Carbon Emission Calculation Method and Low-Carbon Technology for Use in Expressway Construction

Round 1

Reviewer 1 Report

The paper proposes an articulated carbon-emission calculation method for pavement construction and highlights the benefit, in terms of carbon emission reduction, deriving from the application of low carbon technologies. The topic is of great importance and the outcomes can provide useful information to practitioners for environmental protection policies, however the paper needs some improvements as below explained:

 

General comments

1. The paper need a profound revision of English language and punctuation.
2. The logical flow across the different sections is not clear and immediate because of the presence of many sub-sections. In order to improve the readability of the paper, it is suggested to review the subdivision in sections.
3. All the symbols of the formulas must be explained. Please check.

 

Specific comments

 

1. Introduction: Background information is not adequately covered exist relevant recent studies pertaining to this area of research, that merit to be cited, such as:

DOI: https://doi.org/10.3390/su12020704.

DOI: https://doi.org/10.1007/978-3-030-29779-4_12

DOI: https://doi.org/10.1016/j.resconrec.2018.05.028

 

1. Row 96 - authors write “considering the differences in the construction technologies in different areas…………..”. Please, explain better this concept in terms of main differences of such technologies and factors that can affect the emissions.
2. Equation, 1 row 139 - please explain the meaning of “M”
3. Row 155 -replace “I” with “I”
4. Rows 161-163 - eliminate the round parenthesis and specify that mixing correspond to i=5 process
5. Rows 169-172 - rewrite the sentence improving the English language
6. Figure 2, indicate the correlation factor R²
7. Rows 215-217 - some symbols (i.e. v, t) don’t match with formula, other are missing (i.e. H)
8. Formulas 9 - Can the movement of transport vehicle affect the volume and mass concentration? More information about this circumstance should be added
9. Row 276 - replace “T₃” with “t₃”
10. Row 307 - add more reference on low-carbon technologies for asphalt pavement construction
11. 366-369 -revise the sentence, English language mistakes are present
12. row 371 - replace “I” with “I”
13. row 379-380 -Provide more deeper comment to this results.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The topic is of interest and the paper is well written. My first comment relates to the fact the authors published a similar study in the International Journal of Pavement Research and Technology in 2017 titled Key steps of carbon emission and low-carbon measures in the construction of bituminous pavement. The methods seem very similar. Can you indicate what is new in this paper under review?

 

Secondly, some parts of the manuscript seem a bit like a black box, particularly Section 4.1, and it was not easy to follow the authors’ results. For example, calculations in Section 4.1.1 refer to a ton of mixture assuming a transportation distance of 1 km. Please clearly state this in the caption of Figure 5. Then, calculations in Section 4.1.2 assumed a meter of asphalt layer in the longitudinal direction so please also make this clear in the caption of Figure 6.

 

Moreover, since the emissions from energy consumption are calculated assuming a ton of mixture and a km of distance and the emissions from the asphalt mixture assumed a meter of road, how did the authors sum up the results? Details need to be provided in the manuscript. The reviewer could not figure out how the results in lines 393-395 were obtained.

 

Additional comments:

• Please be consistent when presenting units of variables. It is customary to indicate the units in brackets, e.g., (m). The authors used /m, /(m/s, and /(m/s). Correct throughout the paper (text, figures and tables).
• Introduction: clearly indicate the objectives of this study
• l111: compaction is a better word for pressure
• l155: use i instead of I
• Figure 2. How was this relationship obtained? Is it from another study or did the authors develop it during this study?
• l215: the units of volume are (m3)
• l215-216: v and t are not part of Equation 7
• l256: the technical word for screw distributor is auger
• l276: t3
• Not sure about the difference between 3.1 Low carbon and 3.2 warm mixing
• l360-361: what do you mean by heating vessel?
• l420: Define SBS
• Conclusions: bullets (1) through (3) are summary, not conclusions.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The article presents an interesting methodology to estimate the carbon-emissions in road construction. However, some points must be better explained, and others must be corrected. Points are discussed as they appear in the document.

Title and line 42. Why expressways? Why not roads in general? How are defined expressways? They can also be referred to as freeways and motorways, the commonest words. Multi-lane highways are also included? Any kind of bituminous pavement? Please, justify why only expressways and define it.

Line 45. Road workers? Really? I think that people conducting research about roads are researchers, scholars, but not the workers on road construction. Correct it. Moreover, domestic and foreign is not necessary. When observing the literature about a topic, nowadays, with globalization, researches are not regarded taking into account the country. Moreover, some researches come from international collaborations.

Line 47 and 50. If it is commented on the research of Cass et al. it is only possible to include its reference, number [11]. References [12-14] are not authored by Cass et al.

Line 53 and 54. Similar to the previous one. The reference of Kleine et al. is [16], but not [17].

Line 78 and 80. Something similar occurs. It is mentioned the International Panel on Climate Change (IPCC) but the references are other articles. If something mentioned by the IPCC is included, the original reference must be given.

Line 91. Asphalt mixture in high-temperature environment. This concept is constantly repeated in the article and it has great importance. With the expression “asphalt mixture in high-temperature environment”, it seems that a special asphalt mixture is produced to be employed in places with extreme temperatures, like a desert. Do the authors refer to the mix asphalt that is produced at high temperatures? In this case, they are known as Hot Mix Asphalts (HMA) (Biro et al. 2009; Salas et al. 2018). This must be corrected as is one of the main points of the article. Hot Mix Asphalts are different from other techniques, such as a Cold mix asphalts, based on bituminous emulsions and the Warm-Mix Asphalts. It is suggested to include this classification.

Line 95. It is said that the calculation parameters provided by the IPCC and the National Bureau of Statistics were used. Ok, but please, give the references to know how to use the calculation parameters, otherwise, they are not accessible.

Table 1. This table has a great footnote, bigger than the table itself. From lines 106 to 111 it indicates the meaning of the M1,…, M8. They were presented on line 86. That could be the place to present them and not in the footnote of a table. Furthermore, in some of the processes, some equations are shown in the footnote. This cannot be admitted. The processes must be clearly exposed before the table, with bullet points for example and indicate the corresponding equations. The footnote is not the appropriate place.

Line 115. What is the energy consumption list? What do authors refer to? It is difficult to understand.

Line 123. It is true that the use of 1 km of an expressway is a wrong unit. But the thickness of pavements is not different because of the regions. Within the same region, a wide range of thicknesses can be employed. Correct the sentence. Pavements are designed mainly according to the number of heavy vehicles (usually measured as Equivalent Single Axle-Loads, ESAL) in the road.

Lane 132. Include the reference for the Comprehensive Report on Climate Change 2014.

Line 137. The reference of the IPCC proposing the calculation method for carbon emission from energy consumption is needed.

Line 142. Normally, in scientific articles, the term “formula” is no employed. It is more common the term “Equation”. Please, substitute all the “formula” in the paper with “equation”.

Line 175 – 181. Please, rewrite this paragraph, which is very difficult to understand.

Line 197. Which is the escaping gas from asphalt mixtures? Please explain further Figure 1. Which is the gas present in the asphalt mixtures? It is not clear this part of the article.

Figure 2. Where do figure and equation come from? Explain further. Which is the R2 of the equation in the figure?

Line 215. The calculated volume in m2? Correct it.

Line 223. What does this section say? Measures were taken at the mixing plant? Which is the device? Explain its characteristics.

Line 225. Samples WERE taken.

Line 239. Front, middle, and rear parts of vehicles: which vehicles? Trucks? Explain it better. Once again measures of CO2 were taken? Indicate it more clearly.

Figure 3. Explain the variable “distance from one end of the paver/m? per meter? Or the distance is measured in m? Then, indicate as (m).

Line 276. T3 or t3, as indicated in “Equation (10)? (do not use formula).

Line 280. Carbon emission is measured from the beginning of rolling to the emission of greenhouse gases? Please, explain it better because I do not find the meaning.

Figure 4. What is “detection time/s”. Detection time per second? Or Detection time (s)? The way of indicating measures for variables is a basic point.

Line 367 Equations (5)-(12) instead of models.

Line 371. ProcesseS. An S is missing.

Line 392. Equation (13): the first component is from i = 1 to 8 except for 5, but the second component indicates from 5 to 8. Therefore, items 6, 7 and 8 are counted twice. Correct the equation.

Line 420. SBS? Define abbreviations before using them.

In general, explain better and further the procedure because it is difficult to understand some parts of the article.

 

Biro, S., Gandhi, T., & Amirkhanian, S. (2009). Midrange temperature rheological properties of warm asphalt binders. Journal of Materials in Civil Engineering, 21(7), 316-323.

Salas, M. A., Pérez-Acebo, H., Calderón, V., and Gonzalo-Orden, H. (2018). Bitumen modified with recycled polyurethane foam for employment in hot mix asphalt. Ingeniería e Investigación, 38(1), 60-66

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Quite an interesting article, written in good manner, but some things are need to be improved.

1. Title is a bit misleading. The article describe only preparation and construction of asphalt mixtures, not the whole express way construction
2.  Why there are so big differences between each motorway in table 1? Is it related to the used machines? Type of mixture, type of asphalt? Please describe it in more details?
3.  How carbon emission was measured exactly - please provide additional graphs with clear description
4.  What kind of mixtures were analyzed apart of the AC-16? What kind of layer? What kind of binder? What grade of binder? What thickness?
5. Please describe in more details the low-carbon technologies used. Was it also measured on site? Or only analyzed theoretically? How much of WMA was used?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The overall quality of the paper improved after the authors addressed reviewers’ comments. I appreciated the authors introduced the term volatilization to refer to those emissions not related to energy consumption. I recommend using it throughout the paper for clarification (e.g., lines 22, 26, 349, etc.).

Another comment related to Section 4. The authors stated that Huangyan Expressway was selected for a case study. However, the authors presented the results from 12 highways in Figures 6 and 7. How do you reconcile that? Was Huangyan Expressway used to obtained certain parameters or conduct calibration of the models described in Section 2 that were later applied to all highways? Some explanation is needed. Also, keep in mind one of the principles of research is being repeatable. Thus, the authors should provide the information regarding all evaluated highways so anyone can reproduce the results obtained by the authors.

Lastly, it is not clear the basis to point out in lines 483-485 that the use of heavy oil instead of coal for heating can reduce carbon emissions. As far as I understood Table 9, coal and heavy oil were not compared in the same heating process. Is so, please indicate. Also, it is not very intuitive what the reduction rates in Table 9 refer to. I suggest aligning the rate with the corresponding energy type.

 

Minor comments:

l41-42: I don’t understand the relevance of the information in brackets

l133: the authors used oil stone ratio and later asphalt-aggregate ratio.

l121: were

Table 2: any idea why the difference in energy consumption for activities like 1-km transportation of a ton of asphalt, or compaction

l154: spell out IPCC

l228: Figure 2

l273-274: the authors refer to v1 like discharge rate of the outlet of the mixer, but the units are m/s instead of m3/s or t/s. Isn’t v1 the gas diffusion rate from Figure 3?

l290: how was v2 obtained? Also from Figure 3?

l329-330: not clear how the authors combined Figures 5 and 3. I can’t see the connection.

l336: Is rising rate of gas the same as gas diffusion rate or something different?

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript has been improved from the previous version but a few facts should be taken into account.

Line 148. Once again the mistake is repeated. The regions do not affect so much in the pavement structure. To be more precise, it would be better to rewrite like this: “Considering the differences in heavy traffic and regions that produce different bituminous structures, these functional units…”

Line 162-164. The same mistake is repeated. IT is mentioned that the IPCC provided the type of carbon emissions but the references are not provided. Reference 29 is the National Bureau of Statistics Energy Division.

Line 300 – 302. Problems with the units continue although it is said to be corrected. If the x-axis of figure 4 is “distance from one end of the paver”, and if the unit is “meter”, write it correctly “Distance from one end of the paver (m)”. Otherwise, it seems paver/m, paver per meter.

Figure 5. The same mistake as in the previous point. If the variable is “detection time” and it is measured in seconds, it should be: “Detection time (s)”. The same happens for the Y-axis. Concentration of N2O (ppm). Please, review deeply all the figures.

Author Response

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Author Response File: Author Response.pdf