Review Reports - Design and Characteristics of De-Constructable Shelter with Biodegradable Materials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper addresses three critical global challenges: construction waste generation, forced displacement and housing shortage. This paper presents a comprehensive investigation into the design and development of a regenerative, modular housing system utilizing biodegradable composite materials synthesized from locally abundant agricultural waste, specifically rice straw.

(1)The abstract repeats 'research to tackle the three major global challenges' three times, making the sentences very repetitive; the claims of 88% carbon reduction and 64% cost reduction lack a baseline for comparison, so it's unclear on first read that the comparison is with traditional reinforced concrete shelters.

(2)The sandwich panel test design is missing information. The preparation of the bio-composite panels only lists the ratio (70% biomass, 30% sodium silicate) and hot pressing (130℃/50kN/m²), but doesn’t specify raw material pre-treatment processes (straw particle size, palm leaf vein treatment), hot-press insulation time, or panel curing regimen, making the experiment hard to replicate.

(3)Descriptions of the mechanical tests are incomplete. Four-point bending and compression tests only cite ASTM numbers, without mentioning span, loading rate, specimen quantity (number of parallel samples per group), or data selection rules, which makes the test procedures insufficiently standardized. It is recommended to refer to recent research papers in the introduction. The bifurcation characteristics and dynamical evolution rule of non-isothermal seepage mechanical model in fractured rock mass.

(4)Information on wall-roof joint tests is missing. Full-scale joint tests used a universal testing machine with monotonic loading, but details on loading method, displacement measurement points, and strain gauge layout are absent; modifications to ASTM D1761 are not explained, leaving the test process incomplete.

(5)Figure 7 has a spelling error in the title: 'sandwish panel' should be 'sandwich panel'; Figure 8’s legend labels are repeated and confusing (d and c descriptions are identical); Figure 9 only simply marks compressive strength changes, without axis units or group legends.

Author Response

The authors would like to express their gratitude for the useful feedback received from the reviewer. Kindly find attached the updated manuscript together with the response to reviewer comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1.The article lists construction waste, the refugee crisis, and housing shortage as research motivations but does not explain how bio-based materials directly and logically address these three issues. The motivation seems somewhat forced. It's recommended to restructure the introduction, clearly point out the shortcomings of existing temporary housing solutions—like RC structures being non-eco-friendly and tents being uncomfortable—and argue how bio-based shelters, with features like low carbon, quick deployment, and biodegradability, can serve as a solution connecting these challenges, thus strengthening the research premise.

2.The article lacks scientific basis and preliminary experimental support for the formulation and process parameters of the bio-composite panels. It's suggested to add a description of exploratory experiments conducted to determine these key parameters, such as testing mechanical properties under different ratios and temperature-pressure combinations, and to explain the specific reasons for choosing the current parameters.

3.In the sandwich panel experiments, both the face and core thicknesses were changed simultaneously, making it impossible to independently analyze the contribution of each component to performance improvement. This limits the universality of the conclusions. It's recommended to add control experiment groups, for example, fixing the face thickness while changing only the core thickness, to clearly explain the effect of each variable. If additional experiments aren’t feasible, this limitation should be clearly stated in the discussion.

4.The discussion of sandwich panel bending performance is oversimplified, only using axial stress to explain it, and ignores the increase in shear stiffness and overall stability brought by a thicker core. It does not fully utilize composite beam theory. It’s suggested to start from composite beam theory and quantitatively analyze the contribution of core thickness to section inertia, bending stiffness, and shear carrying capacity, providing a deeper and more accurate explanation of the mechanism.

5.In the SAP2000 modeling, the sandwich panel is simplified as an equivalent homogeneous plate, but the article does not explain how key properties like equivalent elastic modulus and shear modulus were determined. This directly affects the reliability of all calculation results. It's recommended to clarify whether the equivalent material properties were calculated based on classical sandwich panel theory formulas or back-calculated from bending test results, and to provide specific values to ensure the analysis is transparent and reproducible.

6.The boundary conditions and semi-rigid connection definitions in the structural model are vague, inconsistent with the dismountable, prefabricated nature of the structure, and the model is not calibrated using connector test data. It’s recommended to quantify the moment-rotation curve from connector tests and use it as model input. Also, re-evaluate the wall base boundary conditions; a hinged support might be more realistic to avoid overestimating structural performance.

7.In the economic comparison, the article compares a 75mm thick bio-based wall with a 150mm thick RC wall and only considers construction costs. This is unfair and does not account for functional equivalence or life cycle costs. It's recommended to clearly acknowledge this limitation in the comparison, discuss what modifications would be needed for the RC wall to achieve the same thermal performance, and include maintenance, operation, and demolition costs in a full life cycle economic assessment, which would better highlight the advantages of bio-based materials.

8.The article's carbon emission assessment overlooks the biocarbon fixed during the growth of bio-based materials, that is, the carbon sequestration effect. This is a significant underestimation of its environmental benefits. It is recommended to use a cradle-to-grave LCA approach, clearly discuss it, and include the negative emissions of biocarbon in the total carbon emission calculation, or at least mention it as an important discussion point, to more fully and accurately reflect its environmental benefits.

9.Although the study highlights designing for disassembly as a core feature, it does not provide any quantitative indicators to assess disassemblability and only stays at a qualitative description. It is recommended to introduce industry-recognized DfD quantitative evaluation metrics, such as disassembly time index and fastener standardization rate, to score the design's disassemblability, elevating this concept from a claim to a verifiable design outcome.

Author Response

The authors would like to express their gratitude for the useful feedback received from the reviewer. Kindly find attached the updated manuscript together with the response to reviewer comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper aims at presenting a comprehensive investigation into the design and development of a regenerative, modular housing system utilizing biodegradable composite materials synthesized from locally abundant agricultural waste. The research directly addresses three critical global challenges: environmental sustainability including construction waste generation, forced displacement, and housing shortage.

1.The biodegradation rate and degradation conditions of the materials are also not verified, which cannot fully support the core conclusion of "biodegradable and suitable for temporary shelters". The mechanical parameters of Casuarina Glauca wood are all cited from the team's previous studies, and no measured values of the wood properties used in this test are given. The material input parameters of the numerical model lack data support from this study. Revision Recommendations: supplement the measured values of mechanical properties of wood used in this test, and clarify the parameter source of the numerical model; demonstrate the rationality of the design service life combined with the weather resistance of materials, and clarify the applicable environment and maintenance requirements.

2.The finite element model equates the sandwich composite panel to a homogeneous shell element with a thickness of 75 mm, without considering the layered mechanical characteristics of face sheets and wood core, nor verifying the accuracy of equivalent section parameters. The paper only states that the stress is lower than the material strength, but does not clarify the structural safety factor and redundancy, nor does it carry out the deformation check under the serviceability limit state, resulting in insufficient demonstration depth of structural safety. Revision Recommendations: supplement unfavorable load combinations such as wind suction and temperature effect, and improve the checking of overall stability, anti-overturning and lateral stiffness; clarify the safety reserve coefficients of each control section, and supplement the deformation check of the serviceability limit state and the description of code compliance.

3.The influence of adhesive use on the disassembly integrity of panels, material recyclability and biodegradability is not discussed, and the differences in disassembly efficiency and resource utilization rate between this scheme and traditional prefabricated buildings are not compared. The conclusion of "complete disassembly" lacks practical verification support. Revision Recommendations: introduce a deconstructability evaluation method to quantitatively evaluate the scheme, and carry out benchmarking analysis with similar building schemes; discuss the influence of adhesives on disassembly and degradation performance, and clarify the reuse times and performance retention level of reusable components.

4.The specific values and sources of carbon emission factors of various materials are not listed, nor is the carbon sink effect of agricultural waste raw materials and alternative emission reduction benefits considered. The accounting method and boundary are not clearly explained. In cost accounting, the basis for setting price sources, inflation coefficient, bulk discount and local deduction coefficient is insufficient. Revision Recommendations: supplement the price basis and parameter setting description of cost accounting, unify the accounting boundary and performance benchmark of comparison schemes, and enhance the rigor of horizontal comparison; supplement sensitivity analysis to discuss the influence of factors such as raw material price and transportation distance on the results.

Author Response

The authors would like to express their gratitude for the useful feedback received from the reviewer. Kindly find attached the updated manuscript together with the response to reviewer comments.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

2.3.3. Eco-friendliness Environmental sustainability Assessment 296

The process of determining embodied carbon emissions for the two building alterna- 297

tives, the bio-composite thesis model and the reinforced concrete (RC) control model, en- 298

tails identifying all constituent materials (rice straw composites, palm midrib fillers, tim- 299

ber framing, concrete, steel reinforcement), quantifying their masses or volumes from the 300

3 m × 3 m × 2.25 m prototype design (e.g., 550 kg total for thesis model vs. 9,400 kg for RC), 301

sourcing cradle-to-gate emission factors (kg CO₂-eq per kg or m³ of each material) from 302

credible life-cycle inventory (LCI) databases and literature such as Ecoinvent v3.9.1 (for 303

concrete at 0.20 kg CO₂-eq/kg and steel at 2.20 kg CO₂-eq/kg), agricultural waste baselines 304

for bio-composites (rice straw at 0.10 kg CO₂-eq/kg) [27], and localized adjustments for 305

Egyptian-sourced timber (0.80 kg CO₂-eq/kg) [10], then multiplying each unit emission 306

factor by the specific quantity required per alternative before summing across categories 307

to derive totals of carbon emissions for each alternative.

I suggest the authors complete your paper with the Life Cycle Assessment. Please include:

Goal and Scope Definition;

Life Cycle Inventory (LCI): An LCI involves data collection to quantify all inputs (e.g., energy, water, raw materials) and outputs (e.g., waste, air emissions, wastewater) associated with the product with the product throughout its entire life cycle;

Life Cycle Impact Assessment (LCIA): This stage evaluates the potential environmental consequences using the LCI data;

Interpretation.

3.5. Results of Eco-friendliness Environmental sustainability Assessment

Complete this section in accordance with the suggestions in 2.3.3.

Author Response

The authors would like to express their gratitude for the useful feedback received from the reviewer. Kindly find attached the updated manuscript together with the response to reviewer comments.

Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

his paper proposes a biomass sandwich panel system fabricated from rice straw and Casuarina equisetifolia timber for 3 m × 3 m emergency shelters. The topic addresses challenges including population displacement and housing shortages, and the research scope covers material characterization, structural analysis, connection tests, as well as life-cycle cost and carbon emission assessments; the breadth of the investigation is commendable. Nevertheless, several critical flaws substantially undermine the validity of the conclusions, including confounding experimental variables, one-sided attribution that disregards stability effects, superficial failure characterization, overstated conclusions, unvalidated disassembly performance, inappropriate sustainability comparison benchmarks, and ambiguous carbon accounting.

The authors revise the manuscript to resolve the specific issues outlined below:

Section 2.1, Table 1 suffers from inadequate control of experimental design variables and a lack of benchmark specimens. The four configurations simultaneously vary both face sheet thickness and core depth, without single-variable comparison groups, core-free reference panels or solid timber control panels. The available data cannot decouple the individual contributions of face sheet thickness and core depth to load-bearing capacity. The observed strength enhancement may stem from either parameter or their interaction, yet the testing program fails to distinguish these effects.
Section 3.1 presents a one-sided analysis of the mechanism underlying improved load-bearing performance. The authors attribute the elevated flexural capacity solely to the increased internal moment arm resulting from greater core depth, while overlooking coupled effects such as delayed local buckling of compressed face sheets, redistribution of sectional stiffness, and shifts in overall failure modes, thereby conflating superimposed contributions from sectional stability. Furthermore, no measured strain distribution data along the cross-sectional depth of specimens are provided throughout the manuscript, leaving the proposed mechanical mechanism unsupported by direct experimental evidence.
Section 3.1 and Figure 7 feature incomplete characterization of failure behavior. Only macroscopic failure photographs are supplied, with no mesoscopic/microscopic fractography or images of interfacial delamination, nor any quantitative classification of failure modes. The nonlinear segments and load-drop features in Figure 7 are not correlated with discrete damage progression, making it impossible to identify the dominant failure mode among face sheet crushing, core shear, and interfacial debonding. The interface of this biocomposite constitutes a critical weak zone; the absence of multi-scale morphological analysis coupled with damage evolution renders the interpretation of failure mechanisms ambiguous.
Grandiloquent claims in the abstract and introduction, such as “directly addressing three major global challenges” and “a holistic solution to displacement and housing crises”, must be removed. The conclusions section shall strictly delineate the scope of applicability: the reported 64% cost reduction and sustainability advantages exclusively apply to the single 3 m × 3 m module examined in this study, utilizing rice straw sourced from the Nile Delta and local Casuarina equisetifolia timber, with a 2-year design service life and operating conditions featuring low wind pressure and no seismic requirements. This prototype remains an exploratory test specimen; multi-module assembly, multi-climate environmental testing, and on-site field validation have not been conducted. It cannot be regarded as a mature, deployable technology, and all relevant conclusions require comprehensive re-evaluation prior to cross-scenario extrapolation.
The formatting of references requires refinement. All citations should be standardized in full compliance with the journal’s reference guidelines.

Author Response

The authors would like to express their gratitude for the useful feedback received from the reviewer. Kindly find attached the updated manuscript together with the response to reviewer comments.