Review Reports - Sustainable Soil Stabilization Using Eggshell-Derived Lime: A Comparative Assessment Against Commercial Lime

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents an experimental investigation into the use of eggshell-derived hydrated lime as a sustainable alternative to commercial hydrated lime for stabilizing a granite residual soil, with and without fly ash. The topic is timely and relevant to sustainability-oriented geotechnical engineering, and the study is generally well written and technically sound.

That said, the manuscript would benefit from a clearer articulation of its novelty relative to existing studies. Several previous works have already demonstrated the feasibility of eggshell-based lime for soil stabilization, and while the present study provides a useful comparative dataset, the authors should more explicitly state what new insight this work adds—particularly with respect to the interaction between eggshell-derived lime and fly ash and the behavior of tropical residual soils.

In addition, it should be noted that the conclusions are drawn primarily from unconfined compressive strength (UCS) testing and limited microstructural observations. While these tests are informative, the overall experimental program remains relatively limited, and the findings should be interpreted accordingly. Expanding the discussion to acknowledge this limitation and to clarify what aspects of soil behavior are not captured by the current testing framework would improve the rigor of the manuscript.

The sustainability discussion could also be strengthened. Although the environmental motivation is well articulated, the sustainability benefits remain largely qualitative. A more critical discussion of the environmental implications—particularly considering the need for high-temperature calcination of eggshells—would better align the manuscript with the scope of Sustainability.

Finally, the practical engineering relevance of the results could be discussed more explicitly. While clear strength improvements are reported, it is not entirely evident how these findings translate to field applications such as subgrade or embankment stabilization. A brief discussion linking the measured strengths to typical engineering requirements and acknowledging the need for long-term durability and performance evaluation would further strengthen the paper.

Author Response

R: Dear Reviewer,

We would like to sincerely thank for your careful evaluation of our manuscript and for the constructive and insightful comments provided. The suggestions greatly contributed to improving the clarity, scientific rigor, and relevance of the paper. We have carefully revised the manuscript and addressed all comments. Below, we provide a detailed, point-by-point response, indicating the changes implemented in the revised version. All modifications have been incorporated into the manuscript.

R: We agree with the reviewer and have clarified the novelty of the study. The Introduction was revised to explicitly highlight the lack of systematic comparisons between eggshell-derived lime and commercial lime under identical experimental conditions, the limited understanding of EHL–fly ash interactions, and the relevance of these mechanisms in tropical residual soils. Additionally, the Discussion section now emphasizes how the findings contribute new insight into reaction hierarchy, microstructural development, and stabilization efficiency in such soils.

R: This important point has been addressed. A dedicated subsection in the Discussion explicitly acknowledges the limitations of the experimental framework, noting that UCS and qualitative SEM analyses do not capture long-term durability, hydraulic behavior, volumetric stability, or performance under cyclic and environmental loading. This clarification strengthens the interpretation and scope of applicability of the results.

R: The sustainability discussion was expanded in the Discussion section. We now explicitly acknowledge the energy and CO₂ emissions associated with eggshell calcination and discuss the environmental trade-offs involved. The revised text emphasizes that the sustainability benefits of EHL are context-dependent and may be enhanced through lower binder demand, waste valorization, and the use of low-carbon energy sources.

R: We have added a subsection in the Discussion linking the achieved UCS values to typical geotechnical applications such as subgrade improvement and embankment construction. The revised manuscript also emphasizes that the results represent laboratory-scale feasibility and that further field validation and long-term performance assessments are required.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors studied the mechanical and microstructural properties of soil stabilized with commercial and eggshell derived lime, with and without fly ash. The paper represents a advancement in this field and addresses the research gap. The paper can be accepted following minor revisions:

Can the authors change the Legend of Figure 1. Change Caol fly ash to Fly ash and be consistent with that throughout the manuscript.
Remove Mv from the legend box in figure 1
Need more experimental details on how the cylindrical samples were made? Example: pressure, temperature
How did authors prepare sample at different dry weight %
Line 224, how was the particle size distribution evaluated
For a specific lime content, the variation in Unconfined compressive strength is greater for EHL mixtures compared to CHL mixtures. What’s the reason behind this?
Line 270, the exponent chosen was 0.20. How was this decided? Can the authors describe the R2 value for other exponents?
Line 270, how was the porosity calculated?
Line 280, can the authors explain in more details why the trend only converges for porosity/lime concentration > 33
Any reference to Line 313?
The dolomitic commercial lime has higher quartz content compared to egg shell derived lime based on XRD. Additionally, Quartz is crystalline in nature. It is surprising to see that Figure 8 a) which is corresponding to soil having commercial lime does not have any crystal like structures whereas Figure 8 b) has crytal like structures.

Author Response

R: Dear Reviewer,

Can the authors change the Legend of Figure 1. Change Caol fly ash to Fly ash and be consistent with that throughout the manuscript.
Remove Mv from the legend box in figure 1R: The legend of Figure 1 was revised as suggested. The term “Fly ash” is now used consistently throughout the manuscript, and “Mv” was removed from the figure legend.
Need more experimental details on how the cylindrical samples were made? Example: pressure, temperatureR: Additional details were included in the Materials and Methods section. The revised text now clearly describes static compaction in a split cylindrical mold using a hydraulic press, ambient laboratory temperature conditions, and the absence of applied curing pressure or external heating during specimen preparation.
How did authors prepare sample at different dry weight R: The methodology was expanded to explain that different dry unit weights were obtained by controlling the mass of dry material placed in the mold while maintaining constant specimen dimensions and molding water content, with target masses calculated based on mold volume and desired γd.
Line 224, how was the particle size distribution evaluatedR: The manuscript was revised to explicitly state the method used for particle size distribution determination (laser granulometry), ensuring methodological clarity.
For a specific lime content, the variation in Unconfined compressive strength is greater for EHL mixtures compared to CHL mixtures. What’s the reason behind this?R: This behavior is now discussed in the Results and Discussion sections. The revised text explains that the higher fineness and reactivity of EHL increase sensitivity to local variations in compaction and microstructural arrangement, leading to greater UCS scatter compared to the more gradual and uniform response of CHL-treated mixtures.
Line 270, the exponent chosen was 0.20. How was this decided? Can the authors describe the R2 value for other exponents?R: The manuscript now clarifies that the exponent was selected through an iterative fitting process aimed at maximizing the coefficient of determination (R²), with trial exponents evaluated within a reasonable range. The chosen value is also shown to be consistent with values reported in the literature.
Line 270, how was the porosity calculated?R: A clear explanation of porosity calculation was added in 2.4, indicating that porosity was determined based on specimen dry unit weight and the weighted average specific gravity of soil, lime, and fly ash constituents.
Line 280, can the authors explain in more details why the trend only converges for porosity/lime concentration > 33
R: This behavior is now explained in the Discussion. The revised text indicates that at higher values of this index, the mechanical response is dominated by the cemented soil skeleton, reducing the relative influence of fly ash, whereas at lower values microstructural heterogeneity leads to divergent trends.
Any reference to Line 313?
R: The indicated statement was revised and appropriate reference was added to support the discussion.
The dolomitic commercial lime has higher quartz content compared to egg shell derived lime based on XRD. Additionally, Quartz is crystalline in nature. It is surprising to see that Figure 8 a) which is corresponding to soil having commercial lime does not have any crystal like structures whereas Figure 8 b) has crytal like structures.
R: The SEM discussion was expanded to explain that quartz detected by XRD may be finely dispersed, embedded within reaction products, or masked by cementitious gels, and therefore not necessarily visible as distinct crystalline features in SEM images.

Reviewer 3 Report

Comments and Suggestions for Authors

This paper presents a study on the using of eggshell waste into hydrated lime (EHL) for soil stabilization. The experimental design employ a full-factorial approach to compare EHL with commercial lime (CHL) based on some key variables. The data is comprehensive and supports the conclusion that EHL can be a technically superior and environmentally friendly alternative due to its finer particle size and higher purity. All in all, the manuscript is well written and well structured. My comments are as follows:

It is suggested to add a Discussion sectionin the main text. The results are presented and followed immediately by conclusions. A separate discussion would provide an essential space to interpret the mechanisms of the observed superior performance of EHL.
While the sustainable premise is clear, the manuscript may be more powerfully to articulate its environmental impact.Itwould be highly impactful to conduct a discussion or even a rough estimate of the potential CO₂ emission savings per ton of lime produced from eggshells versus conventional limestone calcination
In Section 2.8, the statement on the use of AI-assisted tools(Grammarly Premium and ChatGPT (GPT-5.1))is appropriately transparent but feels slightly out of place in the Methods. I am quite confused why this statement is added in the main text? Maybe this information could be integrated into the Acknowledgments section?

4. It is recommended to do a careful proofread to ensure the consistent formatting of references (e.g., completeness of DOIs, uniformity in presentation of accessed dates).

Author Response

R: Dear Reviewer,

It is suggested to add a Discussion sectionin the main text. The results are presented and followed immediately by conclusions. A separate discussion would provide an essential space to interpret the mechanisms of the observed superior performance of EHL.R: A dedicated Discussion section was added to the manuscript. This section integrates mechanical, microstructural, statistical, and sustainability-related interpretations, providing a clearer explanation of the mechanisms governing the observed behavior.
While the sustainable premise is clear, the manuscript may be more powerfully to articulate its environmental impact.Itwould be highly impactful to conduct a discussion or even a rough estimate of the potential CO₂ emission savings per ton of lime produced from eggshells versus conventional limestone calcinationR: The sustainability discussion was expanded to qualitatively address CO₂ emission implications, acknowledging both the benefits of waste valorization and the energy requirements of eggshell calcination, without overstating quantitative claims.
In Section 2.8, the statement on the use of AI-assisted tools(Grammarly Premium and ChatGPT (GPT-5.1))is appropriately transparent but feels slightly out of place in the Methods. I am quite confused why this statement is added in the main text? Maybe this information could be integrated into the Acknowledgments section?R: The sustainability discussion was expanded to qualitatively address CO₂ emission implications, acknowledging both the benefits of waste valorization and the energy requirements of eggshell calcination, without overstating quantitative claims.

4. It is recommended to do a careful proofread to ensure the consistent formatting of references (e.g., completeness of DOIs, uniformity in presentation of accessed dates).

R: The reference list was carefully reviewed to ensure consistent formatting, completeness of DOIs where available, and uniform presentation of access dates.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

In my previous review, I raised a concern regarding the novelty of the study and what new knowledge it adds to the existing literature. In the revised manuscript, the authors have added several statements in the Introduction claiming gaps in prior research, for example:

Despite the growing body of literature supporting the feasibility of eggshell-derived lime as a stabilizing agent, most existing studies have focused on either conventional soils or the isolated use of eggshell-based materials. Limited attention has been given to the combined application of eggshell-derived lime and fly ash, particularly regarding their interaction mechanisms and performance in tropical residual soils, which exhibit distinct mineralogical heterogeneity, fabric, and weathering-induced porosity. Furthermore, systematic comparisons between eggshell-derived lime and commercial hydrated lime under identical experimental conditions remain scarce."

However, these claimed gaps are not actually addressed in the present study. In particular, although the authors emphasize “interaction mechanisms,” the manuscript does not include any experimental program or analytical framework aimed at investigating such mechanisms (e.g., microstructural, mineralogical, or chemical interaction analyses). The work remains primarily limited to strength-based performance evaluation.

Similarly, while the authors highlight the lack of systematic comparisons with commercial hydrated lime, the experimental design and discussion do not convincingly demonstrate how this comparison leads to new mechanistic or practical insights beyond what has already been reported in the literature.

As a result, the newly added statements in the Introduction currently appear aspirational rather than substantiated by the actual scope of the experimental program.

Author Response

Dear Reviewer,

We sincerely thank you for your careful re-evaluation of our manuscript and for your thoughtful comments regarding novelty, research design, and consistency between the stated objectives and the actual scope of the experimental program. We appreciate the opportunity to clarify and improve the manuscript accordingly.

We fully acknowledge your concern that the previous version of the Introduction overstated the mechanistic scope of the study, particularly with respect to “interaction mechanisms” between eggshell-derived lime and fly ash. In response, we have revised the Introduction to remove mechanistic claims that are not directly supported by the experimental framework. The contribution is now clearly framed as a performance-based and comparative experimental investigation, rather than a mechanistic study. Specifically, references to “interaction mechanisms” have been replaced with language emphasizing comparative mechanical response under controlled and identical experimental conditions.

To further improve clarity, we explicitly introduced research questions and a hypothesis in the Introduction, thereby strengthening the articulation of the research design and intent. These additions make clear that the study aims to evaluate (i) the relative mechanical performance of eggshell-derived hydrated lime versus commercial hydrated lime, and (ii) how the incorporation of fly ash influences this comparison in a tropical residual soil. The hypothesis was formulated in a qualitative and performance-oriented manner, fully consistent with the applied methods.

In parallel, the Discussion section was substantially revised to ensure strict alignment with the experimental resolution of the study. The language was refined to distinguish clearly between experimentally supported observations and qualitative interpretations derived from UCS results and SEM imaging. Mechanistic terminology was softened, and causal claims were replaced by evidence-based interpretations supported by comparative trends and microstructural observations at a qualitative level. Limitations of the experimental program are now explicitly acknowledged, and the scope of inference is clearly delimited.

Finally, minor but important refinements were introduced in the Experimental Program description and Abstract to reinforce coherence across the manuscript and to ensure consistency between the stated novelty, research questions, methods, and conclusions.

We believe that these revisions directly address your concerns and result in a manuscript that is conceptually consistent, appropriately framed, and transparent with respect to its scientific contribution and limitations. We are grateful for your insightful feedback, which has significantly improved the clarity and rigor of the manuscript.

Kind regards,
Helena Paula Nierwinski
(on behalf of all authors)

Reviewer 3 Report

Comments and Suggestions for Authors

The authors respond all my coments. I have no other question.

Author Response

Dear Reviewer,

Thank you very much for your careful evaluation of our manuscript and for confirming that all your comments have been satisfactorily addressed. We sincerely appreciate your time, feedback, and positive assessment, which greatly contributed to improving the quality and clarity of the paper.