Mechanical Behavior and Predictive Modeling of Cementitious Composites Incorporating Recycled HDPE

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper conducts relevant research on the properties and prediction models of cementitious composites incorporating recycled HDPE. The work carried out in the manuscript is relatively comprehensive, and the research topic provides certain reference value for understanding the influence of HDPE on the properties of mortar and concrete as well as predicting relevant performance indicators. However, the shortcomings in the manuscript are also obvious: the core purpose and necessity of this research are not clearly elaborated in the Introduction section, and the necessity of conducting this research lacks sufficient basis. The logical connection in the manuscript structure is not clear enough. For example, what is the purpose of the experimental research carried out in the first part? The authors have provided some explanations for the experimental results, which are intended to provide data for the establishment of subsequent prediction models, but the specific data used and the process of model establishment are rather vague. In addition, there are many issues regarding writing standardization, such as the superscripts of numbers, and the explanation of abbreviations. Specific modification suggestions are as follows:

1. What is the purpose of the experimental work in the first part of this research? Judging from the specific work carried out, there is no essential difference in theme of this research from most existing studies in the literature. It would be better to directly summarize the research data of others and systematically conduct research on prediction models.
2. Studies have shown that HDPE significantly reduces the mechanical properties of concrete. What are the specific application scenarios of cementitious composites incorporating recycled HDPE? It is recommended that the authors collect and summarize the performance requirements of concrete in specific cases of non-heavy-load engineering scenarios.
3. In the Introduction section, the authors summarize many previous research results and then directly switch to describing the research work to be carried out in this study. There is a lack of connection and transition between the two parts. The purpose of the literature review is to refine or point out the main problems existing in the current industry, then clarify which aspect of these problems this study intends to solve, and finally elaborate on the specific research work to address the problem. Such an expression is logically connected, and the necessity of this research will have sufficient basis.
4. In Section 2, what are the specific types of the used coarse aggregate (gravel) and fine aggregate (sand), such as granite, quartz sand, etc.? The key performance indicators of coarse and fine aggregates listed in Table 1 are incomplete. For example, alkali reactivity, soundness, crushing value, water absorption rate, and fineness modulus are all important performance indicators.
5. The meanings represented by the abbreviations FA and CA in Figure 1 should be explained.
6. It can be seen from Figure 2 and Table 1 that HDPE has a single particle size. Using HDPE to replace sand in different proportions will obviously affect the gradation of hybrid fine aggregates, thereby influencing the performance of concrete. It is meaningful only to replace sand with the same single particle size.
7. There are still many issues regarding the standardization of paper writing. For example: Times New Roman font is used in Table 1; the numbers in the data units in Table 2 should be superscripted; "Maximum Compressive Stress (MPa) (𝒇𝒄𝒐′)" in Table 4 should be rewritten as "Maximum Compressive Stress (𝒇𝒄𝒐′) (MPa)"; the titles at the top of Figure 6 and Figure 7 should be deleted; "MPa" in Table 8 is not fully displayed.
8. It is recommended to use actual operation diagrams or schematic diagrams to show the specimen preparation and experimental process. At the same time, some important detailed information in Figure 3 needed to be appropriately labeled. It is also suggested to summarize the test conditions of different experiments in a single table, which will make the text more concise and clearer.
9. The properties shown in Table 3 are discussed and analyzed separately later, so there is no need to list them independently here. The manuscript should be concise.
10. The authors directly compare the accuracy of the prediction model proposed in this study with that of models from other studies, which is actually meaningless. The experimental purposes and conditions often differ, so the applicability of the collected basic data is naturally different. In addition, the authors mention that the model established with 3 data points has higher accuracy, which is confusing. Three data points are not sufficient to reflect the variation trend of the data (e.g., it is difficult to determine whether it is a linear or exponential change). Moreover, fewer data points often lead to spurious fitting with seemingly high accuracy.
11. The paper mentions many models, so the authors should provide some recommended schemes at the end. For example, under what objectives or factor conditions are certain prediction models effective?

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The Manuscript entitled " Mechanical Behavior and Predictive Modeling of Cementitious Composites Incorporating Recycled HDPE " is interesting scientific work. However there are some issues that requires more attention:

• References: [15-20] please not use sets of references without explanation the differences between these works. e.g. material a [15] material b [16] material c [17] etc.
• the quality of figures must be improved. eg. figure 1 sieve curve of CA ASTM lower limit seems to present - percentage values which is not possible physically
• Figure 2: please provide at least at one hdpe granulate its diameter.
• Figure 5 - analyses - the Authors have not explained what happened to FS-HDPE-30 why there is a drop in stresses?
• Methodology - how many samples were tested? The Authors have not provided the mean values or standard deviation of the investigated samples. Therefore presenting the percentage of e.g. density as 3.74% is not providing enough information while it might be one measurement within the standard deviation from the mean value or it might not.
• Based on figure 8 the question is - what is the novelty of the provided research? The authors replicate some results without further explanation.

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have fully addressed the comments raised by the reviewer in the first round of review, and the manuscript has been significantly enhanced in terms of completeness, logical coherence, and comprehensiveness. However, the reviewer considers that two issues remain insufficiently resolved:

1. The authors have explained the reason for not providing the type and properties of aggregates (e.g., alkali reactivity, soundness, crushing value, water absorption rate, and fineness modulus). Nevertheless, the properties of composite materials are directly influenced by the type and properties of raw materials—for instance, limestone aggregates and granite aggregates undoubtedly exhibit distinct performances. Typically, detailed raw material information is required as it is critical for ensuring research reproducibility. The lack of such information will seriously hinder readers' understanding of the experimental results. Therefore, the authors are advised to supplement the type and specific property parameters of sand and gravel aggregates.
2. Since all properties presented in Table 3 are discussed one by one in subsequent sections, the reviewer believes there is no need to provide readers with a comprehensive preview of these results in advance. Additionally, there is no direct correlation between the various performances. Thus, the reviewer considers that Table 3 is still unnecessary, and journal papers should emphasize the conciseness of the text.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The Authors should emphasize based on figure 15 what is their contribution to the body of knowledge. As it can be seen in this figure there were papers describing similar issues. So what is new in this paper?

Author Response

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