Study on Harmless Treatment and Performance of Phosphogypsum-Based Inorganic Cementing Material
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper developed a harmless phosphogypsum-based inorganic cementing material based on phosphogypsum, cement, quicklime and stabilizer using laboratory testing data of moisture content, maximum dry density, unconfined compression strength, flexural strength, X-ray diffraction analysis, moisture and freezing resistance. In the reviewer’s opinion, the paper is of high quality, well-structured and good writing. The results may be useful for geotechnical community. The reviewer only has minor suggestions for the authors. They are listed below.
1) the reviewer believe that the literature review of the paper can be improved as current introduction did not summarize all the important progress of the problem.
2) the paper should improve the format of the paper. For instance, all the descriptions of the main text starting with “Figure” have a very large indent, which is not correct. On the other hand, it seems that all the figures are not proportional scaling. The authors should check this aspect.
3) the results of the experiments should be compared with other similar studies to highlight the novelty of the paper
4) limitations and future study can be provided.
Author Response
Please refer to the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe review comments are in the attached text. The article has gaps that need to be addressed by the authors. They didn't correlate the results obtained with each other and also with the literature. This aspect needs improvement.
Comments for author File: Comments.pdf
The language needs to be revised in a few points.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript entitled: “Study on Harmless Treatment and Performance of Phosphogypsum-based Inorganic Cementing Material” is nicely written and designed research paper. Some amendments are required, but the paper is of good quality I recommend it to be accepted after major revision, as a suitable for the journal of Infrastructures.
General comments:
• The introduction is too short and does not provide sufficient background. There is not much of the state-of-the-art presented. Especially paragraph starting with “Recycling of phosphogypsum as raw material…” should be expanded.
• The bibliography is limited to one world’s region, and very limited in number of papers cited.
• Language should be checked. The proofreading is necessary.
• Some minor editing errors are present, i.e. capital letters missing, spaces missing, sub and superscripts missing, etc. Editing is inconsistent.
• Quality of figures should be improved.
• Materials are nicely described
• In the “results and discussion” section results are nicely presented, but the part containing “discussion” is missing. It has to be improved.
• Conclusions are supported by results and clearly presented.
Language should be checked. The proofreading is necessary.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThis manuscript addresses the valorization of phosphogypsum (PG), a major industrial by-product, through its transformation into an inorganic cementitious material using chemical and mineral activators. The study claims to achieve a harmless binder suitable for potential construction applications. Substantial revision is needed to meet the standards of an international peer-reviewed journal.
1) The paper does not clearly explain the chemical reactions or physical mechanisms responsible for the harmlessness.
2) Terms such as “Phos-2 PG” and “reaction environment modulator” are used without proper definition.
3) Key details about material compositions (dosages, activators), w/b ratio, cure conditions and sample preparation are missing.
4) Tables lack units, complete chemical descriptions, or references to standard test methods.
5) There is no evidence of long-term performance.
6) Compressive strength results are shown, but no indication of sample size, standard deviation, or statistical analysis is provided.
7) Weak discussion and vague conclusions. The conclusion section is too general and lacks connection to broader implications or potential applications.
8) The references are outdated. Few papers cited are from the last 3 years.
Comments on the Quality of English LanguageLanguage and style require substantial revision. The manuscript includes many nonscientific phrases.
Author Response
This manuscript addresses the valorization of phosphogypsum (PG), a major industrial by-product, through its transformation into an inorganic cementitious material using chemical and mineral activators. The study claims to achieve a harmless binder suitable for potential construction applications. Substantial revision is needed to meet the standards of an international peer-reviewed journal.
Comment 1: The paper does not clearly explain the chemical reactions or physical mechanisms responsible for the harmlessness.
Response：Thanks for your comments. We agree that the reactions should be elaborated in the text. Chemical reactions of “Ca(OH)2+2F−=CaF2↓+2OH−” and “2PO43−+3Ca2+=Ca3(PO4)2↓” can be used to explain the harmless mechanism.
Comment 2: Terms such as “Phos-2 PG” and “reaction environment modulator” are used without proper definition.
Response：Thanks for your comments. We firmly agree that all terms should be specifically defined before employing them in the manuscript. Corresponding revision had been conducted.
Comment 3: Key details about material compositions (dosages, activators), w/b ratio, cure conditions and sample preparation are missing.
Response：Thanks for your comments. Composition information was provided in Table 5 and described in the text. The mass proportion of cement and stabilizer were carefully revised to avoid possible ambiguity. Quicklime, which was marked as the activator, was revised in the text in this revision. w/b ratio, the optimum moisture content of PCIM was also given as Figure 7 showed. The sample preparation process had been briefly summarized in the text as revision. Curing condition had also been added.
Comment 4: Tables lack units, complete chemical descriptions, or references to standard test methods.
Response：Thanks for your comments. Tables in this manuscript had been carefully checked and revised according to your comments.
Comment 5: There is no evidence of long-term performance.
Response：Thanks for your comments. It was thought that 28d unconfined compression strength and free-thaw cycle could be regarded as the long-term performance. More long-term performance would be conducted in the further experiment according to your comments.
Comment 6: Compressive strength results are shown, but no indication of sample size, standard deviation, or statistical analysis is provided.
Response：Thanks for your comments. Sample size had been added in the text. The standard deviation had been calculated and noted in the text to prove that these results were of statistical significance.
Comment 7: Weak discussion and vague conclusions. The conclusion section is too general and lacks connection to broader implications or potential applications.
Response：Thanks for your comments. The discussion and conclusion had been enhanced according to your suggestion. Especially broader implication, for instance, access road, temporary road, affiliated facility and low-grade pavement, was added in the text.
Comment 8: The references are outdated. Few papers cited are from the last 3 years.
Response：Thanks for your comments. Some references were replaced and added from the last 3 years.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors did not address all the questions raised, failed to correlate the results with each other, and not all findings are supported by references from the literature. Additionally, the graphs are difficult to interpret or provide limited information.
Comments for author File: Comments.pdf
Author Response
The authors did not address all the questions raised, failed to correlate the results with each other, and not all findings are supported by references from the literature. Additionally, the graphs are difficult to interpret or provide limited information.
Response: Thanks for your comments. Some corresponding content and references had been added in this paper according to your comment to enhance its level.
- Line181: What is the quantity?
Response: Thanks for your comments. Property of quick lime had been showed in Table 3, and it content in this manuscript was set as 2% to 5% by previously trial and error. Moreover, “Its quantity in phosphogypsum was set from 0% to 2% when discussed its effect on neutralizing and suppression on harmful ion overflow. Then it was set as 2% to 5% when prepare the inorganic cementing material.” had been added in corresponding text.
- Line207: The use of 46 days for UCS was neither explained nor supported by a reference.
Response: Thanks for your comments. This study introduced 46-days curing since it was observed that the strength of PICM keep increasing after 28-days curing. We would like to see how its strength developing after 28 days. It wasn’t a standard experiment parameter due to the present curing time was simply defined as 7-days and 28-days. Therefore, to ensure standardization and avoid misleading, the data and discussion on 46d strength had been deleted.
- Line236: It was requested that Figure 4 be removed, as it depicts a routine laboratory test, and the authors did not specify which part of the procedure would theoretically differ from standard practice.
Response: Thanks for your comments. Corresponding figure had been deleted as requested.
- Line171: What are the references for these percentages?
Response: Thanks for your comments. PICM was a newly introduced materials that mainly based on phosphogypsum (content over 70%) rather than using it as additives. Therefore, there was no detailed references for the percentages of additives for PICM, and all the content was set by trial and error.
- Line180: How were they determined, and how can it be stated that they are optimal?
Response: Thanks for your comments. It was summarized in the following “.2.3. Compaction parameters”, which introduced the determination method of optimal moisture content.
- Line257: “The request was not addressed.”and the initial comment was “Reference for this?”
Response: Thanks for your comments. It was conducted according to “Test Methods of Materials Stabilized with Inorganic Binders for Highway Engineering (JTG E51-2009)”, which was added in the following text. Apart from that, corresponding citation had been added.
- Line274: “The request was not addressed.”and the initial comment was“Porosity tests and air content may also be investigated for their influence on compaction. It is recommended to add.”
Response: Thanks for your comments. As we responsed and explained in former revision. We do agree that addition of porosity tests or air content of PICM in this section will help to further investigate the volumetric performance. However, the maximum dry density presented in figure 7, which was a standard test method, also indicate the compaction level that indirectly reflect its void volume. For instance, density of P+25%C+2%Q were about 0.1g/cm3 higher than that of P+20%C+2%Q, meanwhile the mixture density of P+25%C+2%Q, namely before chemical reaction, was only 0.06g/cm3 than that of P+20%C+2%Q. Hence, it was analyzed that the porosity of PICM was thus reduced due to more addition of cement. Corresponding statement and analysis had been added in the text. Porosity tests and air content characterization would be conducted by some more accurate and intuitive charaterization approach.
- Line288: “The request was not addressed.”and the initial comment was“Is this process standardized or from the literature? Please provide a reference”.
Response: Thanks for your comments. This part Refer to JTG E51-2009. However, this test was a simple verification for PICM material design and its results were not statistical. The method and result discussion were not included in the revised text. What’s more, corresponding citation had been added.
- Line341 and 355: “The request was not addressed.”and the initial comment was“Transfer to the "Materials" section in 2.1.”
Response: Thanks for your comments. Corresponding text and figure had been transferred to the exact position according to your suggestion.
- Line370: “The request was not addressed.”and the initial comment was“And how does it contribute to the other results? Please review the English.”
Response: Thanks for your comments. The linear relationship was a individual finding. But 2% quick lime will increase the pH value of Q-P mixture to about 9, which will benefit the production of ettringite. Corresponding correlation between quick lime and ettringite had been added in the text. Therefore, citation adn statement of “Corresponding pH value was about 9 when 2% quicklime was introduced, at which Q-P mixture was alkaline and positive for production of ettringite [32], which may result in higher density and strength of PICM. Therefore, 2% quicklime, was highly recommended considering its high cost and benefiting for production of ettringite by creating alkaline environment.” had been added in the text to enhance the manuscript.
- Line402: “The request was not addressed.”and the initial comment was“In general, the graphs should be better related to the other preceding graphs and not just explained individually.”
Response: Thanks for your comments. We approve that results should be analyzed together, it had been optimized in the following text. It was analyzed combine with the result of Figure 6. “Maximum dry density of P+25%C+2%Q was about 0.1g/cm3 higher than that of P+20%C+2%Q, considering that theoretical density increase, namely before chemical reac-tion, was only 0.06g/cm3 when 5% more cement was added. It suggested that more ce-ment addition will result in lower porosity of PICM. Similarly, 2% quicklime was detected to increase maximum dry density but reduce optimum moisture content of PICM with cement. It was analyzed that the alkalinity enhancement presented as Figure 6, had promoted the production of ettringite which contributed to higher compactness of PICM.” had been added in thetext.
- Line422: “The request was not addressed.”and the initial comment was“What is the reason for that?”
Response: Thanks for your comments. It was analyzed that the highest maximum dry density of 25% cement and extra stabilizer which perform as a binder, can further enhance PICM’s strength. The reason of “It was analyzed that higher maximum dry density, shown in Figure 8, may lead to higher strength.” Had been added in the text.
- Line484: “The request was not addressed.”and the initial comment was“Unify Figures 12, 13, and 14.”
Response: Thanks for your comments. It had been unified according to your comment as much as we could.
- Line511: “The request was not addressed.”and the initial comment was“Combine these 3 graphs into one.”
Response: Thanks for your comments. It had been unified according to your comment as much as we could.
- Line524: “The request was not addressed.”and the initial comment was“What is the relation to the material? Does it signify an improvement in performance, or are they just observations?”
Response: Thanks for your comments. This paragraph was mainly focusing on verify the pollution level of original phosphogypsum and present the harmless treating effect in this study. Only when harmful ion overflow of phosphogypsum based material was reduced to meet the requirement of environment standard can environmental friendship of PICM be guaranteed. Provided an environmentally security foundation for following characterization. Corresponding explanation of “These results were over the environmental safety upper limit of harmful ion concentration in phosphogypsum overflow solution, suggesting corresponding haemless treatment was required that was thought to be a essential stage before preparing PICM.” and “Environmental friendship of phosphogypsum based material can be thus achieved through addition of quicklime which also provided alkaline environment that was posi-tive for ettringite generation.” had been added in the conclusion section.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript entitled: “Study on Harmless Treatment and Performance of Phosphogypsum-based Inorganic Cementing Material” is nicely written and designed research paper. It has been corrected and supplemented by authors sufficiently and I recommend it to be accepted as a suitable for the journal of Infrastructures.
Author Response
Thanks for your comments. Your affirmation is a great encouragement to us.
Reviewer 4 Report
Comments and Suggestions for AuthorsThe revised manuscript now meets the scientific and editorial standards of Infrastructures and is suitable for publication.
Round 3
Reviewer 2 Report
Comments and Suggestions for AuthorsSeveral requests for changes to the figures and the general text were not addressed. The figures were not consolidated—that is, three separate graphs were not combined into one. The results were not planned in relation to each other, giving the impression that the observed properties are unrelated.
Comments for author File: Comments.pdf
Author Response
Comment 1:Several requests for changes to the figures and the general text were not addressed. The figures were not consolidated—that is, three separate graphs were not combined into one. The results were not planned in relation to each other, giving the impression that the observed properties are unrelated.
Response：Thanks for your comments. The request for the change of the figures had been carefully treated and the three separated figure were combined into one as possible as we can, thank you.
