Assessing Engineering Behavior of Fly Ash-Based Geopolymer Concrete: Empirical Modeling

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors investigated the compressive, splitting tensile, and flexural strengths, elastic modulus, and stress-strain relationship of fly ash-based geopolymer concrete (GPC). They developed corresponding regression models and proposed a constitutive model to describe the complete stress-strain response of GPC, aiming to accurately predict its mechanical behavior. There may be some minor issues in the article that need to be revised and further studied, and specific suggestions have been proposed for the author's reference.

1. The authors collected a substantial number of mechanical strength data points from existing literature, which represents a significant effort. However, the paper does not specify the criteria or standards used for data collection—whether the dataset consists solely of pure fly ash-based geopolymer test results or also includes geopolymers prepared with fly ash combined with other solid waste materials. It would be helpful if the authors could provide more details regarding the sample data collection methodology.
2. How were the conversion factors in Table 3 obtained? If these coefficient transformation methods were derived from OPC test results, is this approach equally applicable to GPC? There may be inherent differences between OPC and GPC that could potentially affect the outcomes of data standardization.
3. The authors mention "The figure also shows that increasing the amounts of dissolved silicate in the activation solution has increased geopolymer strength ", yet Figure 1 does not show any increase in the amount of dissolved silicate in the activation solution.
4. Additionally, why did a higher NS/Alk ratio lead to reduced sodium ion content? The authors are advised to provide a detailed explanation.
5. How did the authors calculate the Si/Al and Na/Al ratios? Were the Na, Al, and Si element contents from fly ash included in these calculations?
6. To validate the reliability of the established models, why did the authors choose to verify the experimental data from Hardjito et al.'s [53] study using their proposed complete stress-strain model, rather than validating their own experimental data?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

1.Regression Models and Existing Research Compariso
   While the proposed regression models are based on large datasets, the differences and improvements compared to existing studies are not thoroughly discussed. A comparative analysis should be added to highlight the advantages of the new models.  

2.Data Heterogeneity and Applicabilit
   The study integrates 726 data points, but the heterogeneity analysis of the data is unclear. It is recommended to clarify the applicability of partial datasets and validate the conversion factors adopted from OPC standards for GPC.  

Model Explanatory Power for Engineering Design
   The R² values of some models are acceptable but may lack sufficient guidance for engineering design. The alignment between statistical significance and practical relevance needs further evaluation, especially for extreme strength ranges .

4. Quantitative Analysis of FA Types
   The conclusion that "FA type has no critical effect on mechanical properties" requires quantitative validation. Additional analysis should be included to avoid oversimplification of conclusions.  

5. Literature Review Updates
   The references heavily focus on early studies. Recent advancements in GPC standardization should be incorporated to contextualize the proposed models.  

6. Clarity of Figures and Tables
   Some figures suffer from low resolution and unclear axis labels, reducing readability. Enhance graphical quality and add error bars or statistical significance markers where applicable.  

7. Environmental and Economic Considerations
   The study lacks discussion on the environmental impact and economic feasibility of GPC. Additionally, the scope of the proposed models should be explicitly defined.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript "Assessing Engineering Behavior of Fly Ash-based Geopolymer Concrete: Empirical Modeling" essentially focuses on an attempt to predict the properties of geopolymer concrete. Available experimental data were used to develop models, which were then verified through the authors' own laboratory tests. Below, I provide several comments and observations:

1. I suggest adding the term "geopolymer concrete" to the list of keywords.
2. The font used in the figures should be larger, as it is currently difficult to read. Additionally, the figures themselves could be slightly enlarged for better clarity.
3. Lines 166–167: Please provide the criterion used for selecting the research results from individual journals. The phrase "in reputational journals" is insufficiently specific. Perhaps the impact factor could serve as a more objective selection criterion.
4. Lines 219–220 and Figure 2: I disagree with the claim that the optimum Si/Al ratio is between 3.8 and 4. The coefficient of determination (R²) is missing from the graphs, which would support the validity of the fit. A straight line could be plotted instead of a parabola with a similar effect. Similarly, in the second case – the relationship between compressive strength and the Na/Al ratio – although the trend appears more convincing here, the same concerns apply. Please provide clarification.
5. Considering the goals of sustainable development, I would appreciate the author's comment on the sample preparation method—specifically, the use of a temperature of 60°C for 24 hours (The production of geopolymer concrete can be more energy-intensive and costly than that of conventional concrete, which limits its large-scale application).

Author Response

Please see the attachment.

Author Response File: Author Response.docx