Enhancing Asphalt Performance and Its Long-Term Sustainability with Nano Calcium Carbonate and Nano Hydrated Lime

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study presents a comprehensive investigation into the effectiveness of nano calcium carbonate (NCC) and nano hydrated lime (NHL) as modifiers for asphalt binders and mixtures. The experimental approach, including laboratory tests such as penetration, softening point, viscosity, and dynamic shear rheometer (DSR) tests, adds significant depth to the analysis. The findings reveal noteworthy improvements in binder stiffness, rutting resistance, high-temperature stability, and moisture resistance with the addition of both NCC and NHL.

The study effectively highlights NHL's superior performance in terms of rutting resistance, load-bearing capacity, and moisture resistance compared to NCC. The detailed analysis of various properties, including Marshall stability, resilient modulus, and permanent deformation, provides a comprehensive understanding of the impact of these nanomaterials on asphalt performance. The reviewer has the following comments to improve the quality of the manuscript:

Abstract:

·         It would be beneficial for the authors to discuss potential limitations of the study, such as long-term durability and environmental considerations.

Research gap and objectives

·         To strengthen the manuscript, it might be beneficial for the authors to explicitly state how their study aims to address the identified gaps and contribute to the field. Additionally, discussing potential challenges or limitations associated with the proposed methodology could provide transparency and guide future research directions.

Methods and discussion

·         Table 2 can be deleted as it presents the aggregates properties or can be shorten

·         Quality of Figures 1 and 8 should be improved and it would be better to present the gradation of the mix.

·         Figure 2 can be deleted

·         More discussion should be provided on the results of  SEM (Figure 3)

·         Please, shorten the details of Moisture susceptibility and mix design as they are known.

·         Results of rotational viscosity for (a) original binder and (b) after RTFO should be presented as points not a bar chart.

·         Effect of NCC and NHL on Marshall Properties (figure 11) can be deleted or replaced with table.

·         Please provides more clarifications and discussion why the NHL provides better results than NCC.

·         An economic study should be conducted to evaluate the cost benefit analysis of using those materials in asphalt mixes.

Conclusions

Limitation and recommendations to the practitioners should be provided

Comments on the Quality of English Language

should be improved

Author Response

Please refer to the authors' report notes for our responses to this reviewer. Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

General comments:

1. the article shows the results of NCC and NHL tests, which are positive. But the same materials in the normal (non-nano) version also show positive effects on asphalt. Consequently, it is not known whether the positive effect of the nano variant is significantly greater than that of the "non-nano" version. The article lacks a comparison from the results with the classical variants of these materials to show that the nano variant is worthwhile. Nanomaterials are much more expensive than classical ones, and there must be significantly better asphalt performance to use them.

2 There is a lack of low temperature testing, such as BBR. Which makes the verification of compliance with AASHTO M320 only partial and leaves a question mark.

3. do the authors have information to what extent NCC and NHL have been tested for contact (inhalation, transdermal) safety for humans?

4. Wherever %'s appear, add whether they are percentages by weight or volume.

5. overall, the article is carefully written and contains interesting information.

 

Specific comments:

Line 4 and 5 - Amjad H. Albayati's email address does not match the name, please check if this is an error

Line 4 and 9 - Juliana Byzyka's email address is incorrect compared to lines 4 and 13

 

Abstract:

Line 24-25 - the sentence "The resilient modulus of the mixtures 24 consistently increased with the addition of NHL, suggesting improved durability." would require an indication in the text of what this improved durability was supposed to consist of and what durability is involved? It is only in section 3.2.2.3 that there is clarification that it is about permanent deformations. However, it would be better to put this right away in the abstract, e.g. by ending the sentence with "...suggesting improved durability in rutting" or similar.

The percentages given can be understood as percentage by weight of asphalt or percentage by weight of asphalt cement. It should be made clear in the text which percentage is meant, e.g., in the abstract and in the main text (e.g., line 80). The explanation does not appear until line 109.

 

1. Introduction

In this section, please add what is known so far about the positive effects of these materials but not in the nano version but in the classic version i.e. HL and CC.

Line 43 - please provide the chemical formulas of NCC and NHL in parentheses (except that they are in Table 3)

Line 80 - the given contents of modifiers to the binder (0-10%) should result from something. For example, it is believed that the content of ordinary HL for asphalt mix should be from 1 to 2% by weight of the total asphalt mix, i.e. from 10 to 20 kg per 1 ton of asphalt. If we assume that the binder per ton was on average 5% by weight, i.e. 50 kg, then the HL content converted to binder is 10/50 to 20/50, i.e. 20% to 40% by weight of binder. This would be the case for the classical approach with ordinary HL. Here NHL is used. Larger fineness, greater contact/reaction area between the binder and NHL justifies reducing the ratio and still getting good results. However, somehow the 0-10% range used in the study needs to be addressed.

 

2. Materials

Line 113 - the introduction of NCC and NHL into the asphalt cement required the use of a high shear mixer for 15 minutes. What would it look like if someone wanted to do a production trial in an asphalt plant? This is worth addressing in the conclusions of the article, as the results are good and one should move towards industrial trials.

Additional information about the nanomaterials should be provided, such as specific surface area, free spaces according to Rigden (or Anderson's modified method). This would allow us to assess the stiffening potential of these modifiers and generally better understand how they differ from classic HL and CC.

 

3. Mixing and Testing Methods

Line 133 - the modified binder was heated for 2 hours. Was it stirred during this time to avoid sedimentation of the modifier?

Line 147 - RTFOT testing is not only to determine the volatile component content, but also the oxidation potential of the binder. This is evidenced by mass change results which are sometimes positive.

 

5. Results and Discussion

Line 234 and beyond - it might be worth adding what is the volume percentage of modifiers in the binder mixture? Figure 4 gives mass values, it might be worth adding an additional horizontal axis with volume percentages of modifiers. This will perhaps make it easier to understand the changes in penetration and SP.

Fig. 4 - next to the % designation, it should be added that these are mass percentages

Line 246 and onwards - it is worth adding information about the phenomenon of capturing part of the binder by the free spaces in the nanomaterials and the division into "free" and "bound" binders, which explains the stiffening of the mixture.

Line 256 - should be "compatibility"

Line 264 and on - I have a comment that when evaluating the results one should consider the values of a given property, in this case the stability (delta T) we have ranges from 0.5 to 1.9 degrees Celsius. These are very small top-to-bottom differences (delta) and the mere fact that they are increasing (which is logical) does not mean that there is a high susceptibility to segregation. It is worth considering some evaluation criteria. Here, none were applied. For example, in Europe, a cutoff value of 5°C is used to evaluate this characteristic for polymer-modified binders. Results below 2°C would be considered very good.

Fig. 5 - next to the % designation, note that these are percentages by weight

Line 291 and onward - it seems that explaining the increase in mass loss due to RTFOT as solely a volatile release process is too simplistic. It is a much more complicated process. In fact, there is a lack of literature in which this process is well explained. There seem to be complex issues of chemical reactions between CaCO3 and Ca(OH)2 and the group components of the binder. The presence of hydrated lime reduces the amount of ketones, anhydrides and most carboxylic acids that form during aging. For more details, see the attached report file in section 3.2.1 ("Hydrated Lime: A proven additive for durable asphalt pavements" European Lime Association, 2012).

Line 318 et seq. - Brookfield Viscosity Meter workability testing is performed on the unaged binder to check its ability to mix and coat the aggregate grains. Post-RTFOT tests can only give an indication of what would happen if the mixed asphalt mixture is stored too long in a silo. The results show that variants with an NHL of more than 2% could then cause problems. Do the authors agree with this observation?

Line 348 - should be 5000 kPa

Line 367 and onwards - one could possibly add an analysis of the so-called stiffness according to Marshall (Marshall Quotient), i.e. the S/F ratio [kN/mm].

Line 381 and beyond - it seems that explaining why the addition of NHL and NCC act in such a way that AV and VMA are lowered is very important. Please add a few sentences as this is crucial for asphalt mix design.

Line 427 - all Figure 11 - if possible please mark the precision of the results with "whiskers" as in Figure 12.

Line 430 - please annotate the temperature of the Mr. test

Line 443 - caption under figure 12 please annotate the Mr test temperature

Figures 15 and 16 - please indicate the test temperature in the caption of the figures

 

6. Conclusions

The table with comparative results of asphalt mixtures with optimal NHL and NCC contents is very good. I suggest adding a similar one for unmodified binder and with optimal NHL and NCC contents, including a comparison of PG according to AASHTO M320.

Consider adding the conclusion that of the two comparable modifiers, one proved more effective.

 

Comments on the Quality of English Language

Only a few places in the text need editorial corrections (missing dots, commas, spelling errors). Other than that, the text is good.

Author Response

Please refer to the authors' report notes for our responses to this reviewer. Thank you.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study is aimed to evaluate the effect of nano materials on Performance of asphalt binder and mixtures. This study is comprehensive and has several tests done on assessing asphalt properties.  The modified binder  problem and mixtures were assesssd at normal and high temperatures,  however, the unmodified binder selected was bit stiff (penetration about 50 dmm), therefore,low temperature cracking shall be conducted as all tests conducted were at 20 to 25 degree Celsius. 

The problem statement should be stated clearly in the abstract and introduction. 

The objectives should be stated specifically. 

Why the authors chose the binder with Penetrating 50dmm. I believe this nanotechnology modification should be done on a bit softer binder.

The limitations and future work for lab work should be stated..

Pls add the aim and objective description before the remaking points in conclusion 

I believe the authors should discuss thier findings with other previous studies .

My suggested paper 

https://doi.org/10.1007/s42947-021-00131-0

Author Response

Please refer to the authors' report notes for our responses to this reviewer. Thank you.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors didn't address some of the reviewer comments especially the economic study which will enhance the quality of the manuscript.

It is necessary to conduct it.

 

Comments on the Quality of English Language

Still needs improvements 

Author Response

Reviewer 1 comments:

The authors didn't address some of the reviewer comments especially the economic study which will enhance the quality of the manuscript.

It is necessary to conduct it.

Response: The authors have conducted the cost analysis. Please see section 6 in the revised paper.

Sincerely,

The Authors

Reviewer 3 Report

Comments and Suggestions for Authors

No further comments 

Author Response

Thank you.

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

None

Comments on the Quality of English Language

Should be improved