Innovative Lightweight and Sustainable Composite Material for Building Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The submitted manuscript “sustainability-3764939” entitled: “Innovative lightweight and sustainable composite material for building applications” is an experimental study that explores an innovative lightweight composite material (BIOAERMAC) based on anhydrite, CSA cement, rubber particles from end-of-life tyres, and a bio-aeration technique. The study is relevant and timely, addressing critical themes in sustainable construction, circular economy, and eco-efficient materials. However, the manuscript should address the following comments and be revised and reconsidered.

1. The introduction is brief and lacks sufficient engagement with the state-of-the-art. The current version presents the problem and immediately introduces the authors’ solution, without adequately reviewing related studies or situating this work within the broader scientific discourse. Recent trends in production of lightweight mortar materials for structural and non-structural applications include incorporation waste-derived materials, such as polystyrene, rubber, glass, or recycled plastics or other polymer-based waste. These materials are increasingly used to improve sustainability, reduce construction waste, and enhance thermal and lightweight properties in mortars. The authors should broaden the literature review and discuss. For instance, these may serve as useful references to strengthen the context and discuss https://doi.org/10.1016/j.dibe.2024.100580, https://doi.org/10.1016/j.conbuildmat.2024.135018:
   • How does your approach compare to these alternative sustainable options;

This addition would strengthen the green construction dimension of the introduction and broaden the contextual relevance of your study.

2. The manuscript refers to both cubic and prismatic specimens, yet only dimensions for cubic samples are provided. Please clarify whether prismatic specimens were used, and if so, for which tests, including their dimensions.
3. Section 3.1 (Mix Design) would be more appropriately located in Section 2: Materials and Methods rather than under Results. This section describes experimental parameters and should precede the presentation of outcomes.
4. The heading of Table 4 appears to contain a labeling error. While the left column describes the A-type material, the right column is titled XRF Analysis but contains values consistent with the B-type mix. Please revise the table headers for clarity
5. It is recommended to include a clear synthesis table listing the exact mix compositions (g or %) for each specimen tested (e.g., A1, A2, B1, B2, etc.), including all constituents. This would greatly improve the transparency and reproducibility of the work.
6. The manuscript does not present any measurements or discussion of fresh state properties, such as: workability, commonly assessed through mini-slump tests or flow table methods (especially important given the use of a superplasticizer). Setting time, which is critical for materials incorporating rapid-setting binders like CSA and for evaluating compatibility with the bio-aeration process. These parameters are essential to assess the practical applicability and worksite handling behavior of the material, especially when proposing its use for prefabricated blocks or panels. Why did the authors not conduct such tests?
7. No information on water absorption, dimensional stability under humidity, shrinkage, or freeze-thaw resistance. These are crucial for lightweight prefabricated materials.
8. While optical microscopy is included, SEM or porosity distribution by image analysis or MIP would substantiate claims about homogeneity and air voids.
9. In line 209–210, the authors mention the goal of mimicking materials “commonly used in the construction industry.” It is necessary to specify which category of materials this refers to (e.g., non-structural mortars, AAC, insulating panels). Given the compressive strength values, the intended applications should be stated more explicitly.
10. Similarly, in lines 328–330, the authors claim BIOAERMAC performs “as well as or better than commercial lightweight products” without specifying which materials or properties are being compared. Please support such claims with quantitative comparisons, even if approximate (e.g., thermal conductivity and strength ranges of typical AAC blocks or perlite mortars). While compressive strength and λ values are provided, no clear comparison is made to existing commercial lightweight materials or standard performance requirements for gypsum-based panels. Add a comparative table or figure (e.g., with AAC, perlite mortars, or EPS mortars)
11. Please indicate the specific mix type (e.g., A2, B3, etc.) shown in Figure 6, as it is otherwise unclear which formulation is depicted
12. Figure 8 lacks axes labels and scale and presents only a single stress-strain curve without specifying to which specimen it refers. Furthermore, the claim that the behavior is “characteristic of all tested materials” seems inaccurate, given the reported differences in mechanical strength. It is also suggested to report the elastic modulus for each formulation.
13. The number of specimens tested for each formulation is not provided. Please specify the sample size (n) per test and include standard deviation or confidence intervals for compressive strength and thermal conductivity results in all figures and tables.
14. The conclusion claims reductions in “construction costs” and “energy resources” (lines 356–359), yet no economic or energy assessment is provided. It is recommended to either remove or revise these claims, or supplement them with preliminary Life Cycle Assessment (LCA) and/or Life Cycle Costing (LCC) analysis, for instance through activity-based costing
15. Line 328–330 and 333: Avoid vague comparative statements (e.g., “some cases better than competitive products”) unless backed by referenced evidence
16. Line 209–210: Reword vague statements like “new material with similar characteristics” and specify what materials and uses are being referenced
17. Section 4 (Discussion): This section primarily summarizes results and reads like a conclusion. It is suggested to rename it as “Conclusions” and include a separate, more interpretative Discussion section only if further scientific interpretation is provided.
18. Figure 3 caption is placeholder (“This is a figure. Schemes follow the same formatting.”).
19. The conclusions suggest further work is required (e.g., water absorption, other fillers), but these are not elaborated sufficiently. A dedicated section on limitations and future prospects would be beneficial.

Comments on the Quality of English Language

1. Typographic and language issues are present throughout the manuscript (e.g., “determinate” instead of “determine”; “collapse of the specimen due to the not reached setting time”, “determinate the final density”, “dismutation of the hydrogen peroxide”). A thorough language revision by a native English speaker or professional editing service is highly recommended.
2. Repetitive use of phrases (“it should be noted that…”, “in this sense…”)
3. Numerous long sentences hinder clarity — they should be split or rephrased.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents an interesting and up-to date study aimed at improving sustainability and resource efficiency in construction materials production. A cementituous material developed in the research holds much potential, specifically in a form of heat insulation (prefabricated panels or cement rubble - a replacement for expanded clay). Batch components suggested by authors are readily available and the technique may easily be implemented by practitioners.

Still, some issues need to be cleared. In the first place, what was the reason for using a combination of yeast+H₂O₂ as an aerating agent? A great number of inorganic foaming agents are known and introduced in the field with proved environmental effect and economical feasibility. Yeast is an important source of nutrients for food and livestock industries, its use in large-scale construction materials industry needs further assessment. Again, an issue arises of microbiological safety of practical implementation.

Secondly, with regards to hydrogen peroxide - why using yeast as a source of a reducing agent was suggested? It would work on any fine organic matter.

Lastly, it might make the results more informative if a comparison with commercially available foamed cementituous construction materials of the same porosity were provided.

Also, the text contains some unfortunate typos: line 99 (sulpfated), line 109 (C₄A₃s; better denote as C₃A₄SO₄, since S is typically reserved for SiO₂), line 117 (infact), line 133 (solids).

Regardless to these suggestions, the manuscript holds a definite scientific and practical significance and may be accepted to print.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this work, the authors present a novel lightweight construction material, BIOAERMAC, developed using synthetic anhydrous calcium sulfate and a bio-aeration system. The incorporation of end-of-life tire rubber particles is also explored to assess their potential for enhancing thermal performance. While the overall study is complete and presents an interesting and relevant topic within sustainable construction materials, the manuscript requires major revisions to improve clarity and presentation.

1. Figures: Unrelated or non-essential figures, such as the photographs of testing instruments (Figures 4 and 5), should be removed or moved to the supplementary information. These images do not add value to the understanding of the experimental results.
2. Figure Formatting: Several figures need reformatting for consistency. For example, the caption for Figure 3 is vague and should be clarified to accurately describe the content.
3. Language and Readability: The manuscript requires substantial English language editing to improve readability and ensure clear communication of the scientific content.
4. Experimental Detail: The Materials and Methods section should include more comprehensive details of the XRD and XRF analysis procedures, including instrumentation settings, operating conditions, and data processing steps, to support reproducibility and transparency.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript presents a compelling study on BIOAERMAC, a novel lightweight composite material for building applications, emphasizing sustainability through the use of industrial by-products and bio-aeration techniques. These suggestions focus on areas.

1. Abstract - Strengthen Summary of Key Findings

The abstract introduces BIOAERMAC and its sustainability benefits but lacks specific quantitative results. Include key performance metrics, such as density, compressive strength, or thermal conductivity values, to provide a clearer picture of the material’s capabilities. This will make the abstract more informative and engaging for readers.

2. Introduction - Define Scope and Objectives

The introduction effectively discusses the need for sustainable materials but could better define the scope of the study. Clearly state whether the focus is on material development, performance testing, or scalability for industrial applications. Additionally, refine the research objectives to emphasize how BIOAERMAC addresses specific challenges in lightweight construction materials.

3. Materials and Methods - Clarify Sample Preparation

The description of the sample preparation process (Section 3.1) is detailed but lacks clarity on the sequence and timing of mixing steps. Provide a step-by-step flowchart or diagram to illustrate the mixing, aeration, and molding process. This will improve reproducibility and help readers understand the practical implementation of the bio-aeration method.

4. Materials and Methods - Justify Component Selection

The mix design section (Section 3.1) lists components like brewer’s yeast and ELT rubber particles but does not explain why these were chosen over alternatives (e.g., chemical foaming agents or other aggregates). Justify the selection of each component based on cost, availability, or performance benefits to strengthen the rationale for the mix design.

5. Materials and Methods - Detail Testing Conditions

The testing procedures for density, compressive strength, and thermal conductivity (Section 3) reference standards like UNI EN 772-16:2011 but lack details on environmental conditions during testing (e.g., temperature, humidity). Specify these conditions to ensure reproducibility and clarify their impact on test outcomes, particularly for thermal conductivity measurements.

6. Results - Enhance Data Presentation

The results section includes valuable data on thermal conductivity and porosity but could be improved with clearer data visualization. Consolidate results for A-type and B-type materials into a single table comparing density, compressive strength, and thermal conductivity. This will make it easier to assess the impact of ELT particles and aeration levels.

7. Results - Discuss Porosity Distribution

The manuscript describes the homogeneous pore distribution in BIOAERMAC (Section 3) but does not quantify the pore size variability or its effect on performance. Include statistical data (e.g., standard deviation of pore sizes) or additional microscope images to support claims about porosity and its role in mechanical and thermal properties.

8. Discussion - Address Scalability Challenges

The discussion highlights BIOAERMAC’s competitiveness but does not address potential scalability issues for industrial production. Discuss challenges such as sourcing consistent quality brewer’s yeast or ELT particles, production costs, or energy requirements for large-scale manufacturing to provide a realistic perspective on commercialization.

9. Discussion - Elaborate on Plastic Behavior

The manuscript notes that B-type materials exhibit plastic behavior under compression (Section 4), which expands potential applications. Provide a more detailed explanation of this plastic behavior, including its implications for structural versus non-structural uses. Compare this behavior to traditional materials to highlight BIOAERMAC’s unique advantages.

10. Conclusion - Propose Future Research Directions

The conclusion summarizes the study’s findings but lacks suggestions for future research. Propose specific areas for further investigation, such as long-term durability testing, fire resistance evaluation, or integration with other sustainable materials. This will demonstrate the study’s forward-looking perspective and encourage further exploration.

Author Response

Please see the attachment.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have adressed all the comments and improved the manuscript. No further comments.