Effect of Chemical Composition of Bio- and Petroleum-Based Modifiers on Asphalt Binder Rheology

Round 1

Reviewer 1 Report

The article by Singhvi et al. is reporting some result on modifiers. However the structures of the modifiers are keep confidential so this study cannot be replicate. Thus I canot be supportive with the publication, even more in an open access journal…

Moreover, the result are poorly presented

Author Response

Point 1: The article by Singhvi et al. is reporting some result on modifiers. However the structures of the modifiers are keep confidential so this study cannot be replicate. Thus I canot be supportive with the publication, even more in an open access journal…

Response 1: We appreciate the reviewer’s comments and understand concerns. However, we need to make a note that only the names of the modifiers are kept confidential as stated in the manuscript (Line 113-114, page 3) and the generic modifier type is provided in Table 1. In addition, the chemical properties of the modifiers are determined and presented in the paper. Together these properties indicate modifiers’ chemical make-up. Furthermore, the chemistry of these modifiers highly depends on its bio source which is variable in nature. Therefore, the study emphasizes the role of modifier chemistry on modified binders’ rheological response, irrespective of its make or brand. We believe that listing a brand is counterproductive and may appear as prompting specific products.

Point 2: Moreover, the result are poorly presented

Response 2: The paper is organized as follows. We went over the paper again to see how we can improve the presentation of the results. We appreciate any further comments and suggestions from the reviewer.

• Materials sources and their make ups
• Detailed methodology of modification because this is an important part of the study for consistent results
• Introduction of the tests and parameters (chemistry and rheological)
• Then the results are presented in the following order:
  • The chemical characteristics of the modifiers to anticipate their chemical make-up and molecular size.
  • Then, selection of modifier dosage to obtain a target binder grade of PG58-28 for all modified binders with their true grades close to each other as reported in Table 5.
  • Rheological results were presented next at different laboratory aging conditions; long-term to extra long-term aging (upto 60-hr PAV). Because the base binder used for the modification was same for all modifiers, the change in rheological properties are attributed to the modifier alone.

Some of the references we used to present our results and selection of parameters are the following:

• Airey, G.D. Use of Black Diagrams to Identify Inconsistencies in Rheological Data. Road Mater. Pavement Des. 2002, 3, 403–424.
• Kleiziene, R.; Panasenkiene, M.; Vaitkus, A. Effect of aging on chemical composition and rheological properties of neat and modified bitumen. Materials (Basel). 2019, 12.
• Kaseer, F.; Cucalon, L.G.; Arámbula-Mercado, E.; Martin, A.E.; Epps, J. Practical tools for optimizing recycled materials content and recycling agent dosage for improved short- and long-term performance of rejuvenated binder blends and mixtures. Asph. Paving Technol. Assoc. Asph. Paving Technol. Tech. Sess. 2018, 87, 513–555.

Reviewer 2 Report

Asphalt modification is carried out to improve the performance of mineral-asphalt mixtures and to extend the life of the road surface. This requires increasing the resistance of the mineral-asphalt mixtures  to rutting, cracking, fatigue and aging as well as to external factors: water, de-icing agents and low temperature.

The modifier can create a durable system with asphalt, allowing it to be modified earlier before adding to the aggregate. The use of a modifier allows the production of modified asphalt as a new product that can be individually defined and normalized.

The authors used various modifiers during the study. Unfortunately, they did not provide the exact characteristics of these raw materials.  They should characterize these modifiers when they compared them. This is particularly important if they write about their different impact on the properties of the obtained asphalts.

Despite the fact that the authors carried out a number of specialized tests, they did not include data on the composition of the emitted vapors, as well as immissions at the work place in the field of volatile chemical compounds. When conducting research on asphalt modifications, they should not overlook the discussion of environmental problems associated with earlier stages of the production, pouring, transport and processing of asphalt masses. Conducting such tests is very important from the environmental protection point of view.

In my opinion, the conclusions that were presented by the authors of the article do not bring any significant novel information in the development of materials science. They duplicate generally known and available information. In addition, sulfur-containing asphalts are not currently used in road construction due to environmental protection.

 

Author Response

Point 1: Asphalt modification is carried out to improve the performance of mineral-asphalt mixtures and to extend the life of the road surface. This requires increasing the resistance of the mineral-asphalt mixtures to rutting, cracking, fatigue and aging as well as to external factors: water, de-icing agents and low temperature.

Response 1: Yes, we agree.

Point 2: The modifier can create a durable system with asphalt, allowing it to be modified earlier before adding to the aggregate. The use of a modifier allows the production of modified asphalt as a new product that can be individually defined and normalized.

Response 2: Yes, we agree, and this was the motivation too.

Point 3: The authors used various modifiers during the study. Unfortunately, they did not provide the exact characteristics of these raw materials.  They should characterize these modifiers when they compared them. This is particularly important if they write about their different impact on the properties of the obtained asphalts.

Response 3: We appreciate the reviewer’s comments and understand concerns. However, we need to make a note that only the names of the modifiers are kept confidential as stated in the manuscript (Line 113-114, page 3) and the generic modifier type is provided in Table 1. In addition, the chemical properties of the modifiers are determined and presented in the paper. Together these properties indicate modifiers’ chemical make-up. Furthermore, the chemistry of these modifiers highly depends on its bio source which is variable in nature. Therefore, the study emphasizes the role of modifier chemistry on modified binders’ rheological response, irrespective of its make or brand. We believe that listing a brand is counterproductive and may appear as prompting specific products.

Point 4: Despite the fact that the authors carried out a number of specialized tests, they did not include data on the composition of the emitted vapors, as well as emissions at the work place in the field of volatile chemical compounds. When conducting research on asphalt modifications, they should not overlook the discussion of environmental problems associated with earlier stages of the production, pouring, transport and processing of asphalt masses. Conducting such tests is very important from the environmental protection point of view.

Response 4: This is a very good point, thank you. The quality of vapors and fumes emitted from the modified binders during production, pouring, transport and processing of asphalt mixtures should be environmentally safe. Testing the quality of emitted vapors was not in the current scope of study. However, the mass loss calculation, as part of RTFO aging were conducted and the results were within the acceptable limits as per AASHTO specifications. As part of the future work, vapor quality emitted will be considered.

Point 5: In my opinion, the conclusions that were presented by the authors of the article do not bring any significant novel information in the development of materials science. They duplicate generally known and available information. In addition, sulfur-containing asphalts are not currently used in road construction due to environmental protection.

Response 5: The outcome of the study complements available literature and providing a comprehensive evaluation of the following critical parameters: modifiers from variety of sources, binder source, evolution of rheological and chemistry parameters after short to very long aging (including 60 hours of PAV). To the authors knowledge, there is no publication with the scope of an experimental program presented in our paper. From a practical standpoint, as the need for producing softer binders keeps increasing, it is timely for many agencies in the US and elsewhere to adapt specifications to use modifiers that improve pavement performance.

In addition, evaluation of advanced rheological parameters, identifying cracking susceptibility, and impact of aging/long-term and extra long-term (up to 60-hr PAV) were reported. These parameters allowed to distinguish modified binders based on their cracking resistance. Because base binder is kept same for all modifiers, the difference in results of modified binders is mainly attributed to modifier properties.

It is true that sulfur in asphalt binders is restricted for environmental considerations. However, it is still present in smaller quantities in binders. Hence, additional sulfur from modifiers should further be minimized as reported in the findings. Furthermore, there are several recent studies that considered using sulfur as binder extender. There is an increasing quantity of sulfur accumulated at the refineries. Therefore, sulfur modification research studies for partial replacement of asphalt binder is underway by several researchers/agencies.

Some of the recent articles showing the presence of sulfur and modification approach in asphalt binders:

• Sakib, N.; Bhasin, A.; Islam, M.K.; Khan, K.; Khan, M.I. A review of the evolution of technologies to use sulphur as a pavement construction material. Int. J. Pavement Eng. 2019, 1–12.
• Jun, Z.; Maryam, S.; N., L.D.; Amit, B.; Yong-Rak, K. Characterization of Crack Growth Rate of Sulfur-Extended Asphalt Mixtures Using Cyclic Semicircular Bending Test. J. Mater. Civ. Eng. 2018, 30, 4018311.
• Shi, H.; Xu, T.; Jiang, R. Combustion mechanism of four components separated from asphalt binder. Fuel 2017, 192, 18–26.
• An Alternative Asphalt Binder, Sulfur-Extended Asphalt (SEA), https://www.fhwa.dot.gov/pavement/asphalt/pubs/hif12037.pdf

Reviewer 3 Report

The article appears to be overly complicated by the use of many abbreviations and the range of modifiers and aging processes included. Although the focus is identifying properties of asphalt binder modifiers (or specific modifiers) that will reduce the event of 'cracking of asphalt binders' there does not appear to be any results measuring the 'cracking of asphalt binders', modified or otherwise. All measured properties (of modified binder) appear to be ranked using metrics reported elsewhere (delta Tc, delta, Gstar etc).

The final section states 'the focus ...is the chemical properties of the asphalt binder modifiers'. However the chemistry and how aging affects chemistry is not clearly identified (analysis FTIR, GPC, TLC etc are used to provide indication of possible differences only).

The article reports on a significant amount of work but there are no clear conclusions and little evidence to associate the chemistries of the modifiers to the cracking behaviour of the (modified) asphalt binders.

Please refer to attached pdf (article + my notes) for further information.

Comments for author File: Comments.pdf

Author Response

Point 1: The article appears to be overly complicated by the use of many abbreviations and the range of modifiers and aging processes included. Although the focus is identifying properties of asphalt binder modifiers (or specific modifiers) that will reduce the event of 'cracking of asphalt binders' there does not appear to be any results measuring the 'cracking of asphalt binders', modified or otherwise. All measured properties (of modified binder) appear to be ranked using metrics reported elsewhere (delta Tc, delta, Gstar etc).

Response 1: Thank you. The contribution of the paper is well stated in the conclusion. The parameters like Delta Tc, Glover-Rowe, phase angles have been reported to represent cracking behavior of asphalt binders and are used as surrogate for cracking performance. The references are provided below. The use of abbreviations is to minimize the repetition of overly used phrases in the manuscript. We minimized the use of abbreviations.

• Anderson, M.R.; King, G.N.; Hanson, D.I.; Blankenship, P.B. Evaluation of the Relationship between Asphalt Binder Properties and Non-Load Related Cracking. J. Assoc. Asph. Paving Technol. 2011, 80, 615–662.
• Rowe, G. Analysis of SHRP core asphalts—New 2013/14 test results. In Proceedings of the Binder Expert Task Group Meeting; San Antonio, TX, 2014.
• Glover, C.J.; Davison, R.R.; Domke, C.H.; Ruan, Y.; Juristyarini, P.; Knorr, D.B.; Jung, S.H. Development of a New Method for Assessing Asphalt Binder Durability with Field Validation; College Station, TX, 2005; Vol. FHWA/TX-05;
• Asphalt Institute Use of the Delta Tc Parameter to Characterize Asphalt Binder Behavior IS-240; 2019

 

Point 2: The final section states 'the focus ...is the chemical properties of the asphalt binder modifiers'. However the chemistry and how aging affects chemistry is not clearly identified (analysis FTIR, GPC, TLC etc are used to provide indication of possible differences only).

Response 2: The study considers the effect of aging on modified binders’ rheology. The current scope of work is to identify how the modifier chemistry can relate to modified binder’s cracking potential without undergoing a comprehensive chemical characterization of modified binders. The present work focuses on chemical screening of modifiers. This will allow eliminating modifiers that has a potential increasing cracking at an early stage.

Point 3: The article reports on a significant amount of work but there are no clear conclusions and little evidence to associate the chemistries of the modifiers to the cracking behaviour of the (modified) asphalt binders.

Response 3: We reviewed the conclusions and revised to make sure that our findings are communicated clearly. We arrived at the following conclusions which we think is important and add to the body of literature in this area:

• Some chemical functionalities in a bio-based modifier aids resistance to cracking like presence of amines and lower molecular weights of modifiers
• Some contents like presence of sulfur does have a detrimental impact.
• Inefficiency of SARA method, which is a procedure commonly used in research studies.
• Key rheological parameters to distinguish modified binders.

The modifiers are limited proportions to that of total binder. Hence, modified binder characteristics is too complex. Furthermore, conclusions on binder rheology based on modifier chemistry is still not known. However, the results presented herein allow for initial screening of modifiers to eliminate high-risk modifiers. 

Point 4: Please refer to attached pdf (article + my notes) for further information.

Response 4: Comments addressed in the pdf attached.

Author Response File: Author Response.pdf

Reviewer 4 Report

I suggest major revision for this work.

My detailed comments in the attachment.

Comments for author File: Comments.pdf

Author Response

Point 1: Check Pdf.

Response 1: Comments addressed in the pdf attached, some of the comments addressed are as follows:

Point 2: change title on more suitable -> in current version it seems very obvious.

Response 2: The Title of the paper has been changed to “Effect of Chemical Composition of Bio- and Petroleum-based Modifiers on Asphalt Binder Rheology”

Point 3: please present all characteristic and producers of this modifiers.

Response 3: The generic characteristics are mentioned in Table 1. The chemistry of these modifiers is presented in the later sections. The study emphasizes the role of modifier chemistry on modified binders’ rheological response, irrespective of its make or brand. We believe that listing a brand is counterproductive and may appear as prompting specific products.

Point 4: Modification is more cost-effective comparing to "traditional" oxidation in rafinery ?

Response 4: The cost of modification was not considered in the current scope. The modification herein is to soften the binder instead of oxidation. The primary gain expected with those modifiers is actually to reduce costs because there will be less refined petroleum-based binder used. The cost of modifiers from various sources are not expected to be too different.

Point 5: in my opinion this part should be presented prior to discussion about modified bitumen

Response 5: This section is moved as per the suggested recommendation.

Author Response File: Author Response.pdf

Reviewer 5 Report

It is a very well written paper with interesting conclusions. I have just minor comments:

• some of the figures have very small fonts, that are hard to read. If it is possible I would use the same size of the font as in-text.
• The introduction part can be improved. I feel that paragraphs are disconnected and it is hard to follow.
• As the paper is about  the chemical properties of asphalt binder modifiers and its impact on the rheological properties, I would still add some part in the introduction about the asphalt mixture such as: https://journals.sagepub.com/doi/full/10.1177/0361198119846473 and https://doi.org/10.1061/(ASCE)MT.1943-5533.0002839 and more you consider.

Good job!

Author Response

Point 1: It is a very well written paper with interesting conclusions. I have just minor comments:

some of the figures have very small fonts, that are hard to read. If it is possible I would use the same size of the font as in-text.

Response 1: Thank you for your comment. The figures are corrected for font size and updated.

Point 2: The introduction part can be improved. I feel that paragraphs are disconnected and it is hard to follow.

Response 2: Thank you for your comment. The introduction is updated to enhance the readability and connection between paragraphs.

Point 3: As the paper is about the chemical properties of asphalt binder modifiers and its impact on the rheological properties, I would still add some part in the introduction about the asphalt mixture such as: https://journals.sagepub.com/doi/full/10.1177/0361198119846473 and https://doi.org/10.1061/(ASCE)MT.1943-5533.0002839 and more you consider.

Response 3: Included a section in the introduction.

Point 4: Good job!

Response 4: Thank you for your motivation.

Round 2

Reviewer 1 Report

The article by Singhvi et al. is reporting some result on modifiers. However the structures of the modifiers are keep confidential so this study cannot be replicate.

Author Response

Point 1: The article by Singhvi et al. is reporting some result on modifiers. However, the structures of the modifiers are keep confidential so this study cannot be replicate.

Response 1: We appreciate the reviewer’s comments and understand concerns. However, only the names of the modifiers are kept confidential. The chemical tests (FTIR, GPC, and TLC-FID) performed in the study does provide insights on the chemical characteristics and limited structural details. Determining the entire chemical structure is not in scope of current study. Furthermore, the products are proprietary, and determination of complete structure is not considered. The emphasis of the current work is to evaluate the role of modifier irrespective of the knowledge of complete structure.

Reviewer 3 Report

The content of the paper is complicated by use of 6  modifiers (all of different chemistries) and associated data to compare how chemical properties of modifier affect 'rheology' of the modified binder. However the results are not simply chemical data and rheology data but complicated by presenting rheological data in terms of an SG grading and delta Tc. As the modifier is added as a weight percent to achieve a PG grade 58-28 surely this drives the rheology towards a single 'goal'.

The work would be easier to digest had only 2 'similar' modifiers used and a range of mixtures  investigated to determine the impact of modifier on behaviour (demonstrate difference in optimisation).

However the data presented is a significant amount and appears to be acceptable.

There are still some text errors that I identified in first review - eg Abs instead of ABs on p2 l64....and probably others. I advise a proof read by third party to check.

Author Response

Point 1: The content of the paper is complicated by use of 6 modifiers (all of different chemistries) and associated data to compare how chemical properties of modifier affect 'rheology' of the modified binder. However the results are not simply chemical data and rheology data but complicated by presenting rheological data in terms of an SG grading and delta Tc. As the modifier is added as a weight percent to achieve a PG grade 58-28 surely this drives the rheology towards a single 'goal'.

The work would be easier to digest had only 2 'similar' modifiers used and a range of mixtures  investigated to determine the impact of modifier on behaviour (demonstrate difference in optimisation).

However the data presented is a significant amount and appears to be acceptable.

There are still some text errors that I identified in first review - eg Abs instead of ABs on p2 l64....and probably others. I advise a proof read by third party to check.

Response 1: We appreciate the reviewer’s comments and recommendations. A variety of modifier types were considered to include commonly available asphalt modifiers. In addition, same base binder was used for asphalt modification so that the differences can be attributed to modifier chemistry alone. The impact of modification on mixture level will be considered for future work as recommended.

The manuscript is proofread again. The typos and errors as highlighted are corrected in the revised version.

Thank you again for your comments and recommendations.

Reviewer 4 Report

Dear Authors,

This manuscript was significantly improved. However, still some minor revision should be peformed:

• modifier A type - Table 1 infomrmation not provided by the suppliers -> in this case try to define type based on your results (FTIR, GPC, elemental analysis, etc.)
• numbering of equations is not correct (first equation in text starts from (3))

Author Response

Point 1:

Dear Authors,

This manuscript was significantly improved. However, still some minor revision should be peformed:

• modifier A type - Table 1 infomrmation not provided by the suppliers -> in this case try to define type based on your results (FTIR, GPC, elemental analysis, etc.)
• numbering of equations is not correct (first equation in text starts from (3))

 

Response 1: We appreciate the reviewer’s comments and recommendations.

Chemical testing suggests that modifier ‘A’ corresponds to a bio-based source and is included in the result section.

The numbering of equations is checked and corrected as recommended.

Thank you again for your comments and recommendations.