Geopolymer Cement in Pavement Applications: Bridging Sustainability and Performance
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis review specifically explores the performance and application of GPC as a sustainable material in highway construction, and explores key research and advances in geopolymer technology, especially its applicability for pavement applications. The reviewer would like to recommend a major revision based on the current version:
1. Introduction: The Introduction section should focus on describing the research gap, and the current version needs to be improved.
2. Introduction: The authors should compare to state-of-the-art researches in order to highlight the relative merits. Moreover, to benefit our readers and provide further narrative, researches of mechanical properties changes of soil treated with new solidification materials and solidification techniques other than the present topic should also be included in the 'Introduction' section. To this end, I would like to bring your attention to the following articles for your inclusion in the background to reinforce / echo the usefulness of your manuscript: (1) doi.org/10.1016/j.jobe.2023.106459. (2) doi.org/10.3390/ma15155114.
3. Chapters 2-4: why not any quantitative results? All over the qualitative interpretation? Provide some quantitative results here. Please highlight the limitations and strengths. This section repeats extensively the results described in Ref. Provide some quantitative results on macroscopic tests here.
4. Please provide diagrams and data descriptions from the existing literature to quantitatively illustrate the evolution of the material's performance to enhance readability.
5. More emphasis is placed on summarizing the performance differences between the two, rather than focusing on the application of pavement materials as described in the title, as outlined in Chapters 3-4.
6. Please describe the performance advantages of geopolymer as a substitute for cement in terms of cured soil, road subgrade, road performance and other aspects of the road sector in terms of environmental characteristics, not just at the level of material properties.
7. The language of the manuscript should be elaborated and revised carefully. It is of my opinion that there are some sentences that may be difficult for some readers to understand them. It may interest to rewrite some parts of the paper in order to reach a bigger audience for your work.
8. The summary statement of the conclusion is not accurate and detailed, please improve it. The number of conclusions is too many. It is recommended to merge and abbreviate.
Comments on the Quality of English LanguageMinor editing of English language required
Author Response
We acknowledge your reviews and input on our manuscript. kindly see to the revised version.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript provides A Review Study of Geopolymer Cement in Pavement Applications: Bridging Sustainability and Performance. The article needs a major revision based on the following comments before publication.
1. References need to be updated up to 2024.
2. Sections 3.1, 3.2, and 3.3 must be discussed in depth to show the ratios and compare several studies, and the reasons must be addressed. 3. The conclusions should be revised to outline the contribution of this study. Please list the conclusions one by one, such as 1), 2), 3), etc.
Author Response
We acknowledge your reviews and input on our manuscript. kindly see to the revised version.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript is intended to be a review paper on geopolymer cement (GPC) in pavement applications. The manuscript is well addressed to this journal.
C1) The research results of this manuscript provide little guidance on how the GPC is really applied to pavements. It is too general and the gap in the research is not very clear.
C2) Very likely the potential readers wonder whether this manuscript is a review paper on geopolymer cement (GPC) regarding the pavement applications or is a general manuscript GPC versus OPC.
C3) Reading the manuscript, in many spots, it is not very clear whether GPC means a geopolymer cement or geopolymer concrete or it is the same thing. C4) It is recommended to add some photos with the products (GPC) and their applications.
C5) Reading the manuscript, in some spots the authors mention about OPC and in others mention about concrete based OPC which is a completely different material. The authors should decide in between these two material. It is worth to mention that Portland cement is just a powder.
C6) In Introduction the authors state that "Although various procedures have been developed for capturing CO2 discharged from cement power plants, the need for developing eco-friendly cementing systems (such as GPC and GPBs) for sustainable pavement construction applications is crucial [15–17]. Hence, reducing the global production of OPC and non-geopolymer-based binders will aid in the reduction of the amounts of CO2 (and other cement-based pollutants) emissions from cement, construction, and mining industries towards sustainability and healthy environments." What the authors mention above it is just an alternative. For example in Europe, the cement industry developed various types of cements containing a high percentage of supplementary cementing material (SCM) having a reduced footprint on the environment. Therefore, the point is not to reduce the production of OPC where the infrastructure is very well developed.
C7) The heading 1.1. is interesting but is related to OPC not to GPC. What is the point to put a such text here. The manuscript is intended to be a review paper on geopolymer cement (GPC) in pavement applications.
C8) Reading this manuscript, it is not very clear how large is the author’s experience with the geopolymers for pavements. The heading 2.2 should be well developed because represents what the manuscript's title announces. The heading 2.2 contains only 18 lines about GPC as sustainable pavement construction material. Once again it is not very clear whether it is about geopolymer concrete as pavement material or geopolymer cement.
C9) Table 2 is without connection to GPC as pavement material. In fact what is the point of the heading 2.3. Within this heading there is not the word "pavement" mentioned.
C10) Heading 2.4.........Why do the authors deem that it is necessary a comparison between GPC and OPC. Besides, in this comparison the pavement application is not deemed.
C11) Within Table 3 some criterions are too general, for example durability, sustainability, costs, but the main issue is that the most criteria mentioned in the table regarding the compared materials are usually required for the final construction material like concrete no matter if is based on OPC or geopolymers. It shouldn't forgot that, within ordinary concret the cement is just 11 to 13% from the concrete volume, the rest is cheap material, aggregate and water.
C12) Heading 3 ...... All the performances mentioned by the authors are mainly performances required to the ordinary concrete, concrete based on OPC not to OPC as it is mentioned by the authors in many spots of the manuscript. Table 4 is in contradiction to Table 2. In Table 4 the concrete based on OPC is one of the commented subject and in Table 2 is ordinary Portland cement (OPC) commented.
C13) The way of addressing to readers of the section devoted to prospects (heading 6) do not focus on the pavement area. The section devoted to prospects must be increased. Some aspects are not catch like
- durability of GPC-based foundations in the long term.
- the cost of activators is a major challenge toward the wide applications of geopolymers
- lowering the energy footprint
- lowering overall cost of geopolymerization
- sustainability of geopolymers based on industrial wastes and by-products and other wastes such as municipal and agricultural wastes with emphasize on the waste management and circular economy
C14) The conclusions must be written in a enumerating shape.
C15) The authors should improve the conclusions.
THE MANUSCRIPT MUST BE REJECTED. THE AUTHORS SHOULD IMPROVE THE MANUSCRIPT STRONGLY IN ORDER TO GET A REVIEW ON GEOPOLYMER CEMENT (CONCRETE) AS PAVEMENT MATERIAL.
Moderate editing of English language required
Author Response
We acknowledge your reviews and input on our manuscript. kindly see to the revised version.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe manuscript aims to present an in-depth review on geopolymer cement in pavement applications, focusing on sustainability and performance issues. However, the title of the paper may be misleading, as the body of the paper does not mention any specific applications of geopolymer cement in pavement applications at all. The manuscript primarily focuses on the basic strength and physical properties of the material in general construction applications. Whenever the phrase “in pavement applications” appears in the paper, any other field of construction could just as well be mentioned here and it would not change the content of the sentence.
Another, very important flaw of the manuscript is the misnomer. The authors explain that by the abbreviation GPC they mean “geopolymer cement”, while from the content of the paper it is clear that many times it is not geopolymer cement but “geopolymer concrete”, and these are two completely different expressions. Using them interchangeably shows a misunderstanding of the basic concepts.
In addition, I have a lot of relevant comments on the content of the paper, but I will present only the most important ones:
(1) In general, the abstract section of the manuscript should be concise, highlighting the research purpose, methods, content, and important conclusions. This abstract does not highlight the focus of the manuscript, and the expression of conclusions is insufficient and not in-depth enough.
(2) The “Introduction” chapter is written very superficially, without delving deeply into the topic, which is essential, particularly in review-type papers. In the subchapter 1.2. “Historical developments of geopolymer technology” there is a lack of references to such important achievements as the soil silicates/soil cement (Glukhovsky, 1957), alkali-activated cement (Narang, Chopra, 1983), F-cement (Forss, 1983), SKJ-binder (Changgo, 1991), geocements (Krivenko and associates, 1991), alkaline cements (Krivenko, 1994) etc. It is recommended that entire chapter “Introduction” be rewritten.
(3) All figures in the paper are taken from the referenced papers and are not the product of the authors of this manuscript
(4) The title of the Figure 2 is completely misleading. It does not present any pavement applications.
(5) The Figure 4 presents advantages of geopolymer concrete in general, and these advantages are not limited only to the pavement applications.
(6) Different types of GPC are presented in Table 2. GPC based on mine waste is definitely missing here (see the works of F. Pacheco-Torgal, J.P. Castro-Gomes, S. Jalali).
(7) Some data in the Table 3 are puzzling. Parameter like e.g. compressive strength can be investigated for geopolymer concrete not for geopolymer cement. On the other hand, costs of geopolymer concrete production are higher than OPC concrete (because of the high costs of chemical activator). So, low cost can be associated with geopolymer cement, and not with geopolymer concrete.
(8) Chapter 3. Mechanical Properties, Durability, Workability, Setting Time and Density, Rheological Behaviour, and Thermal Resistance and Conductivity of GPC Performance compared to OPC should be rewritten in full from the beginning. In scientific paper it is not necessary to specify such a basic definition like: compressive strength, flexural strength, modulus of elasticity etc. The aim of this chapter was to compare the different properties of GPC concrete with OPC concrete. The method of testing of the strength properties for concrete is well known and standardised. However, when it comes to geopolymers, there are no standards on the procedure for testing them. The comparison presented in this chapter was made on what basis? What were the dimensions of the test specimens used? What about scale effect? The strength tests were performed after what time?
(9) The most important objection concerns the way the comparison of properties between OPC concrete and GPC concrete is carried out. Why do the Authors compare the properties of GPC concrete with fibres to those of OPC concrete without fibres? Such a comparison completely misses the point.
(10) The subchapter related to corrosion performance concerns the corrosion of concrete or corrosion of the reinforcement? It is commonly known that chemical activator (NaOH or KOH) reacts with the steel reinforcement.
(11) What image do Authors mean in Table 4, point 2a?
(12) Many of the conclusions presented in the Chapter 7 “Conclusion” are obvious and sometimes even trivial.
(13) Some of the referenced sources are given in a way which is not sufficient (e.g. [105]).
Comments on the Quality of English LanguageGenerally, the paper is written with the use of good English. However, there are some minor editing and punctuation errors.
Author Response
We acknowledge your reviews and input on our manuscript. kindly see to the revised version.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for Authors1. Geopolymer can reduce CO2 release. But Alkali is used for the polymerization of this material. Is its impact on the environment negligible during production?
2. In addition to section 2.1, can the author review the reaction kinetics of geopolymerization?
3. In table 3, the criterion for each item is not clear and consistent. How did the author set the criteria (low, moderate, high, extreme high, ultra-high)? Is it objective enough or purely subjective? For each specific item, the author should list the literature if the conclusion came from other people’s work.
4. Section 2.4 needs to be expanded more to explain each item in table 3.
5. Section 3’s title ‘Mechanical Properties, Durability, Workability, Setting Time and Density, Rheological Behaviour, and Thermal Resistance and Conductivity of GPC Performance compared to OPC’ is unnecessarily long. Can the authors simplify it?
6. In section 3.4, how unique the rheological properties GPC exhibit? Can the author expand it more, compared to OPC?
7. In section 3.4, the author claimed ‘it’s generally reported that GPC shows lower yield stress, higher apparent viscosity, and more complex rheological performance than OPC’. How can it be general? It’s only reported by [71]. Depending on the degree of polymerization, the rheological properties of the final melt can be hugely different.
8. In Section 3.5, line2, is it GPC instead of GFC? Same thing on page 21
Author Response
We acknowledge your reviews and input on our manuscript. kindly see to the revised version.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAll issues have been well resolved.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors covered all aspects
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have improved the manuscript accordingly with the made comments.
Comments on the Quality of English LanguageMinor editing of English language required
Reviewer 5 Report
Comments and Suggestions for Authorsit can be accepted
