Performance of Stone Mastic Asphalt Mixtures Fabricated by Different Compaction Methods
Round 1
Reviewer 1 Report
See attachment
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewer:
On behalf of my co-authors, we thank you very much for giving us an opportunity to revise our manuscript, we appreciate editor and reviewers very much for their positive and constructive comments and suggestions on our manuscript entitled “Performance of Stone Mastic Asphalt Mixtures Fabricated by Different Compaction Methods”. (No.: applsci-758894).
We have studied the comments carefully and have made revision which marked in red in the paper. We have tried our best to revise our manuscript according to the comments. We took into account of editor and two reviewers’ comment, the main corrections in the paper and the responds to the reviewer’s comments are as following:
Responds to the reviewer’s comments:
1、Wording/grammar comments
Response: Thanks for the reviewer’s comments. Vocabulary and grammatical errors have been revised in the manuscript.
2、I think that the definition of “asphalt-aggregate ratio” should be provided by the Authors. Is it the binder content by weight of dry aggregate?
Response: Thanks for the reviewer’s comments. Asphalt-aggregate ratio refers to the percentage of the asphalt-mineral mass ratio in the asphalt mixture. In short, the asphalt content of the asphalt mixture.
3、The introduction of the “mechanical properties” behavior of the investigated mixes required the explanations of what property/ies are
Response: Thanks for the reviewer’s comments. Mechanical properties refer to the ability of asphalt mixtures to resist compression, shear, and tensile strength, and include compressive strength, shear strength, and split strength.
4、What do the authors mean by “short-term aging and long-term aging degree”? Even if we are only in the Abstract it would be appropriate to define it in order to not create misunderstandings
Response: Thanks for the reviewer’s comments. The aging test includes short-term aging and long-term aging. The short-term aging refers to the aging process from mixing to the paving completion of the asphalt mixture. The long-term aging refers to the aging process of asphalt pavement opened to traffic for 3 to 5 years.
5、It is not clear the meaning of “is difficult to adapt to modern transportation”. Does it mean transportation infrastructures? If yes, Authors should provide adequate references to the related issues of Marshall design methods (since it is still worldwide used with fair results)
Response: Thanks for the reviewer’s comments. The meaning of “is difficult to adapt to modern transportation” is that transportation infrastructures must keep pace with the times and Marshall has certain limitations. With an increase in traffic, vehicle load, and occurrence of extreme weather events increased, such that a higher requirement for pavement structural strength. Marshall 75 blows on each side is difficult to meet the compaction requirements. However, with the increase of the number of compactions, a stronger impact force will apply to the mixture, such that the more aggregate will be broken. Moreover, due to the inconsistency between the vibration compaction of the Marshall method and the on-site directional vibration roller, the correlation of the samples produced by the Marshall method and the on-site cores was poor.
References:
[1]Memon N A. Comparison between Superpave gyratory and Marshall laboratory compaction methods[D]. Universiti Teknologi Malaysia, 2006.
[2]Tapkın, S.; Keskin, M. Rutting analysis of 100 mm diameter polypropylene modified asphalt specimens using gyratory and Marshall compactors. Mater. Res. 2013,16,546–564.
[3]Button,J.W.;Little,D.N.;Jagadam,V.;Pendleton,O.J.Correlationofselectedlaboratorycompactionmethods with field compaction. Trans. Res. Rec. 1994, 1454, 193–201.
6、It is not clear the meaning of “compactions”. Does it mean “blows”?
Response: Thanks for the reviewer’s comments. Yes, compactions here represent the blows of the Marshall hammer.
7、Authors stated that “…aggregates are easily crushed 35 during compaction …” This is not really true since this particular behavior is strongly dependent upon the type of aggregate employed. It is better to add References to support this assumption
Response: Thanks for the reviewer’s comments. Yes, “… aggregates are easily crushed 35 during compaction…”is really related to the type of aggregate. Moreover, it is also related to the working principle of Marshall compaction. Because the Marshall compactor exerts an impact force on the mixture and forces the mineral particles to move downward and gradually reaches a compact state, the friction force in the aggregate is large, resulting in the aggregate at both ends of the test piece being broken. The stronger the impact forces on the mixture, the more aggregate will be broken.
References:
[1]Tapkın, S.; Keskin, M. Rutting analysis of 100 mm diameter polypropylene modified asphalt specimens using gyratory and Marshall compactors. Mater. Res. 2013, 16, 546–564. [2]Button,J.W.;Little,D.N.;Jagadam,V.;Pendleton,O.J.Correlationofselectedlaboratorycompactionmethods with field compaction. Trans. Res. Rec. 1994, 1454, 193–201.
8、It is not clear the meaning of “pavement core”
Response: Thanks for the reviewer’s comments. We are sorry that this part was not clear in the original manuscript. Pavement cores are samples taken from inside the paved road. Fig. 1 shows the cores drilled from the field.
Figure 1. the core drilled from the field.
9、I would avoid the term “bearing capacity” for asphalt layers, it is a typical definition for subgrade/subbase layers
Response: Thanks for the reviewer’s comments. Yes, we have changed the “bearing capacity” to “structural strength”.
10、Authors stated correctly that “Cui et al. [9] concluded that when designing SMA mixtures by SGC in China, the number of rotations should be reduced”. They should explain why, since, for example, AASHTO standard M 325 defines the typical value of 100 gyrations, to be reduced only when the Los Angeles coefficient of aggregates exceed 30
Response: Thanks for the reviewer’s comments. We have modified this expression, and when designing SMA mixtures by SGC in China, the number of rotations must match the traffic volume and highway grade.
11、Authors stated that “Wang et al. [10] compared the road performances of SMA mixtures designed by the Marshall and SGC methods, and reported that gyratory compaction equipment is too expensive to be popularized [11,12]”. I totally disagree with such a statement since across the world the SGC nowadays represents the most used compaction technique together with slab/roller compactors
Response: Thanks for the reviewer’s comments. My statement is unreasonable, so it was modified in the manuscript. This shows that SGC is widely used worldwide.
12、Does a negative mass loss value mean an increase in the weight of sample after conditioning at high temperature? If yes, does it mean that oxidation had more effect than volatilization? Please provide an explanation
Response: Thanks for the reviewer’s comments. Yes, During the aging process of asphalt, a series of complex physical and chemical reactions including oxidation, volatilization of light components, polymerization and agglomeration of asphaltenes, and oxidation and cracking of modifiers occurred. Therefore, in principle, it is possible to increase or decrease the quality of the asphalt after aging. That is, both positive and negative values are possible.
13、Which tests on aggregate have been carried out? A Table like Table 1 should be added
Response: Thanks for the reviewer’s comments. Necessary changes have been made in the revised manuscript.
14、What is the dimensional fraction of the fine aggregate?
Response: Thanks for the reviewer’s comments. We are sorry that this part was not clear in the original manuscript. The dimensional fraction of the fine aggregate is 0-2.36mm.
15、Does the gradation follow a Technical Specification? If yes, gradation band should be added. All sieve sizes follow ASTM opening except the 13.2 mm. Normally the 12.5 mm is used. There any reason for this variation? A Figure of aggregate skeleton and gradation band could make the analyses easier
Response: Thanks for the reviewer’s comments. The gradation(see figure 2) does not follow the ASTM, but follows the gradation requirements of the Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40-2004).
Figure 2. gradation diagram of SMA-13
References:
[1] Research Institute of Highway Mcorinistry of Transport. Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40-2004). China Communications Press: Beijing, China, 2004. (In Chinese)
16、Since “porosity” describes the fraction of void space in the material (in which the void may contain also water), it is typical for porous media as soil rather than concrete in which it is preferable to call it “void content”
Response: Thanks for the reviewer’s comments. Necessary changes have been made in the revised manuscript.
17、“VA” has the same meaning of the previous “VV”?
Response: Thanks for the reviewer’s comments. We are sorry for this typo, and necessary changes have been made in the revised manuscript.
18、The SGC specimen has the same diameter of the Marshall one? Or 100 mm?
Response: Thanks for the reviewer’s comments. The diameter of SGC specimen is 100mm, and necessary changes have been made in the revised manuscript.
19、Figure 1 and 2 are not present in the manuscript
Response: Thanks for the reviewer’s comments. We are very sorry for this mistake, and necessary changes have been made in the revised manuscript.
20、The Authors stated that “The symmetric arrangement of the two eccentric blocks cancels the horizontal forces, so that only vertical forces are generated during work”. My question is more a curiosity based on my lack of knowledge about this technique and the absence of Figure 1 and 2: is this technique simulative of the rearrangement at which aggregate particles are subjected due to field action of vibratory roller?
Response: Thanks for the reviewer’s comments. Yes, The VVTE is designed with reference to the working principle and structural characteristics of directional vibration rollers. The VVTE structure consists of a control platform, a power equipment and a vibration system. The control platform is used to adjust the design operation parameters (including the working frequency and time) and control the equipment operation (including the lifting of the boarding and disembarking system); the power equipment is composed of a motor and a transfer box to provide power to the equipment; the vibration system is the equipment that generates the vibration effect structure, mainly including loading and unloading systems and shakers, as well as equipment frames and indenters. The vibration system is the most important of the three parts of the VVTE, and the exciter is the core component of the vibration system. The exciter is composed of eccentric blocks arranged symmetrically on parallel rotation axes. When the motor is working, the two sets of eccentric blocks rotate in the opposite direction and rotate at the same angular speed, so that they can cancel their respective centrifugal forces at the horizontal plane, and ensure that the equipment does not shake horizontally. The direction causes the respective centrifugal forces to be superimposed, and a sinusoidal excitation force is generated during rapid rotation, which brings the vertical vibration compaction effect to the mixture.
21、Figure 3 and 4 are not present in the manuscript
Response: Thanks for the reviewer’s comments. We are very sorry for this mistake, and necessary changes have been made in the revised manuscript.
22、Some parameter of the equation 1 are not explained, others are wrong. Please pay attention
Response: Thanks for the reviewer’s comments. We are very sorry for this mistake, and necessary changes have been made in the revised manuscript.
23、Does the aging procedure (for short and long-term) followed a specific standard or internal procedure? If yes, please provide the reference
Response: Thanks for the reviewer’s comments. Yes, aging procedure follow Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011)
References:
[1] Research Institute of Highway Ministry of Transport. Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011); China Communications Press: Beijing, China, 2011. (In Chinese)
24、Why the Authors used the stress control mode for the fatigue test? SMA, adopted for surface layers, are thin layers, believed to be damaged in the fatigue life by strain-control rather than stress-control mode
Response: Thanks for the reviewer’s comments. It is certain that the strain-control mode is better when the pavement surface is thinner, but there are some practical reasons for this article to use the stress-control mode. Theoretical analysis of the two control modes. First, the stress control mode has better reproducibility and shorter test time, the test specimen breaks at the end of the test, the definition of fatigue failure is clear; in addition, the number of test specimens required to control the stress test is shorter, the test time is shorter, and the data obtained are less discrete, which is convenient for analysis. In summary, the stress-controlling mode was employed for loading, which exhibited good test reproducibility, clear definition of fatigue failure, and reliable accuracy control. Under the controlled strain mode, the test piece generally does not show obvious fracture failure. Generally, the stiffness of the mixture is reduced to 50% of the initial stiffness, or lower is the fatigue damage standard. Therefore, it has certain randomness, and there are certain difficulties in the application of technology.
25、The Authors defined that the stress level was varied as 0.3, 0.4, 0.5, 0.6, and 0.7. I didn’t understand what these numbers mean
Response: Thanks for the reviewer’s comments. The stress ratio is defined as the ratio of the load force to the limit strength of the pavement materials. Necessary changes have been made in the revised manuscript.
26、Second column: is it a Specific Gravity or a density? If it represents a density provide units
Response: Thanks for the reviewer’s comments. Pa in the second column represents the asphalt–aggregate ratios, which refers to the percentage of the asphalt-mineral mass ratio in the asphalt mixture.
27、SGC VFA block, third specimen: it is quite strange that increasing the binder dosage, decreasing void and VMA, VFA could decrease. Normally it is a constant increasing function of the binder dosage
Response: Thanks for the reviewer’s comments. We are sorry for this typo, and necessary changes have been made in the revised manuscript.
28、Why the optimal mixture was selected by choosing the dosage which reached the highest density?
Response: Thanks for the reviewer’s comments. When an optimal asphalt usage is determined, the range of the amount of bitumen that satisfies all the design technical requirements is obtained, with the median value being the optimal amount of bitumen. Some problems were found using this method. After using high-quality asphalt, when estimating the amount of asphalt, although there were five different changes in the amount of asphalt, the variation range reached 2.0%, and the VV and VMA peaks did not appear. There is only one indicator of the density that determines the optimal amount of asphalt, so the peak density is selected as an indicator of the optimal amount of asphalt.
29、The paragraph “This result can be explained by the volume parameters of the VVTM design method, which are based on heavy-traffic compaction standards; namely, the compaction standards for heavy asphalt mixtures should be 1.02 times the laboratory standard Marshall density. At higher densities, the mixture is compacted by the low bitumen content. Aggregates also migrate with the vibration compaction, further compacting the structure” is not clear. Please try to clarify this statement since it seems crucial for the gooness evaluation of the vibratory method
Response: Thanks for the reviewer’s comments. We have modified the original manuscript representation. Because the VVTM compaction standard is higher, the optimal amount of asphalt can be reduced, with the result that the density of the mixture increases, it can be seen from Table 11 of the manuscript that compared with the Marshall method, the density of the SMA-1 mixture designed by VVTM is increased by about 2%, which is also verified by the references. At this time, the density is high, the amount of asphalt is small, therefore, VV and VMA are appropriately reduced, that is, the space between the aggregates is reduced, so the mixture is further compacted.
References:
[1] ZJ. Chen, X.H. Xu, YJ. Jiang, Compaction criterion and evaluation of asphalt mixture for heavy-traffic road.. Transp. Stand.42(07)(2014).22-26+32(in Chinese).
30、In my humble opinion the evaluation of the Marshall Stability for specimens not compacted by Marshall methods lose any meaning. The Marshall Stability is functional for the definition of the optimal binder dosage in the Marshall mix design procedure but cannot be used as a performance related property
Response: Thanks for the reviewer’s comments. We are sorry for our lack of consideration, and necessary changes have been made in the revised manuscript.
31、The improved mechanical performances are related to the highest density and lowest void content of specimens tested. An image analyses evaluation (or at least adequate References) can corroborate the statement “improved the skeleton embedding effect of the mineral”. I have some doubts that aggregate interlocking provide by the SGC is less than that provide by the vibratory method. Maybe it can be a function of the reduced number of gyrations used
Response: Thanks for the reviewer’s comments. When the mixture is compacted by the VVTM, the aggregates are compacted in a moving state, the internal friction between the aggregates is relatively small, so that the aggregates with smaller particle diameters are better filled in the voids of the skeleton of the coarse aggregate, improving the effect of mineral skeleton embedding. Regarding the number of gyrations used, you may be right and we will in-depth study in our further work.
32、The paragraph “Meanwhile, the VVTM-designed asphalt mixture contained relatively little asphalt at a high asphalt saturation. Most of this mixture was structural asphalt; the low proportion of free asphalt significantly improved the cohesion and internal content of the mixture” is not clear. Please try to clarify
Response: Thanks for the reviewer’s comments. We are sorry that this part was not clear in the original manuscript. Therefore, we put it another way. Meanwhile, VVTM is more conducive to aggregate arrangement and less aggregate crushing rate.
33、The “aggregate crushing” that Authors suggested that Marshall compaction did it is a function of the type of aggregate and not a common rule. Aggregates which show very low value of the Los Angeles coefficient (normally used in the formation of SMA layers) are not subjected to such a problem
Response: Thanks for the reviewer’s comments. Yes, aggregate crushing is related to the type of aggregate, here refers to the test piece formed by the Marshall method under the same compaction work and aggregate, the aggregate crushing rate of samples compacted using Marshall method is relatively higher. The SGC compaction process is closer to the actual compaction of the road surface, reducing the crushing of the aggregate during the compaction process.
34、“By virtue of its vibration-compaction mechanism, the VVTM better arranges the coarse aggregates in the mixture than the other methods, thereby forming a stronger framework”. See previous comments
Response: Thanks for the reviewer’s comments. Theoretically, under the action of the vibration pressure wave generated in the process of vibration sustainability, the aggregate in the mixture will gradually change from a relatively static state to a relatively moving state process. With the reduction of the frictional resistance between the aggregates, the aggregates can be completely moved and interlocked to form a dense frame structure, and the mixture can be easily compacted.
35、Authors say “The superior mechanical properties and small asphalt contents of VVTM-designed mixtures have been demonstrated in previous studies”. Please provide adequate References
Response: Thanks for the reviewer’s comments. The superior mechanical properties and small asphalt contents of VVTM-designed mixtures have been demonstrated. The following references give proof.
Reference:
[1] Jiang, Y.; Fan, L. An experimental investigation of optimal asphalt–aggregate ratio for different compaction methods. Constr. Build. Mater. 2015, 91, 111–115.
[2] Jiang, Y.J.; Deng, C.Q.; Li, Q.; Liu, H.P. Effect of Compaction Methods on Physical and Mechanical Properties of Asphalt Mixture. J. Mater. Civ. Eng., 2019, 31(6).
[3] Deng, C.Q.; Jiang, Y.J.; Lin, H.W.; Chen, Z.J.; Ji, X.P. Influence of gradations on performance of emulsified asphalt cold recycled mixture produced using vertical vibration compaction method, Road Mater. Pavement Des. 2019, DOI: 10.1080/14680629.2019.1659174.
[4] Liu, H.; Jiang, Y.; Hu, Y.; Ye, W.; Cao, Z.; Cai, Y. Influence of Gradation on Strength of Emulsified Asphalt Cold Recycled Mixture. J. Build. Constr. 2018, 21, 503–510. (In Chinese)
[5] Ji, X.; Jiang, Y.; Liu, Y. Evaluation of the mechanical behaviors of cement-stabilized cold recycled mixtures produced by vertical vibration compaction method. Mater. Struct. 2015, 49, 2257–2270.
[6] Jiang, Y.J.; Deng, C.Q.; Xue, J.S.; Chen, Z.J. Investigation into the performance of asphalt mixture designed using different methods, Constr. Build. Mater. 2018, 177, 378-387.
36、How many replicates were run for each test? To reduce uncertainties, especially in definition of the fatigue life, a minimum number of replicates should be used. If multiple specimens were tested, please provide the coefficient of variation of the obtained results
Response: Thanks for the reviewer’s comments. Each test was replicated five times and the coefficient of variation of the obtained results has provided in the revised manuscript.
37、Normally the fatigue lines are expressed in the form S=f(N) (power law model)
Response: Thanks for the reviewer’s comments. Necessary changes have been made in the revised manuscript.
38、Please pay attention to use the same formatting for all References (capital initials, full name, size of the font used, year, missing/added spaces…) and avoid replicates (5-6, 15-23, 17-24)
Response: Thanks for the reviewer’s comments. Necessary changes have been made in the revised manuscript.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear editor,
I consider this manuscript a very interesting paper. The manuscript suits Applied Sciences journal’s scope, and the results are valuables for the pavement materials sector. In my opinion the paper worth to be published in Applied Sciences journal. The structure of the paper, description of the test process, conclusions are very interesting.
However, I suggest some minor changes before its publication.
Figures must be renumbered. It stars in number 5.
Figure 7. The “dots” of each line must be changed by different shapes (eg, triangle, square, rhomboidal, etc). If the paper is printed black and white, it is not possible to understand the figure.
Conclusions are a bit confused. The authors must rewrite them in a clear way.
“Literature review” provides an interesting background of the research carried out. Nonetheless, authors should include other references in the section “Introduction” about asphalt mixtures, as for example.
DOI: 10.1016/j.matdes.2015.02.026
Author Response
Dear Reviewer:
On behalf of my co-authors, we thank you very much for giving us an opportunity to revise our manuscript, we appreciate editor and reviewers very much for their positive and constructive comments and suggestions on our manuscript entitled “Performance of Stone Mastic Asphalt Mixtures Fabricated by Different Compaction Methods”. (No.: applsci-758894).
We have studied the comments carefully and have made revision which marked in red in the paper. We have tried our best to revise our manuscript according to the comments. We took into account of editor and two reviewers’ comment, the main corrections in the paper and the responds to the reviewer’s comments are as following:
Responds to the reviewer’s comments:
1、Figures must be renumbered. It starts in number 5.
Response: Thanks for the reviewer’s comments. We are sorry for our lack of consideration, and necessary changes have been made in the revised manuscript.
2、Figure 7. The “dots” of each line must be changed by different shapes (eg, triangle, square, rhomboidal, etc). If the paper is printed black and white, it is not possible to understand the figure.
Response: Thanks for the reviewer’s comments. The Figure has been reworked.
3、Conclusions are a bit confused. The authors must rewrite them in a clear way.
Response: Thanks for the reviewer’s comments and they are very important. We are sorry that this part was not clear in the original manuscript. Necessary changes have been made in the revised manuscript.
4、“Literature review” provides an interesting background of the research carried out. Nonetheless, authors should include other references in the section “Introduction” about asphalt mixtures, as for example.
Response: Thanks for the reviewer’s comments. and the following articles have been added in the review of literature:
[1]Button,J.W.;Little,D.N.;Jagadam,V.;Pendleton,O.J.Correlationofselectedlaboratorycompactionmethods with field compaction. Trans. Res. Rec. 1994, 1454, 193–201.
[2] Deng, C.Q.; Jiang, Y.J.; Lin, H.W.; Ji, X.P. Mechanical-strength-growth law and predictive model for cement-stabilized macadam. Constr. Build. Mater., 2019, 215, 582-594.
[3] Deng, C.Q.; Jiang, Y.J.; Tian, T.; Chen, Z.J. Resilient modulus and influencing factors of vertical vibration compacted cement-stabilized macadam, Int. J. Pavement Eng. 2019, DOI: 10.1080/10298436.2019.1696462.
[4] Chen, Z.J.; Xu, X.H.; Jiang, Y.J. Compaction criterion and evaluation of asphalt mixture for heavy-traffic road.. Transp. Stand.42(07)(2014).22-26+32(in Chinese).
Author Response File: Author Response.docx
