The Use of Natural Zeolites in Cement-Based Construction Materials—A State of the Art Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review paper focused on the utilization of zeolites in concrete materials. The paper is well-written and it covers the various aspects such as fresh, hardened, and durability properties of concrete mixes with zeolite. This manuscript should be further improved to enhance the quality before publication. The following are suggestions for improvement;

1- The introduction should be improved. The need for such a study is not clearly projected. It will be good to present the structure of this review using a flow diagram. 

2- Line 102 to 110, the findings seem to be contradicting, please can you provide a better justification

3- All the tables have to be revised. The authors present too much text in the table which should be avoided. Instead please represent some of the information in Figures.

4- Line 196, It should be two main approaches

5- A separate chapter on the limitations of zeolite material should be mentioned

6- It will be good to provide a discussion on the cost analysis of such material

7- Authors can also provide a section on the life cycle analysis of such material

8- Please also add one chapter on recommendations and future scope

9- Overall, this study is well undertaken, however, it should be significantly improved before publication

 

Comments on the Quality of English Language

The English language is fine. Minor editing is necessary.

Author Response

The answers to reviewer's comments can be found in the attached file.

Thank you for your time and effort in helping us to improve the manuscript.

1- The introduction should be improved. The need for such a study is not clearly projected. It will be good to present the structure of this review using a flow diagram.

-Introduction section was changed to highlight the need for such a study.

2- Line 102 to 110, the findings seem to be contradicting, please can you provide a better justification

-The study [3] compared to study [4] does show some contradictions; nevertheless w/c ratio is a reasonable explanation. First of all, workability does decrease in both studies, as does the initial setting time. Nevertheless, both final and setting time absolute values can be observed to be quite different. The final setting time in [3] does get lower for zeolite mortar compared to control, but in small amounts. This could be also a result of the small replacement percentage. Water to cement ratio in [4] is substantially higher than for [3], and studies indicate that higher w/c does not only add more water to the mix, but rather influences the pore structure (higher total porosity for increased w/c) [Influence of water-to-cement ratio and curing period on pore structure of cement mortar, Xudong Chen, Shenxin Wu, Construction and Building Materials, 2013]. This, in turn, may affect pozzolanic activity, as stated in [Interpreting the setting time of cement pastes for modelling mechanical properties, Tsardaka, Sougioultzi …, Case Studies in Construction Materials, 2023].
Adding zeolite in higher amounts would further increase the porosity also. This could account for a higher setting time.

3- All the tables have to be revised. The authors present too much text in the table which should be avoided. Instead please represent some of the information in Figures.

-It is true that tables hold a lot of information. This was chosen as an ordering method because studies are not consistent over the parameters they employed. While papers can be grouped, variations appear in experimental programmes (i.e. 50 freeze-thaw cycles, 150 freeze-thaw cycles etc.). For this reason, it was considered inappropriate to show these diverse results on the same graph.
A new section “Discussions” has been added to the manuscript and some of the results presented in the form of tables are also shown in the form of graphical representations.

4- Line 196, It should be two main approaches

-Correction done

 

5- A separate chapter on the limitations of zeolite material should be mentioned

-A new section “Discussions” has been added to the manuscript to include, among other information, the limitations of zeolite

6- It will be good to provide a discussion on the cost analysis of such material

-Cost analysis plays an important role in validating a new material. Nevertheless, we do not have access to the necessary variables that have to be taken into consideration for such a study (processing and handling costs, installation costs, environmental impact costs, etc.). While acquisition cost is important, and of course known, it is not the only one that has to be taken into account. Consequently, we cannot provide such an analysis.

7- Authors can also provide a section on the life cycle analysis of such material

-Similar to the previous comment, there is little information (close to none) on raw material extraction and processing and manufacture and transportation regarding
zeolite. Thus, life cycle analysis was not taken into consideration.
Only 1 such research paper was found in the scientific literature on zeolites. The international databases used by the specialized software to assess the life cycle impact lack the required information to run such analyses.

8- Please also add one chapter on recommendations and future scope
-A new section “Discussions” has been added to the manuscript to include reviewer’s suggestion

9- Overall, this study is well undertaken, however, it should be significantly improved before publication

-We hope that the changes that were made to the manuscript answered the reviewer’s comments.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents a good review on the utilization of natural zeolites in cement-based construction materials. However, the paper needs a lot of improvement. There are still a lot of missing information in the paper. Here are some comments:

1. It is better to present in the paper: the types of natural zeolite used and the ranges of the chemical contents of the natural zeolites used in the research papers reviewed. It is also better to provide information regarding the types of treatment to the zeolites used in the research, if any (no treatment?, with physical treatment? Or chemical treatment? Or other?); the water content of the mixture used etc.

It is better to also discuss the weakness of zeolite from physical and chemical point of view?

2. No quantitative information provided on the characteristic of the strength development at earlier and later ages. How reactive is the pozzolanic content in the natural zeolites? Are they amorphous?

3. Because the zeolite material is honeycombed, what kind of treatment applied in the research paper reviewed to control the mixing water?

4. The paper reviews the use of zeolite as cement or aggregate replacement. As only two papers use the zeolite as aggregate replacement then it is better to focus only on the use of the zeolite as cement replacement. Furthermore, please be reminded that the philosophy and the requirement of using zeolite as cement and aggregate replacement are basically different.

5.  There are no quantitative, absolute values of the properties being measured provided in Table 1 till Table 11. It is better to have that information so that we can compare it with other references. It is also better to use graphics to show the sensitivity of the behaviour with respect to certain test variables.

6.  There are limited academic explanation provided to justify the effects of various test variables on the concrete or mortar behaviour shown from different studies.

7.  There are also limited academic explanation provided to justify the contradictory test results from different studies

8.  The sentence in line 590 till 592 is not so clear. Please rewrite....

Comments on the Quality of English Language

No comment

Author Response

The answers to reviewer's comments can be found in the attached file.

Thank you for your time and effort in helping us to improve the manuscript.

1. It is better to present in the paper: the types of natural zeolite used and the ranges of the chemical contents of the natural zeolites used in the research papers reviewed. It is also better to provide information regarding the types of treatment to the zeolites used in the research, if any (no treatment?, with physical treatment? Or chemical treatment? Or other?); the water content of the mixture used etc. It is better to also discuss the weakness of zeolite from physical and chemical point of view?

-The type of natural zeolite mostly used in research works is clinoptilolite. Hence, this study focuses on this type of natural zeolite as it possesses several advantages over its counterparts (lines 47-64)
With the sole exception of 1 research paper, all other studied research works used the natural zeolite without any prior treatment. In the research work in question, the authors of the study used 2 types of treatments: calcination, milling and a combination of the two. The conclusion was that milling had the strongest influence on the obtained results (improved mechanical properties) with the least energy consumption.
The water/mineral binder ratio is presented in each provided table as it is one of the governing parameters, apart from
replacement percentage, that influences the results. The conclusion of several studies was that increasing the water/binder ratio has minimal beneficial effects as opposed to keeping the same water/binder ratio and increasing the superplasticizer content with the increase in zeolite content (Table 1, references 2, 17)
A new section Discussions was added to the manuscript where the chemical composition of natural zeolites from the surveyed scientific literature is presented (where available)

2. No quantitative information provided on the characteristic of the strength development at earlier and later ages. How reactive is the pozzolanic content in the natural zeolites? Are they amorphous?

-A new section “Discussions” has been added to the manuscript where data is presented in terms of normalized values with respect to the reference mix considered in each individual study. This was chosen so that to have a common denominator in assessing the influence of natural zeolites on the mechanical properties.

3. Because the zeolite material is honeycombed, what kind of treatment applied in the research paper reviewed to control the mixing water?

-Increase the superplasticizer content in case of zeolite as SCM.
Pre-soaking the aggregates before mixing of concrete but subtract the absorbed water from the total water in the mix.

4. The paper reviews the use of zeolite as cement or aggregate replacement. As only two papers use the zeolite as aggregate replacement then it is better to focus only on the use of the zeolite as cement replacement. Furthermore, please be reminded that the philosophy and the requirement of using zeolite as cement and aggregate replacement are basically different.

-The reviewer is right that the philosophy behind cement and aggregate replacements are different. On the matter of zeolites, since they are porous and soft, studies have shown that zeolite aggregates either contain a large percentage of powdery material or tend to be crushed during mixing resulting in a powdery material. This promotes pozzolanic reaction as if cement was replaced by zeolite, although given the particle dimensions the reaction is significantly slower. Moreover, zeolite aggregates themselves act as nucleation sites because of the pozzolanic
reaction between the silica and CH (Reference 12).

5. There are no quantitative, absolute values of the properties being measured provided in Table 1 till Table 11. It is better to have that information so that we can compare it with other references. It is also better to use graphics to show the sensitivity of the behaviour with respect to certain test variables.

-The data presented in each research paper considered for this review varies significantly from one source to another. Hence, we chose to summarize the information in terms of: replacing material (cement/aggregates), percentage replacement, water/binder ratio, age of specimens and the main finding of the study.
A new section “Discussions” has been added to the manuscript where some of the data is graphically represented, normalized with respect to the characteristics of the reference material of each study. This could help in a more clear understanding of the trends observed and reported in the scientific literature.

6. There are limited academic explanation provided to justify the effects of various test variables on the concrete or mortar behaviour shown from different studies.

-The possible explanations of observed phenomena were extracted from the cited papers. An additional Discussions section was added to the manuscript to further explain the observed mechanisms.

 

7. There are also limited academic explanation provided to justify the contradictory test results from different studies

-The possible explanations of observed phenomena were extracted from the cited papers. An additional Discussions section was added to the manuscript to further explain the observed mechanisms.

8. The sentence in line 590 till 592 is not so clear. Please rewrite....

-Revised

Reviewer 3 Report

Comments and Suggestions for Authors

The review is well written, incorporating concurrent literature, and containing only minor errors.

In the section of durability testing it should be mentioned at what age of specimens were the tests concluded as, as concludes from strengths of mortars/concretes with zeolites, the possitive/negative effects of NZ are dependent on the age.

The correct unit for resistivity has to be used.

 

However the biggest concern is the overall contribution of the work to the field as there are few similar papers published already.

I believe, that authors would justify the publication by incorporation of more recent results while compared to: Tran, Y.T.; Lee, J.; Kumar, P.; Kim, K.-H.; Lee, S.S. Natural zeolite and its application in concrete composite production. Compos. Part B Eng. 2019, 165, 354–364, doi:10.1016/j.compositesb.2018.12.084 used as [38] in the literature, however it would be necessary to mention this work in the introduction and present ther the main improvements/benefits of more recent work.

Much more concerning is the recently published review by M. Shekarchi et el. : Natural zeolite as a supplementary cementitious material – A holistic review of main properties and applications,Constr. Build. Mater,
Vol. 409, 2023, 133766, doi:10.1016/j.conbuildmat.2023.133766

which apart from carbonation resistance and detailed study on electrical resistivity deals with very simillar topics.

 

I believe that it is not beneficary to have several different publications presenting the very simillar/same outcomes and therefore I'm inclined to not recommned the work for publication.

Author Response

The answers to reviewer's comments can be found in the attached file.

Thank you for your time and effort in helping us to improve the manuscript.

1.In the section of durability testing it should be mentioned at what age of specimens were the tests concluded as, as concludes from strengths of mortars/concretes with zeolites, the possitive/negative effects of NZ are dependent on the age.

-The information on the age of specimens when the durability tests were conducted is mentioned in the Findings.

2. The correct unit for resistivity has to be used.

-Correction done.

3. However the biggest concern is the overall contribution of the work to the field as there are few similar papers published already.

-The reviewer is right especially in terms of references [12] and [63].
Compared to reference [12], the present manuscript considers an updated list of published references starting from a selection of highly cited papers from before reference [12] was published in order to build an overall clearer picture. Still the reported results are conflicting but there is some kind of consensus in terms of zeolite contribution to improving the durability properties.
The present study discusses the results on several aspects that reference [12] did not mention: acid attack, carbonation, electrical resistivity, drying shrinkage of mortar.
Reference [63] on the other hand, was not published (to the authors knowledge) when the present manuscript was submitted. This, however, does not combat reviewer’s comment. The authors believe that the two papers (present paper and reference [63], are complementary to one another, tackling the same topic but from a different perspective.
There is no clear differentiation between the effect of natural zeolites on different cement-based materials: paste, mortar and concrete. The results are not always explained but
rather presented as observations from the surveyed scientific literature (reference 63). More than half the length of manuscript presented as reference 63 deals with the selection algorithm and source of information for the review. This, of course, helps the reader create an image of the rationale behind the review and it is, at the same time, different from the present manuscript.

4.I believe, that authors would justify the publication by incorporation of more recent results while compared to: Tran, Y.T.; Lee, J.; Kumar, P.; Kim, K.-H.; Lee, S.S. Natural zeolite and its application in concrete composite production. Compos. Part B Eng. 2019, 165, 354–364, doi:10.1016/j.compositesb.2018.12.084 used as [38] in the literature, however it would be necessary to mention this work in the introduction and present ther the main improvements/benefits of more recent work.

-Compared to reference [12], the present manuscript considers an updated list of published references starting from a selection of highly cited papers from before reference [12] was published in order to build an overall clearer picture. Still the reported results are conflicting but there is some kind of consensus in terms of zeolite contribution to improving the durability properties.
The present study discusses the results on several aspects that reference [12] did not mention: acid attack, carbonation, electrical resistivity, drying shrinkage of mortar.
This information is briefly presented in the Introduction section and then throughout the manuscript to either support some academic justifications of the observed phenomena or to highlight the difference between the previous studies.

5. Much more concerning is the recently published review by M. Shekarchi et el. : Natural zeolite as a supplementary cementitious material – A holistic review of main properties and applications,Constr. Build. Mater, Vol. 409, 2023, 133766, doi:10.1016/j.conbuildmat.2023.133766 which apart from carbonation resistance and detailed study on electrical resistivity deals with very simillar topics.

-The authors believe that the two papers (present paper and reference [63], are complementary to one another, tackling the same topic but from a different perspective.
There is no clear differentiation between the effect of natural zeolites on different cement-based materials: paste, mortar and concrete. The results are not always explained but rather presented as observations from the surveyed scientific literature (reference 63).
We have tried to connect the dots between the pieces of information related to strength and durability properties and attempted to explain the reported data from the point of view of: pozzolanic reaction, particle size of zeolites, replacement percentage, water/binder ratio, age of specimens. We are aware that there is information we might have missed and that there is scientific information that will help explain some of the not so clearly understood phenomena.
We want to emphasize, again, that the two studies, although refer to the same topic, are complementary rather that overlapping.

6.I believe that it is not beneficary to have several different publications presenting the very simillar/same outcomes and therefore I'm inclined to not recommned the work for publication.

-We hope that the changes we have done to the manuscript and our answers to reviewer’s previous 2 comments worked towards alleviating reviewer’s concerns on similar / identical studies.

Reviewer 4 Report

Comments and Suggestions for Authors

Reviewer’s Comments

The authors comprehensively reviewed the recent findings on the use of natural zeolites in cement based construction materials in terms of the mechanical and durability properties for cement paste, mortar and concrete. The mechanical properties includes the compressive strength, flexural strength and modulus of elasticity, and the durability covers the freeze-thaw resistance, chloride diffusion resistance, acid attack resistance, water transport properties, carbonation resistance, electrical resistivity and drying shrinkage. Differences between the usage of natural zeolites as supplementary cementitious materials and their usage as aggregates are also highlighted.

The manuscript is overall worthwhile to be published in Coatings. Thus, a minor modification is required to address the following concerns.

1.       Some content of Abstract and Conclusions Sections are redundant. For example, Line 25-29 vs. Line 564-567, Line 29-30 vs. Line 574-575, Line 30-32 vs. Line 583-584, Line 32-34 vs. 593-595, Line 34-36 vs. 602-604 are exactly the same. In addition, Conclusion section is expected to be more concise. The current Conclusion section contains too much information.

2.       The authors summarized the impacts of zeolite on so many different aspects of cement based construction materials, and also claimed that the majority of durability factors are interconnected and complicated. How to balance the trade-off among all factors for a specific applications? Recommend to list out some applications as examples to instruct the decision-making process.

3.       There are some wording and grammar issues the authors should take care in order to make the flow better. Please double check throughout the entire manuscript. For example,

a.       Line 26, “… revealed that increasing the zeolite content reduction of workability compared to the control mixes” is supposed to be “… revealed that increasing the zeolite content led to the reduction of workability compared to the control mixes”

b.       Line 43-46, I could not understand the sentence “… and was attributed to it based on the observations of Cronstedt who discovered that rapidly heating this mineral produced steam from the water that was previously absorbed by the material”.

c.       Line 67, “their high porosity and configuration of internal structure, Figure 1, leads to …” is supposed to be “their high porosity and configuration of internal structure, as shown in Figure 1, leads to …”.

4.       Some typos and errors in the manuscript should be corrected. Please revise the entire manuscript. For example,

a.       Page 1, Line 28, “final set-ting” is supposed to be “final setting”; same to Page 1, line 36, “to ad-dress these challenges” is supposed to be “to address these challenges”.

Comments on the Quality of English Language

The manuscript is overall easy to read and follow, but still need to revise throughout the manuscript regarding some grammar issues and typos.

Author Response

The authors would like to thank the reviewer for helping us improve the manuscript. Your time and contribution was greatly appreciated.

1. Some content of Abstract and Conclusions Sections are redundant. For example, Line 25-29 vs. Line 564-567, Line 29-30 vs. Line 574-575, Line 30-32 vs. Line 583-584, Line 32-34 vs. 593-595, Line 34-36 vs. 602-604 are exactly the same. In addition, Conclusion section is expected to be more concise. The current Conclusion section contains too much information.

-The second part of the abstract contains also some of the conclusions of the review work so that the potential reader could set the right expectations from reading the manuscript. The Conclusions section was organized so that to include information on the influence of natural zeolites on fresh and hardened properties of cement paste, mortar and concrete. A paragraph was also dedicated to the durability part of the manuscript.

2. The authors summarized the impacts of zeolite on so many different aspects of cement based construction materials, and also claimed that the majority of durability factors are interconnected and complicated. How to balance the trade-off among all factors for a specific applications? Recommend to list out some applications as examples to instruct the decision-making process.

-According to the statements from lines 663-669, an up to 20% replacement of cement by natural zeolite can improve both mechanical and durability properties. The peak performance was obtained for 10% zeolite content. This would address the largest number of concerns from the point of view of durability of cementitious materials.

3. There are some wording and grammar issues the authors should take care in order to make the flow better. Please double check throughout the entire manuscript. For example,

-A re-checking of English language was conducted and some corrections were done, as highlighted.

4. Line 26, “… revealed that increasing the zeolite content reduction of workability compared to the control mixes” is
supposed to be “… revealed that increasing the zeolite content led to the reduction of workability compared to the control mixes”

- Done

5. Line 43-46, I could not understand the sentence “… and was attributed to it based on the observations of Cronstedt
who discovered that rapidly heating this The name “zeolite”, meaning “boiling stone”, was attributed to this mineral to describe the water evaporation process mineral produced steam from the water
that was previously absorbed by the material”. 

-The name “zeolite”, meaning “boiling stone”, was attributed to this mineral to describe the water evaporation process from the pores of the internal structure of the mineral when being rapidly heated.
Due to the porous structure of zeolite, it absorbs water which is later on released when a pressure gradient occurs. Because of this, it has been used as “internal curing” agent in high-strength concrete.

6. Line 67, “their high porosity and configuration of internal structure, Figure 1, leads to …” is supposed to be “their high porosity and configuration of internal structure, as shown in Figure 1, leads to …”.

- Done

7. Some typos and errors in the manuscript should be corrected. Please revise the entire manuscript. For example,

- A re-checking of English language was conducted and some corrections were done, as highlighted.

8. Page 1, Line 28, “final set-ting” is supposed to be “final setting”; same to Page 1, line 36, “to ad-dress these challenges” is supposed to be “to address these challenges”.

- Done

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed most of my comments. However, I feel the paper can further be improved by improving the overall presentation of the data. The tables are still very clumsy and should be revised appropriately to make it more concise and readable. 

Comments on the Quality of English Language

Minor improvements in the quality of English are necessary before publication.

Author Response

The authors would like to thank the reviewer for helping us improve the manuscript. Your time and contribution was greatly appreciated.

1. The authors have addressed most of my comments. However, I feel the paper can further be improved by improving the overall presentation of the data. The tables are still very clumsy and should be revised appropriately to make it more concise and readable.

• The main findings of the research works cited in all tables were reworded in order to make them clearer and more concise. The findings are complementary to the statements from the body of the manuscript.

2. Minor improvements in the quality of English are necessary before publication.

• A re-checking of English language was conducted and some corrections were done, as highlighted.

Reviewer 2 Report

Comments and Suggestions for Authors

The significant revision has been added to the paper. The revised paper is therefore acceptable for publication.  

Comments on the Quality of English Language

Only need minor revision, e.g. missing preposition in some sentences.  

Author Response

The authors would like to thank the reviewer for helping us improve the manuscript. Your time and contribution was greatly appreciated.

A re-checking of English language was conducted and some corrections were done, as highlighted.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors addressed the comments of the reviewers, improved the manuscript and explained the main differences between the presented work and currend literature availible.

The added part 5. Discussions provides more valuable informations however, in my opinion the Figures 2 and 3 with corresponding discussion could be added to appropriate parts of section 3, and overall most of this section could be included into previous parts of the manuscript rather than just beeing added to the end. The language in the added section should be slightly revised.

 

 

Author Response

The authors would like to thank the reviewer for helping us improve the manuscript. Your time and contribution was greatly appreciated.

 

Section 5 was added to try and connect the chemical composition of natural (clinoptilolite) zeolite to, mostly, mechanical properties but also to durability.
The additional explanations provided in this section would summarize the findings from Sections 3 and 4 but without the assertion to substitute the Conclusions section.
We would kindly ask the reviewer to agree with authors’ decision to keep Section 5 and not merge it with Sections 3 and 4.