Research on Durability and Long-Term Moisture Stability Improvement of Asphalt Mixture Based on Buton Rock Asphalt
, Yutong Zhou 1, Xiaodi Hu 1, Jiuming Wan 1,*, Wenxia Gan 1, Yafei Jing 1, Jiakun Liu 1 and Zongwu Chen 2
Round 1
Reviewer 1 Report
In this study, the authors investigated how rock asphalt affected the durability (fatigue resistance, thermo-oxidative aging resistance and long-term moisture stability) of asphalt mixture. The improvement on long-term moisture stability of asphalt mixture containing BRA modified asphalt (BRAM) was also discussed.
1. The literature review should include some recent studies about the effect of aging on moisture damage resistance. The long-term aging of asphalt can exacerbate the moisture damage (e.g., moisture damage mechanism and thermodynamic properties of hot-mix asphalt under aging conditions)
2. The capture of Figure 1 should include (a) and (b).
3. The base asphalt of BRA modified asphalt in table 2 the same as the neat asphalt in Table 3?
4. The moisture conditioning method must be described in detail because the standard was not based on ASTM standard. How long did you freeze the samples/store them in 60C water?
5. More discussion should be provided on the role of fiber on the moisture resistance. Stripping is more related to the adhesion between asphalt and aggregate. What is the mechanism of using fiber?
Author Response
- The literature review should include some recent studies about the effect of aging on moisture damage resistance. The long-term aging of asphalt can exacerbate the moisture damage (e.g., moisture damage mechanism and thermodynamic properties of hot-mix asphalt under aging conditions).
Response: Thanks for your constructive comments. We do agree with you that this introduction requires revision. We have added some recent studies about the effect of aging on moisture damage resistance in the introduction.
- The capture of Figure 1 should include (a) and (b).
Response: Thanks for your comments. We have made modifications to the capture of Figure 1.
- The base asphalt of BRA modified asphalt in table 2 the same as the neat asphalt in Table 3?
Response: Thanks for your comment. The base asphalt of BRA modified asphalt, SBS modified asphalt and neat asphalt all meet the requirement of a penetration of 60-80. Their origin may be different due to their producers were different.
- The moisture conditioning method must be described in detail because the standard was not based on ASTM standard. How long did you freeze the samples/store them in 60℃ water?
Response: Thanks for your comment. We have made some revision, samples were frozen at -18℃ for 16h, and stored at 60℃for 24h. The moisture conditioning method had been fully explained in 2.4.6.
- More discussion should be provided on the role of fiber on the moisture resistance. Stripping is more related to the adhesion between asphalt and aggregate. What is the mechanism of using fiber?
Response: Thanks for your comment. We believe that it is necessary to study the mechanism of the impact of using fiber on long-term moisture damage. Fibers constrain internal structural changes of asphalt mixtures during moisture damage through reinforcement. HL was supposed to develop the adhesion between asphalt binder and aggregate. Moisture resistance was consequently improved. More detailed mechanism will be continued in subsequent research. Thank you again for your rigorous attitude and helpful suggestions in the review.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The Manuscript "Research on Durability and Long-term Moisture Stability Improvement of Asphalt Mixture Based on Buton Rock Asphalt" is well written, methods are properly described but prior to publication I propose the following improvements:
1. In Tables 1-4: units are missing.
2. In Tables 5 and 6: no unit at apparent specific gravity.
3. In Tables 7: no unit at density.
4. Line 361: incorrect title of table 11.
5. How were BRA added? BRA were added to neat (pure) asphalt in the amount of 30% of the binder weight? Did I understand correctly? Please explain.
6. Line 124-151: Please explain why the authors chose these three specific types of fibres (CF, BF and PF)?
7. How were the fibers added? Fibers were added to the hot aggregate before adding the hot binder? Were there any problems?
8. Which means N in the formula 1?
9. Formula 1-3: the symbols in the explanations should be the same as in the formulas (e.g. is "t1, t2 and d1, d2" should be "t1, t2 and d1, d2" etc.).
10. The Manuscript presents the results of AC-20C asphalt mixture. In what layer of pavement can this asphalt mixture be used?
11. Are there requirements for the index MSR0, TSR (Figure 10 and 11) and DS (Figure 12)?
12. There is no information about the air void content. The index value (MSR0, especially TSR) depend on air voids content. What was the content of air voids in the samples in the individual tests? How the fibers affected the content of voids?
13. Please explain why the authors chose mixture no. 4 (50% HL + 0.2% CF) to the next stage of research as the best one? For example, mixtures 4, 5, 7, 8 and 9 are characterized by a similar value of both MSR0 and TSR (regardless of the number of freezing cycles). In my opinion, the differences are within the limits of measurement uncertainty.
14. The list of references can be extended.
Author Response
- In Tables 1-4: units are missing.
Response: Thanks for your constructive comments. The missing units were checked and added.
- In Tables 5 and 6: no unit at apparent specific gravity.
Response: Thanks for your constructive comments. We confirmed that apparent specific gravity was unitless.
- In Tables 7: no unit at density.
Response: Thanks for your constructive comments. The unit had been added in the table.
- Line 361: incorrect title of table 11.
Response: Thanks for your constructive comments. The title had been corrected.
- How were BRA added? BRA were added to neat (pure) asphalt in the amount of 30% of the binder weight? Did I understand correctly? Please explain.
Response: Thanks for your constructive comments. The preparation method of BRA modified asphalt is exactly as you mentioned. The optimal weight ratio of BRA powder to original neat asphalt in BRA modified asphalt was 100%:30% after trial and error
- Line 124-151: Please explain why the authors chose these three specific types of fibres (CF, BF and PF)?
Response: Thanks for your constructive comments. We do agree with you that this introduction requires revision. We have added some recent studies about the effect of aging on moisture damage resistance in the introduction.
- How were the fibers added? Fibers were added to the hot aggregate before adding the hot binder? Were there any problems?
Response: Thanks for your constructive comments. This study introduced fibers as additives in asphalt mixture mixing process. 1/3 of the fibers was added and mixed with hot aggregate. Another 1/3 of the fibers was added and mixed when mixing with asphalt binder while the last 1/3 was added when mixing with fillers. No clear problem was found. Corresponding explanation had been added in the text.
- Which means N in the formula 1?
Response: Thanks for your constructive comments. N refers to Rolling speed of test wheel round-trip, 42 cycles/min.
- Formula 1-3: the symbols in the explanations should be the same as in the formulas (e.g. is "t1, t2 and d1, d2" should be "t1, t2 and d1, d2" etc.).
Response: Thanks for your constructive comments. All symbols had been checked and revised.
- The Manuscript presents the results of AC-20C asphalt mixture. In what layer of pavement can this asphalt mixture be used?
Response: Thanks for your constructive comments. AC-20C asphalt mixture was usually used as binder layer in three layer pavement construction.
- Are there requirements for the index MSR0, TSR (Figure 10 and 11) and DS (Figure 12)?
Response: Thanks for your constructive comments. Yes, there are requirements for the MSR0, TSR and DS. MSR0 should be over 80% for neat asphalt based mixture and over 85% for polymer modified asphalt based mixture. TSR should be over 75% for neat asphalt based mixture and over 80% for polymer modified asphalt based mixture. DS should be over 800 for neat asphalt based mixture and over 2400 for polymer modified asphalt based mixture. Corresponding statement about they had meet the specification had been added in the text.
- There is no information about the air void content. The index value (MSR0, especially TSR) depend on air voids content. What was the content of air voids in the samples in the individual tests? How the fibers affected the content of voids?
Response: Thanks for your constructive comments. We do agree with you that fibers showed some effect on asphalt mixture’s volumetric performance. How the fibers affect asphalt mixture’s content of voids will be presented in further research.
- Please explain why the authors chose mixture no. 4 (50% HL + 0.2% CF) to the next stage of research as the best one? For example, mixtures 4, 5, 7, 8 and 9 are characterized by a similar value of both MSR0 and TSR (regardless of the number of freezing cycles). In my opinion, the differences are within the limits of measurement uncertainty.
Response: Thanks for your constructive comments. No.4 group was chosen as the optimal since it showed the highest value in TSR value of freeze-thaw cycle test. It is true that difference between the data may not be very discriminative, thereby statistical significance of data will be enhanced in our next research. On the other hand, No.4 group as few as possible used the additives, which was superior to other group in economy. Consequently, No.4 was selected. Corresponding explanation had been added in the text.
- The list of references can be extended.
Response: Thanks for your constructive comments. The references list was extended.
Author Response File: Author Response.docx
Reviewer 3 Report
(1) The units of properties in Table 1, 2, 3, and 4 are missed.
(2) please specify the reason of using a frequency of 2Hz for the R-SCB test.
(3) In Figure 7, there are two compaction process, whether the first one is only for the unaged mixture, or for both the unaged and short-term aged mixture.
(4) What is the meaning of the long-term moisture stability, and especially how to clarify the expression of long-term?
(5) In Figure 1, whether the BRA is used in its natural state, or the powder state, and because the natural BRA has its own gradation. In addition, one great advantage of using BRA modified asphalt, as well as BRA mixture is its economic benefit. It is suggested to briefly compare the neat asphalt, sbs asphalt and BRA asphalt cost, and discuss this point in the manuscript.
The English is fine and easy to follow.
Author Response
- The units of properties in Table 1, 2, 3, and 4 are missed.
Response: Thanks for your constructive comments. We added the units of properties in Table 1, 2, 3, and 4.
- Please specify the reason of using a frequency of 2Hz for the R-SCB test.
Response: Thanks for your comments. It was found that the difference in fatigue life of samples under different factors showed more statistical significance when the frequency was 2Hz after trial and error. Corresponding explanation had been elaborated in the text.
- In Figure 7, there are two compaction process, whether the first one is only for the unaged mixture, or for both the unaged and short-term aged mixture.
Response: Thanks for your comment. The first compaction process is only for the unaged mixture while the asphalt mixture for short-term aging will be compacted at the second compaction process. Corresponding explanation had been added in the text.
- What is the meaning of the long-term moisture stability, and especially how to clarify the expression of long-term?
Response: Thanks for your comment. Long-term moisture stability refers to the moisture stability durability of asphalt mixtures under long-term service conditions.
Long-term refers to a long period of time for asphalt mixture service, during which asphalt mixture will withstand repeated moisture and freeze-thaw damage. Freeze-thaw cycle splitting test was used to characterize the long-term moisture stability according to previous research.
- In Figure 1, whether the BRA is used in its natural state, or the powder state, and because the natural BRA has its own gradation. In addition, one great advantage of using BRA modified asphalt, as well as BRA mixture is its economic benefit. It is suggested to briefly compare the neat asphalt, SBS asphalt and BRA asphalt cost, and discuss this point in the manuscript.
Response: Thanks for your comment. It is the BRA powder whose particle size was smaller than 0.075 mm was used as the additives of BRA modified asphalt, which had been additionally explicated in text. We strongly agree with your suggestion for economic discussions. However, the cost accounting of composite materials, especially those involving international bulk futures raw materials, is actually quite complex. This involves volatile factors such as crude oil prices, mining costs and transportation costs, and requires highly professional personnel to accurately calculate the cost of materials. Therefore, the detailed cost evaluation will be carried out in the following studies.
Thank you again for your rigorous attitude and helpful suggestions in the review.
Author Response File: Author Response.docx
Reviewer 4 Report
RE: Research on Durability and Long-term Moisture Stability Improvement of Asphalt Mixture Based on Buton Rock Asphalt
This manuscript is very well prepared and of high quality. I find this manuscript suitable for acceptance for publication in the journal. However, before accepting the manuscript for publication in the journal, the authors need to make minor edits on the article, which are mentioned below: 1- One of the important points in this manuscript is related to the captions of figures and tables, which are written very briefly. Authors should rewrite the captions of figures and tables. 2- It is better for the authors to be very careful about how to write the references at the end of the manuscript based on the journal format. Please check that all references are written according to the journal format.
RE: Research on Durability and Long-term Moisture Stability Improvement of Asphalt Mixture Based on Buton Rock Asphalt
This manuscript is very well prepared and of high quality. I find this manuscript suitable for acceptance for publication in the journal. However, before accepting the manuscript for publication in the journal, the authors need to make minor edits on the article, which are mentioned below: 1- One of the important points in this manuscript is related to the captions of figures and tables, which are written very briefly. Authors should rewrite the captions of figures and tables. 2- It is better for the authors to be very careful about how to write the references at the end of the manuscript based on the journal format. Please check that all references are written according to the journal format.
Author Response
- One of the important points in this manuscript is related to the captions of figures and tables, which are written very briefly. Authors should rewrite the captions of figures and tables.
Response: Thanks for your comments. We have made revisions to the titles of some charts.
- It is better for the authors to be very careful about how to write the references at the end of the manuscript based on the journal format. Please check that all references are written according to the journal format.
Response: Thanks for your comments. We had carefully checked whether all references are written in the format of journal format.
Thank you again for your rigorous attitude and helpful suggestions in the review.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
This paper has been revised and should be ready for publication.
