Experimental Investigation on Flexural Strength Enhancement of Eucalyptus based Bamboo Composite Deck Board

Abstract

The study investigates the effect of the relative height position of specimen and bamboo layering in the preparation of composite flexural material from Eucalyptus Globules and Oxytenanthera abyssinica bamboo for the purpose of floor deck construction. Furthermore, flexural improvement was tested by laminating bamboo beneath eucalyptus, which has a high tensile stress resistance, using unsaturated polyester resin as the bonding medium. The experiment was carried out on specimens taken from the bottom and middle parts of the sample with regard to total height. The results of the tests revealed that single and double-layer bamboo laminated eucalyptus in the bottom part showed an increase in flexural strength by 26.5% and 33.06%, respectively, and that the bottom portion strength had improved due to the addition of bamboo. However, in the case of the middle part specimen, the addition of a bamboo lamination on the Eucalyptus resulted in a (20.31%) increase for single and (−41.79%) decrease for double layer in strength compared to the non-laminated middle part Eucalyptus.

Keywords:

• Eucalyptus wood bamboo composite
• flexural strength
• strength enhancement
• floor deck
• experimental investigation

1. Introduction

The building sector is responsible for a significant portion of environmental harm, whether directly or indirectly. The growing reliance on traditional energy-intensive materials for building, such as cement, steel, and bricks, has resulted in a number of environmental repercussions, including the release of greenhouse gases during the manufacturing process. Timber has been described as the “Gift of God and friend of man” (Hudson, 1986). Timber has a lengthy history of use as a construction material for human-made structures. Timber has proven to be a valuable construction resource over the centuries. Fast-growing woods, on the other hand, have a chance to be employed in constructions due to the rapidly diminishing amount of natural forests and tougher anti-deforestation legislation (Zhang et al., 2016). The Structural Timber Association (Jack & Abdy, 2014) reports that Hardwoods are typically used for exposed structures, floor, deck, and cladding where durability and particular aesthetic characteristics, such as color or grain pattern, are required.

With growing worries about climate change and sustainable development, eucalyptus and bamboo have emerged as a very promising construction material, requiring less energy to produce. There is a means to employ a glued element for the rebuilding of timber structural components in the building industry—for strengthening or replacing damaged wood parts (JyotiKalita & Kumar Singh, 2018) but it is also applied for preparing new construction elements especially timber-bamboo laminated members (F. Chen et al., 2016; Dong et al., 2021; Wei et al., 2021). As a result, multiple researchers have undertaken experimental studies to better understand the physical and mechanical characteristics of various wood materials, such as eucalyptus and bamboo.

Experts have largely agreed on the mechanical properties of Eucalyptus wood since the beginning of its use, more than 200 years ago, and hence a great potential for a variety of uses (Ruiz & Lopez, 2010). Because of their rapid growth, eucalypt species have emerged among the major alternatively used for lumber production (Nogueira et al., 2018). Remarkably, nowadays eucalypts have become one of the most widely planted in the world. It is among the most preferred trees because it grows fast and has a good survival capacity in marginal environments (Pais, 2016). Eucalyptus have versatile uses, which have made them economically important trees and have become a cash crop in poor areas (Contributors, 2020) including Ethiopia. After comparing the qualities of the two types of wood, Ozarska confirmed that laminated wood and Laminated Verner Lumber could be manufactured by substituting hardwood with eucalyptus (Ozarska, 1999).

Bamboo has consisted of around 1250 species in the world. Bamboo, as a fast-growing, renewable, and sustainable material with an easy production process, is so expected to be an alternative for more traditional building materials, such as concrete, steel, and timber (J. Chen et al., 2019; Van der Lugt et al., 2006). Ethiopia’s lowland bamboo is mostly a solid culm with higher densities and a smaller diameter. Lowland bamboo accounts for up to 80% of Ethiopia’s bamboo resources (Kelbessa et al., 2000; Liese, 2002). While this species is only used for fencing or as an important energy resource. However, from different literature and findings (Dinesh, 2014; Janssen, 2000; Wegst et al., 1993), bamboos have good bending strength and flexibility, so it can be utilized in the construction industry as a structural member (Sharma et al., 2015).

Various research programs were developed for the use of bamboo as a low-cost and energy-saving material for civil construction (Abdul Khalil et al., 2012), particularly focussing as an alternative for steel reinforcement in concrete structures and spatial structures (Ghavami, 2008) due to the case of strength of bamboo in tension is significantly higher than its compression strength (Zhou & Bian, 2014). The flexural performance of Parallel Strand Bamboo beam was investigated and the result given the tension strength was far greater than the compression strength and the mechanical performances of Parallel Strand Bamboo made from the bottom raw bamboo were inferior to that of the upper bamboo (Zhou & Bian, 2014). In Addition, bamboo has been an application as flooring for manufacturing from the bamboo plant. Bamboo is selected because of its durability and being environmental (Abdul Khalil et al., 2012). Laminated bamboo is an attractive alternative for traditional building materials well suited to use as deck, beams, and columns, and the experimental result shows laminated bamboo underwent a long nonlinear process before failure (Nurul Fazita et al., 2016).

In comparison with natural composite, bamboo has high stiffness and strength due to its low density and high mechanical strength (Nurul Fazita et al., 2016). Furthermore, wood is a cost-effective alternative to other regularly used construction materials due to its high specific stiffness and strength (Da Silva & Kyriakides, 2007). The research was sparked by the abundance of these resources, but the study and application were not focused on Ethiopia for modern building. Thus, knowledge of the physical and mechanical qualities of wood, as well as the strength class classification, is required for wooden building structures. The study in the paper includes individual mechanical properties and investigates the composite flexural capacity of Eucalyptus-Bamboo by using experimental investigation in a longitudinal direction. The purpose of this work was to look at the influence of specimen relative position on strength in terms of plant height and bamboo layering on flexural strength. In this article, Eucalyptus Globulus and Oxytenanthera Abyssinica Bamboo hardwood species will be chosen to assess their qualities for usage as home floor deck preparation. The importance of specimen location on strength, the influence of bamboo layering, the flexural capacity of Eucalyptus bamboo composite material, and its strength class classification were all discussed in the article. In addition, the purpose of this was work explores feasibility of Eucalyptus-bamboo laminated structural member.

2. Research method

2.1. Methodological approaches

To address the study’s purpose, a factual experimental research design was adopted, with quantitative research methodologies being applied. As a result, it was necessary to determine how much the increase in flexural strength was related to the change in relative sample position in longitudinal direction and the bamboo layer. So, laminate Bamboo underneath the Eucalyptus globulus using adhesive resin (Unsaturated Polyester Resin) as bonding agent and fix mechanically by clamper to create uniform bond. Flexural tests were made by varying the layer of bamboo of making single and double to investigate the feasibility of bamboo to increase the flexural strength of Eucalyptus globulus. A three-point load bending test was applied at a steady rate and the load versus deflection result was recorded with universal testing machine.

2.2. Materials and data

The materials that will be used in the experiment are.

• Eucalyptus Globulus was gathered from Gondar, Ethiopia.

• Bamboo (Oxytenanthera Abyssinica) was gathered from a Gondar, Ethiopia—Quara (Aletash National Park).

• Adhesive resin (Unsaturated Polyester Resin) taken from the market commercially available Aypols manufactured by Aypols Polymers Private Limited. Polyester (unsaturated) Resin is a liquid polymer that, once cured (cross-linked with styrene using certain compounds called hardeners), maintains the solid shape taken in the mold (Davallo et al., 2010).

For the investigation, the location of specimen was taken from the bottom and middle part of the sample relative to the height as shown in Figure 1. The Eucalyptus globules harvested for test was a total height of around 13 m and 12.5 cm diameter from the bottom on average. The bamboo harvested for this research was a total height of around 8 m and 3.5 cm diameter from the bottom on average.

Figure 1. Samples position taken (dimensions are not Scale).

Because there is a loss in strength and the specimen may have a different defect at the bottom, the test specimen can be taken by removing roughly 50 cm from the bottom of the sample. Thus, according to the standards for specimen dimension, the sample had measured and taken from bottom and designated as the bottom part for both Eucalyptus globulus and Oxytenanthera Abyssinica bamboo. In the same manner, the middle part of the specimen is taken according to the reference height. The middle part for Eucalyptus was taken from a height of 6 m and for the bamboo it was taken from 3.75 m by referring (ASTM-D5536-09, ASTM–D5536–09, 2009; X2.1.1).

The number of specimens can be determined by the principles of factorial design and fractional factorial design (Montgomery, 2017). The mechanical properties of the sample depend on its species, specimen location, and layer of bamboo. For the three factors, the number of repetitions was determined using the fractional factorial design approach, which is provided by the equation Eq. 1(1) $\mathrm{Number}\mathrm{of}\mathrm{specimens}\mathrm{for}\mathrm{asingle}\mathrm{test}\frac{2^n}{2}$(1) :

(1) $\mathrm{Number}\mathrm{of}\mathrm{specimens}\mathrm{for}\mathrm{asingle}\mathrm{test}\frac{2^n}{2}$(1)

$\mathrm{Number}\mathrm{of}\mathrm{specimens}\mathrm{for}\mathrm{the}\mathrm{single}\mathrm{test}\frac{2^3}{2}=4$ Where n = number of factors

In the study, five specimens were prepared for each case for compression, tension for each species, and flexural specimen, it includes the non-laminated eucalyptus globulus, single-layer bamboo, and double-layer bamboo-laminated Eucalyptus. The total specimens prepared for the experiment were 70 in number. Data for flexural tests were prepared in the manner shown on the flow chart (Figure 2).

Figure 2. Flow chart shows flexural test specimen.

The physical and mechanical properties of both bamboo and Eucalyptus were determined according to small clear specimen test (ASTM-D143-09, 2009), moisture content (ASTM–D4442–09, 2009), specific gravity (ASTM-D2395-09, ASTM–D2395–09, 2009), method for the structural panel in flexure (ASTM-D3043-09, ASTM–D3043–09, 2009), and laminated timber physical and mechanical property (BS-EN-408, 2011) recommendations. In reality, eucalyptus and bamboo are orthotropic materials, with mechanical characteristics unique to each of the three mutual directions (longitudinal, radial, and tangential). However, this study was carried out to investigate the tensile, compression, and flexural strength in the longitudinal direction (parallel to the grain). The significant value of the sample position and bamboo layering on the strength was studied using statistics from Analysis of variance, and if the value was less or more than 5%, the influence of sample position and bamboo layering on the strength was investigated, as suggested in Figure 2.

2.3. Specimen preparation

The following steps would be taken to prepare the test specimen: The eucalyptus and bamboo culms are plucked from the forest and placed in an open, covered environment to dry out and lose moisture. Remove 0.5 m from the bottom and then take a sample at 2.5 m and at 6 m for the bottom and middle part for Eucalyptus, in the same case for bamboo at 2 m and at 3.75 m for the bottom and middle part, respectively, regarding the total height, which is the required portion for the test. The samples are dimensioned as 50*50*200 mm for compression and 4.8*9.5*453 mm for tension tests according to the standard and recommendation in (ASTM-D143-09, 2009). For flexural specimens’ preparation split, the solid bamboo by hand tool longitudinally prepared into small splice and make it plane with an average thickness of 3 mm and sand it for an appropriate bond with Eucalyptus. The Eucalyptus was created using a planning machine with dimensions of 750 mm x 50 mm x 20 mm, as illustrated in (Figure 3A). Arrange the bamboo with Eucalyptus that makes the best fit along the width. Prepare adhesives from unsaturated polyester resin by adding 1% hardener to makes the unsaturated polyester resin to set and harden. Because the resin was applied by hand, it was impossible to regulate the amount, but using a brush, it was attempted to distribute the resin uniformly with a thickness of 1–3 mm. Apply the glue to the eucalyptus and bamboo of the contacting face (Figure 3B), then tie with wire (Figure 3C), and secure with three clamps, two at each end and one in the middle. However, adjusting the applied pressure might be problematic.

Figure 3. Lumber preparation, smearing and fixing two materials composites.

Finally, as demonstrated in (Figure 3D), use an adhesive to seal any disconnected openings that develop owing to decrease real test strength. As a result, the steps for double layer bamboo are identical to those for single layer bamboo; the only difference is that an extra layer of bamboo is laminated on top of the previously laminated bamboo.

The standards for bending experimental tests used as described for deck board structural panels in use include plywood, waterboard, oriented strand board, and composites of veneer and of wood-based layers on (ASTM-D3043-09, ASTM–D3043–09, 2009). For checking the flexural capacity, it is possible to take a strip from the structural panel and conduct the test. By considering the standard in the code for this study a material that represents the strip with the dimension of 750 mm x 50 mm x 20 mm eucalyptus set. The increase in strength can be investigated by providing single-layer bamboo and double-layer bamboo laminated underneath the eucalyptus. During the test, a load shall be applied continuously throughout the test at a rate of motion of the movable crosshead of 2 mm/min. Mathematically, the mechanical properties of flexural stress (Eq. 2(2) $\mathit{Flexural}\mathit{Stress}{\sigma }_f=\frac{3\mathit{FL}}{2b{d}^2}$(2) ), and the flexural modulus of elasticity (Eq. 3)(3) $\mathit{Flexural}\mathit{Modulus}{E}_f=\frac{L^3\mathit{m}}{4\mathit{b}{d}^3}$(3) for three-point bending can be calculated.

(2) $\mathit{Flexural}\mathit{Stress}{\sigma }_f=\frac{3\mathit{FL}}{2b{d}^2}$(2)

(3) $\mathit{Flexural}\mathit{Modulus}{E}_f=\frac{L^3\mathit{m}}{4\mathit{b}{d}^3}$(3)

where:

${\sigma }_f$- Flexural stress on outer fiber at mid-point

$E_f$-Flexural modulus of elasticity

$\mathit{F}$- Load at given point on load deflection curve

$\mathit{L}$- Support span

b—width of test beam

d—depth of thickness of tested beam

m—Gradient (slope) of initial straight-line portion of load deflection curve

3. Result and discussion

3.1. Experimental results and discussion

The test results were conducted to determine the physical as well as mechanical properties. The test results analysis was presented in tables 1. From the test results with the relation of stress-strain, we can find the ultimate strength of the material and the modulus of elasticity are also the behavior of failure.

Table 1. Laminated specimen flexural capacity

Specimen code- single layer bottom part	Ultimate Stress (Mpa)	Specimen code- single layer middle part	Ultimate Stress (Mpa)	Specimen code- double layer bottom part	Ultimate Stress (Mpa)	Specimen code- double layer middle part	Ultimate Stress (Mpa)
ESBB1	146.02	ESBM1	115.00	EDBB1	156.54	EDBM1	81.20
ESBB2	145.96	ESBM2	118.70	EDBB2	152.98	EDBM2	81.60
ESBB3	155.51	ESBM3	127.30	EDBB3	168.38	EDBM3	101.80
ESBB4	147.32	ESBM4	126.30	EDBB4	154.72	EDBM4	87.20
ESBB5	167.32	ESBM5	124.70	EDBB5	168.64	EDBM5	95.50

Given that the samples are normally distributed as shown in Figure 5 tested data distribution, two-way ANOVA was performed to verify the difference significance among the groups to verify if location of the specimen and layer of bamboo has a significant effect on the flexural enhancement of eucalyptus. Statistical hypotheses of the test are established by two conditions, where means do not differ with Null Hypothesis (H₀: µ₁ = µ₂) and the means have Differences, that is, Alternate Hypothesis (H₁: µ₁ ≠ µ₂). Decision was focused on P-value significance level (5%). H₀ hypothesis was rejected when P-value was lower than 5% that means the means have significant effect. Statistical analyses were carried out using IBM SPSS Version 26.0.

Figure 4. Three-point flexural test for non-laminated versus laminated.

Figure 5. Tested data distribution (result in MPa).

For safety reasons, wood strength values are essential for structural dimensioning and calculated based on the characteristic value using Eq. 4(4) ${\mathrm{f}}_{\mathrm{k}}={\mathrm{X}}_{\mathrm{mean}}-1.645\ast \mathrm{SD}$(4) , which corresponds to the 5% percentile of a given probability distribution model. The basic principle is that the strength class can be determined by three main properties: the bending strength, the modulus of elasticity, and density. For the bending strength and density, the 5%-lower fractile has to be determined and for the modulus of elasticity the mean value (BS-EN-408, 2011).

(4) ${\mathrm{f}}_{\mathrm{k}}={\mathrm{X}}_{\mathrm{mean}}-1.645\ast \mathrm{SD}$(4)

where:

f_k—Characteristic Strength

X_mean—mean strength

SD- Standard Deviation

Compressive and tensile properties of Eucalyptus globulus and Oxytenanthera Abyssinica bamboo are shown in Figures 6 and 7. The tensile strength of bamboo on the bottom part gives higher value as compared with eucalyptus, so it concretes the idea of laminating bamboo on the lower face of eucalyptus for flexural member to resist tensile stress. However, because the tensile strength of bamboo middle part specimens is lower than eucalyptus, flexural members made from the middle part are likely to be weaker.

Figure 6. Physical and Mechanical Property of Eucalyptus.

Figure 7. Physical and Mechanical Property of Bamboo.

Flexural test was conducted on Eucalyptus, with single layer bamboo on the bottom and with double layer bamboo on the bottom and result displayed in Figure 8. It is clear to see that the bottom section had increased strength, but the middle part had decreased strength, which might be attributed to the effect of reduced bamboo strength, as the statistics reveal a 42.35% loss in tensile strength when compared to the bottom part (see Figure 7).

Figure 8. Mechanical property of Eucalyptus Bamboo specimen.

Initially, the load-displacement curve from the experimental test reveals a linear relationship. After reaching ultimate resistance, the failure condition for bare Eucalyptus tension splintered below the neutral axis, according to an observation in (Figure 8), (Figure 9) and also brittle type failure (Figure 10) but not fractured totally it come back to the original alignment after release of loading for most tested specimens.

Figure 9. Load displacement curve for middle position on layer eucalyptus flexural test result.

Figure 10. Load displacement curve for bottom position on layer eucalyptus flexural test result.

For single layer bamboo laminated eucalyptus, the load displacement graph shows a linear relationship Figure 11. Failure types for single layer bamboo laminate indicate that some of the sample failed by debonding followed by eucalyptus tension splintering as shown in Figures 12 and 13; samples 2, 4 and 5 of single layer bamboo laminated eucalyptus; the other failure type was Eucalyptus brash tension failure followed by deboning Figure 4.

Figure 11. Load displacement single layer bamboo laminated Eucalyptus bottom part Result.

Figure 12. Load displacement single layer bamboo laminated Eucalyptus middle part result`.

Figure 13. Failure type for single laminated Eucalyptus.

In the case of double layer bamboo laminated Eucalyptus, sample taken from the bottom failed by compression of Eucalyptus (Figure 16) followed by debonding, but the middle location sample showed two types of failure; one of the failures was the same as the bottom location that is compression failure and another failure conditions observed were debonding followed by eucalyptus tension splintering. In addition, as observed from the load displacement curve, the bottom location sample shows brittle failure type (Figure 15) when it reaches ultimate strength, but for the middle location sample, after reaching the ultimate load, it does not fail directly but rebounds again and resist the applied load shows some delamination type of failure (Figure 14).

Figure 14. Load displacement curve for middle part eucalyptus with double layer bamboo flexural test.

Figure 15. Load displacement curve for bottom part eucalyptus with double layer bamboo flexural test.

Figure 16. Double layer laminated bamboo fractured Sample.

Two-way ANOVA statistical analysis was used to suggest the influence of location and the application of a layer of bamboo on flexural strength. The p-value (significance) for the sample’s position was 0.000, while the layer of bamboo yielded 0.01 and the interaction of position and layer yielded 0.000. Because these numbers are smaller than 0.05, they have a considerable impact on flexural strength. Furthermore, the amount of influence for location was 63.7%, and the amount of effect for bamboo stacking was 31.9%, indicating the importance of the parameter seen on flexural strength.

A post hoc study was carried out to see which layering’s had a substantial impact. There is no substantial difference between non-laminated Eucalyptus and single layer bamboo laminated Eucalyptus, according to the results. There is a considerable difference in mean strength between double-layer bamboo laminated Eucalyptus and non-Laminated Eucalyptus, as well as between single-layer bamboo laminated Eucalyptus and non-Laminated Eucalyptus.

Furthermore, examining the mean strength from the bottom position of specimen strength improves by applying the layer of bamboo, but in the middle position, the sample strength substantially drops owing to the application of bamboo layering, as demonstrated above (Figure 17). This is owing to the fact that the middle bamboo was weaker than the bamboo at the bottom. As a result, adding a layer of bamboo to the specimen at the center site had no benefit.

Figure 17. Comparison of position of sample layer.

When compared to previous relevant studies, the experimental data on flexural strength in Table 2 and Table 3 below demonstrate better results.

Table 2. Experimental result comparison with other studies

Material	Mean Ultimate flexural Strength (MPa)	Modulus of Elasticity (GPa)	Density (kg/m^3)
Mean Flexural strength for single Laminated Eucalyptus of this study	137.42	14.86	707
Mean Flexural strength for double Laminated Eucalyptus of this study	124.83	13.96	710
Timber Property of Eucalyptus by G. Desalegn and A. Gezahegn (2003; Desalegn & Gezahegn, 2010)	124	11.566	780
Mechanical Property of E. Globulus By J. Crespo and M. Guaita (2020; Crespo et al., 2020)	124.1	22.27	847
Flexural Performance of Parallel Strand Bamboo Beams by A. Zhou and Y. Bian (2014)	89.32	12.66

Table 3. Selected mechanical properties of ESWood and eucalyptus-based materials (J. Chen et al., 2019)

Species/products	Flexure (MPa)	Modulus of Elasticity (GPa)	Density (kg/m^3)
ESWood	111	-	864
Solid eucalyptus 1	86	-	539
Solid eucalyptus 1	89.5	-	800
LVL 1	94.9	-	674
LVL 2	89	-	690

It is vital to understand the strength qualities of the species to be utilized while designing wood constructions. A representative sample of the wood species must be tested and assigned a strength class in order to ascertain these qualities. The basic premise is that three key parameters define the strength class: bending strength, modulus of elasticity, and density according to (BS-EN-338, 2016). Finally, for this study, the strength class designation will be issued when the appropriate experimental value has been adjusted to the standard. The highest grade for double layer Bamboo Laminated Eucalyptus (bottom) was D60, while the minimum grade for non-Laminated Eucalyptus was D40, although the minimum strength classification for laminated Eucalyptus was D50.

4. Conclusions

The goal of this investigation was to see whether bamboo laminated Eucalyptus might be used as an alternative structural material for floor decks because of its flexural capabilities. The investigation came to the following conclusions:

1. Because of their strength, Eucalyptus Globules and Oxytenanthera Abyssinica (solid culm bamboo species) might potentially be used as structural components in floor deck construction.

2. The influence of specimen location on strength was one of the important aspects investigated. The bottom and center locations of the sample in this study have a significant influence on the strength.

3. The testing results suggest that laminating bamboo with eucalyptus beneath improves or significantly enhances the strength of the bottom position specimen. However, adding a layer of bamboo to the middle location sample did not improve the strength of either single layer or double layer laminated eucalyptus, according to the test results. This would demand a different preparation process or the fabrication of only the bottom location sample.

4. The bottom location Eucalyptus has a mean ultimate strength of 130.0 Mpa, which is smaller than the strength of 166.4 Mpa on the same position of Bamboo. The strength of middle sample, on the other hand, was a close call between Eucalyptus and bamboo, with Eucalyptus having 104.6 Mpa and bamboo having 95.9 Mpa, which was less than Eucalyptus.

5. The compression test shows that the bottom position of Eucalyptus has a mean strength of 54.1 Mpa, which is much lower than the bottom position of bamboo, which has a value of 79.6 Mpa. In the same circumstance for middle specimen, Eucalyptus has a mean strength of 53.0 Mpa, which is lower than bamboo’s mean strength of 104.0 Mpa. Bamboo has a higher position strength value than Eucalyptus.

Finally, whenever there are sufficient resources of eucalyptus and solid culm bamboo, using these materials as an alternative structural material in the design of floor decks is essential. Changing the status quo of the conventional method of implementation would be crucial for societal, environmental, and economic significance. More research on bamboo as a structural material are needed, especially on its structural suitability.

Acknowledgements

The researchers acknowledged the technical, infrastructural, and financial support for data collection from Ethiopian Road Authority, Bahirdar University, and Addis Ababa University.

Disclosure statement

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

Some or all data and models that support the findings of this study are available from the corresponding author upon reasonable request (list items).

Additional information

Funding

The authors received no direct funding for this research.