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F1000Research

2046-1402

F1000 Research Limited

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10.12688/f1000research.176250.2

Research Article

Articles

Sustainable RC Beams with Agricultural Waste Fine Aggregate and Glass Powder: Structural Evaluation under Bending

[version 2; peer review: 2 approved with reservations]

Ali

Ziadoon M.

Investigation Methodology Writing – Original Draft Preparation 1 Mahmoud Hama

Sheelan

Methodology Supervision Writing – Original Draft Preparation Writing – Review & Editing https://orcid.org/0000-0001-7265-583X a 2 Hilal

Nahla

Writing – Original Draft Preparation Writing – Review & Editing https://orcid.org/0000-0001-9403-9982 b 3 Mhedi

Nebras M.

Investigation 2 Harrat

Zouaoui R.

Writing – Review & Editing 4 1Construction and Projects Department, University of Anbar, Ramadi, Anbar, Iraq 2Department of Civil Engineering, University of Anbar, Ramadi, Al Anbar Governorate, Iraq 3University of Fallujah, Al-Fallujah, Al Anbar Governorate, Iraq 4Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, Djilllali Liabes University, Sidi Bel Abbes 22000, Algeria

a drsheelan@uoanbar.edu.iq b nahla.naji@uofallujah.edu.iq

No competing interests were disclosed.

9 6 2026

2026

3 6 2026

2026

This is an open access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background

This experimental study evaluates the structural behavior of reinforced concrete (RC) beams incorporating walnut shell fine aggregate (WFA) and 15% powdered waste glass (PWG).

Method

Eight simply-supported RC beams were cast and tested in two series: Group 1 (beams with transverse stirrups i.e. flexure-dominated) and Group 2 (beams without stirrups i.e. shear-dominated). Mixes included a control (0% WFA) and three WFA replacement levels (10%, 20%, 30% by volume of sand), with PWG fixed at 15% of cement in all mixes. Tests included 28-day compressive strength, density measurements, and two-point bending load–deflection tests.

Results

Results show that 10% WFA replacement enhanced compressive strength by 3–5%, flexural capacity by ~6%, and ductility by 64%, while reducing density by 6–8%. Higher WFA contents reduced stiffness but improved energy absorption and crack distribution.

Conclusions

The findings confirm that moderate WFA replacement (≤10%) combined with PWG yields eco-efficient RC beams with improved ductility and reduced dead load.

Sustainable reinforced concrete beams; Agricultural waste fine aggregate; Waste glass powder in concrete; Flexural behavior of RC beams; Shear performance of concrete beams.

The author(s) declared that no grants were involved in supporting this work.

Revised Amendments from Version 1

The revised version of the manuscript includes substantial improvements in response to the reviewers’ comments. The Introduction was condensed and reorganized to reduce repetition and better highlight the research gap concerning the combined use of walnut shell fine aggregate and powdered waste glass in reinforced concrete beams. The abstract was completely rewritten to improve clarity, logical flow, and presentation of the main findings and contributions. Additional discussions were incorporated throughout the manuscript to provide deeper interpretation of the structural behavior, including stiffness degradation, crack propagation, stress redistribution, and the temporary load reduction observed in the load–deflection curves prior to ultimate failure. The methodology section was expanded to clarify the procedures used for crack width measurement, determination of first-crack load, and calculation of ductility parameters. Quantitative improvements were also made by reporting exact percentage increases and decreases in compressive strength, density, shear load capacity, and deflection behavior instead of approximate ranges. Furthermore, first-crack loads and their percentage variations relative to the control beam were added for both flexural- and shear-dominated specimens. The Conclusions section was revised to provide more concise and structurally focused findings. Additional statements regarding sustainability implications, lightweight structural efficiency, and future research needs were also included. Finally, the manuscript underwent comprehensive English language editing to improve grammar, clarity, consistency, and academic writing quality throughout the paper.

Introduction

Concrete production is a major contributor to CO ₂ emissions, mainly due to cement and aggregate consumption. ¹ In response to the increasing environmental concerns, researchers have explored alternative materials, such as agricultural waste and industrial by-products, for use in concrete to reduce its environmental footprint. ^{2–
4} The integration of waste materials in structural members such as RC slabs and beams remains underexplored. Some efforts include using of recycled concrete aggregates in flexural members, ⁵ incorporation of eggshell and plastic waste in some structural application. ^{4–
7}

Among various agricultural residues, walnut shell have emerged as a promising partial replacement for fine aggregates due to their lignocellulosic composition and favorable physical properties. ^{8,
9} Microstructural and thermal performance under elevated temperatures were also favorable when walnut shell replaced sand, showing resistance to cracking and improved insulation. ¹⁰

Flexural and compressive behavior of concrete incorporating walnut shell was studied in multiple works, indicating a moderate strength reduction but significant weight savings and enhanced sustainability. ^{11–
13} Several studies confirm the potential of walnut shell in reducing the density of concrete while maintaining acceptable mechanical strength. ^{14–
16} Optimization techniques have been employed to identify ideal substitution levels of walnut shell, balancing strength and environmental benefits. ^{12,
15,
17} Despite these advancements, limited studies have investigated the structural performance of RC beams incorporating walnut shell aggregate, especially under bending loads.

Use of glass waste in structural concrete beams and its positive contribution to stiffness and load capacity. ^{18,
19} Nonetheless, research on hybrid use of walnut shell and glass powder in reinforced concrete beams remains limited, especially in terms of structural behavior under bending moments, load-deflection characteristics, and failure modes. Waste glass powder (WGP) is another sustainable alternative that can replace cement or fine aggregates due to its high silica content and pozzolanic activity. ^{20–
22} Numerous studies report that WGP can enhance; compressive and flexural strength by filling voids and densifying the matrix. ^{19,
21,
24} Durability properties such as reduced permeability and improved resistance to sulfate attack, ^{23,
25} Thermal and microstructural stability under elevated temperatures. ²⁰ PWG also compensates for strength loss caused by agricultural waste use, making it an excellent synergistic additive for hybrid sustainable concrete. ¹⁹ However, few studies have explored its combined role with organic fine aggregates like walnut shell in reinforced concrete elements.

Although the sustainability potential of both agricultural waste and glass powder in concrete has been well demonstrated individually, their combined effect in RC beams has not been sufficiently studied. In particular: •

There is a lack of experimental data on load-bearing capacity, crack propagation, and mode of failure of RC beams with walnut shell and PWG.

•

Structural implications of using organic fine aggregate and pozzolanic glass powder need to be validated under realistic flexural loading conditions.

This study addresses the aforementioned gap by evaluating the flexural behavior of sustainable RC beams incorporating walnut shell as fine aggregate and glass powder as a strength-enhancing additive. The research contributes to the development of eco-efficient structural elements, offering a dual benefit of waste management and carbon footprint reduction in construction.

For all mixes the cement was replaced with 15% glass powder. The selection of 15% glass powder (GP) as a partial replacement for cement in all concrete mixes was based on prior experimental findings that demonstrated its optimal contribution to mechanical and structural performance. Several studies have investigated the influence of PWG content on the strength and behavior of concrete, and consistently reported that 15% replacement yields superior results. Recent reviews have summarized the environmental and mechanical benefits of incorporating glass powder in green concrete systems, emphasizing its pozzolanic and filler effects. ²⁶ Yassen et al. ²⁷ experimentally investigated the shear behavior of reinforced concrete beams incorporating waste glass powder and concluded that 15% replacement provides the best balance between strength gain and material efficiency. Similarly, Khudair et al. ²⁸ conducted an optimization study on self-compacting concrete using varying P contents and identified 15% as the optimum dosage for enhancing workability, compressive strength, and overall performance. Additionally, Ubeid et al. ²⁹ confirmed that 15% PWG enhances not only the compressive and flexural strength, but also significantly improves the energy absorption capacity and bond resistance of concrete key indicators of ductility and structural integrity. These findings collectively validate the selection of 15% PWG in the current study as a performance-based and scientifically supported choice to achieve both environmental and mechanical benefits. ²⁹

Recent studies on hybrid waste materials in concrete indicate significant environmental and mechanical benefits; however, there remains limited evidence on their combined structural performance in reinforced elements. ^{30–
33} This study uniquely examines RC beams containing both WFA and PWG under bending, filling this gap.

The selection of 15% PWG as cement replacement was based on previous optimization studies ^{27–
29} that identified this level as providing maximum strength and matrix densification. It is anticipated that higher PWG contents could reduce workability and slightly delay hydration, whereas lower contents might yield less pozzolanic benefit.

Materials and Method A. Materials

In this study, locally sourced materials were selected with an emphasis on sustainability and structural performance. 1.

Cement: Ordinary Portland Cement (OPC) conforming to Iraqi Standards No. 5/2019 ³⁴ was used as the primary binder. To enhance sustainability and reduce cement consumption, part of the cement was replaced with glass powder.

Fine Aggregate: Natural river sand, classified as Zone 2 according to Iraqi Specification No. 45/1984, ³⁵ was used as the control fine aggregate with specific gravity of 2.63. For the sustainable mixes, a portion of the sand was replaced by WFA, an agricultural waste product.

The walnut shells were first cleaned to remove organic residues, oven-dried at 105 ± 2 °C for 24 hours, and crushed using a jaw crusher into irregular particles. The crushed shells were then sieved through a series of standard sieves (4.75 mm, 2.36 mm, 1.18 mm, and 0.6 mm) to obtain a particle size distribution comparable to that of natural fine aggregate, with a maximum size limited to 10 mm. Particles retained between 0.6–4.75 mm were used in the mixes to ensure proper grading and packing. Its specific gravity was measured at 0.96, with a water absorption capacity of 10%. Walnut shells were used as partial fine aggregate replacements, taking advantage of their lightweight and lignocellulosic composition, which promotes sustainability and reduces concrete density. The procedure of preparing fine WFA is illustrated in Figure 1. 3.

Coarse Aggregate: Crushed gravel with a maximum nominal size of 10 mm was used as the coarse aggregate in all concrete mixes.

Powdered Waste Glass (PWG): Waste glass was collected, crushed, and ground into a fine powder, then sieved through a No. 200 sieve (75 μm) to ensure uniform particle size. The resulting PWG had a high silica content and exhibited significant pozzolanic activity. As confirmed by ASTM C1240, ³⁶ the pozzolanic activity index (PAI) of the glass powder at 28 days was 95.28%, satisfying the requirements for pozzolanic materials. In all mixes, 15% of the cement content was replaced by PWG to enhance mechanical performance and durability while reducing the environmental footprint.

Water: Tap water was used for both mixing and curing purposes.

Figure 1. Steps of preparing WFA. B. Mix proportion and specimen preparation

The experimental program included four concrete mixes: one control mix using natural fine aggregate (sand) and four sustainable mixes incorporating varying proportions of WFA as partial fine aggregate replacement. In all mixes, 15% of the cement was replaced by PWG by weight. This fixed glass powder content was selected based on previous studies demonstrating its optimal contribution to strength and durability. ^{27–
29} A constant water-to-binder ratio of 0.38 was adopted for all mixtures with 1% superplasticizer (SP). Table 1 presents the detailed mix proportions, including the control mix and the replacement levels of WFA (10%, 20%, and 30%) by volume of fine aggregate.

Table 1. Mix proportion in kg/m <sup>3</sup>.

Mix ID	WFA replacement (%)	Cement	PWG	Water	Superplasticizer	Sand	WFA	Gravel
R	0	405	45	171	4.5	640.0	0.0	1150.0
10%WFA	10	405	45	171	4.5	576.6	23.4	1150.0
20% WFA	20	405	45	171	4.5	511.3	46.7	1150.0
30% WFA	30	405	45	171	4.5	447.0	70.1	1150.0

All constituent materials were measured by weight and mixed in a pan mixer. The mixing process involved the following steps. First, dry mixing of sand, walnut shell (as per the replacement level), cement, and glass powder for 2 minutes. Then gradual addition of water with SP and continued mixing for an additional 3–4 minutes until a uniform consistency was achieved.

A total of eight reinforced concrete beam specimens were cast, grouped into two series (four specimens per group). Each beam had dimensions of 150 mm × 150 mm × 1000 mm and was designed for testing under bending loading. The reinforcement details were kept identical for all beams to ensure consistent comparison.

For group 1, the reinforcement consisted of two longitudinal tension bars of 12 mm diameter (bottom), two compression bars of 6 mm diameter (top), 6 mm diameter stirrups spaced at 55 mm centers along the length of the beam for group 1. While group 2 free from stirrups to check shear strength and the rest reinforcement details is just same as group 1.

After casting, the beams were covered with plastic sheets and kept in the molds for 24 hours. The reinforcing details are shown in Figure 2. Thereafter, all specimens were demolded and cured in water at 23 ± 2°C for 28 days to ensure proper hydration.

Figure 2. Details of reinforcement.

To evaluate the compressive strength of the concrete mixes, three cube specimens measuring 100 mm × 100 mm × 100 mm were cast for each mix. Also, dry density has been measured.

C. Test set up

The compressive strength test was performed at 28 days of curing using an ELE Digital Compression Testing Machine with a load capacity of 2000 kN. The loading was applied continuously at a controlled rate until failure. All procedures conformed to the British Standard BS EN 12390-3:2009, ²³ which outlines the methodology for determining the compressive strength of hardened concrete. The structural performance of the concrete mixes was assessed through flexural testing of eight reinforced concrete beams. Each beam specimen had dimensions of 150 mm × 150 mm × 1000 mm. The bending tests were conducted using a hydraulic jack with a maximum capacity of 500 kN, employing a two-point loading setup to simulate realistic flexural conditions. The load was applied in 5 kN increments, starting from zero and increasing gradually until the beam reached structural failure. A Linear Variable Differential Transformer (LVDT) was installed at the mid-span of each beam to measure the deflection response accurately under increasing load. The LVDT provided real-time displacement data synchronized with the applied load readings. During the testing process, the applied load was continuously recorded using a computer-based data acquisition system. Load-deflection behavior, crack propagation, and failure mode were closely observed and documented. The flexural test setup and instrumentation arrangement are illustrated in Figure 3.

Figure 3. Test set up. Results and discussion A. Compressive strength of concrete mixes

The 28-day compressive strength results of the concrete mixes are presented in Figure 4. The control mix (RC-0) achieved a compressive strength of approximately 60 MPa, which satisfied the design requirement. At 10% walnut shell replacement (RC-10), a ~3–5% increase in compressive strength was recorded compared with the control. This enhancement can be attributed to the fiber-like morphology and flaky texture of walnut shell particles, which improved crack-bridging and stress transfer within the cementitious matrix. Similar strengthening effects of walnut shell on interfacial bonding and crack resistance were reported by Cheng et al. ¹¹ and Hilal et al. ¹⁴ The presence of 15% pozzolanic waste glass (PWG) in all mixes further contributed to matrix densification and additional hydration reactions, thus counteracting part of the strength loss normally associated with agricultural waste aggregates. ^{20,
21} However, at 20% and 30% replacement levels (RC-20 and RC-30), the compressive strength declined by approximately 8–12% and 15–20%, respectively, compared to the control mix. This reduction is mainly attributed to the lower density, higher porosity, and weaker bonding of walnut shell relative to natural sand. ^{8,
16} Despite these reductions, all mixes maintained compressive strengths within acceptable structural ranges. Comparable findings were reported in other studies that evaluated lignocellulosic waste aggregates. ^{12,
15}

Figure 4. Compressive strength vs. WFA. B. Density of concrete mixes

As presented in Figure 5, a progressive reduction in density was observed with increasing levels of walnut shell replacement. The dry density values were consistently lower than the corresponding fresh densities, which is attributed to hydration of cement and the evaporation of free water during drying. The control mix exhibited the highest density of approximately 2400 kg/m³, whereas the incorporation of walnut shell at 10%, 20%, and 30% replacement levels led to decreases of nearly 2%, 4%, and 6–8%, respectively, compared with the control. The lowest density recorded at 30% replacement highlights the intrinsic lightweight and porous structure of walnut shell. ^{14,
16} This density reduction is advantageous in producing lightweight concretes, offering potential applications in both structural and non-structural elements, as also demonstrated in previous studies. ¹³

Figure 5. Density vs. WFA.

The combined results demonstrate that partial replacement of fine aggregate with walnut shell up to 10% not only maintained but slightly enhanced compressive strength (~3–5% higher than control), while higher replacement levels led to strength reductions (up to ~20% at 30% replacement) but simultaneously reduced density (~6–8% lighter). These findings suggest that walnut shell can serve as a sustainable lightweight aggregate in structural concrete when used at moderate levels, particularly when combined with pozzolanic waste glass to compensate for potential strength losses. This aligns with current research directions aimed at developing environmentally friendly and resource-efficient concrete. ^{3,
19,
23,
25}

C. Load–deflection behavior

•

Flexural Load–Deflection Behavior (Group 1)

The curves in Figure 6 show that beams with 10% WFA replacement achieved higher ultimate load capacity and greater ductility compared with the control beam. This indicates that a limited amount of WFA enhances the post-cracking behavior of beams, acting somewhat like discrete fibers that improve energy absorption and crack bridging. However, at 20% and 30% replacement, the load capacity and stiffness decreased. This reduction is consistent with the decline in compressive strength at higher WFA content, mainly due to the porous and organic nature of WFA, which weakens the matrix continuity and reduces aggregate interlock. Even so, these higher replacement levels still maintained reasonable ductility, which is advantageous for applications requiring lightweight materials with better energy dissipation capacity.

Figure 6. Flexural Load–Deflection Behavior (Group 1).

The addition of glass powder across all mixes refined the pore structure and improved the bond between cement paste and aggregate, which reduced brittleness and contributed positively to flexural performance. •

Shear Load–Deflection Behavior (Group 2)

Beams in this group failed predominantly in shear rather than flexure. The curves in Figure 7 show a sharper load drop after peak load compared to flexural failure, reflecting the more brittle nature of shear failure. With increasing WFA content (10%, 20%, 30%), there is a general reduction in peak load capacity, similar to the flexural group. However, the deflection at failure increased slightly with higher WFA content, suggesting some improvement in ductility even under shear-dominated behavior. The presence of glass powder again contributed to improved crack control and bond strength, mitigating the suddenness of shear failure to some extent.

Figure 7. Shear Load–Deflection Behavior (Group 2). D. Crack patterns and failure modes

•

Flexural Behavior-Group 1

Crack propagation and failure modes are illustrated in Figure 8. All beams failed in flexural tension, with initial cracks forming at mid-span and progressing toward the compression zone as loading increased. The control beam showed fewer, more localized vertical cracks, indicative of a brittle failure mode. The 10% WFA beam exhibited wider but more distributed cracks, reflecting enhanced ductility and better energy dissipation capacity. Beams with 20% and 30% WFA displayed multiple fine cracks along the span, and the failure occurred more gradually a hallmark of ductile behavior, likely promoted by the combined effect of glass powder and the flexible nature of the walnut shell. These results reinforce that 10% WFA is an optimum replacement level, providing performance improvements in both compressive and flexural behavior, while higher WFA contents offer benefits in terms of lightweight characteristics and ductility, albeit with a trade-off in strength. •

Shear Behavior-Group 2

Figure 8. Crack pattern (Group 1).

In Group 2, all beams were tested without transverse stirrups to intentionally provoke shear-governed failure, see Figure 9. The observed cracking patterns and failure mechanisms are consistent with diagonal shear cracking and sudden shear-slip mechanisms typical of lightly reinforced beams lacking shear reinforcement.

Figure 9. Crack pattern (Group 2).

The first visible cracks formed near the expected critical shear span (approximately at the support region and along the shear span between the loading point and support). Initial cracks were predominantly inclined (diagonal) relative to the beam axis and developed at relatively low load levels, indicating the early development of principal tensile stresses due to combined shear and bending. With increasing load the inclined cracks widened and propagated rapidly toward the compression zone and adjacent support regions. In the control beam, diagonal cracks were fewer but coarser and rapidly progressed to a single dominant diagonal shear crack, culminating in a brittle drop in load. In WFA-containing beams, cracks tended to be more distributed: a network of multiple diagonal micro-cracks coalesced prior to formation of the dominant crack. This distribution was more pronounced with higher WFA contents (20–30%), likely related to reduced stiffness and increased deformability of the matrix and weaker aggregate interlock.

All Group 2 beams failed by diagonal shear characterized by sudden propagation of the principal diagonal crack connecting the load application zone to the support. The failure in the control beam occurred more abruptly, with a clean diagonal fracture plane and limited post-peak load capacity. In contrast, WFA mixes exhibited a slightly more progressive failure: although the peak load was lower, the post-peak decay of load was less instantaneous in mixes with PWG, and the crack pattern near failure included additional secondary splits and localized crushing at the compression zone adjacent to the diagonal crack. At higher WFA replacements (20–30%), the diagonal cracks were accompanied by more pronounced sliding and wider crack openings, indicating reduced aggregate interlock and frictional resistance along the crack plane.

Across WFA percentages, the presence of 15% PWG improved matrix cohesion and limited crack width growth in the tension face, delaying the abruptness of full shear collapse. PWG appears to refine the microstructure and improve bond, producing finer and more numerous cracks rather than a single catastrophic fracture surface. This effect mitigated the brittleness of shear failure to some degree, though it did not fully compensate for the reduction in shear capacity caused by increased WFA content. The observed behavior indicates that while moderate WFA replacement (≤10%) maintains shear performance close to the control and offers benefits in ductility and energy absorption, higher replacements (≥20%) significantly reduce shear capacity and increase the risk of brittle shear failure. For structural applications where shear governs, the use of WFA should be limited or accompanied by adequate shear reinforcement (stirrups) and/or shear-strengthening measures.

E. Toughness, ductility, and stiffness indexes

The evaluation of toughness, ductility, and stiffness indices provides an in-depth understanding of the overall structural efficiency of reinforced concrete (RC) beams incorporating WFA and PWG. These indices move beyond peak strength alone, offering insights into the energy absorption capacity, deformation behavior, and load–deflection response of sustainable beams under both flexural and shear-dominated conditions. The results are illustrated in Table 2 and Figure 9.

Table 2. Beam performance indexes.

Beam ID	Group	Toughness T (kN·mm)	Ductility μ (Δu/Δy)	Initial stiffness k (Pcr/Δcr) (kN/mm)
R	1	551.0	3.00	22.5
10WFA	1	662.6	4.93	32.0
20WFA	1	606.6	3.27	15.64
30WFA	1	590.3	3.50	8.89
R	2	269.9	1.76	19.23
10WFA	2	347.7	1.79	24.0
20WFA	2	273.1	2.29	12.8
30WFA	2	293.0	2.18	11.38

1. Toughness

Toughness, measured as the area under the load–deflection curve, reflects the total energy absorption before failure. The results are shown in Figure 10a.

Figure 10. Toughness, ductility, and stiffness indexes vs. WFA.

For flexure-dominated beams (Group 1), the control beam absorbed 551 kN·mm, while the 10% WFA beam reached the highest toughness (662.6 kN·mm), reflecting a 20% improvement. This enhancement demonstrates the crack-bridging role of WFA particles and the matrix refinement from PWG, both of which delay catastrophic cracking and enable greater energy dissipation. At 20% and 30% WFA replacement, toughness values were 606.6 kN·mm (+10.1%) and 590.3 kN·mm (+7.1%), respectively, showing that even higher WFA levels preserved or slightly improved toughness compared to control. This behavior indicating that even at higher replacement levels, beams retain significant energy absorption capacity despite reduced stiffness and peak load. In shear-dominated beams (Group 2), overall toughness values were much lower due to the inherently brittle nature of shear failure. Nevertheless, 10% WFA increased toughness by nearly 29% compared to the control (347.7 vs. 269.9 kN·mm), again highlighting its effectiveness in delaying brittle collapse. At 20% and 30% WFA, toughness values were 273.1 kN·mm (+1.2%) and 293.0 kN·mm (+8.6%), indicating marginal but consistent improvements. At higher WFA levels, toughness remained slightly above or comparable to the control, suggesting that WFA contributes to spreading micro-cracks and distributing shear stresses more evenly, even though the ultimate shear strength decreases. Thus, toughness improvements were most pronounced at 10% WFA, with benefits extending even to shear-dominated beams that typically exhibit brittle failure.

2. Ductility

The ductility index (μ = Δu/Δy) reflects the deformation capacity beyond yielding, which is a crucial safety parameter, especially for seismic applications. The results of ductility are shown in Figure 10b.

In flexural beams, ductility improved significantly at 10% WFA (μ = 4.93), representing a ~64% increase relative to the control (μ = 3.0). This demonstrates the ability of the sustainable mix to undergo larger deflections without sudden failure, a desirable trait for structural resilience. At 20% and 30% replacement, ductility remained above the control (μ = 3.27 and 3.50), confirming that higher WFA levels enhance deformability even though they reduce strength and stiffness.

For shear-dominated beams, ductility was much lower overall due to the abrupt nature of Diagonal shear cracking. The control beam recorded μ = 1.76, while 10% WFA showed only a marginal improvement (μ = 1.79). Interestingly, higher WFA levels (20% and 30%) resulted in improved ductility (μ = 2.29 and 2.18), suggesting that although shear strength declined, the distributed cracking promoted by WFA allowed a more gradual failure process. ³⁷

3. Initial Stiffness

Initial stiffness (k = Pcr/Δcr) is a measure of the beam’s elastic rigidity prior to cracking. It is acknowledged that determining the exact first-cracking load may involve minor uncertainty, as micro-cracks can develop before visible cracking is observed. Therefore, Pcr was defined as the load at which the first visible surface crack appeared and a noticeable deviation from linearity occurred on the load–deflection curve. This practical definition aligns with standard flexural testing procedures and provides a consistent basis for comparing the stiffness of different beam mixes.

For Group 1 beams, stiffness increased markedly at 10% WFA (32.0 kN/mm vs. 22.5 kN/mm for control), showing that moderate WFA replacement combined with PWG produces a stiffer and stronger matrix. However, at 20% and 30% WFA, stiffness dropped significantly (15.64 and 8.89 kN/mm), consistent with the reduced compressive strength and increased porosity at higher replacement levels. In Group 2 beams, a similar pattern was observed. The control beam exhibited a stiffness of 19.23 kN/mm, while the 10% WFA beam showed improvement (24.0 kN/mm). At 20% and 30% replacement, stiffness declined (12.8 and 11.38 kN/mm), reflecting the weaker aggregate interlock of WFA and reduced crack resistance in shear. The combined analysis indicates that 10% WFA replacement offers the most favorable balance across all indices: increased toughness, markedly improved ductility, and enhanced stiffness, both in flexural and shear behavior. This confirms the synergistic role of WFA and PWG in producing beams with superior energy dissipation and resilience. Higher WFA contents (20–30%) reduce stiffness and peak strength but improve ductility and crack distribution, making them suitable for lightweight or seismic-resistant applications where deformability is prioritized over load capacity.

The reduction in stiffness with higher WFA content can be attributed to the porous and lightweight nature of walnut shells, which decreases aggregate interlock and elastic modulus. ^{8,
16} Conversely, PWG refines the cement matrix and improves bond integrity, contributing to the observed increase in cracking resistance and ductility.

Conclusions

Incorporating 10% WFA as a sand replacement enhanced both compressive and flexural strength, attributed to its fiber-like role in bridging cracks and improving post-cracking resistance. At higher replacement levels (20–30%), a gradual reduction in strength was observed; however, ductility and cracking performance were significantly improved.

The use of PWG was for enhanced the homogeneity and compactness of the matrix because its pozzalanic effect, which likely contributed to better stress transfer and crack control.

Beams with 10% WFA replacement demonstrated the most favorable balance between strength and ductility, confirming their suitability for structural applications where flexural performance is a governing factor. PWG enhanced the homogeneity and compactness of the matrix.

Increasing WFA content beyond 10% reduced stiffness and ultimate load capacity but enhanced ductility, highlighting its potential in applications that prioritize lightweight construction, seismic energy dissipation, and improved deformability.

In shear-dominated behavior, walnut shell replacement reduced shear capacity due to weaker aggregate interlock; nevertheless, it improved energy absorption and delayed brittle shear failure, enhancing overall structural resilience.

At low replacement levels (≤10%), the shear behavior of WFA beams remained comparable to the control mix, whereas higher replacement levels led to reduced shear strength but preserved improved ductility.

For beams where shear strength is critical, WFA replacement should be limited to moderate levels (≤10%). Conversely, higher replacement levels can be adopted in scenarios where dead load reduction, ductility, and sustainability are prioritized over peak strength capacity.

The density reduction achieved through WFA replacement directly contributes to lowering the dead load of concrete members. At 30% replacement, reductions of up to 6–8% in density were observed, offering advantages in structural efficiency, foundation design, and overall material savings.

Overall, the 10% WFA replacement mix (10 WFA) provided optimal performance, combining strength, ductility, and sustainability. This mix is recommended for structural applications aiming to balance mechanical efficiency, dead load reduction, and environmental benefits.

The findings presented are valid within the experimental scope of this study, which involved small-scale beams and fixed PWG content (15%). Future investigations on full-scale members and varied PWG levels are necessary to generalize these conclusions for design applications.

Data availability

The datasets supporting the finding of this study are openly available in Zenodo repository at https://doi.org/10.5281/zenodo.18057324. ³⁸

This project contains the following underlying data: •

the data avialable.xlsx

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).

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10.5256/f1000research.194291.r454083

Reviewer response for version 1

Smith

Abutu Simon John

1 Referee https://orcid.org/0009-0002-1620-1766 1Civil Engineering, Federal University of Technology, Babura, Jigawa, Nigeria

Competing interests: No competing interests were disclosed.

9 2 2026

2026

This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

recommendation

approve-with-reservations

The paper assesses the structural performance of RC beam made with walnut shell fine aggregate (WFA) and 15% powdered waste glass (PWG) in order to sanitize the environment from Agricultural waste and to investigate if the agricultural wastes can improve the structural integrity of RC beam. The following comments may improve the quality of the paper:

(1) The abstract should be re-written in the following sequence: (a) introduce the paper using the current written sentence under background, (b) write one or two sentences about the method used in carrying out the research (c) report the major findings (d) conclude the abstract with either an innovation from the study or recommend further research that can be done as an improvement to the current study.

(2) In paragraph four of the “INTRODUCTION” section, the first sentence and the second sentence should be checked and re-written because they appeared disjointed and were not linked properly.

Please check the abbreviation “PWG” used in the fourth paragraph of the “INTRODUCTION” section and the first bullet point in paragraph five of the “INTRODUCTION” section. Is it supposed to be WGP? Also check and correct it throughout the manuscript and if it means Powdered Waste Glass, the full meaning should be written at the first mention.

Paragraph seven of the “INTRODUCTION” section should be moved to sub-section B (i.e. Mix proportion and specimen preparation) of the “Materials and Methods” section of the manuscript.

Paragraph eight of the “INTRODUCTION” section should be incorporated into paragraph six of the “INTRODUCTION” section; and paragraph nine of the “INTRODUCTION” section should be deleted.

(3) The percentage increase and percentage decrease in compressive strength reported in sub-section A of the “Results and Discussion” section should be in the exact percentage instead of in range like 3-5%, 8-12%, etc. The same exact percentage reduction in density should also be reported (Report the exact percentage and avoid using nearly 2%, 4%, etc.). Figure 4 should be moved from its present location and placed under subsection A (Compressive strength of concrete mixes) of the “Results and Discussion” section.

(4) Under “C. Load-Deflection Behavior” section, it can be seen in Figure 6 (i.e. Flexural Load–Deflection Behavior (Group 1) that there was a point for 0%, 10%, 20% and 30%WFA replacement where each beam load decreased before it continued to increase up to the ultimate load. Please try to explain the reason(s) for this behavior. Additionally, the explanation for this sub-section is shallow, and more analyses and discussion should be done.

https://f1000research-files.f1000.com/linked/781718.Figure_6_176250.png

The percentage increase or decrease in shear load should be reported for the Shear Load–Deflection Behavior (Group 2) sub-section of the “C. Load-Deflection Behavior” section. In the same way, the improved resistance to deflection for group 2 should be reported in percentage.

(5) The value of load corresponding to the first crack that appeared in the beams should be reported for both the Flexural Behavior-Group 1 and the Shear Behavior-Group in the “D. Crack patterns and failure modes” section of the manuscript. Furthermore, the difference in the first crack load in terms of percentage increase or decrease should be discussed with reference to the control beam.

(6) Conclusion no.2 should be re-written like this: “The use of PWG enhanced the homogeneity and compactness of the matrix because of its pozzolanic effect, which likely contributed to better stress transfer and crack control.”

Is the work clearly and accurately presented and does it cite the current literature?

Yes

If applicable, is the statistical analysis and its interpretation appropriate?

Yes

Are all the source data underlying the results available to ensure full reproducibility?

Yes

Is the study design appropriate and is the work technically sound?

Yes

Are the conclusions drawn adequately supported by the results?

Yes

Are sufficient details of methods and analysis provided to allow replication by others?

Yes

Reviewer Expertise:

Integrity of structures, Use of Internet of Things in Structural Analyses and Design, Ultra-high Performance Fibre Reinforced Concrete, Finite Element Analyses, Numerical Modelling and Simulation of Structures, Concrete/Construction/Civil Engineering Materials, Structural Reliability Analyses

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

Hama

Sheelan

Civil Engineering, University of Anbar, Ramadi, Al Anbar Governorate, Iraq

Competing interests: No competing interests were disclosed.

23 5 2026

Response to reviewer: The abstract has been completely revised and reorganized to improve clarity and logical flow. The revised version now follows the recommended sequence by introducing the study background, briefly describing the experimental methodology, presenting the major findings, and concluding with the key contribution and future research perspective.

“Background This study investigates the structural behavior of sustainable reinforced concrete (RC) beams incorporating walnut shell fine aggregate (WFA) and powdered waste glass (PWG) under bending loading. The use of agricultural and industrial waste materials in structural concrete offers a promising approach for reducing environmental impact and conserving natural resources. Method An experimental program was conducted on eight simply supported RC beams divided into two groups: flexure-dominated beams with stirrups and shear-dominated beams without stirrups. Walnut shell was used as a partial replacement of natural fine aggregate at replacement levels of 10%, 20%, and 30%, while 15% PWG was used as a partial cement replacement in all mixes. The beams were evaluated in terms of compressive strength, density, load–deflection response, crack propagation, ductility, toughness, stiffness, and failure modes.

Results The results showed that 10% WFA replacement improved compressive strength by approximately 3–5%, enhanced flexural capacity, and increased ductility by nearly 64% compared with the control beam. Increasing WFA content reduced stiffness and ultimate load capacity; but, it improved crack distribution, deformability, and energy absorption. In shear-dominated beams, higher WFA contents reduced shear strength because of weaker aggregate interlock, although a more gradual failure response was observed. In addition, the incorporation of PWG contributed to matrix densification and improved crack control.

Conclusions The findings demonstrate that moderate WFA replacement combined with PWG can produce eco-efficient RC beams with improved ductility and reduced dead load while maintaining acceptable structural performance. Future studies are recommended to investigate full-scale structural members, varying PWG replacement levels, and analytical prediction models for sustainable RC beam applications.”

(2) In paragraph four of the “INTRODUCTION” section, the first sentence and the second sentence should be checked and re-written because they appeared disjointed and were not linked properly.

Paragraph seven of the “INTRODUCTION” section should be moved to sub-section B (i.e. Mix proportion and specimen preparation) of the “Materials and Methods” section of the manuscript.

Paragraph eight of the “INTRODUCTION” section should be incorporated into paragraph six of the “INTRODUCTION” section; and paragraph nine of the “INTRODUCTION” section should be deleted.

Response to reviewer: The authors appreciate the reviewer’s careful observations and valuable suggestions. The manuscript has been revised accordingly.

Response to reviewer: The compressive strength and density variations reported in Sub-section A and Sub-section B of the Results and Discussion section have been revised to present the exact percentage increase and decrease values instead of approximate ranges. In addition, Figure 4 has been relocated and placed directly under Sub-section A ( Compressive Strength of Concrete Mixes) to improve the organization and readability of the manuscript.

( 4) Under “C. Load-Deflection Behavior” section, it can be seen in Figure 6 (i.e. Flexural Load–Deflection Behavior (Group 1) that there was a point for 0%, 10%, 20% and 30%WFA replacement where each beam load decreased before it continued to increase up to the ultimate load. Please try to explain the reason(s) for this behavior. Additionally, the explanation for this sub-section is shallow, and more analyses and discussion should be done.

Response to reviewer: Additional discussion has been added to explain the temporary load reduction observed in the load–deflection curves before reaching the ultimate load. This behavior is attributed to the initiation and propagation of flexural cracks, localized stiffness degradation, and stress redistribution within the beam after first cracking. Following crack stabilization and redistribution of internal stresses between concrete and reinforcement, the beams regained load-carrying capacity until ultimate failure.

Also, the discussion in the Load–Deflection Behavior section has been expanded to provide deeper interpretation of stiffness degradation, crack propagation, post-cracking response, and the influence of WFA and PWG on ductility and energy absorption. Exact percentage changes in shear load capacity and deflection response for Group 2 beams have also been added to improve quantitative interpretation of the results.

“It was observed that all beams exhibited a slight temporary reduction in load before continuing toward the ultimate load capacity. This behavior can be attributed to the initiation of major flexural cracks and the associated localized stiffness degradation immediately after first cracking. The sudden formation and propagation of cracks caused partial stress redistribution within the beam section, leading to a short-term reduction in load resistance. As loading continued, the internal stresses were redistributed between the reinforcement and surrounding concrete, allowing the beams to regain load-carrying capacity until reaching the ultimate state. This response is typical in reinforced concrete beams undergoing transition from uncracked elastic behavior to cracked inelastic behavior.”

“At higher WFA contents resulted in smoother post-peak behavior and larger deflection capacity, indicating improved deformability and energy dissipation. The incorporation of PWG contributed to refining the cement matrix and improving bond characteristics, which helped delay sudden crack propagation and enhanced crack distribution along the beam span.”

“The ultimate shear load of the 10%WFA beam increased by 8.63% compared with the control beam. Increasing the WFA content to 20% and 30% reduced the ultimate shear load by 6.72% and 17.30%, respectively, compared to the control beam. This reduction is mainly attributed to the porous structure and lower stiffness of walnut shell particles, which weaken aggregate interlock and reduce resistance to diagonal shear cracking.

While the maximum deflection capacity increased with increasing WFA content. Compared with the control beam, the deflection resistance improved by 15.60%, 20.60%, and 31.40% for 10%, 20%, and 30%WFA beams, respectively. This behavior indicates enhanced deformability and energy dissipation capacity associated with the lightweight and more flexible nature of WFA containing concrete. ”

Response to reviewer: The first-crack behavior has been further clarified in the revised manuscript. The exact crack initiation load was identified experimentally through visual observation and crack microscope monitoring. Additional discussion has been included regarding the relative delay or acceleration of crack initiation with increasing WFA content and its relationship with stiffness degradation and aggregate interlock.

“The first flexural crack load of the control beam was approximately 22 kN. Compared with the control beam, the first-crack load increased by approximately 13.64% for the 10%WFA beam, indicating improved crack resistance and matrix integrity. The increasing the WFA replacement level to 20% and 30% reduced the first-crack load by 9.09% and 22.73%, respectively, due to the lower stiffness and weaker aggregate interlock associated with the porous walnut shell particles. The incorporation of PWG contributed to delaying crack propagation through matrix densification and improved bond characteristics.”

“The estimated first diagonal crack load of the control beam was approximately 20 kN. Compared with the control beam, the first-crack load increased by approximately 10.00% for the 10%WFA beam, indicating slightly improved crack resistance at moderate replacement levels. However, the first-crack load decreased by 10.00% and 25.00% for the 20%WFA and 30%WFA beams, respectively, because of the reduced stiffness and weaker aggregate interlock associated with higher WFA contents. The earlier formation of diagonal cracks at higher replacement levels reflects the reduced shear transfer capability of the lightweight porous matrix.”

Response to reviewer: The authors appreciate the reviewer’s valuable correction. Conclusion no. 2 has been revised accordingly to improve grammatical accuracy and clarity.

10.5256/f1000research.194291.r454088

Reviewer response for version 1

Sathe

Sandeep

1 Referee 1MIT World Peace University (MIT-WPU), Pune, Maharashtra, India

Competing interests: No competing interests were disclosed.

3 2 2026

2026

recommendation

approve-with-reservations

Comment 1. The manuscript presents experimental results on RC beams incorporating walnut shell fine aggregate (WFA) and waste glass powder (PWG). While the study is technically sound, the novelty is limited. Similar investigations on walnut shell as fine or coarse aggregate, waste glass powder as cement replacement, and hybrid sustainable concrete systems have already been reported extensively in the literature (including several works cited by the authors themselves). The current study largely confirms known trends rather than providing fundamentally new insights or mechanisms.

Comment 2. The use of a constant 15% PWG replacement is justified only by citing previous studies. However, from a scientific standpoint, fixing PWG content: prevents understanding interaction effects between WFA and PWG, limits the originality of the experimental design, and reduces the general applicability of the conclusions.

Comment 3. At least one additional PWG level or a sensitivity discussion is necessary to strengthen the experimental rationale.

Comment 4. Only eight beam specimens were tested (four per group). While acceptable for exploratory studies, this sample size is insufficient for a high-impact or reputed journal, especially when conclusions are extended to structural applicability. Statistical variability and repeatability are not addressed.

Comment 5. The manuscript lacks: comparison with design code predictions (ACI, Eurocode, etc.), analytical modelling of flexural or shear capacity, or validation against existing empirical equations. Without such comparisons, the work remains primarily descriptive rather than advancing structural engineering knowledge.

Comment 6. The conclusions suggest suitability for “structural applications,” yet: durability, long-term behavior, creep, shrinkage, and environmental degradation are not addressed, shear performance shows clear degradation at higher WFA contents. These limitations should be explicitly acknowledged, and claims should be toned down accordingly.

Comment 7. Although sustainability is emphasized, the manuscript does not include embodied carbon analysis, material efficiency metrics, or quantitative sustainability indicators. As a result, the sustainability argument remains qualitative rather than evidence based.

Comment 8. The manuscript requires careful English editing. There are repeated grammatical errors, awkward phrasing, and inconsistent tense usage, particularly in the Introduction and Conclusions.

Comment 9. Several paragraphs reiterate similar findings from previous studies. The literature review should be condensed and focused on clearly identifying the research gap.

You may refer following Research articles:

Reference no. 1,2, & 3

Comment 10. Details such as: crack width measurement methodology, definition of yield and ultimate points for ductility calculations, uncertainty in first-crack load determination should be described more rigorously.

Is the work clearly and accurately presented and does it cite the current literature?

Yes

If applicable, is the statistical analysis and its interpretation appropriate?

Yes

Are all the source data underlying the results available to ensure full reproducibility?

Yes

Is the study design appropriate and is the work technically sound?

Yes

Are the conclusions drawn adequately supported by the results?

Yes

Are sufficient details of methods and analysis provided to allow replication by others?

Yes

Reviewer Expertise:

Concrete

References 1

: An experimental study on rice husk ash concrete. Materials Today: Proceedings .2023;77: 10.1016/j.matpr.2022.11.366 724-728

10.1016/j.matpr.2022.11.366

: Mechanical properties, impact resistance and bond strength of green concrete incorporating waste glass powder and waste fine plastic aggregate. Innovative Infrastructure Solutions .2022;7(1) : 10.1007/s41062-021-00652-4

10.1007/s41062-021-00652-4

: Structural performance of recycled coarse aggregate concrete beams containing waste glass powder and waste aluminum fibers. Case Studies in Construction Materials .2023;18: 10.1016/j.cscm.2022.e01751

10.1016/j.cscm.2022.e01751

Hama

Sheelan

Civil Engineering, University of Anbar, Ramadi, Al Anbar Governorate, Iraq

Competing interests: No competing interests were disclosed.

23 5 2026

Response to Comment 1: While walnut shell aggregate and waste glass powder have been individually investigated in previous studies, the novelty of the present work lies in their combined application in reinforced concrete beams and the comprehensive evaluation of both flexural- and shear-dominated structural behavior. Unlike earlier studies that mainly focused on material-level properties, the current research investigates load–deflection response, ductility, toughness, stiffness, crack propagation, and failure mechanisms of RC beams incorporating WFA and PWG. In addition, the study uniquely compares beams with and without stirrups to evaluate both flexural and shear performance.

The manuscript has been revised to further clarify these contributions and better highlight the research gap addressed by this study.

“Although previous studies have investigated walnut shell aggregate or waste glass powder separately at the material level, limited research has addressed their combined use in reinforced concrete beams under both flexural and shear-dominated behavior. The present study extends existing knowledge by evaluating not only the mechanical properties, but also the structural response, ductility, toughness, stiffness degradation, crack propagation, and failure mechanisms of RC beams incorporating WFA and PWG. This provides a more comprehensive assessment of the feasibility of hybrid sustainable concrete for structural applications.”

Response to Comment 2: The 15% PWG replacement level was selected based on previous optimization studies reporting it as the optimum dosage for enhancing strength, matrix densification, and durability. Therefore, the present study focused on evaluating the structural influence of varying WFA contents while maintaining PWG at a constant optimum level to reduce experimental variables and allow clearer interpretation of beam behavior.

The authors acknowledge that investigating multiple PWG levels could provide further insight into the interaction between WFA and PWG, and this has been recommended for future research.

“In the present study, PWG content was maintained at the previously optimized level (15%) to isolate the structural influence of WFA replacement on RC beam behavior and reduce the complexity of experimental variables. Future studies may investigate the coupled interaction between different PWG and WFA replacement levels.”

Comment 3. At least one additional PWG level or a sensitivity discussion is necessary to strengthen the experimental rationale.

Response to Comment 3: Although additional PWG replacement levels were not included in the current experimental program, a sensitivity discussion has been added to clarify the expected influence of varying PWG contents based on previous optimization studies. The present work intentionally maintained PWG at the previously established optimum level (15%) to isolate the structural effect of WFA replacement on RC beam behavior. Future investigations considering multiple PWG levels are recommended to evaluate the coupled interaction between WFA and PWG in greater detail.

“The selection of 15% PWG was based on previous optimization studies reporting this level as the optimum dosage for balancing strength, workability, and matrix densification. Lower PWG contents may provide reduced pozzolanic contribution, whereas higher replacement levels could adversely affect workability and hydration characteristics. Therefore, the current study maintained PWG at a constant optimum level to isolate the structural influence of WFA replacement on RC beam behavior.”

Response to Comment 4: The authors appreciate the reviewer’s important comment. The experimental program was designed as an exploratory structural investigation intended to evaluate the behavioral trends of RC beams incorporating WFA and PWG under flexural- and shear-dominated conditions. Due to laboratory and testing limitations, the number of beam specimens was restricted; however, all specimens were prepared, cured, and tested under identical controlled conditions to ensure consistency and reliable comparative assessment. The authors acknowledge that a larger sample size and statistical repeatability analysis would further strengthen the generalization of the findings. Accordingly, this limitation has been clarified in the revised manuscript, and future studies involving larger experimental datasets and statistical evaluation have been recommended.

“It should be noted that the present experimental program was conducted as an exploratory structural study to evaluate the behavioral trends of RC beams incorporating WFA and PWG. Although the number of beam specimens was limited, all specimens were cast, cured, and tested under identical conditions to ensure consistency in comparative evaluation. Future investigations involving larger sample sizes and statistical variability assessment are recommended to further validate the findings and improve general applicability. The findings presented are valid within the experimental scope of this study, which involved small-scale beams and fixed PWG content (15%). Future investigations on full-scale members and varied PWG levels are necessary to generalize these conclusions for design applications.”

Response to Comment 5: The primary objective of the present study was to experimentally investigate the structural behavior and failure characteristics of RC beams incorporating WFA and PWG. Therefore, the scope of the work focused mainly on comparative experimental evaluation rather than analytical modeling or code-based prediction. Nevertheless, the authors agree that comparison with design code provisions and analytical models would further strengthen the structural significance of the study. Accordingly, additional discussion has been added in the revised manuscript to relate the observed flexural and shear behavior to conventional RC beam response predicted by standard design approaches. Future work will focus on developing analytical and empirical prediction models for sustainable RC beams incorporating hybrid waste materials.

Response to Comment 6: The primary objective of the present study was to experimentally investigate the structural behavior and failure characteristics of RC beams incorporating WFA and PWG. Therefore, the scope of the work focused mainly on comparative experimental evaluation rather than analytical modeling or code-based prediction. Nevertheless, the authors agree that comparison with design code provisions and analytical models would further strengthen the structural significance of the study. Accordingly, additional discussion has been added in the revised manuscript to relate the observed flexural and shear behavior to conventional RC beam response predicted by standard design approaches. Future work will focus on developing analytical and empirical prediction models for sustainable RC beams incorporating hybrid waste materials.

“The observed structural behavior generally agrees with the conventional response expected for reinforced concrete beams according to established design approaches such as ACI 318. Beams with higher WFA contents exhibited reduced stiffness and lower ultimate capacity due to the lower elastic modulus and weaker aggregate interlock associated with lightweight organic aggregates. In shear-dominated beams, the development of wider diagonal cracks and more brittle post-peak response is consistent with classical shear behavior of beams with reduced aggregate interlock and without transverse reinforcement. Conversely, the improved crack distribution and ductility observed at moderate WFA replacement levels may be attributed to enhanced energy dissipation and stress redistribution within the cementitious matrix refined by PWG.”

“Future investigations on full-scale members and varied PWG levels are necessary to generalize these conclusions for design applications and research should include analytical modeling and comparison with international design codes to develop predictive formulations for sustainable RC beams containing hybrid waste materials.”

Response to Comment 7: The primary focus of the present study was the experimental structural performance of RC beams incorporating WFA and PWG. The sustainability discussion was therefore mainly based on waste utilization, reduction of natural aggregate consumption, and density reduction.

The authors agree that quantitative sustainability indicators such as embodied carbon analysis and material efficiency metrics would further strengthen the environmental assessment. Accordingly, additional discussion has been added in the revised manuscript to highlight the potential environmental benefits associated with partial cement and natural aggregate replacement, while comprehensive life-cycle and embodied carbon analyses are recommended for future studies.

“From a sustainability perspective, the incorporation of WFA and PWG contributes to reducing the consumption of natural fine aggregate and cementitious materials, while simultaneously lowering concrete density and promoting waste reutilization. The observed density reduction (up to 6–8%) may also contribute to lower structural dead loads and potential savings in supporting structural elements and foundations. Although a detailed embodied carbon or life-cycle assessment was beyond the scope of the present study, the proposed hybrid system demonstrates promising potential for improving material sustainability and resource efficiency in structural concrete applications.”

Comment 8. The manuscript requires careful English editing. There are repeated grammatical errors, awkward phrasing, and inconsistent tense usage, particularly in the Introduction and Conclusions.

Response to Comment 8: The manuscript has been carefully revised and thoroughly proofread to improve grammatical accuracy, sentence structure, academic style, and consistency of tense throughout the paper, particularly in the Introduction and Conclusions sections.

Comment 9. Several paragraphs reiterate similar findings from previous studies. The literature review should be condensed and focused on clearly identifying the research gap.

You may refer following Research articles:

Reference no. 1,2, & 3

Response to Comment 9: The Introduction has been revised and condensed to reduce repetitive discussion of previous studies. Greater emphasis has been placed on clearly defining the research gap related to the combined incorporation of WFA and PWG in reinforced concrete beams subjected to both flexural and shear behavior. In addition, the suggested references have been incorporated to strengthen the background discussion on sustainable structural concrete and hybrid waste-material systems, see reference 30 to 32.

Response to Comment 10: Additional clarification has been added in the revised manuscript regarding the crack observation procedure, the definition of yield and ultimate points used in ductility calculations, and the determination of first-crack load. The methodology section has been expanded to improve the rigor and reproducibility of the experimental procedures.

" Crack initiation and propagation were continuously monitored during testing. Crack widths were measured using a crack microscope at different loading stages, while crack distribution and propagation patterns were documented through visual observation and photographic recording. The first-crack load was identified based on the appearance of the first visible crack together with the initial deviation from linearity in the load–deflection response."

“The first-crack load was determined based on the appearance of the first visible flexural or diagonal crack during testing, together with the initial deviation from linearity in the load–deflection response. It is acknowledged that minor micro-cracks may develop prior to visible cracking; therefore, the reported cracking load represents the first observable surface crack under experimental conditions.”

“The ductility index was calculated as the ratio between ultimate deflection (Δu) and yield deflection (Δy). The yield point was identified from the load–deflection curve as the point corresponding to the first significant deviation from linear elastic behavior associated with steel yielding, while the ultimate point corresponded to the maximum recorded deflection prior to major strength degradation or failure.”