Decontamination-Sludge-Induced Corrosion of Steel in Simulated Pore Solutions and Alkali-Activated Slag Pastes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.    The abstract and introduction sections need rewriting/modifying to be more concise.

2.    I recommend modifying (some) subheadings to enhance readability, make the content more accessible to the audience, and improve clarity.

3.    Please clarify all abbreviations when they first appear.

4.    The FTIR spectrum data in Figure 2 has been clearly presented in the narrative. Therefore, I suggest that the authors eliminate Table 2.

 

5.    I recommend that the authors reorganize the manuscript to enhance clarity and understand the experimental design and results, especially materials and testing methods (section 2).

Comments on the Quality of English Language

The English could be improved to express the research more clearly.

Author Response

The authors appreciate the reviewer's suggestions and trust that their implementation will improve the quality of the manuscript. Responses to suggestions and corresponding modifications to the manuscript are given below:

 

Reviewer 1

 

Comments and Suggestions for Authors

1. The abstract and introduction sections need rewriting/modifying to be more concise.

The authors agree with the comment and the abstract and introduction sections have been modified to be more concise and clearer, highlighting the objective, novelty, and specific research gap of the study.

 

2. I recommend modifying (some) subheadings to enhance readability, make the content more accessible to the audience, and improve clarity.

The authors have taken this recommendation into account and new subheadings have been added and others modified to improve the readability and clarity of the manuscript.

 

3. Please clarify all abbreviations when they first appear.

All abbreviations have been clarified once they appear in the manuscript.

 

4. The FTIR spectrum data in Figure 2 has been clearly presented in the narrative. Therefore, I suggest that the authors eliminate Table 2.

The authors agree with the comment and they have deleted Table 2.

 

5. I recommend that the authors reorganize the manuscript to enhance clarity and understand the experimental design and results, especially materials and testing methods (section 2).

The authors have taken this recommendation into account and a new paragraph has been added in the subsection 2.3. and a research diagram has been incorporated to enhance the clarity and understanding of section 2.

 

First, a study of the corrosion of steel sheets in contact with synthetic pore solutions or embedded in cement pastes was carried out using electrochemical techniques, such as corrosion potential analysis, current density, and electrochemical impedance spectros-copy. Subsequently, the surface of the steel was evaluated via visual inspection, bifocal microscopy, and Raman spectroscopy, depending on the type of starting material. Fi-nally, the cement pastes with the wastes were characterised to determine the effect of the sludge on their mineralogy and microstructure. The research diagram used is shown in Figure 3a.

 

Figure 3. (a) Research diagram and electrochemical testing setups (b) in simulated cement pore solutions and (c) in cementitious pastes.

 

Comments on the Quality of English Language

The English could be improved to express the research more clearly.

The manuscript has been revised by a professional to improve it.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript by Criado et al., attempts to investigate the decontamination sludge-induced corrosion of steel using simulated pore solutions and alkali-activated slag pastes. The study is scientifically sound and the manuscript is generally well written. In my opinion, the article is a good fit for the journal of CMD. However there are some minor to moderate points that need clarification to enhance the quality of the submitted paper.

 

Abstract:

- The Abstract does not provide a concise summary and would need to be reviewed. It is not sharp and includes some unnecessary details. Tangible results are also needed herein.

 

Keywords:

Please avoid duplication of words given in the title. The key words of the paper should not contain any words already in the title, but can include abbreviated terms or location information not suitable for the title.

 

Introduction:

- One of the major concerns is the lack of novelty/originality in this research work. I understand that authors have used a robust approach, however it gives the impression of a well-written and well-structured report and well-written report rather than a research work. As the concept of decontamination through alkali-activation has matured over the years, the authors are suggested to explicate the novelty of this research work.

- A clear and detailed identification of the main objectives will improve the readability of the manuscript. Objectives should be provided at the end of this section rather than in the middle (L.59)

- In the introduction section a more detailed review of existing studies is a must. In general, very few references are provided in this section which underestimates the whole work. For example, only 2 refs up to L.85.

 

Materials and methods:

L.117. Please rewrite “it is borne in mind”.

Where the steel plates were originated? How were analysed in terms of elements composition?

Sections 2.1 and 2.2. are lacking protocols/methodology followed. This will enhance the data reproducibility of the already well-carried out work.

Figure 2. There is no information regarding the peaks shown at the FTIR spectrum of the decontamination sludge below 1000 cm-1 i.e. inorganic compounds.

L.241. DRX? Do you mean XRD? Otherwise the authors should provide details on this technique?  

2.3.3. This section is written in several different font types and sizes. Please maintain uniformity.

Figures. Please use bigger fonts/titles and use appropriate captions. A detailed legend should be included with every figure and thus make it stand-alone. Do the same for the rest figures provided in this manuscript.

 

Results and discussion:

- There are 2 main properties of alkali activated material which are critical because its own nature and minor information is given: workability (and setting time) and shrinkage. I suggest to include some paragraph for discussing this because the applicability of the binder will very much depend in these properties.

- Section 3.3. The images are of very low resolution (e.g. Figure 11). Please use SEM images otherwise higher magnification to support the statements made in this sections.

 

Conclusions:

Conclusions should be compact text rather than bullet points. In addition, the conclusions lack original results and specifics for the advances made in the understanding compared to literature.

 

Author Response

The authors appreciate the reviewer's suggestions and trust that their implementation will improve the quality of the manuscript. Responses to suggestions and corresponding modifications to the manuscript are given below:

 

Reviewer 2

Comments and Suggestions for Authors

The manuscript by Criado et al., attempts to investigate the decontamination sludge-induced corrosion of steel using simulated pore solutions and alkali-activated slag pastes. The study is scientifically sound and the manuscript is generally well written. In my opinion, the article is a good fit for the journal of CMD. However there are some minor to moderate points that need clarification to enhance the quality of the submitted paper.

 Abstract:

- The Abstract does not provide a concise summary and would need to be reviewed. It is not sharp and includes some unnecessary details. Tangible results are also needed herein.

 R: The authors agree with the comment and the abstract section has been modified and shortened to be more concise and clearer.

In most countries, low- and intermediate-level wastes (LILWs) are cemented in carbon steel drums for later disposal. The durability of waste packages is determined by the chemical environment generated by both cement-based engineered barrier systems and the aggressive species present in the waste. Decontamination sludges are challenging wastes that are currently not accepted for final disposal due to their acidic nature and high concentrations of organic species and complexants. Thus, it was proposed to use electrochemical measurements to study the corrosion of steel sheets, simulating drums embedded in new alkali-activated slag (AAS) formulations with surrogate decontamination liquids, and determine their viability for use as confining matrices in order to increase the service life of the drumsThe carbon steel coupon embedded in the Portland cement reference (R-L) paste showed the best corrosion resistance, followed by that of steel embedded in sodium silicate-activated slag (BFS-S-L) paste. This behaviour may be related to an improvement in the protective nature of the surface film. However, in sodium carbonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix seemed to be more intense, leading to a pH decrease in the paste porewater, an effect that could hinder the formation of a passive layer on the surface of the carbon steel. Under such conditions, the initiation of the corrosion process seems to be favoured, resulting in the formation of a non-protective scale consisting mainly of hematite.

Keywords:

Please avoid duplication of words given in the title. The key words of the paper should not contain any words already in the title, but can include abbreviated terms or location information not suitable for the title.

R: The keywords have been modified in the light of these assessments.

 radioactive waste; sludge; simulated pore solution; AAS; corrosion waste packages; electrochemical measurements; Raman spectroscopy

Introduction:

- One of the major concerns is the lack of novelty/originality in this research work. I understand that authors have used a robust approach, however it gives the impression of a well-written and well-structured report and well-written report rather than a research work. As the concept of decontamination through alkali-activation has matured over the years, the authors are suggested to explicate the novelty of this research work.

R: The authors have taken this recommendation into account and the introduction section has been modified to highlight the objective, novelty, and specific research gap of the study.

- A clear and detailed identification of the main objectives will improve the readability of the manuscript. Objectives should be provided at the end of this section rather than in the middle (L.59)

R: The authors appreciate this suggestion and a final paragraph in the introduction has been added with the objectives.

Thus, this work aimed to develop a new alkali-activated formulation to immobilise a surrogate (an acidic/ organic-based) decontamination sludge with adequate compres-sive strength and suitable for disposal in NSDF, providing an environment that delays the corrosion of the containers and extends their service life. To address this objective, the study of the corrosion process was proposed using carbon steel sheets simulating real drums, previously in direct contact with the synthetic cementitious pore solutions, to verify that corrosion occurred; and subsequently embedded in Portland cement and alkali-activated slags pastes by means of electrochemical techniques to see which of them offered greater resistance to corrosion and select the most suitable cementitious matrix.

- In the introduction section a more detailed review of existing studies is a must. In general, very few references are provided in this section which underestimates the whole work. For example, only 2 refs up to L.85.

 R: A new paragraph has been included with the advances in using AAS formulations for sludge immobilization, for example, dredged and sewage sludges. There are no previous results regarding the immobilisation of decontamination sludge in this type of alkaline cements. New references have been included, references 3 and 4.

In previous studies 12–14, AAMs were proposed to be used for the stabilisa-tion/solidification of different types of sludge, such as dredged or sewage sludge. Kozaie et al.14 observed that AAMs exhibited better performance for sewage sludge ash contaminated via radiocesium encapsulation than OPC formulations, showing higher mechanical strength and lower levels of Cs leaching.

Materials and methods:

L.117. Please rewrite “it is borne in mind”.

R: The sentence has been rewritten.

Initially, it took into account that LILWs from nuclear power plants are usually cemented in carbon steel drums.

Where the steel plates were originated? How were analysed in terms of elements composition?

R: The carbon steel plates were supplied by Microtorrejon company and the elements' composition was provided by this company. The information about the origin of the steel plates has been added to the manuscript.

Therefore, carbon steel plates were chosen to simulate the real drums. They were provided by Microtorrejon company.

Sections 2.1 and 2.2. are lacking protocols/methodology followed. This will enhance the data reproducibility of the already well-carried out work.

R: Thank you for your comment, the authors have been reviewing sections 2.1 and 2.2 and they consider that the methodology described can be reproduced by other researchers in their humble opinion.

Figure 2. There is no information regarding the peaks shown at the FTIR spectrum of the decontamination sludge below 1000 cm-1 i.e. inorganic compounds.

R: The authors are grateful for this suggestion, but the main components of the sludge are organic compounds and their representative vibrations appear above 1000 cm-1. The rest of the bands do not allow the identification of this type of components and for this reason, they are not considered.

L.241. DRX? Do you mean XRD? Otherwise the authors should provide details on this technique?  

R: The mean of XRD has been included. Information about this technique is provided: X-ray diffraction (XRD) was conducted on a diffractometer (D8 Advance instrument, Bruker) with Cu-Kα1,2 radiations (1.5406 Å and 1.5444 Å), no monochromator, a goniometer radius of 217.5 mm, and a nickel filter. The X-ray tube worked at 40 kV and 30 mA. The settings were as follows: variable 6-mm divergence slit (hydrated pastes); 2θ angle 5–70°; step time, 0.5 seconds; step size, 0.02°. The software used for the analysis of the XRD diffractograms was DIFRAC.EVA, using the free crystallographic database Crystallography Open Database (COD).

2.3.3. This section is written in several different font types and sizes. Please maintain uniformity.

R: The font type and size of this section have been modified.

Figures. Please use bigger fonts/titles and use appropriate captions. A detailed legend should be included with every figure and thus make it stand-alone. Do the same for the rest figures provided in this manuscript.

 R: Figure fonts are the size required by the journal. Figure captions have been revised and enlarged where necessary.

Results and discussion:

- There are 2 main properties of alkali activated material which are critical because its own nature and minor information is given: workability (and setting time) and shrinkage. I suggest to include some paragraph for discussing this because the applicability of the binder will very much depend in these properties.

R: The authors agree with the comment and a paragraph about the characteristics of the fresh and hardened has been included in subsection 2.2. Moreover, they want to inform you that a research manuscript has already been written about it and it is going to be submitted to a journal soon.

The presence of decontamination sludge increased the flowability and setting time in the R-L, BFS-C-L and BFS-SL samples, with BFS-C-L having the highest values for both parameters. The hydration and activation reactions were delayed due to the more acidic initial medium from which the samples started due to the presence of the waste. Their presence also reduced the mechanical strength and increased the total porosity of all formulations, resulting in higher strengths and lower porosities for the AAS.

- Section 3.3. The images are of very low resolution (e.g. Figure 11). Please use SEM images otherwise higher magnification to support the statements made in this sections.

 R: The images done with the bifocal microscope showed the surface of steel and the corrosion products have good resolution, and Raman spectroscopy helped to identify the nature of corrosion products. The authors, in their humble opinion, believe that it is not necessary to use SEM images.

Conclusions:

Conclusions should be compact text rather than bullet points. In addition, the conclusions lack original results and specifics for the advances made in the understanding compared to literature.

R: The conclusions have been rewritten concerning the set goals and as compact text.

The study of the corrosion of the steel in simulated Portland cement reference (R-L) and alkali-activated slag waste pore solutions verified that corrosion occurred, wherein the Ecorr and icorr values measured for carbon steel indicated that it was in an active state due to the very low pH of the solutions that accelerated the corrosion process. There was also a great decrease in mass, as indicated by the decrease in the thickness of the carbon steel sheet, causing the steel to break in the AAC pore solution.

On the other hand, in the cementitious pastes, carbon steel coupons embedded in the R-L paste showed the best corrosion resistance, followed by those embedded in the sodium silicate-activated slag (BFS-S-L) paste. This fact seems to be related to an improvement in the protective nature of the surface film. However, in the sodium carbonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix was more significant, resulting in a decrease in porewater pH. This pH decrease could prevent the formation of a passive layer on the surface of the carbon steel and encourage the initiation of the corrosion process. The EIS measurements confirmed that corrosion was more intense in the BFS-C-L paste matrix and tended to increase over time, and the images of the carbon steel sheets after their extraction from this matrix showed small deposits of corrosion products, particularly hematite. Therefore, this matrix offered the lowest corrosion resistance and should not be used for sludge immobilisation.

Finally, the sludge in the R-L sample did not seem to affect the formation of the reaction products while inhibiting the formation of hydrotalcite in the alkali-activated slag pastes. Its acidic nature results in a decrease in pore-water pH, favouring the initiation of the corrosion process in the BFS-C-L paste.

Reviewer 3 Report

Comments and Suggestions for Authors

1) The manuscript must be entirely revised by a professional to improve the reading, correct typos and revise technical terms.

 

2) The statement of the significance of the study in the abstract is not clear enough. Please emphasize the application scope of the research.

 

3) Introduction, the research gap must be clearly indentified.

 

 

4) Introductoin, what's the novelty of this work?

 

 

5) In the introduction, please add references to the literature in the appropriate places.

 

6) In Fig. 3 a and b please add the research diagram.

 

7) Please emphasize more clearly what the aim of the research and the article was and in the conclusions present whether these aims were achieved

 

8) It seems that after the first tests which found corrosion of steel caused by low pH, further tests were unnecessary, but perhaps I misread the author's intentions. Please provide clear justification for further research.

 

9) Please comment and clearly present your conclusions in relation to the set goals.

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The manuscript must be entirely revised by a professional to improve the reading, correct typos and revise technical terms.

Author Response

The authors appreciate the reviewer's suggestions and trust that their implementation will improve the quality of the manuscript. Responses to suggestions and corresponding modifications to the manuscript are given below:

 

Reviewer 3

Comments and Suggestions for Authors

1) The manuscript must be entirely revised by a professional to improve the reading, correct typos and revise technical terms.

R: The manuscript has been revised by a professional to improve it.

 

2) The statement of the significance of the study in the abstract is not clear enough. Please emphasize the application scope of the research.

R: The authors agree with the comment and the abstract section has been modified and shortened to be more concise and clearer.

In most countries, low- and intermediate-level wastes (LILWs) are cemented in carbon steel drums for later disposal. The durability of waste packages is determined by the chemical environment generated by both cement-based engineered barrier systems and the aggressive species present in the waste. Decontamination sludges are challenging wastes that are currently not accepted for final disposal due to their acidic nature and high concentrations of organic species and complexants. Thus, it was proposed to use electrochemical measurements to study the corrosion of steel sheets, simulating drums embedded in new alkali-activated slag (AAS) formulations with surrogate decontamination liquids, and determine their viability for use as confining matrices in order to increase the service life of the drumsThe carbon steel coupon embedded in the Portland cement reference (R-L) paste showed the best corrosion resistance, followed by that of steel embedded in sodium silicate-activated slag (BFS-S-L) paste. This behaviour may be related to an improvement in the protective nature of the surface film. However, in sodium carbonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix seemed to be more intense, leading to a pH decrease in the paste porewater, an effect that could hinder the formation of a passive layer on the surface of the carbon steel. Under such conditions, the initiation of the corrosion process seems to be favoured, resulting in the formation of a non-protective scale consisting mainly of hematite.

 

3) Introduction, the research gap must be clearly indentified.

R: The authors have taken this recommendation into account and the introduction section has been modified to highlight the objective, novelty, and specific research gap of the study.

 

4) Introductoin, what's the novelty of this work?

R: The authors have taken this recommendation into account and the introduction section has been modified to highlight the objective, novelty, and specific research gap of the study.

 

5) In the introduction, please add references to the literature in the appropriate places.

R: The references to the literature in the introduction have been moved to the appropriate places and new references have also been included.

 

6) In Fig. 3 a and b please add the research diagram.

R: The authors agree with the comment and the research diagram has been included in Figure 3.

 

 

Figure 3. (a) Research diagram and electrochemical testing setups (b) in simulated cement pore solutions and (c) in cementitious pastes.

 

7) Please emphasize more clearly what the aim of the research and the article was and in the conclusions present whether these aims were achieved

R: The authors appreciate this suggestion, the aim of the research and the article were incorporated as previously they have explained and the conclusions have been modified to explain which of the cementitious pastes can be used as a confining matrix for the immobilisation sludge, offering higher resistance to corrosion of the metal drums used in the storage of radioactive waste.

 

On the other hand, in the cementitious pastes, carbon steel coupons embedded in the R-L paste showed the best corrosion resistance, followed by those embedded in the so-dium silicate-activated slag (BFS-S-L) paste. This fact seems to be related to an im-provement in the protective nature of the surface film. However, in the sodium car-bonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix was more significant, resulting in a decrease in porewater pH. This pH decrease could prevent the formation of a passive layer on the surface of the carbon steel and encourage the initia-tion of the corrosion process. The EIS measurements confirmed that corrosion was more intense in the BFS-C-L paste matrix and tended to increase over time, and the images of the carbon steel sheets after their extraction from this matrix showed small deposits of corrosion products, particularly hematite. Therefore, this matrix offered the lowest corrosion resistance and should not be used for sludge immobilisation.

8) It seems that after the first tests which found corrosion of steel caused by low pH, further tests were unnecessary, but perhaps I misread the author's intentions. Please provide clear justification for further research.

R: The authors initially carried out tests on simulated cement pore solution to find out whether or not corrosion of the carbon steel (metal drum) induced by the acidic nature of the sludge was taking place. Once it was confirmed that it did initiate corrosion, they began the study with cement pastes that can be used as confinement matrices in the storage of this type of waste. For this reason, the authors did not carry out further tests on simulated cement pore solution.

 

9) Please comment and clearly present your conclusions in relation to the set goals.

R: The conclusions have been rewritten concerning the set goals.

The study of the corrosion of the steel in simulated Portland cement reference (R-L) and alkali-activated slag waste pore solutions verified that corrosion occurred, wherein the Ecorr and icorr values measured for carbon steel indicated that it was in an active state due to the very low pH of the solutions that accelerated the corrosion process. There was also a great decrease in mass, as indicated by the decrease in the thickness of the carbon steel sheet, causing the steel to break in the AAC pore solution.

On the other hand, in the cementitious pastes, carbon steel coupons embedded in the R-L paste showed the best corrosion resistance, followed by those embedded in the sodium silicate-activated slag (BFS-S-L) paste. This fact seems to be related to an improvement in the protective nature of the surface film. However, in the sodium carbonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix was more significant, resulting in a decrease in porewater pH. This pH decrease could prevent the formation of a passive layer on the surface of the carbon steel and encourage the initiation of the corrosion process. The EIS measurements confirmed that corrosion was more intense in the BFS-C-L paste matrix and tended to increase over time, and the images of the carbon steel sheets after their extraction from this matrix showed small deposits of corrosion products, particularly hematite. Therefore, this matrix offered the lowest corrosion resistance and should not be used for sludge immobilisation.

Finally, the sludge in the R-L sample did not seem to affect the formation of the reaction products while inhibiting the formation of hydrotalcite in the alkali-activated slag pastes. Its acidic nature results in a decrease in pore-water pH, favouring the initiation of the corrosion process in the BFS-C-L paste.

Reviewer 4 Report

Comments and Suggestions for Authors

This manuscript investigates the corrosion behavior of carbon steel in the presence of decontamination sludges encapsulated within Portland cement and alkali-activated slag (AAS) matrices. While the study addresses a critical challenge in nuclear waste management, significant improvements are necessary to enhance the manuscript’s clarity and overall impact. In particular, the flow of writing and the organization of results require substantial revision to improve readability. Below are specific comments categorized as major and minor concerns.

Major:

1.     The introduction provides a general overview of the challenges associated with radioactive waste encapsulation. However, it lacks a clear articulation of the specific research gap addressed by this study. The authors should explicitly identify how their work advances current knowledge, particularly in the context of using AAS formulations for decontamination sludge immobilization.

2.     The experimental methodology is detailed but requires additional context to enhance its justification. For instance, the rationale behind choosing sodium carbonate and sodium silicate as activators for AAS formulations needs further elaboration. Additionally, the selection of the liquid-to-solid ratio (l/s = 0.55) should be explained in terms of its relevance to real-world applications. Providing this context will improve the applicability and understanding of the experimental approach.

3.     The abstract effectively introduces the study but is overly lengthy. Background information should be condensed to two or three sentences at most, allowing the key findings and contributions to take center stage.

Minor:

4.     Ensure consistent use of acronyms throughout the manuscript. For example, "LILW" appears in the abstract but is not used again in the text (e.g., Line 117).

5.     Some figures are difficult to interpret due to small font sizes. For example, the font in Figure 11 and the right panel of Figure 12 should be enlarged to improve readability.

6.     A thorough proofreading of the manuscript is necessary to address grammatical and typographical errors. Examples include inconsistent use of punctuation in Table 3 (e.g., “.” versus “,”), unnecessary capitalization of “Low and Intermediate-Level Wastes” in the abstract, and the use of dashes before each paragraph in the conclusion. These corrections will enhance the manuscript's professionalism.

Author Response

The authors appreciate the reviewer's suggestions and trust that their implementation will improve the quality of the manuscript. Responses to suggestions and corresponding modifications to the manuscript are given below:

 

Reviewer 4

Comments and Suggestions for Authors

This manuscript investigates the corrosion behavior of carbon steel in the presence of decontamination sludges encapsulated within Portland cement and alkali-activated slag (AAS) matrices. While the study addresses a critical challenge in nuclear waste management, significant improvements are necessary to enhance the manuscript’s clarity and overall impact. In particular, the flow of writing and the organization of results require substantial revision to improve readability. Below are specific comments categorized as major and minor concerns.

Major:

1. The introduction provides a general overview of the challenges associated with radioactive waste encapsulation. However, it lacks a clear articulation of the specific research gap addressed by this study. The authors should explicitly identify how their work advances current knowledge, particularly in the context of using AAS formulations for decontamination sludge immobilization.

R: The authors appreciate this suggestion, the introduction sections have been modified to highlight the objective, novelty, and specific research gap of the study. A new paragraph has been included with the advances in using AAS formulations for sludge immobilization, for example, dredged and sewage sludges. There are no previous results regarding the immobilisation of decontamination sludge in this type of alkaline cements.

 

. In previous studies 12–14, AAMs were proposed to be used for the stabilisa-tion/solidification of different types of sludge, such as dredged or sewage sludge. Kozaie et al.14 observed that AAMs exhibited better performance for sewage sludge ash contaminated via radiocesium encapsulation than OPC formulations, showing higher mechanical strength and lower levels of Cs leaching..

 

2. The experimental methodology is detailed but requires additional context to enhance its justification. For instance, the rationale behind choosing sodium carbonate and sodium silicate as activators for AAS formulations needs further elaboration. Additionally, the selection of the liquid-to-solid ratio (l/s = 0.55) should be explained in terms of its relevance to real-world applications. Providing this context will improve the applicability and understanding of the experimental approach.

R: The authors have taken these recommendations into account and two new paragraphs have been included about the choice of the alkaline activator and the liquid-to-solid ratio in the manuscript.

 

First paragraph: Sodium silicate has good workability and a high pH that favours the dissolution of precursors, enabling the generation of materials with good mechanical strengths. However, due to its production process, it has become the main factor contributing to AAC’s carbon footprint. Therefore, in this study, sodium carbonate was considered, as its use implies a greater reduction in the environmental impact of the material, but it should be mentioned that it has some drawbacks, such as delayed hardening and poor mechanical performance in its early stages¹⁵

Second paragraph: This ratio allowed the maximum amount of decontamination sludge to be immobilised in the alkali-activated slag pastes meeting the mechanical acceptance criterion of 10 MPa after 28 days of curing.

 

3. The abstract effectively introduces the study but is overly lengthy. Background information should be condensed to two or three sentences at most, allowing the key findings and contributions to take center stage.

R: The authors agree with the comment and the abstract section has been modified and shortened to be more concise and clearer.

 

In most countries, low- and intermediate-level wastes (LILWs) are cemented in carbon steel drums for later disposal. The durability of waste packages is determined by the chemical environment generated by both cement-based engineered barrier systems and the aggressive species present in the waste. Decontamination sludges are challenging wastes that are currently not accepted for final disposal due to their acidic nature and high concentrations of organic species and complexants. Thus, it was proposed to use electrochemical measurements to study the corrosion of steel sheets, simulating drums embedded in new alkali-activated slag (AAS) formulations with surrogate decontamination liquids, and determine their viability for use as confining matrices in order to increase the service life of the drumsThe carbon steel coupon embedded in the Portland cement reference (R-L) paste showed the best corrosion resistance, followed by that of steel embedded in sodium silicate-activated slag (BFS-S-L) paste. This behaviour may be related to an improvement in the protective nature of the surface film. However, in sodium carbonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix seemed to be more intense, leading to a pH decrease in the paste porewater, an effect that could hinder the formation of a passive layer on the surface of the carbon steel. Under such conditions, the initiation of the corrosion process seems to be favoured, resulting in the formation of a non-protective scale consisting mainly of hematite.

 

Minor:

4. Ensure consistent use of acronyms throughout the manuscript. For example, "LILW" appears in the abstract but is not used again in the text (e.g., Line 117).

R: The use of acronyms throughout the manuscript has been revised taking into account the comment of the reviewer.

 

5. Some figures are difficult to interpret due to small font sizes. For example, the font in Figure 11 and the right panel of Figure 12 should be enlarged to improve readability.

R: The font in Figure 11 and the right panel of Figure 12 have been enlarged to improve readability, please see the manuscript.

 

6. A thorough proofreading of the manuscript is necessary to address grammatical and typographical errors. Examples include inconsistent use of punctuation in Table 3 (e.g., “.” versus “,”), unnecessary capitalization of “Low and Intermediate-Level Wastes” in the abstract, and the use of dashes before each paragraph in the conclusion. These corrections will enhance the manuscript's professionalism.

R: The authors appreciate these suggestions and the authors have made these corrections to improve the manuscript.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors sufficiently replied to my comments and addressed them accordingly. The revised data article can now be accepted for publication.

Reviewer 4 Report

Comments and Suggestions for Authors

The comments and questions have been well addressed, except for the font on the axis in the right panel of Figure 12, which is still too small to read.

Comments on the Quality of English Language

The first sentence of the last paragraph in the Introduction is too long, which makes it difficult to follow.