Effect of Quartz Nano-Particles on the Performance Characteristics of Asphalt Mixture

Round 1

Reviewer 1 Report

• paragraph 2.1, line 162-163, the authors state that the bitumen used has 4 groups based on size and reactivity. What does it mean? do they refer to SARA?

• futhermore, how does the information that the non-polar behavior is due to the aromatic fraction help to define the type of bitumen used? the percentage indicated (40-65%) is the generic one referring to aromatic oils.

• paragraph 4.1, line 345, in my opinion, in order to establish that the protocol is acceptable, tests should have been made with higher and lower rpm and with different mixing times. If such tests have been done they should be indicated.
• paragraph 4.3, line 373. Hw it is possible to evaluate the homogeneity of a sample by FTIR? It is not clear how to explicitly cite the work of Yao et al. can support the main purpose (line 372) of using FTIR. If, on the other hand, the citation serves the purpose of analysing the results obtained, then it should be relocated.
• paragraph 4.3, line 376. The authors have already clarified in line 372 what is reported in an FTIR graph.
• paragraph 4.3, line 381-382. The authors make no comment regarding the change in the shape of the IR peaks. For example, peaks referring to aromatic hydrocarbons, or those referring to carbonyl. Furthermore, in the unmodified sample there appears to be a peak around 2300-2400 which is not present in the other samples.
• paragraph 4.3, line 386-391. How can it be said that there is a strong resistance to aging if samples subject to aging have not been tested?
• Figure 6 please improve resolution.
• paragraph 4.3, line 403-406. Please explain how strong chemical functional groups are produced, and how the tendency to chemical bonds increases.
• paragraph 4.4, line 412. Ductility is repeated twice.
•  paragraph 4.5 , line 472. The authors say that 4 samples were analyzed, but in table 6 the number of samples analyzed is 8.

• Why is each sample analyzed with two plates of different diameters (table 6)?

• chapter 5, line 639. What any chemical mixing means.
• Please improve the FTIR bibliography. Here some suggestion:
• Performance evaluation of Al2O3 nanoparticle-modified asphalt binder DOI: 10.1080/14680629.2016.1208621
• Performance of nanoceramic powder on the chemical and physical properties of bitumen DOI: 10.1016/j.conbuildmat.2017.09.014
• Additives on aged bitumens: What probe to distinguish between rejuvenating and fluxing effects? DOI: 10.1016/j.molliq.2021.116742
  
  
  
   

Author Response

Dear Reviewer 1,

Please see the attachment. 

Author Response File: Author Response.docx

Reviewer 2 Report

This is interesting work. Some comments:

1. Line 16: PG should include two temperature, please highlight it.
2. Line 16: what are physical tests, please be more specific.
3. Line 25: how about fatigue properties?
4. Consider the climate in Pakistan, the effect of UV aging on bitumen should be conducted. Please include this reference in the introduction:

Cheraghian, G., Wang, D., Kim, Y. S., & Wistuba, M. P. (2020, December). Experimental Investigation on Ultraviolet Aging Properties of Silica Nanoparticles-Modified Bitumen. In RILEM International Symposium on Bituminous Materials (pp. 879-885). Springer, Cham.

1. The introduction is well organized. Line 156: the mixture tests should be added.
2. The optimal content selection and blending process are well organized.
3. Figure 2: “Material Characterization”. According to my knowledge, mixtures should be included. It is not clear how the additives are evaluated.
4. Figure 3b: is sth. burning?
5. Figure 17 is blurry, please improve it if possible.
6. DSR tests on 1.59Hz is not enough to evaluate the anti rutting performance, please include MSCR tests in the future study.
7. Analysis and conclusion are reliable.

Author Response

Dear Reviewer 2,

Please see the attachment. 

Author Response File: Author Response.docx

Reviewer 3 Report

Ms ID: infrastructures-1636487, entitled "Effect of Quartz Nano Particles on the Performance Characteristics of Asphalt Mixture" submitted to Journal: Infrastructures, authors: Waqas Haroon, Naveed Ahmad, Nuha Mashaan

In this study, the authors tested the effect produced by adding QNPs at various amounts to a bitumen with certain basic properties. In particular, SEM, FTIR and DSR results confirmed that an optimum concentration of 5% was able to improve the viscoelastic properties and rut resistance of asphalt at high temperature. Overall, the paper is worth to be published in Infrastructure Journal after the authors would pay attention to the following point:

Lines 142-144: “Various pavement engineers and research community have used quartz nano particles to enhance the properties of base bitumen; but, as per publish records, no comprehensive research is presented on QNPs asphalt mixture performance”. Here, the following articles could be cited: 1) Ghasemi M. et al. “Modification of stone matrix asphalt with Nano-SiO2”. J Basic Appl Sci Res 2012; 2, 1338–1344. 2) Crucho JML et al. “Mechanical performance of asphalt concrete modified with nanoparticles: Nanosilica, zero-valent iron and nanoclay”. Construct Build Mater 2018; 181, 309–318. 3) Caputo et al. “Bitumen and asphalt concrete modified by nanometer-sized particles: Basic concepts, the state of the art and future perspectives of the nanoscale approach”. Adv Colloid Interface Sci. 2020, 285, 102283.

Figure 1 might be skipped as it does not add any relevant information other than that shown in Table 1.

Figure 6. Please, provide a figure with higher resolution as Figure 7.

Figure 8 shows the structural index for several characteristic chemical bonds; however, it is not clear to me how this index has been derived for both base bitumen and bitumen modified with increasing amounts of QNPs. Please, explain and add the correspondent error bars inside the bar chart.

As a final comment, I would like to ask if the authors would expect to observe the same outcomes on bituminous samples modified with chemically different NPs, such as e.g. iron oxide or polymeric NPs, but with same particle sizes and concentrations of the used quartz NPs. 

Author Response

Dear Reviewer 3,

Please see the attachment. 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Paper has been significantly improved over the previous version.

However, I think it would be better to add the IR spectrum of the QNPs to highlights that the intensities increase due to an "additive" effect of the IR signals of the bitumen and those of the QNPs.

Finally, what is meant by "tendency of chemical bonding". Perhaps it would be useful to better explain the concept expressed in line 453-456, paragraph 4.3.  

Author Response

Dear Reviewer, 

Please see the attachment. 

Author Response File: Author Response.docx

Reviewer 2 Report

Thanks for the authors' hard work. Since all my comments are carefully revised, no further review process is needed.

Author Response

Many thanks for your valuable comments. We gratefully acknowledge the reviewer for the time spent making constructive remarks and useful suggestions, which has significantly raised the quality of our manuscript.