Mechanical Behavior of Low-Density Polyethylene Waste Modified Hot Mix Asphalt

Round 1

Reviewer 1 Report

1-In the Introduction, It is suggested to write the authors' names instead of numbers when you cite an article by the beginning of the line. Example line 73.

2-The main idea of this article is to reduce the environmental impact of asphalt emissions. How did you monitor the impact before and after? What I am seeing in your article is only pavement performance 

 

Author Response

25-march, 2022

 

Dear Editor and Reviewer 1,

 

We would like to thank you for your valuable and insightful comments that have helped us to improve our manuscript. Please find also in the following paragraphs our answers to the comments. We have tried our best to clarify all the points raised. We hope that this new version of the manuscript is satisfactory for publication.

 

 

Reviewer 1

 

1. In the Introduction, It is suggested to write the authors' names instead of numbers when you cite an article by the beginning of the line. Example line 73.

 

Answer: Thank you very much for your comment. Based on your comment, we made the respective changes.

 

2. The main idea of this article is to reduce the environmental impact of asphalt emissions. How did you monitor the impact before and after? What I am seeing in your article is only pavement performance.

 

Answer: You are right. The main idea was reducing the mixing temperature of the LPDE with the asphalt binder, obviously seeking to reduce emissions. However, we did not measure emissions before, during and after of the mixture. This was a limitation of the study. At the end of the conclusions, we make a recommendation in this regard (see lines 531 to 535). We look forward to your understanding in this regard.

Author Response File: Author Response.docx

Reviewer 2 Report

Please address all comments and revise the manuscript.

 

L35 to L40: Delete this paragraph which is too general introduction, and revise it more relevant to the topic.

 

L60 to L96: The authors discussed some of other studies concerning LDPT for asphalt. What are the major findings from others? What is the difference between your study and others’?

 

L102: One of significant issues is that the compatibility of LDPE with asphalt binders. How did authors consider this?

 

L135: What is the degradation process? What is the melting point?

 

Table 2: What did authors mean by “no plastic” by performing Index Plasticity ASTM D4318? This is not a test for plastic, but for soil.

 

In Table 2, what are the requirements for each parameter? Please provide them.

 

L143: Please delete those abbreviations (MT, mt, and MS), and use the full name for each term. They are just two-word term. This would be helpful for the readers.

 

L148: How did authors ensure the LDPE is well dispersed in asphalt?

 

L149 to L160: Why did authors mixing and time? If you cannot get a good quality, the LDPE modified asphalt is not feasible for use.

 

L268: Are all specimens submerged into hot water for wheel track test?

 

Please provide a flow chart to include all testing in an organized way, so that the objectives and methods can be easily visualized.

 

Table 5: How many replicates for each test? Please provide standard deviation.

 

Figure 3: Please provide standard deviation.

 

Tables 6, 7, and other tables and figures: Please provide standard deviation.

 

Figure 4 can be deleted.

 

Figure 5 can be deleted. You would need to provide fatigue life results from LAS test. Also, different aging conditions should be included to present.

 

Figure 9: The TSR results show that the addition of LDPE is not helpful. Please discuss it.

 

Figure 12: Did authors observe stripping inflection point (SIP) from loaded wheel test? Why the time is in seconds? Shouldn’t the x-axis be number of cycles?

 

It is unclear what the air voids for all Marshall specimens for mixture testing. For fatigue test in Section 3.7, why the stress control is selected, rather than strain control?

 

The conclusions need to be revised to make it simple and to-the-point. Please clearly summarize the effect of waste plastic (LDPE) on the performances.

 

L487 to L489: Please revise the sentence. How does brittleness relate to fatigue cracking?

 

For all figure titles, please remove “Source: Authors”. There is no need to cite your own authentic work if this is presented the first time.

 

L449: The observation that “as the asphalt binder ages, the modified mixture with LDPE undergoes less resistance to fatigue” is not supported by Figure 13, because there is no comparison between aged and unaged specimen. Also, L449 to L454 are not supported by Figure 13.

 

Figure 14: Cantabro loss test results indicate that the LDPE has negative impact on the durability of asphalt mixture.

 

L491: Why do the mixing and compacting the modified mixtures have lower temperature?

 

L514 to 521: The authors would need to be cautious about the recommendation, based on a limited study in this paper.

Author Response

25-march, 2022

 

Dear Editor and Reviewer 2,

 

We would like to thank you for your valuable and insightful comments that have helped us to improve our manuscript. Please find also in the following paragraphs our answers to the comments. We have tried our best to clarify all the points raised. We hope that this new version of the manuscript is satisfactory for publication.

 

 

Reviewer 2

 

Please address all comments and revise the manuscript.

 

1. L35 to L40: Delete this paragraph which is too general introduction, and revise it more relevant to the topic.

 

Answer: We consider valuable your comment. However, we believe that this paragraph is important to highlight the importance of the use of modified asphalt binders. For this reason, we prefer not to remove it. We look forward to your understanding in this regard.

 

2. L60 to L96: The authors discussed some of other studies concerning LDPT for asphalt. What are the major findings from others? What is the difference between your study and others’?

 

Answer: The main finding of the other studies was that LDPE notably increases the stiffness of the asphalt binder and therefore the resistance to permanent deformation (rutting resistance) of the asphalt mixtures (lines 62 to 64). The difference between our study and the others is described in lines 97 to 111.

 

3. L102: One of significant issues is that the compatibility of LDPE with asphalt binders. How did authors consider this?

 

Answer: We do not perform direct measurements to assess the compatibility of asphalt binder and polymeric waste. However, we carry out a rheological characterization to evaluate the interaction between both materials at high and intermediate service temperatures. The conclusion is that at high temperatures, the waste could enhance the properties of the asphalt binder, while at intermediate temperatures the opposite could occur. We look forward to your understanding in this regard.

 

4. L135: What is the degradation process? What is the melting point?

 

Answer: Thank you very much for your comment. We removed the sentence to avoid confusion. However, we had obtained the melting point in a previous study by performing DSC tests. For this reason, we include the following sentence (see lines 140 to 141): “Based on DSC (Differential Scanning Calorimetry) tests, their melting point begins to appear from 130 ° C [21]”.

 

5. Table 2: What did authors mean by “no plastic” by performing Index Plasticity ASTM D4318? This is not a test for plastic, but for soil.

 

Answer: A soil is considered non-plastic when plasticity index = 0.

 

6. In Table 2, what are the requirements for each parameter? Please provide them.

 

Answer: Thank you very much for your comment. We placed the requirements in Table 2.

 

7. L143: Please delete those abbreviations (MT, mt, and MS), and use the full name for each term. They are just two-word term. This would be helpful for the readers.

 

Answer: We agree with the observation and remove the abbreviations.

 

8. L148: How did authors ensure the LDPE is well dispersed in asphalt?

 

Answer: We did not make direct measurements to evaluate the dispersion of the waste in the asphalt binder. However, the melting point of LDPE is lower than the mixing temperature and visually no lumps were found in the modified asphalt.

 

9. L149 to L160: Why did authors mixing and time? If you cannot get a good quality, the LDPE modified asphalt is not feasible for use.

 

Answer: The main objective of the study was to evaluate the use of LPDE waste as an asphalt modifier in a more environmentally friendly way. In the end, it is concluded that the possible use would be in high temperature climate and forming asphalt mixtures used as asphalt course base. On the other hand, the results obtained help to deepen the discussion on the subject of study.

 

10. L268: Are all specimens submerged into hot water for wheel track test?

 

Answer: The partial saturation process with water does, which is explained in lines 237 to 240. After this conditioning process, samples were tested in the wheel track test.

 

11. Please provide a flow chart to include all testing in an organized way, so that the objectives and methods can be easily visualized.

 

Answer: Thank you very much for your comment. We insert a flow chart showing the methodology in a flow char (line 127 to 130).

 

12. Table 5: How many replicates for each test? Please provide standard

 

Answer: In order to answer your comment, we introduce in lines 297 to 298 the next sentence: “Each test was performed on three samples (Table 5 shows the average of the results obtained)”. Additionally, we place the standard deviation.

 

13. Figure 3: Please provide standard deviation.

 

Answer: Placing the deviation in the viscosity curve would generate a difficult image to visualize. For this reason, we prefer not to show it. We look forward to your understanding in this regard.

 

14. Tables 6, 7, and other tables and figures: Please provide standard deviation.

 

Answer: Thanks for your observation. In Tables 5, 6, 7 and 8, the respective standard deviations were placed. In Figures 5 and 6 the coefficients of variation were very small (less than 0.5%). In figures 7 and 10 the deviations were placed and the others already had them. In Figure 14 (fatigue test) this observation does not apply.

 

15. Figure 4 can be deleted.

 

Answer: We prefer to keep it, since it shows visually that the modified asphalt deforms less in the test. We hope your understanding in this aspect.

 

16. Figure 5 can be deleted. You would need to provide fatigue life results from LAS test. Also, different aging conditions should be included to present.

 

Answer: We did the LAS test based on the AASHTO TP101 standard, aging the binders in the long-term condition (see lines 193 to 202). We think that it is better to keep the Figure, since it clearly shows the decrease in the fatigue resistance of the modified asphalt. We hope your understanding in this aspect.

 

17. Figure 9: The TSR results show that the addition of LDPE is not helpful. Please discuss it.

 

Answer: You are right, LDPE decrease resistance to moisture damage. However, this decrease was not statistically significant respect to the control mixture. This decrease in TSR was mainly due to the higher porosity of the mixture (the mixture with LDPE was tested with Va=7%, while the control one with 5.1%) (see lines 403 to 408). If the control mix had been tested also at 7% of Va, the TSR value would have been less.

 

18. Figure 12: Did authors observe stripping inflection point (SIP) from loaded wheel test? Why the time is in seconds? Shouldn’t the x-axis be number of cycles?

 

Answer: You have reason, these SIP should not exist. However, it must be taken into account that each point is the average of three tests carried out. For this reason, the points can go up or down with the number of cycles. In order not to confuse the reader, we decided to remove the points and present the general trend. Additionally, taking in account your observation, we change the x-axis by number of load cycles (see Figures 12 and 13).

 

19. It is unclear what the air voids for all Marshall specimens for mixture testing. For fatigue test in Section 3.7, why the stress control is selected, rather than strain control?

 

Answer: Thank you very much for your comment. The samples for the fatigue tests were manufactured using the OAC. On average, the control samples with this OAC had Va=4.9±0.4%, while the samples with LDPE were more porous (Va=7.3±0.3%). In lines 462 to 463 it is mentioned. On the other hand, the controlled-stress fatigue test was chosen because it better simulates the behavior of an asphalt mixture when it is used in a thick asphalt layer. This is mentioned in the lines 275 to 276.

 

20. The conclusions need to be revised to make it simple and to-the-point. Please clearly summarize the effect of waste plastic (LDPE) on the performances.

 

Answer: Taking in to account your comment, the conclusions were reviewed and changes were made.

 

21. L487 to L489: Please revise the sentence. How does brittleness relate to fatigue cracking?

 

Answer: The sentence was revised and improved. The term “brittleness” was removed so as not to confuse the reader.

 

22. For all figure titles, please remove “Source: Authors”. There is no need to cite your own authentic work if this is presented the first time.

 

Answer: We removed “Source: Authors”.

 

23. L449: The observation that “as the asphalt binder ages, the modified mixture with LDPE undergoes less resistance to fatigue” is not supported by Figure 13, because there is no comparison between aged and unaged specimen. Also, L449 to L454 are not supported by Figure 13.

 

Answer: We agree with you. We changed the sentence (see lines 458 to 459 and lines). On the other hand, lines L49 to L454 (now lines 459 to 464) are explanations for the lower fatigue strength undergo for the mixtures with LDPE. These explanations are based on the test results presented earlier in the manuscript.

 

24. Figure 14: Cantabro loss test results indicate that the LDPE has negative impact on the durability of asphalt mixture.

 

Answer: Yes, and so it was described in chapter 3.8 and in the conclusions.

 

25. L491: Why do the mixing and compacting the modified mixtures have lower temperature?

 

Answer: The main objective of the study was to evaluate the use of LPDE waste as an asphalt modifier in a more environmentally friendly way. Mainly for this, both temperatures are lower.

 

26. L514 to 521: The authors would need to be cautious about the recommendation, based on a limited study in this paper.

 

Answer: Taking in account your observation, we change the paragraph (see lines 525 to 536).

 

Author Response File: Author Response.docx

Reviewer 3 Report

This paper presents the use of polymeric waste in the modification of asphalt binders and the mechanical behavior of a modified HMA with LDEP polymeric waste was evaluated. The paper is well presented and of high interest to researchers.

Please address the following comments before accepting it for publication.

1. First, the authors should distinguish the contribution of this work from that of the existing similar works. Add or expand the last paragraph of the introduction to clearly state what is new in this paper.
2. Provide more the limitations of the current study and recommendation to future research to overcome the limitations.

 

Author Response

25-march, 2022

 

Dear Editor and Reviewer 3,

 

We would like to thank you for your valuable and insightful comments that have helped us to improve our manuscript. Please find also in the following paragraphs our answers to the comments. We have tried our best to clarify all the points raised. We hope that this new version of the manuscript is satisfactory for publication.

 

 

Reviewer 3

 

This paper presents the use of polymeric waste in the modification of asphalt binders and the mechanical behavior of a modified HMA with LDEP polymeric waste was evaluated. The paper is well presented and of high interest to researchers.

 

Please address the following comments before accepting it for publication.

 

1. First, the authors should distinguish the contribution of this work from that of the existing similar works. Add or expand the last paragraph of the introduction to clearly state what is new in this paper.

 

Answer: We consider valuable your comment. We describe the differences with other studies in lines 97 to 111.

 

2. Provide more the limitations of the current study and recommendation to future research to overcome the limitations.

 

Answer: Thank you very much for your comment. Taking in to account your observation, we write lines 530 to 535.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors did a great job addressing the reviewers' comments. However, I still have the same concern  regarding this comment below. IF this will be a future work and one of the limitations you may submit this work to pavement performance-related work

2. The main idea of this article is to reduce the environmental impact of asphalt emissions. How did you monitor the impact before and after? What I am seeing in your article is only pavement performance.

Author Response

29-march, 2022

Dear Editor and Reviewer 1,

 

We would like to thank you for your valuable and insightful comments that have helped us to improve our manuscript. Please find also in the following paragraphs our answers to the comments. We have tried our best to clarify all the points raised. We hope that this new version of the manuscript is satisfactory for publication.

 

 

Reviewer 1

 

The authors did a great job addressing the reviewers' comments. However, I still have the same concern regarding this comment below. IF this will be a future work and one of the limitations you may submit this work to pavement performance-related work.

 

2. The main idea of this article is to reduce the environmental impact of asphalt emissions. How did you monitor the impact before and after? What I am seeing in your article is only pavement performance.

 

Answer: Perhaps most of the study shows the performance of the modified asphalt binder and mixture from a technical point of view (evaluation of mechanical properties), but the main objective and motivation is merely environmental. The idea is to help reduce environmental pollution in the future due to the uncontrolled disposal of plastic waste materials and to propose techniques that allow us to reduce energy use. For this reason, we decided to use a waste of LDPE as an asphalt binder modifier and lower the mixing temperature in order to reduce emissions and negative environmental impacts. For us this is evident even though we do not measure it directly. In other words, the decrease in the negative environmental impact was evident for us (as reported by multiple studies on the subject), but the mechanical performance of the mixture with LDPE was not. For this reason, we conducted this study in this way. The results help deepen the discussion on the subject. The idea is to continue research seeking to achieve a technical, economic and environmental balance on the use of LDPE as an asphalt modifier.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have addressed comments and revised the manuscript, which is appreciated. A few more comments below for authors’ consideration.

 

The authors would need to add the standard deviation for Figure 4, which can reveal the results in a more significant and scientific manner.

 

Figure 14: The authors answered that “fatigue test this observation does not apply”. Why not apply? Replicates of samples should be used for fatigue test as well.

 

The authors mentioned that the mixture with LDPE was tested with Va = 7% while the control one with 5.1%, when explaining the previous comment about the TSR results. Why not compact all specimens at the same air voids content to eliminate the effect of the air voids on the mechanical performances?

 

Figure 12: The authors should not average the three tests results for loaded wheel test, but show each curve and identify if there is stripping inflection point. As found by TSR results, the LDPE modified mixture has worse moisture damage resistance, it would be also found by the loaded wheel test “Hamburg wheel test”. 

Author Response

29-march, 2022

Dear Editor and Reviewer 2,

 

We would like to thank you for your valuable and insightful comments that have helped us to improve our manuscript. Please find also in the following paragraphs our answers to the comments. We have tried our best to clarify all the points raised. We hope that this new version of the manuscript is satisfactory for publication.

 

 

Reviewer 2

 

The authors have addressed comments and revised the manuscript, which is appreciated. A few more comments below for authors’ consideration.

 

1. The authors would need to add the standard deviation for Figure 4, which can reveal the results in a more significant and scientific manner.

 

Answer: Taking into account your comment, we present all the measured viscosity results and it is observed that the variations are statistically insignificant.

 

2. Figure 14: The authors answered that “fatigue test this observation does not apply”. Why not apply? Replicates of samples should be used for fatigue test as well.

 

Answer: Each sample was exposed to a different stress. That is, three samples were not manufactured for each stress to determine an average. Each test result is statistically independent of the others. The nine points that appear in the Figure are independent results of measuring the number of load cycles required to fail each sample under each cyclic stress. We could have tested three samples for three cyclic stresses and averaged them. However, we prefer to fail each sample under different stresses.

 

3. The authors mentioned that the mixture with LDPE was tested with Va = 7% while the control one with 5.1%, when explaining the previous comment about the TSR results. Why not compact all specimens at the same air voids content to eliminate the effect of the air voids on the mechanical performances?

 

Answer: Normally to measure the TSR, the test is performed on samples with Va = 7 ± 1%. However, the modified mixtures with LDPE presented that range of Va, while the control ones around 5%. Our idea was always to measure all the mechanical parameters with the Va obtained by design since it is more representative of the real manufacturing conditions (see lines 251 to 255).

 

4. Figure 12: The authors should not average the three tests results for loaded wheel test, but show each curve and identify if there is stripping inflection point. As found by TSR results, the LDPE modified mixture has worse moisture damage resistance, it would be also found by the loaded wheel test “Hamburg wheel test”. 

 

Answer: The permanent deformation curves show the general trend of the test. Traditionally, this is one of the most common ways to present them. We think that the presentation of the figure could be suitable for display. Perhaps we have not adequately answered the comment because we do not fully understand it. We apologize for this. On the other hand, we do not perform permanent deformation tests on submerged (underwater) samples to evaluate stripping potential. All samples were evaluated for rutting at air dry condition specimens (line 279-280). One sample was previously conditioned STOA + LTOA + Water, but this sample was then placed like the others in the equipment to be tested in dry condition. Stripping inflection point (SIP) is a parameter that is obtained on submerged samples (water-immersed conditions) in the permanent deformation test and in our study, we did not test submerged samples.

Author Response File: Author Response.pdf