Economic and Environmental Benefit Analysis between Crumb Rubber Concrete and Ordinary Portland Cement Concrete
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript presents the comparative analysis of the cost and carbon emissions for conventional concrete and the concrete made with rubber from tire wastes. The literature and methodology become the main part of this manuscript with very limited emphasis on results and their contribution.
Specific comments are:
1) In the second paragraph of Introduction (around line 43-45), it was mentioned that the application of rubber tires in Civil Engineering practice is very limited. This cannot be the justification for the research study coz the waste tire may be more useful for another industry sector rather than Civil or Construction Engineering. The properties of construction materials made with waste rubber tire are worse than that of the counterparts made without using the rubber tire.
2) The main body of this manuscript has 17 pages. But 8 pages out of the 17 pages were about literature review. The contribution of sections 1- 3.3 is quite limited. The introduction and the section 2 are basically about what material with rubber tire was investigated and no attention paid to the environmental and economic performance. But they are repeated with different literature referenced there.
3) The section 3 doesn’t present effective methodology. It is roughly the literature review as well. From Sections 3.1 to 3.3, the mix designs and some material data from literature were presented there. Firstly, they are not methods. Secondly, they are not the contribution of this research study as this research is not a review study.
4) In Tables 1 and 2, there are three mix designs which look very strange. They are 40R4, 40R5 and 30R4. The water to cement ratios are 0.61, 0.81 and 1.1 respectively. With these ratios, it is quite unlikely the concrete can give compressive strength above 29MPa. From the referencing, it looks like these mix designs were from reference [23] which actually shows very low strength of the material.
5) The mix design 30R9 in Table 2 also looks strange. The rubber is 280kg/m3 which is a large quantity. The rubber content is shown as 15 for this mix design. But if looking at mix design 30R1 with rubber content 16.22 even higher than that of mix 30R9, the rubber quantity is just 42.44 kg/m3 for 30R1 which is about only 15% of that for 30R9 mix. The same issue also exists for 30R8.
6) In section 3.2, some mechanical properties for the mix designs in Tables 1 and 2 were given, such as the tensile strength, elastic modulus and flexural strength. Are all these data from the corresponding studies where the authors found the mix designs? Some of the studies might not have presented all these material properties.
7) The descriptions in Section 3.2 are not meaningful. Those description such as material properties increase or decrease or vary without insightful discussion. The authors mentioned that the deviations of CRC specimens’ mechanical properties were within 20% of that from OPCC specimens. This statement is not meaningful. The comparison is also inappropriate coz there are many variables. The mix designs were from different studies with different water-to-cement ratios, different aggregates properties etc. And adding more cement can compensate the strength reduction due to the rubber tire particles.
8) Section 3.3 doesn’t show any data from design codes or predictions based on design codes. So, it is not meaningful.
9) The analysis in Section 4 is very approximate and inadequate for scientific research. It is not the correct cost or embodied carbon analysis. The cost of materials was simply calculated by adding the costs found from companies. But the costs of transport due to project locations were not considered.
10) The estimation of carbon emissions used the carbon coefficient in Table 7. The references for table 7 are not accurate. Although several references were listed below the table, the authors should explain which reference provides the data for the specific material. Is the ‘0.124’ for crumb rubber from reference [22] or another study? And why is it very low?
11) The high carbon savings mentioned in conclusion, such as 223.28% or 269.59 %, were obtained from the very unrealistic mix designs (40R5 and 30R4). These mix designs are not accurate, as per comment 4. Besides, the carbon emissions for 30R8 and 30R9 are also inaccurate, especially the mix designs have issues (according to comment 5).
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe reviewed article concerns the technical and economic aspects of the use of crumb rubber concrete (CRC) and the comparison of its properties with ordinary Portland cement concrete (OPCC).
As part of the introduction and literature review, the problem of the growing amount of used car tires and their disposal was outlined. One of the solutions to the problem was the use of tires for the production of CRC. A literature review on CRC properties, design of their mixtures and economic aspects is presented.
In the research part, proposals for CRC mixtures in two strength groups, namely approximately 30 and 40 MPa, were adopted from the literature. The strength properties of CRC were compared with OPCC. The analysis shows that in group 40, the addition of crumb rubber reduced the compressive strength up to approximately 20%, but the tensile strength generally increased. In group 30, it was not possible to clearly determine the trend.
The next part of the work included a comparative analysis of the costs of producing particular types of concrete. Generally, CRC was characterized by comparable (generally slightly lower) strength parameters at slightly lower (several percent) production costs.
According to the authors, the greatest advantage of using CRC is a significant reduction in CO2 emissions compared to OPCC, as demonstrated in section 4.3.1. This is a factor that may potentially determine the choice of OPCC technology.
The article is certainly very interesting, it concerns a current problem encountered in engineering practice, especially in the face of climate change and the proposed policy of economical management of natural resources.
According to the reviewer, the article may be published provided that the following comments are taken into account:
- Were the mechanical properties in tables 3 and 4 determined by the authors or taken from the literature? Why are some values missing?
- The analysis presented in the article, although certainly very valuable, is only a fragment of the problem. To discuss cost aspects, a life cycle assessment (LCA) should be performed. Does the addition of rubber affect the durability of the structure and the related operating costs? Is CRC disposal more costly and energy-intensive than OPCC? If these aspects were not analyzed, they should at least be mentioned in the text of the article.
- the manuscript requires editing refinements (missing spaces, inconsistent table numbering, etc.).
Comments on the Quality of English LanguagePlease see the general remarks.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe paper presents an interesting topic. However, the original manuscript needs major revision before possible publication.
1 The order of references was chaotic. Furthermore, in "2 Literature Review", some references needed to be updated.
2 In "3.1 Mix proportions of CRC with similar strength", was the mass replacement rate or the volume replacement rate of crumb rubber used in the mix proportions?
3 The manuscript lacked an analysis of the reasons for the changes in the mechanical properties of concrete caused by CRC.
4 The quality of Figures 1, 2, 3, and 4 needed to be improved.
5 Line 225: How did the author apportion the processing and transportation costs to the purchase price of each component? Please explain in detail.
6 In "4.3 Analysis of Environmental Benefit", the manuscript analyzed some data from literature, such as Mahasenan et al (2003) [30], Kajaste and Hurme (2016) [22], Turner and Collins (2013) [43] and EFCAA (2002) [12]. Collins (2013) [43] and EFCAA (2002) [12], please provide a brief description of the methodology used in the literature for counting and evaluating CO2 emissions, and analyze the error in the CO2 emissions data.
7 In "4.4 Other environmental benefits", the manuscript mainly introduced other environmental benefits of processing waste automobile tires into CRC, but lacked quantitative analysis.
8 In "5. Discussion and Conclusion", the expression of the manuscript was not sufficiently concise and cohesive, and the manuscript lacked prospects for the specific application of CRC.
Comments on the Quality of English LanguageMinor editing of English language required
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe submitted paper presents of the comparative analysis of the economic and environmental benefit between Crumb Rubber Concrete (CRC) and Ordinary Portland Cement Concrete (OPCC).
In the opinion of this Reviewer the study is worthy of publication after major revisions. The introduction is quite complete as it includes the necessary information about the investigated topic. However, this Reviewer would prefer more information about the practical use of this new material of the possibilities to use this material in practaical field. Has research been done on this?
Further, in chapter 3 the Authors described and presented comparative results between CRC and OPCC considering their material properties. Did the Authors constructed and tested all this specimens or they collected these data from literature? Please make it clearer through the text. Furthermore, considering the overall organization of this paper, figures considering the tested specimens, the used waste materials added in concrete mixture or etc.
Chapter 3.3 needs a graphic to present clearer the analytical results considering the comparative analysis between OPCC constitutive model design model and the standard codes. Moreover, the Authors should add extra details considering the modified CRC concrete constitutive model.
Considering the overall organization of the text, this research paper looks more like a review paper than an research on a comparative anlysis between CRC and OPCC. Please improve the organisation of the paper and mention better the highlights of this research.
Comments on the Quality of English Language
The way the text has been written needs extra check to be more understandable to the readers. So, the Authors should refer to a specialist to correct and to improve the quality of the used English
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe comments are addressed.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe reviewer believes that the manuscript can be considered for acceptance.
