Compaction Procedures and Associated Environmental Impacts Analysis for Application of Steel Slag in Road Base Layer

Round 1

Reviewer 1 Report

The paper deals with the problem of application of waste materials in pavement construction. Natural aggregates are always treated as the best choice, but sometimes comparable results may be obtained with alternative aggregates. In reviewed paper this aggregate is the steel slag used for aggregates with gradation higher than 4.75 in case in hydraulically bound base layer. A typical paper dealing with that subject consists mostly from laboratory tests, but in case of reviewed paper the steel slag was used in real life for pavement construction of “Baotou-Moaming” motorway located in China. Authors in the paper focus on the following properties of the base layer: flatness, compaction, compressive strength, energy consumption and CO2 emission. All of these features are very important, but in my opinion there is no information about some possible side effects connected with application of steel slag aggregate such as the presence of certain harmful compounds (pollutants) that could be leached from the material (especially in the case of cracking and crushing). We may assume that it is not the topic of the paper, but some information would be good for the completeness of the study. In case of mechanical properties, also some information is not present in the paper. I think that in case of base materials which are hydraulically bound the shrinkage effect is very important in view of potential cracking of the materials. This information is also connected with the limitation of the length of the base following slabs (is there any difference between mixture with and without steel slag?). Another mechanical parameter is the resistance to water and frost of the material, which in my opinion will be different for analyzed materials.

However reviewed paper has to be positively estimated, mainly thanks to the very detailed analysis of the compacting methods and compacting processes for the material with steel slag (C3) and material without it (C1) in view of energy consumption and CO2 emission. From the analysis result that compacting of the mixture with steel slag is more energy consuming process, than in case of traditional aggregate. Of course, in that analysis the fact that once we are using natural aggregate which somehow is lost to the nature and the other time waste material which is the problem when stored is not included. In my opinion this fact is reducing the negative effect of energy consumption in case of steel slag application. The paper is worth publishing, but first Authors have to solve the following problems:

• Referencing Figures and Tables have to be corrected.
• The Figure numbering in the text is rather odd: Fig. 1 is located in page 6 while Fig.2 in page 4?
• Tables 3, 5 are too wide.
• In my opinion the equation in page 4 and 9 are not needed (both have number 1). Texture index and surface flatness are a well known concepts around the world.
• The English is ok in general, but in some places a few improvements may be done. See for example line 119-120: “the investigation also investigated..”.

 

Regarding the References - The possibility of application of steel slag in application to hydraulically bound materials are indicated in the work: Gao, D.; Wang, F.-P.; Wang, Y.-T.; Zeng, Y.-N. Sustainable Utilization of Steel Slag from Traditional Industry and Agriculture to Catalysis. Sustainability 2020, 12, 9295. https://doi.org/10.3390/su12219295. In the mentioned paper also some positive effects and physical and chemical mechanisms behind them are indicated. In my opinion it is worth to cite.

Author Response

Point-by-point Response to Reviewer 1#

1. The paper deals with the problem of application of waste materials in pavement construction. Natural aggregates are always treated as the best choice, but sometimes comparable results may be obtained with alternative aggregates. In reviewed paper this aggregate is the steel slag used for aggregates with gradation higher than 4.75 in case in hydraulically bound base layer. A typical paper dealing with that subject consists mostly from laboratory tests, but in case of reviewed paper the steel slag was used in real life for pavement construction of “Baotou-Maoming” motorway located in China.

Response: Thanks for your kind comments. The reviewer does grasp our research points and associated significances. The manuscript has been revised already. We have improved the English and format expressions, making the research more logical and readable. You can check it from the uploaded files.

2. Authors in the paper focus on the following properties of the base layer: flatness, compaction, compressive strength, energy consumption and CO₂ All these features are very important, but in my opinion, there is no information about some possible side effects connected with application of steel slag aggregate such as the presence of certain harmful compounds (pollutants) that could be leached from the material (especially in the case of cracking and crushing). We may assume that it is not the topic of the paper, but some information would be good for the completeness of the study.

Response: Thanks for your kind comments. Several existing literatures have investigated the content of toxic elements and heavy metals in steel slag leachate, and confirmed that the utilizing steel slag in road construction is allowed according to official standards. We have supplemented associated explanations towards the safety of steel slags. Part of contents is listed below.

Considerable concerns have been raised in road construction studies regarding the releases of potential hazardous components by steel slag aggregates. Ivana et al analysed the potential adverse impacts of steel slag leachate. The results indicated that the leachates from 2 tested steel slags showed weak alkalinity, and the concentrations of toxic elements (heavy metals) are far below to limited value, posing little risk to ecological environment [12]. Moustakas et al investigated the leaching impacts of air-cooled and water-cooled slags. The results considered the European official decision (2003/33/EC) and leaching procedures test, confirming the safety of slag utilization [13]. Sasmita et al collected the slags leachates from 3 steelmaking manufacturers and assessing their contents of heavy metals. The results presented that toxic elements (As, Cd, Se and V) have not been leached and other heavy metals were below the warning value [14]. Xie et al evaluated the utilization possibility of steel slag from both laboratory and in-place perspectives. The results showed that the leachate fulfilled most of global environmental laws and regulations [15]. Hence, steel slag can be considered as a sustainable material recycling in road construction in terms of economy and environmental protection.

References:

[12] Barišić, I., I. Netinger Grubeša, and B. Hackenberger Kutuzović, Multidisciplinary approach to the environmental impact of steel slag reused in road construction. Road Materials and Pavement Design, 2017. 18(4): p. 897-912.

[13] Moustakas, K., et al., Leaching properties of slag generated by a gasification/vitrification unit: The role of pH, particle size, contact time and cooling method used. Journal of Hazardous Materials, 2012. 207-208: p. 44-50.

[14] Chand, S., B. Paul, and M. Kumar, Short-term leaching study of heavy metals from LD slag of important steel industries in Eastern India. Journal of Material Cycles and Waste Management, 2017. 19(2): p. 851-862.

[15] Xie, J., et al., Evaluation the deleterious potential and heating characteristics of basic oxygen furnace slag based on laboratory and in-place investigation during large-scale reutilization. Journal of Cleaner Production, 2016. 133: p. 78-87.

3. In case of mechanical properties, also some information is not present in the paper. I think that in case of base materials which are hydraulically bound the shrinkage effect is very important in view of potential cracking of the materials. This information is also connected with the limitation of the length of the base following slabs (is there any difference between mixture with and without steel slag?). Another mechanical parameter is the resistance to water and frost of the material, which in my opinion will be different for analyzed materials.

Response: Thanks for your kind comments. The steel slag aggregates need pretreat before used in road construction, including the aged, crushed, and sieved procedures. During the aged procedure, the steel slag would be treated by climate conditions (UV, oxygen and water), aiming to decrease its expansion and shrinkage effects. Hence, we have not considered its shrinkage effect and water resistance here, instead focusing on the surface textures, compaction, and compressive strength via comparative study with andesite. We will attach much significance for shrinkage effect and water resistance in further research.   

4. However reviewed paper has to be positively estimated, mainly thanks to the very detailed analysis of the compacting methods and compacting processes for the material with steel slag (C3) and material without it (C1) in view of energy consumption and CO2 emission. From the analysis result that compacting of the mixture with steel slag is more energy consuming process, than in case of traditional aggregate. Of course, in that analysis the fact that once we are using natural aggregate which somehow is lost to the nature and the other time waste material which is the problem when stored is not included. In my opinion this fact is reducing the negative effect of energy consumption in case of steel slag application. The paper is worth publishing, but first Authors have to solve the following problems:
   • Referencing Figures and Tables have to be corrected.

Response: Thanks for your valuable comments. We have revised the format of referenced figures and tables. Please check associated revisions in uploaded files.

• The Figure numbering in the text is rather odd: Fig. 1 is located in page 6 while Fig.2 in page 4?

Response: Thanks for your valuated comments. We have revised the mistaken numbers for Figures. Please check the revisions in uploaded files.

• Tables 3, 5 are too wide.

Response: Thanks for your kind comments. We have adjusted the format and size of Tables. Please check the revisions in uploaded files.

• In my opinion the equation in page 4 and 9 are not needed (both have number 1). Texture index and surface flatness are a well-known concept around the world.

Response: Thanks for your kind comments. The listed equations can improve the readability of our study, especially the basic principle of associated issues. Although the texture index and surface flatness are well-known concepts, we decide to retain the equations considering the logicality and completeness.

• The English is ok in general, but in some places a few improvements may be done. See for example line 119-120: “the investigation also investigated.”.

Response: Thanks for your valuated comments. We have revised inappropriate English expressions in uploaded version; this sentence has been revised as ‘the study also investigated…’.

5. Regarding the References - The possibility of application of steel slag in application to hydraulically bound materials are indicated in the work: Gao, D.; Wang, F.-P.; Wang, Y.-T.; Zeng, Y.-N. Sustainable Utilization of Steel Slag from Traditional Industry and Agriculture to Catalysis. Sustainability2020, 12, 9295. https://doi.org/10.3390/su12219295. In the mentioned paper also some positive effects and physical and chemical mechanisms behind them are indicated. In my opinion it is worth to cite.

Response: Thanks for your kind recommendation. The mentioned reference reviewed the properties and applications toward utilization of steel slag which enhance the recycling and reusing references in the future. It is closed connect with our research topic and we have cited it in revised version. 

Reviewer 2 Report

This research paper investigates the pavement construction of a motorway located in China, analyzing the compaction procedures and assessing the environmental impacts regarding the road base layer containing steel slag. The comparison between natural aggregate (andesite aggregate) and manufactured aggregate (steel slag aggregate) revealed the advantages and disadvantages of the manufactured aggregates. However, the reviewer feels this paper has some points to be improved and complemented for possible publication.

 

1. Title

• What is the meaning “Compacting Implementation”? Ambiguous title is not good.

2. Abstract

• Abstract is very important part. This is one of the most important parts of an academic paper, as it is often treated as a replacement for the body of the paper. The authors are required to rewrite the abstract in a neat manner.
• 14^th thru 15^th

Change “road base layer construction” into “road base layer construction field”.

• 15^th

Clarify “its alleviation”.

• 20^th

Change “physical appearances” into “appearances”.

• 25^th

A simple example on the “traditional base layer” is required.

• 25^th thru 28^th lines “Compared to … respectively”.

Complementing the reasons for reducing compaction vibration period.

 

3. Introduction

• A brief literature review on the use of steel slag in road base layer construction field.
• 38^th thru 40^th

Change “40Substantial studies indicate … in developing countries” into “In many studies, the rapid expansion and improvement of new road construction can be seen, especially in developing countries.

• 41^th

Ambiguity in expression. “is often questioned”.

• 49^th

“Previously, …” to the next paragraph.

• 87^th

A detailed explanation on the terminology “material production stage”.

• 98^th thru 100^th

There are two verbs. Use a conjunction.

• Is it possible to find out overall environmental impacts if only CO2 emissions and energy consumption are investigated? It would be nice to add contents about other environmental factors.

4. Section 2.1

• 98^th thru 100^th

The reviewer feels that reference should be included in the sentence “the size designating the limit between coarse and fine dimension was considered equal to 4.75 mm”.

• 124^th thru 144^th

Remove the sentences “Error! Reference source not found.”

• 147^th thru 148^th

State why you used the arithmetic mean as your representative value. Andesite is mostly moderate and Steel slag is mostly high. You'd better think about ways to give weight.

• 148^th thru 149^th

“Hence, Lucheng steel … for cement workability.”, Complement the contents of the association between surface texture and cement workability.

• 158^th

Make a better distinction between depth, width and height.

• 158^th thru 163^th

Remove the sentences “Error! Reference source not found.”

5. Section 2.2

• 173^th

Remove the sentences “Error! Reference source not found.”

6. Section 3.1

• 188^th

Clarify “mass”.

7. Section 3.1.1

• 193^th thru 234^th

Remove the sentences “Error! Reference source not found”.

8. Section 3.1.2

• 247^th

Change “Equation 2” into “Equation 1”.

9. Section 3.1.3

• 259^th

A detailed explanation of why it was divided into tow groups.

• 265^th

Remove the sentences “Error! Reference source not found.”

• 298^th

A detailed explanation of why α was assumed to be 40%.

10. Section 3.2.2

• 323^th thru 335^th

Remove the sentences “Error! Reference source not found.”

11. Conclusion

• 337^th

Change “for base layer” into “for road base layer”.

• 370^th thru 372^th

Remove the contents.

12. the reviewer feels it is good to be able to achieve higher compressive strength and workability by using steel slag aggregate. However, the use of steel slag aggregate seems good from a life cycle perspective, but it is limited in that it is inevitable to have bad environmental effects. Compare which of steel waste stockpiles or CO2 emissions would be worse for the environment.

 

 

 

Author Response

Point-by-point Responses to Reviewer 2#

This research paper investigates the pavement construction of a motorway located in China, analyzing the compaction procedures and assessing the environmental impacts regarding the road base layer containing steel slag. The comparison between natural aggregate (andesite aggregate) and manufactured aggregate (steel slag aggregate) revealed the advantages and disadvantages of the manufactured aggregates. However, the reviewer feels this paper has some points to be improved and complemented for possible publication.

Response: Thanks for your valuable and helpful comments. The reviewer has point out the mistakes and inappropriate expressions in the manuscript. We have revised related places according to the comments already, especially in the English and format expressions, making the research more logical and readable. You can check it from the uploaded files.

1. Title: What is the meaning “Compacting Implementation”? Ambiguous title is not good.

Response: Thanks for your valued comments. we have revised the ambiguous expression and the title ‘Compacting Implementation’ has been changed as ‘Compaction Procedures’ already. 

2. Abstract: Abstract is very important part. This is one of the most important parts of an academic paper, as it is often treated as a replacement for the body of the paper. The authors are required to rewrite the abstract in a neat manner.

Response: Thanks for your valued comments. We agree with your point. The ambiguous expression has been revised. The title ‘Compacting Implementation’ has been changed as ‘Compaction Procedures’. You can check the revisions in uploaded version.  

3. 14^ththru 15^th: Change “road base layer construction” into “road base layer construction field”.

Response: Thanks for your valued comments. We agree with your point and inappropriate expression has been revised. Please check it in uploaded files. 

4. 15^th: Clarify “its alleviation”.

Response: Thanks for your valued comments. The sentence has revised as ‘In current years, recycling steel slag is receiving growing interests in road base layer construction field due to its alleviating land occupation and resource shortage’. Please check the revisions in uploaded files.

5. 20^th: Change “physical appearances” into “appearances”.

Response: Thanks for your valued comments. We have revised the vague phrase as ‘texture appearances’ already. You can check it in uploaded files.

6. 25^th: A simple example on the “traditional base layer” is required.

Response: Thanks for your valued comments. We have revised the vague phrase. The ‘traditional base layer’ means ‘the base layer by andesite aggregates’ here. Please check it from uploaded version.

7. 25^ththru 28^th lines “Compared to … respectively”. Complementing the reasons for reducing compaction vibration period.

Response: Thanks for your valued comments. We have supplemented the explanations for the reasons to reduce compaction vibration period. Part of revised content is showed below.

Compared to the base layer by andesite aggregate, the compaction vibration period of the course containing steel slags should be reduced to achieve a proper density due to the ‘hard to hard’ effect occurred between the adjacent steel slag particles. Consequently, the additional energy and the equivalent CO2 are generated at 2.67 MJ/m3 and 0.20 kg/m3, respectively.

8. Introduction: A brief literature review on the use of steel slag in road base layer construction field.

Response: Thanks for your valued comments. We have supplemented the literature reviews toward steel slag in base layer by cement mixture. Part of content is listed below:

Monshi et al proved that the steel slag concrete had better compressive strength than the original Portland cement concrete [17]. Maslehuddin et al proved that some physical and mechanical properties (i.e. resistance to reinforcement corrosion and compressive strength) of steel slag concrete were better than limestone concrete [18]. Srinivasa et al found an improvement in the cementing property as using quenched slag products in hydraulically bound mixture [19]. Altun et al reported that applying steel slag as aggregate can obtain an acceptable physical and mechanical performance [20]. The existing literatures indicate that steel slag cement mixtures can be well applied to the road base layer.

Václavík et al replaced natural aggregate by steel slag in cement concrete and investigate associated environmental impacts by LCA. The results show that steel slag aggregate can diminish 7% of environmental burdens [24]. Anastasiou et al considered the sustainability by utilizing industrial by-products (fly ash and steel slag) in cement mixture. The results found that cement clinker content is critical for GHG emissions and transport distances of steel slag aggregate could strikingly affect the environmental burdens in materials production stage [25].

Reference:

[17] Monshi, A. and M.K. Asgarani, Producing Portland cement from iron and steel slags and limestone. Cement and Concrete Research, 1999. 29(9): p. 1373-1377.

[18]   Maslehuddin, M., et al., Comparison of properties of steel slag and crushed limestone aggregate concretes. Construction and Building Materials, 2003. 17(2): p. 105-112.

[19]   Reddy, A.S., R.K. Pradhan, and S. Chandra, Utilization of Basic Oxygen Furnace (BOF) slag in the production of a hydraulic cement binder. International Journal of Mineral Processing, 2006. 79(2): p. 98-105.

[20] Akın Altun, İ. and İ. Yılmaz, Study on steel furnace slags with high MgO as additive in Portland cement. Cement and Concrete Research, 2002. 32(8): p. 1247-1249.

[24] Václavík, V., et al., Sustainability Potential Evaluation of Concrete with Steel Slag Aggregates by the LCA Method. Sustainability, 2020. 12(23): p. 9873.

[25] Anastasiou, E.K., A. Liapis, and I. Papayianni, Comparative life cycle assessment of concrete road pavements using industrial by-products as alternative materials. Resources, Conservation and Recycling, 2015. 101: p. 1-8.

9. 38^ththru 40^th: Change “Substantial studies indicate … in developing countries” into “In many studies, the rapid expansion and improvement of new road construction can be seen, especially in developing countries.

Response: Thanks for your valued comments. We have revised the sentence, which becomes more readable and reasonable. Please check it in uploaded files.

10. 41^th: Ambiguity in expression. “is often questioned”.

Response: Thanks for your valued comments. We have revised the expressions. Part of content is below. Please check it in uploaded files.

Nevertheless, the sustainability of road construction and development is rising questioned due to various environmental issues, such as the large consumptions of natural aggregate resources.

11. 49^th: “Previously, …” to the next paragraph.

Response: Thanks for your valued comments. We have transferred this part to next paragraph.  sentence, which becomes more readable and reasonable now. Please check it in uploaded files.

12. 87^th: A detailed explanation on the terminology “material production stage”.

Response: Thanks for your valued comments. We have revised the vague sentence and supplemented associated expressions already. Please check it in uploaded files

13. 98^ththru 100^th: There are two verbs. Use a conjunction.

Response: Thanks for your comments. We have checked the expression and confirmed that the sentence is correct. We used ‘while’ and ‘which’ here.

14. Is it possible to find out overall environmental impacts if only CO2 emissions and energy consumption are investigated? It would be nice to add contents about other environmental factors.

Response: Thanks for your kind comments. Several existing literatures have investigated the content of toxic elements and heavy metals in steel slag leachate, and confirmed that the utilizing steel slag in road construction is allowed according to official standards. We have supplemented associated explanations towards the safety of steel slags. Part of contents is listed below.

Considerable concerns have been raised in road construction studies regarding the releases of potential hazardous components by steel slag aggregates. Ivana et al analysed the potential adverse impacts of steel slag leachate. The results indicated that the leachates from 2 tested steel slags showed weak alkalinity, and the concentrations of toxic elements (heavy metals) are far below to limited value, posing little risk to ecological environment [12]. Moustakas et al investigated the leaching impacts of air-cooled and water-cooled slags. The results considered the European official decision (2003/33/EC) and leaching procedures test, confirming the safety of slag utilization [13]. Sasmita et al collected the slags leachates from 3 steelmaking manufacturers and assessing their contents of heavy metals. The results presented that toxic elements (As, Cd, Se and V) have not been leached and other heavy metals were below the warning value [14]. Xie et al evaluated the utilization possibility of steel slag from both laboratory and in-place perspectives. The results showed that the leachate fulfilled most of global environmental laws and regulations [15]. Hence, steel slag can be considered as a sustainable material recycling in road construction in terms of economy and environmental protection.

References:

[12] Barišić, I., I. Netinger Grubeša, and B. Hackenberger Kutuzović, Multidisciplinary approach to the environmental impact of steel slag reused in road construction. Road Materials and Pavement Design, 2017. 18(4): p. 897-912.

[13] Moustakas, K., et al., Leaching properties of slag generated by a gasification/vitrification unit: The role of pH, particle size, contact time and cooling method used. Journal of Hazardous Materials, 2012. 207-208: p. 44-50.

[14] Chand, S., B. Paul, and M. Kumar, Short-term leaching study of heavy metals from LD slag of important steel industries in Eastern India. Journal of Material Cycles and Waste Management, 2017. 19(2): p. 851-862.

[15] Xie, J., et al., Evaluation the deleterious potential and heating characteristics of basic oxygen furnace slag based on laboratory and in-place investigation during large-scale reutilization. Journal of Cleaner Production, 2016. 133: p. 78-87.

15. Section 2.1: 98^ththru 100^th: The reviewer feels that reference should be included in the sentence “the size designating the limit between coarse and fine dimension was considered equal to 4.75 mm”.

Response: Thanks for your kind comments. Here the coarse and fine aggregate is a well-known concept in engineering field, so we skipped the reference previously. We have supplemented the citation now. Please check the uploaded files.

16. 124^ththru 144^th: Remove the sentences “Error! Reference source not found.”

Response: Thanks for your kind comments. The mistake comes from the wrongly referencing in Figures and Tables. We have revised the mistakes. Please check it in uploaded version.

17. 147^ththru 148^th: State why you used the arithmetic mean as your representative value. Andesite is mostly moderate and Steel slag is mostly high. You'd better think about ways to give weight.

Response: Thanks for your kind comments. The method, using arithmetic mean as representative value consulted from cited references, which is the default measuring method in using AIMS to test surface roughness.

18. 148^ththru 149^th: “Hence, Lucheng steel … for cement workability.”, Complement the contents of the association between surface texture and cement workability.

Response: Thanks for your kind comments. We have supplemented the explanation for the relations between texture and workability. Please check the revisons from uploaded files.

19. 158^th: Make a better distinction between depth, width and height.

Response: Thanks for your kind comments. This distinction is a default standard, formulated by AIMS developers. So, we have to retain this version here.

20. 158^ththru 163^th: Remove the sentences “Error! Reference source not found.”

Response: Thanks for your kind comments. The mistake comes from the wrongly referencing in Figures and Tables. We have revised the mistakes. Please check it in uploaded version.

21. Section 2.2: 173^th: Remove the sentences “Error! Reference source not found.”

Response: Thanks for your kind comments. The mistake comes from the wrongly referencing in Figures and Tables. We have revised the mistakes. Please check it in uploaded version.

22. Section 3.1: 188^th: Clarify “mass”.

Response: Thanks for your kind comments. Mass is the quality of materials.

23. Section 3.1.1: 193^ththru 234^th: Remove the sentences “Error! Reference source not found”.

Response: Thanks for your kind comments. The mistake comes from the wrongly referencing in Figures and Tables. We have revised the mistakes. Please check it in uploaded version.

24. Section 3.1.2: 247^th: Change “Equation 2” into “Equation 1”.

Response: Thanks for your kind comments. Equation 1 and 2 are different. The former is used for assessing the texture of aggregate materials and the latter is used for assessing the flatness of base layer during compaction. So, we have to retain the version here.  

25. Section 3.1.3: 259^th: A detailed explanation of why it was divided into two groups.

Response: Thanks for your kind comments. 2 groups are used to compare the difference and evaluate the errors result, increasing the reliability of conclusions.  

26. 265^th: Remove the sentences “Error! Reference source not found.”

Response: Thanks for your kind comments. The mistake comes from the wrongly referencing in Figures and Tables. We have revised the mistakes. Please check it in uploaded version.

27. 298^th: A detailed explanation of why α was assumed to be 40%.

Response: Thanks for your kind comments. Please check the cited reference, we have stated that 40% is referenced by citation.

28. Section 3.2.2: 323^ththru 335^th: Remove the sentences “Error! Reference source not found.”

Response: Thanks for your kind comments. The mistake comes from the wrongly referencing in Figures and Tables. We have revised the mistakes. Please check it in uploaded version.

29. Conclusion: 337^th: Change “for base layer” into “for road base layer”.

Response: Thanks for your kind comments. we have revised the vague sentence. Please check it from uploaded file.

30. 370^ththru 372^th: Remove the contents.

Response: Thanks for your kind comments. We have revised the sentence. Please check it in the uploaded file.

31. the reviewer feels it is good to be able to achieve higher compressive strength and workability by using steel slag aggregate. However, the use of steel slag aggregate seems good from a life cycle perspective, but it is limited in that it is inevitable to have bad environmental effects. Compare which of steel waste stockpiles or CO₂ emissions would be worse for the environment.

Response: Thanks for your kind comments. The authors think that it is hard to say which environmental index is more important or worse to research. But energy consumption and CO₂ emission should be 2 widely researched aspects in environmental impacts globally. Hence, this study aims to assess these 2 impacts during steel slag utilization. Meanwhile, we have discussed the potential risks for steel slag aggregate in Introduction part, especially the toxic elements and heavy metal releasing. After confirming the safety of steel slag aggregate, we decide to quantify the energy used and CO₂ emitted in actual application.

 

Reviewer 3 Report

Comments are attached. 

Comments for author File: Comments.pdf

Author Response

Point-by-point Response to Reviewer 3#

1. The manuscript investigates the application of steel slag in road base layer, the compacting implementation and associated environmental impacts were discussed. Overall, the manuscript is not well-written. Unprofessional problems can be found from the methodology to formatting. The review suggests an intensive revision before it is qualified for publication. My detail comments are as follows:

Response: Thanks for your kind comments. The reviewer has point out the mistakes and inappropriate expressions in the manuscript. We have carefully revised related places according to the comments already, especially in the English and format expressions, making the research more logical and readable. You can check it from the uploaded files.

 

2. Formatting problem should be corrected. The current state of the figures and citation editing does not fit the requirements of scientific paper.

Response: Thanks for your kind comments. The mistake comes from the wrongly referencing in Figures and Tables. We have revised the mistakes. Please check it in uploaded version.

3. Since the steel slag is used for pavement, the wearing of tires of vehicles should be considered which is as import as the compactness, flatness, and strength.

Response: Thanks for your kind comments. The tires of vehicles can surely make negative impacts in pavement, but its wearing effect appears in usage stage or service stage. In this study, we would like to investigate the construction stage, and analyze the compaction procedure. So, we have not considered the wearing effects by tires here.

4. The corrosion of steel slag and its influence on sustainability of the pavement should be considered. This might be more essential than the strength for a road.

Response: Thanks for your kind comments. The steel slag aggregates need pretreat before used in road construction, including the aged, crushed, and sieved procedures. During the aged procedure, the steel slag would be treated by climate conditions (UV, oxygen and water), aiming to decrease its corrosion and shrinkage effects. Hence, the used steel slag is stable in road base layer. Meanwhile, we will attach much significance for detail corrosion effect in our further research.  

5. The author only tested one composition for the aggregate of steel slag. However, in pavement, different composition with different percentage of aggregate should be tested. Then a reasonable conclusion for the usage of steel slag can be made.

Response: Thanks for your kind comments. Using steel slag as coarse aggregate is widely discussed and accepted, rather than fine aggregate. Meanwhile, this research was conducted from a Chinese case study, so, we presented one composition for steel slag aggregate according to in-place situation. We will provide more available compositions and approaches in steel slag usage in our future research.

6. It is not clear the calculation of additional energy and equivalent CO₂ How to consider the energy and carbon balance?

Response: Thanks for your kind comments. Based on the listed equations and principles, we calculated the energy consumption and CO₂emission generated by 2 base layer compaction (steel slag and andesite aggregate), respectively. Afterwards, the additional environmental impacts can be obtained by result differences.  

7. How does the authors consider the trace/heavy metal in the slag, which play key role in the environment impact?

Response: Thanks for your kind comments. Several existing literatures have investigated the content of toxic elements and heavy metals in steel slag leachate, and confirmed that the utilizing steel slag in road construction is allowed according to official standards. We have supplemented associated explanations towards the safety of steel slags. Part of contents is listed below.

Considerable concerns have been raised in road construction studies regarding the releases of potential hazardous components by steel slag aggregates. Ivana et al analysed the potential adverse impacts of steel slag leachate. The results indicated that the leachates from 2 tested steel slags showed weak alkalinity, and the concentrations of toxic elements (heavy metals) are far below to limited value, posing little risk to ecological environment [12]. Moustakas et al investigated the leaching impacts of air-cooled and water-cooled slags. The results considered the European official decision (2003/33/EC) and leaching procedures test, confirming the safety of slag utilization [13]. Sasmita et al collected the slags leachates from 3 steelmaking manufacturers and assessing their contents of heavy metals. The results presented that toxic elements (As, Cd, Se and V) have not been leached and other heavy metals were below the warning value [14]. Xie et al evaluated the utilization possibility of steel slag from both laboratory and in-place perspectives. The results showed that the leachate fulfilled most of global environmental laws and regulations [15]. Hence, steel slag can be considered as a sustainable material recycling in road construction in terms of economy and environmental protection.

References:

[12] Barišić, I., I. Netinger Grubeša, and B. Hackenberger Kutuzović, Multidisciplinary approach to the environmental impact of steel slag reused in road construction. Road Materials and Pavement Design, 2017. 18(4): p. 897-912.

[13] Moustakas, K., et al., Leaching properties of slag generated by a gasification/vitrification unit: The role of pH, particle size, contact time and cooling method used. Journal of Hazardous Materials, 2012. 207-208: p. 44-50.

[14] Chand, S., B. Paul, and M. Kumar, Short-term leaching study of heavy metals from LD slag of important steel industries in Eastern India. Journal of Material Cycles and Waste Management, 2017. 19(2): p. 851-862.

[15] Xie, J., et al., Evaluation the deleterious potential and heating characteristics of basic oxygen furnace slag based on laboratory and in-place investigation during large-scale reutilization. Journal of Cleaner Production, 2016. 133: p. 78-87.

 

Round 2

Reviewer 2 Report

The revised manuscript have reflected all issuses raised by the reviewer and hence can be accepeted in its present form

Reviewer 3 Report

The authors have addressed the comments and the manuscript has significant improvements compared to the original version. It is qualified for publication.