Six-Year-Old Ecological Concrete in a Marine Environment: A Case Study
Round 1
Reviewer 1 Report
The durability of reinforced concrete structures (RCS) in marine and coastal environments is a major concern. The biocarbonate sedimentary overlay, effective chloride diffusion, carburizing and mineralogical characteristics of ecological concrete submerged in East Mediterranean breakwater for 6 years were analyzed. Overall, there are some shortcomings and modifications are suggested before publication. The modifications are as follows.
1. The rules to select two cores are not clear and strict. How to avoid the influence of error?
2. For Section 2.1, what is the relationship between "shell valves, and shells of sessile gastropods of the Vermetidae family" and "biogenic carbonate deposition"? Is there consistency?
3. For the measuring points mentioned in Section 2.5, it is suggested to give clear figure.
4. The expression "The chloride concentration-to-concrete weight decreased as a function of depth within the antifer" in section 3.2 is unclear.
5. In Section 3.2, it is proposed to supplement the test of the diffusion coefficient of concrete without biological volume.
6. In the editing process of the article, there are formatting errors in lines 172, 179, etc. Please check and correct.
7. Two pictures 5 appear in line 215 and 216. Please check and modify them.
8. It is suggested to supplement the sources and measurement methods of data in Section 3.3.
9. Table 1 in line 261 should be changed to Table 4. Please check and modify it.
10. Lack of detailed analysis of Figure 5 data.
11. More discussions and results are suggested to be added.
Author Response
Thank you for the time and the efforts you invested in my manuscript. We appreciate your effort to improve the quality of our paper. Below are point-to-point responses to your comments. If the corrections are not satisfying, or you find more points for improvement, we will be willing to have a third round.
- The rules to select two cores are not clear and strict. How to avoid the influence of error?
Ans. The paper presents a case study, not controlled research. Hence, we made the best of what we could receive. Submarine core drilling is an expensive procedure. We received two cores as a courtesy of ECOncrete®.
We added a statement in the text to make this limitation clear for the reader, like “Unfortunately, the absence of a control specimen is one of the major drawbacks of a case study, in comparison to designed research. Hence, utilization of an accredited model is suggested” and “Accepting the limitations of an uncontrolled case study and controlled research, which cannot emulate field conditions, is a practical conclusion to support the engineers' decision-making must be made.”
The cost of such an investigation makes the data for biological influence on concrete rare. That makes the publication of the results important for the accumulation of knowledge base in the literature, for the investigators to come.
- For Section 2.1, what is the relationship between "shell valves, and shells of sessile gastropods of the Vermetidae family" and "biogenic carbonate deposition"? Is there consistency?
Ans. For clarity, the sentence was rephrased to:
"Several distinct surfaces can be detected: a concrete surface (with a reddish tan due to algae), biogenic carbonate deposition which consist of shell valves, and shells of sessile gastropods of various sizes apparently belonging to the Vermetidae family [18]"
- For the measuring points mentioned in Section 2.5, it is suggested to give clear figure.
Ans. For clarity, the following sentence was added: The measurement points were evenly distributed along the face, excluding 1 cm from each corner.
- The expression "The chloride concentration-to-concrete weight decreased as a function of depth within the antifer" in section 3.2 is unclear.
Ans. For clarity the sentence was rephrased to: “The chloride concentration (gr Cl- to Kg concrete) decreased as a function of depth from the concrete surface within the antifer (Figure 5).”
- In Section 3.2, it is proposed to supplement the test of the diffusion coefficient of concrete without biological volume.
Ans. That is right. This is again part of the limitation of a case study. We do not have control. We rephrased it to make it clearer. “Unfortunately, the absence of a control specimen is one of the major drawbacks of a case study, in comparison to designed research. Hence, utilization of an accredited model is suggested. LIFE-365 [1] model was selected for estimation of Deff value.
- In the editing process of the article, there are formatting errors in lines 172, 179, etc. Please check and correct.
Ans. It appears that something went interfered when the article was processed to PDF. In the Word original the format is fine. If the problem persists, it will be addressed by the technical editor.
- Two pictures 5 appear in line 215 and 216. Please check and modify them.
Ans. It seems that something went interfered when the article was processed to PDF. In the Word original the numbering is correct as to Table 4 (comment 9)
- It is suggested to supplement the sources and measurement methods of data in Section 3.3.
Ans. The methods are described in section 2.5. We added the following sentence for clarification: " A caliper was used for the measurement. The measurement points were evenly distributed along the face, excluding 1 cm from each corner.”
- Table 1 in line 261 should be changed to Table 4. Please check and modify it.
Ans. It seems that there is a problem with the PDF creation. We will recheck the resubmission, but if the problem persists, it will be addressed by the technical editor.
- Lack of detailed analysis of Figure 5 data.
Ans. The results of the analysis are presented in Table 2. For clarity, a cross-reference to Figure 5. was entered into Table 2.; and cross-references to eq. (2) and Table 2 were entered into the Figure 5. caption.
- More discussions and results are suggested to be added.
Ans. The discussion was slightly widened where we found that to be appropriate. The number of published works on the topic is very limited, so comparison to the literature is limited.
Reviewer 2 Report
Comments for author File: 
Comments.pdf
Author Response
Thank you for the time and effort you invested in my manuscript. We appreciate your effort to improve the quality of our paper. Below are point-to-point responses to your comments. If the corrections are satisfying, or you find more points for improvement, we will be willing to have a third round.
(1) The introduction part is lack of organization, and does not express the research significance from simple to deep. The main objective is to research the influence of marine organisms on the durability of concrete, including concrete carbonization, chloride corrosion and sulfate corrosion. However, the research background for these three aspects of OC, and the interaction between chloride penetration and carbonization, or between chloride penetration sulfate corrosion was not clearly introduced, before line 77.
Ans. This paragraph was separated into two paragraphs. The first discusses the carbonation and the second the sulfate attack.
(2) Check the reference mistake in line 109. line 172, line 179, line 199.
Ans. Reviewer 1 also found several reference problems. However, the problems do not occur in the word file. It seems like a technical problem in the conversion to PDF. If the problem persists, we will have to address it with the technical editor.
(3) What’s the definition of ecological concrete? What’s the main differences? What’s the general mechanical properties, like splitting tensile strength and compressive strength of the concrete?
Ans. An explanation was added to the paragraph introducing ecological concrete.
(4) The detailed test methods and test contents was introduced in the last paragraph of Introduction part, which is suggested to move to the part 2 Materials and Methods.
Ans. This data is indeed repeated in the methods. It is common to have a short overview of the procedure in the introduction immediately after the aims. We left the general information in the introduction section and deleted from it the more specific information, which appears in the methods.
(5) As explained in section 3.3, line 223, there is no carbonation when the specimen in the seawater, the carbonation 953days after drilling has no connection with the marine organisms. What’s the necessity of this part?
Ans. Some engineers in the design of the Thames sea-wall project were concerned about carbonization, due to carbon dioxide emission from the organism's metabolism. Hence, even though the carbonation data itself does not have a high scientific value, it has value in reducing the engineering community’s objection to the introduction of new material.
(6) In Section 3.4, it is not convincing to determine that the marine concrete is not subject to sulfate corrosion only from the XRD test results.
Ans. Sulfate attack products are ettringite and thaumasite. Both are crystalline minerals, which can be detected by XRD. Ettringite (and monosulfate) is a product of C3A. Neither was detected in XRD, so there is no reactant for this attack and no products that testify to this attack. Thaumasite appears in the literature only with ettringite. Thaumasite forms only at low temperatures (5–15 °C) and in carbonated concrete. So, it is irrelevant to the specific environment of this study. Hence, while we cannot offer proof we may assume that it will not form in the specific concrete.
(7) There is no test results of Ordinary concrete. How did you get your last conclusion? “During coastal development, ecological concrete should be considered, as it has ecological and long-term performance benefits as compared to ordinary concrete.”
Ans. The LIFE-365 [1] model was selected for estimation of the Deff value for ordinary concrete. The limitation of no control was addressed. “The conclusions were edited to be more accurate: “Evidence for improved durability of the ecological concrete versus ordinary con-crete was found, including reduction of chloride ingress, reduction of carbonation rate, and absence of sulfate attack products.”
Reviewer 3 Report
This manuscript may be accepted with major regulations. The subject is original but the presentation is not very effective. The 2nd revision still contains deficiencies.
It can be accepted after significant changes.
Major Offers:
1. SEM photographs should be added to examine the changes in the pore size distribution of the surface layer.
2. More detailed information can be given about the semi-Rietveld analysis its quantity in Table 4 and the results can be provided to support each other by applying the experimental
method.
3. Abstract should be improved.
4. If the mechanical test is added, the manuscript will be richer.
Typos
Lines 159-165 have exponent errors and line space mismatch.Kg/m3 should be kg/m3
bc[BK1] ?…..[BK2] ? (line 146)
min-1. (Line 169)
Is I v4.2.44.0 correct(Line 172)
(Figure 5Error! Reference source not found.) (Line 191)
SO4 -2 (Line 283)
[BK3] ? (Line 204)
Table 2.Figure 5, eq. (2) there is a comma error in the spellingDeff
eq.1 not found
Author Response
We thank you for the time you spent reviewing our paper. Hereafter are point to point responds for your comments
Comment: SEM photographs should be added to examine the changes in the pore size distribution of the surface layer.
Answer: I agree with that. Unfortunately taking such images will postpone the revision for several months (the author's physical condition does not allow it). However the references site a work that made such images, which show coverage of the concrete by a non-porous calcareous layer, with no change to the substrate.
Comment: More detailed information can be given about the semi-Rietveld analysis its quantity in Table 4 and the results can be provided to support each other by applying the experimental method.
Answer: I'm not sure that I correctly understood your comment. We added more details in lines 290-294. Do you mean creating an artificial mix of the proposed mineral to verify that the method accurately measures them?
Comment: Abstract should be improved.
Answer: Some editing was done. A more specific comment will be appreciated.
Comment: If the mechanical test is added, the manuscript will be richer.
Answer: We added a mechanical test. This was the main cause of the revision delay. Shimrit Perkol-Finkel was tragically killed in an accident a couple of years ago. Her co-worker had to locate the remaining cores. The original compressive strength results have not been located. Hence we used the data from an internal report.
Comment: Typos
Lines 159-165 have exponent errors and line space mismatch.Kg/m3 should be kg/m3
bc[BK1] ?…..[BK2] ? (line 146)
min-1. (Line 169)
Is I v4.2.44.0 correct(Line 172)
(Figure 5Error! Reference source not found.) (Line 191)
SO4 -2 (Line 283)
[BK3] ? (Line 204)
Table 2.Figure 5, eq. (2) there is a comma error in the spellingDeff
eq.1 not found
Answer: corrected
Reviewer 4 Report
The authors have carried out an experimental study pertains to six-year-old ecological concrete behavior in a marine environment. The results are interesting, though as a case study have limitation pertains to absence of the control sample. The comments of this reviwer is as under:
· What is the chloride ion penetration depth in the ecological concrete after six years of exposure to a marine environment, and how does this compare to traditional concrete?
· Line 191: Error reference source not found? Correct!
· Based on the conducted study, what are the limitations and challenges associated with the use of ecological concrete in marine structures, and how can these be addressed to romote wider adoption of this technology?
· What is the microstructure of the ecological concrete after six years of exposure to a marine environment, and how does it differ from traditional concrete in terms of pore size distribution, porosity, and other factors?
· Does authors consider the compressive strength which is critically important considering the long-term behavior of the ecological concrete.
There are many grammatical mistakes. Please pay attention to it!
Author Response
We thank you for the time you spent reviewing our paper. Hereafter are point to point responds for your comments
Comment: What is the chloride ion penetration depth in the ecological concrete after six years of exposure to a marine environment, and how does this compare to traditional concrete?
Answer: There are no definitions for chloride ion penetration depth and traditional concrete. The acceptable concentration at rebar depth should be selected at the design stage, taking into account: confidence, type of reinforcement, and usage of inhibitors. The diffusion model enables calculating required concrete coverage, taking into account all the above and concrete properties. The properties of equivalent concrete without biological coverage were calculated using an accepted model for comparison. This is explained from line 245 to line 267. If editing for more clarity is needed, please inform us.
"Our next question was: is this diffusion coefficient value the same as that in concrete with no biogenic cover, or does the coverage decrease the chloride diffusion? Unfortunately, the absence of a control specimen is one of the major drawbacks of a case study, in comparison to designed research. Hence, the utilization of an accredited model is suggested. LIFE-365 [25] model was selected for the estimation of the Deff value. Deff was calculated according to the assumptions in LIFE-365 [25] … …This simulation allows the estimation of the diffusion coefficient after different periods. The resulting Deff after 28 days and 6 years under an assumption of a fixed temperature of 20⁰C is shown in Table 3. The expected Deff for this ecological concrete formed mainly from slags is 1.12·10-12 m2/s after 6 years. The experimental value obtained (7.5·10-13 m2/s) was 67% of this value, indicating that the diffusion coefficient had decreased due to biogenic carbonate coverage that was estimated to be close to 60% by optic means. It is interesting to note that a similar trend appeared in the research of Kawabata et al., where a diffusion coefficient of 1.68·10-12 m2/sec was found in concrete with no organisms on it, while specimens with about 50% coverage of organ-isms had 30-60% of this value, i.e. 5.04·10-13 to 1.01·10-12 m2/sec [26]. Accepting the limitations of an uncontrolled case study and controlled research, which cannot emulate field conditions, a practical conclusion to support engineers' decision-making must be made. All evidence supports the postulation that a biological settlement on marine con-crete improves its resistance to chloride ingress."
Comment: Line 191: Error reference source not found? Correct!
Answer: It seems that there was some problem with the document conversion to PDF. All internal cross-references were redone to fix it.
Comment: Based on the conducted study, what are the limitations and challenges associated with the use of ecological concrete in marine structures, and how can these be addressed to romote wider adoption of this technology?
Answer: We edited the conclusion to answer this question. Please note that we have to be very careful not to claim things that are not backed by evidence. The most important thing is that engineers do not have to worry about long-term underperformance relative to conventional concrete. Such worries were raised by several engineers in European coastal projects.
Comment: What is the microstructure of the ecological concrete after six years of exposure to a marine environment, and how does it differ from traditional concrete in terms of pore size distribution, porosity, and other factors?
Answer: This research is unfounded. Hence measures were based on "favors" and limited to accessible equipment. Pore size distribution was not measured.
Comment: Does authors consider the compressive strength which is critically important considering the long-term behavior of the ecological concrete.
Answer: We added a mechanical test. This was the main cause of the revision delay. Shimrit Perkol-Finkel was tragically killed in an accident a couple of years ago. Her co-worker had to locate the remaining cores. The original compressive strength results have not been located. Hence we used the data from an internal report.
Comment: There are many grammatical mistakes. Please pay attention to it!
Answer: We apologize for the mistakes. Hopefully, all of them are corrected.
Reviewer 5 Report
In this paper, the durability of ecological concrete in the Marine environment is studied. The research results are quite beneficial to engineering applications. However, there are some suggestions in this manuscript needed to be considered as follows.
1. In the introduction, the author should point out the significance or value of undertaking the research.
2. For some important test equipment used in the test, it is recommended to add their photos.
3. The introduction of sand fineness modulus is missing in the manuscript, so it is suggested to add.
4. XRD is usually used for qualitative analysis of substances, but there will be a large error when it is used for semi-quantitative analysis. In view of this problem, how do the authors consider it.
5. In section 3.2 on page 6, there is a corresponding text error. Please check the full text carefully.
6. In the conclusion section, it is suggested to add a paragraph summary before stating the conclusion point by point.
Author Response
We thank you for the time you spent reviewing our paper. Hereafter are point to point responds for your comments
Comment: In the introduction, the author should point out the significance or value of undertaking the research.
Answer: a paragraph was added from lines 114-119 :
" Answering the questions above is significant for the coastal engineering community. Engineers are reluctant to adopt new materials and methods, for very high-budget projects that are often designed for a service life of 70 years and more in an aggressive environment. Thus, this research comes to reduce the gap in knowledge regarding the long-run performance of the ecological concrete as is in a standing marine structure. The research focused on the abovementioned durability indicators."
Comment: For some important test equipment used in the test, it is recommended to add their photos.
Answer: as a reader and reviewer, I don't like equipment photos, unless it is a specific non-commercial equipment built or changed for the experiment. All the equipment, in this case, is standard, so I don’t see what will it contribute to the reader.
Comment: The introduction of sand fineness modulus is missing in the manuscript, so it is suggested to add.
Answer: the concrete was cast many years ago by a commercial provider. We cannot locate this data.
Comment: XRD is usually used for qualitative analysis of substances, but there will be a large error when it is used for semi-quantitative analysis. In view of this problem, how do the authors consider it.
Answer: the importance of the XRD are not the quantities found but the things that were not found: tri-calcium-aluminate hydrate, ettringite, and Thaumasite. These indicate susceptibility and the product to sulfate attack. See paragraph starting at line 296:
" Ettringite and thaumisite, two common sulfate-containing minerals in concrete, were not detected by XRD, indicating that sulfates did not incorporate into the crystalline structures. This is even though the Mediterranean Sea contains 1,920-3,840 ppm SO42- [27], while at the depth of 0.5 meters, a concentration of 2,880 ppm was measured [28]. The absence of these phases probably results from the absence of C3A hydrates in the hydrated cement of the ecological concrete. Thaumasite appears only with ettringite and forms only at low temperatures (5–15 °C) [11]. So, it is expected to form in the specific environment of this study. Hence, we may assume that it will not form in the ecological concrete, due to the absence of C3A; but to support this assumption, specimens from colder climates are needed. Another sulfate-containing crystal, gypsum, was detected in low concentrations. It is not clear whether the sulfates were part of the original concrete mix, or penetrated later and reacted with calcium hydroxide from the cement paste to form the gypsum. If the sulfate came from the seawater, a concentration drop with depth is expected, as the results indeed show. This drop can have two explanations: (1) lower sulfate diffusion into the concrete dipper from its surface; (2) reduction of the sulfate on the concrete surface by sulfate-reducing bacteria which develop as a biofilm on the concrete surface. Such a bacteria may hinder the ingress of additional sulfates as can be seen in sediments, where the sulfate concentration decreases with depth [27]. These explanations are speculative and should be investigated experimentally."
Comment: In section 3.2 on page 6, there is a corresponding text error. Please check the full text carefully.
Answer: It seems that there was some problem with the document conversion to PDF. All internal cross-references were redone to fix it.
Comment: In the conclusion section, it is suggested to add a paragraph summary before stating the conclusion point by point.
Answer: The following paragraph was added:
" Coastal engineers' concern about the introduction of new construction material, eco-logical concrete can be diminished. All examinations of the concrete specimens found that there is no deterioration of the ecological concrete performance for its first six years of exposure. There is no evidence for concern for longer-term exposure. The specific findings are summarized below."
Round 2
Reviewer 3 Report
SEM photographs were not included in the manuscript.
More detailed information can be given about the semi-Rietveld analysis its quantity in Table 4 and the results can be provided to support each other by applying the experimental method.
Author Response
Dear reviewer,
My medical condition will not enable me to prepare SEM images before October. Since such images are local, they cannot add more information except to confirm the carbonate deposition is sealing the concrete surface. For this, we prefer submitting the paper as is and not delaying it more.
Regarding your comment on the XRD, it is not clear what you mean by "applying the experimental method". As we used commercial software for semi-Rietveld analysis, we do not find it necessary to add more information regarding its algorithm. Can you be more specific regarding this comment?
Reviewer 4 Report
The authors have addressed my comments the manuscript is acceptable for publication.
Author Response
Thank you for your contribution
Reviewer 5 Report
作者修改了手稿。它可以发布。
Author Response
Thank you for your contribution
