A Sustainable and Environmentally Friendly Concrete for Structural Applications
Round 1
Reviewer 1 Report
I congratulate the authors of a very interesting article on the possibility of using waste materials and aggregates from concrete recycling. The goals set in the research were achieved and the presented results show that it is possible to use up to 25% PCC and 37.5% or 50% UCA.
Despite the high evaluation of the research carried out, I lack durability tests. Therefore, I would like to ask the authors to supplement the analysis with frost and water resistance tests as well as salt resistance tests.
Author Response
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Comments 1: [I congratulate the authors of a very interesting article on the possibility of using waste materials and aggregates from concrete recycling. The goals set in the research were achieved and the presented results show that it is possible to use up to 25% PCC and 37.5% or 50% UCA. Despite the high evaluation of the research carried out, I lack durability tests. Therefore, I would like to ask the authors to supplement the analysis with frost and water resistance tests as well as salt resistance tests] Respond 1: |
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We appreciate your constructive comments on our research in which frost/water resistance, salt-resistance and durability tests were not included in the initial trials of PCC and UCA in concrete. These are important considerations in the performance of concrete, however, the initial test results given in the paper were necessary to determine whether or not these materials are viable for use in concrete. Without the initial trials, additional research work would be unproductive. Since our initial study produced favourable results, future work will include such tests to reduce the loop on the use of PCC and UCA in concrete and reduce the carbon footprint.
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Reviewer 2 Report
The paper "A Sustainable and Environmentally Friendly Concrete for Structural Applications" presents mechanical results of concretes replaced with precipitated calcium carbonate from sugar beet and recycled concrete aggregates. The paper is extensive, needs to better organize its structures and sections and to reduce unnecessary content.
Section 1.3. Is it essential to mention organization names trying to achieve zero carbon emissions?
Section 1.4. Line 131-132. This sentence says nothing.
Section 1.5. The state of the art of the article is somehow too long and with unnecessary reference figures (for example Figures 2 and 3).
Lines 164 and 168. You don't need to mention the article title.
Line 139. Please rewrite. It looks like you split this study into 2 papers.
Line 298. Rewrite
Line 313: Unnecessary information (Home Depot, Pocatello Ready Mix, ...)...
Line 320: Sieved Portland cement???? It is necessary a particle size distribution to small particle powder.
Line 351: Why was the concrete cast in 3 different types of molds?
Figures 9 and 11: Unnecessary figures for a simple test.
3.1. Line 440: What is the relevance of this information?
Line 445: Why have you started XRD analysis at 20°?
3.2.8. You need to organize the paper better. The information about fly ash in the paper is just mentioned in line 720, but never before. This needs to be in the methodology.
Conclusions: There are a lot of points in the conclusion. Please summarize better.
The international system of units should be used.
Author Response
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Comments 1: [The paper "A Sustainable and Environmentally Friendly Concrete for Structural Applications" presents mechanical results of concretes replaced with precipitated calcium carbonate from sugar beet and recycled concrete aggregates. The paper is extensive, needs to better organize its structures and sections and to reduce unnecessary content. Section 1.3. Is it essential to mention organization names trying to achieve zero carbon emissions? |
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Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have deleted the names of organizations.
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Comments 2: Section 1.4. Line 131-132. This sentence says nothing. Response 2: I have deleted these sentences.
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Comments 3: Section 1.5. The state of the art of the article is somehow too long and with unnecessary reference figures (for example Figures 2 and 3. |
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Response 3: Thank you for pointing this out. I have deleted unnecessary figures.
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Comments 4: Lines 164 and 168. You don't need to mention the article title. |
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Response 4: Thank you for pointing this out. I have deleted these titles.
Comment 5: Line 139. Please rewrite. It looks like you split this study into 2 papers. Response 5: I have rewritten this line. This is the initial phase of the project, which has not been split into 2 papers.
Comment 6: [Line 298. Rewrite] Response 6: I have rewritten this line.
Comment 7: Line 313: Unnecessary information (Home Depot, Pocatello Ready Mix, ...) Response 7: I have deleted unnecessary information.
Comment 8: Line 320: Sieved Portland cement???? It is necessary to have a particle size distribution to small particle powder. Response 8: I have removed the sieve analysis of Portland cement part.
Comment 9: Line 351: Why was the concrete cast in 3 different types of molds? Response 9: There were not enough steel molds to cast more than 15 cylinders per day for the compression test using 4 in. diameter by 8 in. height mold. Additionally, we employed larger 6 in. diameter by 12 in. height cylinders for the split tensile strength test in accordance with ASTM.
Comment 10: Figures 9 and 11: Unnecessary figures for a simple test. Response 10: I have deleted figures 9 and 11.
Comment 11: 3.1. Line 440: What is the relevance of this information? Response 11: Agree, this is not relevant as Dr. Mondal is the co-author of the paper. I have deleted this line.
Comment 12: Line 445: Why have you started XRD analysis at 20°? Response 12: The XRD analysis was initiated at 20 degrees to ensure accurate measurement of diffraction peaks while minimizing interference from baseline drift, amorphous content, and X-ray exposure. Comment 13: You need to organize the paper better. The information about fly ash in the paper is just mentioned in line 720, but never. This needs to be in the methodology. Response 13: I have organized the paper, as per your suggestions.
Comment 14: There are a lot of points in the conclusion. Please summarize better. Response 14: I have summarized the conclusion.
Comment 15: The international system of units should be used. Response 15: I have changed all my units to international system of units.
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Reviewer 3 Report
The article systematically conducts extensive experiments and discusses the replacement rates of Precipitated Calcium Carbonate (PCC) and Upcycled Recycled Concrete Aggregate (Upcycled RCA or UCA) in concrete mixes.
Comment
1. Average 28-Days Compressive Strength of concrete with 20% cement replaced by PCC is less than 4000 psi. Please explain why this is happening? Because its compressive strength differs significantly from that of concrete with 15 per cent and 25 per cent replacement rates.
2. Line 558-575: The article is only objectively analysing the data in the charts and graphs, and needs to further explain the mechanism or reasons for this situation.
3. The whole article reads like a simple experimental report, with too little analysis of the experimental phenomena, and it is recommended that the authors conduct an in-depth analysis of the compressive and tensile strength of concrete.
4. Conclusions need to be simplified.
Author Response
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Comments 1: [Average 28-Days Compressive Strength of concrete with 20% cement replaced by PCC is less than 4000 psi. Please explain why this is happening. Because its compressive strength differs significantly from that of concrete with 15 per cent and 25 per cent replacement rates.]
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Response 1: [The PCC utilized in this study fine sized particles. However, the specific gradation of the fines in each mix was not measured even though they fell within a range based on composite gradation tests. Samples in all three test percentages were taken from the same bucket. Based on observations in the lab and the consistent test results within each mix with strength differences of 50 to 200 psi from average (5123 psi at 15%, 3829 psi at 20% and 5122 psi at 25%), the most reasonable explanation for the compressive strength differences were variations in the percentages of aggregates and fines in the samples tested at 20% PCC replacement. Moreover, the lower strength values in the 20% mix were likely caused by a significantly lower fines content in the samples with 20% PCC when the materials for all three samples were taken for the bucket. ]
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Comments 2: [Line 558-575: The article is only objectively analysing the data in the charts and graphs, and needs to further explain the mechanism or reasons for this situation] |
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Response 2: Most of the data in this paper are presented in the bar graph form for ease of visualization and interpretation of results. In addition, the test results are consistent as illustrated in Comment 1. For example, with a 15% substitution of PCC for cement, the strength values ranged between 5032 and 5239 psi (approximately 4% of the average value). As such the data were not provided in table format.
Comments 3: The whole article reads like a simple experimental report, with too little analysis of the experimental phenomena, and it is recommended that the authors conduct an in-depth analysis of the compressive and tensile strength of concrete.
Response 3: The study is not simply an experimental report. The whole purpose of the study and the paper is to determine whether PCC and/or UCA can be successfully substituted for cement and aggregate in the production of concrete. In addition, the study provided practical guidelines for percentages of PCC/UCA substitution in concrete without compromising its engineering properties. The test results clearly show that the mixes have compressive and tensile strength values that meet the requirements of conventional concrete (4000 psi and 300 psi, respectively) used in design within the percentage limits identified in the paper. Such studies are useful and needed when new materials and methods are incorporated in the concrete industry. Additional work such as freeze-thaw durability tests as recommended by Reviewer I or gradation variability tests on concrete strength need to be performed, but the initial study as given in this paper must be carried out to establish feasibility. Clearly, the results show that PCC and/or UCA substitution for cement and aggregate is feasible and viable in the concrete industry. |
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Comments 4: Conclusions need to be simplified. |
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Response 4: The conclusions have been simplified. |
Reviewer 4 Report
Dear authors
I am sending you my comments in the attached file
Best regards
Comments for author File: 
Comments.pdf
Author Response
A Sustainable and Environmentally Friendly Concrete for 2 Structural Applications
Abstract
The summary is clear and informative, effectively presenting the study's objectives, methods, and key findings. Introduction The introduction provides a broad overview of the problem and objectives of the study. It also outlines the goals and motivations of the research. Furthermore, it conducts a very comprehensive literature review.
Material and methods
Comment 1: The materials and methods are clearly specified. From my point of view, Figure 9 is overly cluttered with arrows and labels. Perhaps simplifying it, considering that these are well-known procedures, would be advisable.
Response 1: Agree, Figure 9 has been simplified.
Results
Comment 1: What are the implications of the XRD results indicating a high concentration of calcite and quartz in the PCC? How does this affect the quality or properties of the PCC?
Response 1. Limestone and quartz are both cementing agents in rocks and soils. Further, Portland cement is a product of calcium carbonate. Since both are present in high concentrations (particularly limestone (CaCO3 in Figure 13) they may help explain the bonding process provided by the PCC in concrete. Further research is needed to address this mechanism.
Discussion
4.1 Environmental Considerations of Study
Comment 2: Could the authors provide more details on the potential environmental benefits of utilizing PCC waste in civil works projects and substituting Portland cement with it? How significant might these benefits be in terms of carbon sequestration and emissions reduction? Concerning the use of chemically treated crushed waste concrete (UCA) as a substitute for fine and coarse aggregate in fresh concrete, what specific environmental impacts are expected to be reduced, and are there any challenges or limitations associated with implementing this approach on a larger scale in construction projects?
Response 2: The use of PCC in concrete will reduce the carbon footprint in three ways: first - PCC contains approximately 9% carbon. PCC containing carbon is usually landfilled and is not bound in the landfill waste. In concrete, the PCC is sequestered in the hardened paste. Second - the production of cement has a large carbon footprint from mining, transport, storage, crushing and finally processing the limestone in a kiln with a corresponding large energy consumption with the discharge of the heated gasses into the atmosphere. A carbon balance sheet has not been developed and presented in this paper, however, based on our work in the cement industry the contrast between the production of cement and the use of PCC is very significant.
Utilization of UCA helps to reduce the environmental impact of landfill and quarry development, both of which are restrained by available sources and government regulation. For example, in the Chicago metropolitan area, no additional quarries for the production of aggregate can be developed. Any new quarries must be located at great distances from the Chicago area where concrete is in demand. Further, available landfill space for the disposal of concrete is very limited. At least one landfill site in south Chicago is at capacity. The use of concrete waste to produce aggregate, although more costly to process than conventional mining at the same location, is a clear benefit for environmentally sensitive land use. The obvious limitation of the use of UCA is availability - available quantities can be limited and tend to fluctuate significantly during the construction season.
4.2 Use of PCC in Concrete
Comment 3: Could the authors provide additional details regarding how substituting up to 30% of cement with PCC in the concrete mix affected other concrete properties beyond compressive strength, such as durability or workability? Given that the flexural strength of PCC-containing concrete falls within an acceptable range in your research, what could be the practical applications of this type of PCC concrete in construction or civil engineering projects? Have any additional advantages in terms of sustainability or cost been identified?
Response 3: Durability tests on PCC and PCC/UCA concrete including freeze-thaw cyclic tests will be conducted during the second phase of the project. At least in the lab, the workability of the concrete with and without PCC is similar. The addition of extra water for fluidity was not needed to mix the concrete and prepare the samples. Clearly, additional testing including tests on larger structures is needed before PCC and UCA are used on civil engineering projects. Our intent is to perform the necessary durability, chloride/ sulfate resistance, permeability and water absorption laboratory tests needed for verification. Based on the results of the present and added lab work, the long-range goal is to build and perform tests on much larger specimens such as precast PCC concrete pipe/slabs at the Idaho State University Engineering Research Lab before these materials are used in actual construction on civil works projects. As yet, sustainability and cost have not been addressed in the present project. Thus far the only material cost for the PCC has been transport from the processing plant to the university - some 110 miles in a university vehicle.
4.5. Comparison between Concrete with PCC and Reduced Cement or Fly Ash in a Concrete
Comment 4: Regarding the substitution of up to 30% of cement with PCC and the possibility of replacing up to 100% of aggregates with UCA, what are the practical and economic considerations that need to be considered when implementing this technology in large-scale construction projects?
Response 4: The main concern for the practical application of PCC and UCA use is the availability of the materials. In our opinion, the tests to date show very promising results on the engineering, construction and environmental sides of the process.
Comment 5: Conclusions The conclusions are appropriate to the study carried out.
Response 5: The authors appreciate your questions and insights - it is very apparent that you have a lot of experience in the new product areas of civil engineering. Thank you.
Comment 6: References The number of references is adequate.
Response 6: Thank you.
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Round 2
Reviewer 2 Report
The paper is improved and can be published as it is.
Reviewer 3 Report
The author answered all questions very well.
