assessment, with upper and 264
lower results in several impact categories, without any major tendency.
4. How the authors get the value in below paragraph? It was not clearly explained in the manuscript
For every single square meter of sustainable pavement constructed with HMA + 290
RPET and taking a mass of 57 grams for each PET bottle discarded, it represents usage of 291
an equivalent of approximately 87 PET bottles. This is also representative of an annual 292
16.373 Km of a two-lane highway paved using the total of annual estimate of 566.000 t of 293
PET bottles discarded in Brazi
5. The manuscript was written with poor linkages from one topic to the next topic.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 3 Report
The paper presents a good topic related to. Environmental impact comparison analysis between a traditional hot mixed asphalt (HMA) and with the addition of recycled post-consumer polyethylene terephthalate (RPET) through the life cycle assessment (LCA) methodology. The attached file contains many comments to improve the paper before publication.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
This is interesting and timely work. Some comments:
1. The abstract is easy to follow.
2. What is the key contribution/innovation of this study? Please highlight it.
3. The literature review of LCA is not enough, please include different LCA tools.
4. The motivation of this study should be improved.
5. What is the knowledge gap the authors want to fulfill?
6. Please highlight the LCA analysis only conducted during the construction period.
7. How do the authors consider the operation period? According to my knowledge, the data is not easy to collect.
8. Detailed mix design and basic properties of binder, aggregates, and additives should be given.
9. How do the authors calculate the impact? Commercially available software or self-developed tool?
10. The conclusion is confusing, please rephrase it.
Author Response
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Author Response File: Author Response.docx
Reviewer 5 Report
Through environmental impact analysis, the advantages of post-consumer polyethylene terephthalate application can be obtained, which plays an important role in promoting the recycling and application of waste daily materials and reducing resource waste. Comments are as follows:
1. Please specify the type of asphalt used in HMA, matrix asphalt or modified asphalt? Because the condition (mixing temperature and mixing time) for producing the mixture will be of great different between different types of asphalt, and it will definitely influence the environment analysis.
2. When using the RPET, is there any difference of the production condition of the mixture as that of conventional HMA? Generally, when using such material, the mixing temperature would increase and the mixing time may also extend comparing with HMA made with matrix asphalt. If so, the production condition should be considered in the analysis. They cannot considered as the same as stated from 104 to 109.
Moreover, how is RPET used in an asphalt mixing process? Is there special machine for delivery? If so, how should the energy consumption and environmental impact of this machine considered?
3. Please explain why two types of RPET (Micronized and Flakes) are used in the mixture. What is the necessity or advantage? It could be more energy saving when using only single type of the material, because we could only fabricating the PRET material with one type of processing then.
4. In Figure 2, the content of Rock Filler seems very high, should it be the fine aggregate together with the filler?
5. Line 129: please give the reason why 10 year is to be observed? Not others. When making analysis for various years, there could be great difference between the results.
6. In Figure 3. Please explain why different thickness of the top layer are used for the three structure and why the thickness of FU1 is 220, not 200 as in other structure?
7. As given in Figure 2 and Figure 3, the resilient modulus, tensile strength, rutting and cracked area are estimated, but it is unclear how those parameters used in the environment impact assessment? what are the relations between those parameter with the LCA? From my opinion, only when all the parameters are equal (or at equal level), the environment impact assessment could be reasonable.
8. In 2.3.1 Impact Assessment Methodology: Whether the impact of micro plastic particles on the environment and human health is considered in the assessment by the tool TRACI 2.0?
9. In 3.2 Functional Unit Comparison and Interpretation, it is better to provide the formula or an example to show how the indicators in Figure 7 are calculated. It could be convenient for readers to understand.
10. Please give necessary explain of the indicators shown on the vertical axis. Especially what is raw material mean? For Fuel Combustion, where is the combustion from in detail?
11. Expression and Writing：
1) In Figure 1, “A5: Installation” should be “A5: Construction”
2) Traction Resistance should be “tensile strength”?
3) The unit should be MPa, not Mpa.
4) In Figure 2, the range displayed on horizontal axis should be 0 to 100. Because there will be no 120%, the maximum is 100.
5) g/cm3, there should be superscript of “3”, not g/cm3, or g/cm^3. Please check similar problem through the article.
6) Full names should be given when the abbreviations appear first time, for example PAC(50/70).
7) In Figure 3. the layout of the structures from left to right is suggested to be FU1, FU2， FU3. At current version, it seems to be FU1, FU3, FU2.
8) Track sinking should be “rutting”.
9) In Table 2, “specific mass, Optimal water content, Compaction Energy, Los Angeles Abrasion”, please make it uniform whether or not capitalizing the first letter of each word.
10) Line 206-208: it is suggested to move the last sentence to the start of the paragraph “The declared unit environmental life-cycle impact assessment results are presented in figure 5, and the relative comparison of the environmental impact assessment for each DU is presented in Figure 6.” Make it uniform “figure” or “Figure” in the whole paper.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The manuscript is suitable for publication.
Reviewer 4 Report
Thanks to the authors' hard work, almost all my comments were revised. No further review process is needed.
Reviewer 5 Report
Detailed modifications have been made by the authors. There is no other problems and I agree to accept it.
