Abstract
This study investigated the compressive performance of 24 three-layered laminated bamboo specimens made with four different parameters, primarily bamboo species, adhesive type, lay-up pattern, and arrangement of laminated bamboo. The goal for this study was to investigate the compression parallel to the grain performance of laminated bamboo. A total of 288 laminated bamboo specimens were tested. Modulus of elasticity (MOE) and compressive strength were conducted to simulate the utilization of this material into construction material. The laminated bamboo produced were comparable to wood strength group A to B for vertical and horizontal arrangements and SG D for mixed arrangements. Laminated bamboo was produced based on Gigantochloa scortechinii and Gigantochloa levis and bonded with phenol resorcinol formaldehyde (PRF) and one-component polyurethane (PUR) adhesive. Four failure types were classified. All specimens experienced the elastic stage at the beginning of the loading process and then changed to elastic-plastic stage. There was a significant difference in the parallel and perpendicular lay-up for vertical, horizontal, and mixed arrangements.
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Effects of Species, Adhesive, and Structural Configurations on Compression Parallel to the Grain of Laminated Bamboo
Norwahyuni Mohd Yusof 
,a Paridah Md Tahir ,a,c,* Lee Seng Hua ,a,b,* Mohd Zuhri Mohamed Yusoff ,a,d Redzuan Mohammad Suffian James ,a Izwan Johari ,e and Syeed Sailful Azry Osman Al- Edrus a,f
This study investigated the compressive performance of 24 three-layered laminated bamboo specimens made with four different parameters, primarily bamboo species, adhesive type, lay-up pattern, and arrangement of laminated bamboo. The goal for this study was to investigate the compression parallel to the grain performance of laminated bamboo. A total of 288 laminated bamboo specimens were tested. Modulus of elasticity (MOE) and compressive strength were conducted to simulate the utilization of this material into construction material. The laminated bamboo produced were comparable to wood strength group A to B for vertical and horizontal arrangements and SG D for mixed arrangements. Laminated bamboo was produced based on Gigantochloa scortechinii and Gigantochloa levis and bonded with phenol resorcinol formaldehyde (PRF) and one-component polyurethane (PUR) adhesive. Four failure types were classified. All specimens experienced the elastic stage at the beginning of the loading process and then changed to elastic-plastic stage. There was a significant difference in the parallel and perpendicular lay-up for vertical, horizontal, and mixed arrangements.
DOI: 10.15376/biores.20.1.527-547
Keywords: Laminated bamboo; Compression parallel; Modulus of elasticity; Compressive strength; Construction; Gigantochloa scortechinii; Gigantochloa levis
Contact information: a: Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia (UPM), 43400 UPM Serdang, Selangor, Malaysia; b: Department of Wood Industry, Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM); c: Faculty of Forestry and Environment, UPM, 43400 UPM Serdang, Selangor, Malaysia; d: Advanced Engineering Materials and Composites Research Centre (AEMC), Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia (UPM), 43400 UPM Serdang, Selangor, Malaysia; e: School of Civil Engineering, Universiti Sains Malaysia, Nibong Tebal, 14300, Malaysia; f: Institute of Ecosystem Science Borneo, Universiti Putra Malaysia Bintulu Sarawak Campus, Nyabau Road, 97008 Bintulu, Sarawak, Malaysia;
* Corresponding author: parida@upm.edu.my; leesenghua@uitm.edu.my
GRAPHICAL ABSTRACT
INTRODUCTION
Bamboo is valued for its strength, cost-effectiveness, and market potential. It is increasingly used as a laminate in construction, furniture, and decoration due to its environmental benefits, high strength, and aesthetic appearance (Huang et al. 2015; Nkeuwa et al. 2022; Zhang et al. 2024). Similar to wood, optimising bamboo use necessitates a thorough understanding of its physical and mechanical properties (Ribeiro et al. 2017). In recent decades, various widely used bamboo engineering materials have been developed, such as laminated bamboo, parallel strand bamboo, cross laminated bamboo, and glued laminated bamboo (Dauletbek et al. 2023). Compression is essential in almost all construction products. Compression can occur when compressive force is applied parallel to the grain and produces stress that deforms (shortens) the cell along its longitudinal axis (Qiang et al. 2021). The maximum crushing strengths are referred to as compression parallel to the grain, representing the highest level of stress endured by compression in the same direction as the grain (Green et al. 1999). Many Malaysian studies have focused on the bending properties rather than the performance under compression with different thicknesses of laminated bamboo such as bending parallel to the fibers (Ong et al. 2023), physical and bending strength of bamboo (Osman et al. 2022), tensile and bending of layered laminated woven bamboo (Rassiah et al. 2018), and properties of laminated woven bamboo (Abidin et al. 2022). Compression strength is heavily influenced by bamboo species, lamina thickness, configurations, and adhesive types. In some studies, some of these influence factors on the compression strength properties of laminated bamboo were investigated. It was found that a parallel lay-up is the best angle for laminated bamboo (Yang et al. 2020). In addition, different layers affect the mechanical properties of laminated bamboo products (Suhaily et al. 2020), and species greatly effect strength properties (Mateus de Lima et al. 2023; Kumar and Mandal 2022). The type of adhesive also has been found to affect the bonding strength of laminated bamboo lumber (Sulastiningsih et al. 2021).
Chen et al. (2018) bonded moso laminated bamboo with phenol formaldehyde (PF) adhesive and investigated the effect of curing temperature, moisture content of bamboo strips, resin consumption, and hot-pressing parameters. However, the adhesive strength is the most influential factor in compression failure, with the three common failure modes being folding, glue line cracks, and bottom lamina cracks. Anokye et al. (2016) investigated how nodes and resin affect the mechanical properties of bamboo timber. Over PVaC, which had the highest compressive strength, PF was chosen as the best adhesive for manufacturing bamboo timbers. On laminated bamboo, adhesive types were found to differ significantly in compression strength but not in spread rate. With a 46.9% difference, PF was chosen as the best adhesive for manufacturing bamboo timbers over PVaC. The large difference could be attributed to hot pressing-induced plasticization of PF within the vascular bundles closer to the glue line.
Shangguan et al. (2015) investigated the effect of different load-grain angles on the compressive properties of bamboo scrimber. The ultimate compression strength was found to vary significantly with angle, with increasing angles having a greater influence on compressive strength with a lower value and less impact on failure. It was concluded that increasing lamina angles by more than 50º decreased compressive strength and caused microcracks in the samples. A small change in grain angle can cause a significant change in mechanical properties when grains are nearly parallel to the load direction. Yang et al. (2020) discovered that the compression strength of laminated bamboo decreased as the lamina angle increased. Sharma and Van der Vegte (2020) discovered that the direction influenced bamboo scrimber rather than laminated bamboo compressive stress. Rahman (2015) discovered that different orientation angles and layers of laminated bamboo affect compressive strength. The 3-ply and 5-ply lay-ups demonstrated higher compressive strength with combination lay-ups 0º/45º /0º and 0º/90º /0º /90º /0º compared to 45º/90º /45º and 45º/90º /45º /90º /45º lay-ups, indicating that such lay-ups are unsuitable for lamination work.
Previous research by Verma and Chariar (2012) investigated the mechanical properties of layered laminated bamboo composites using epoxy resin, as well as the effect of laminate layer orientation on strength properties, with an average compressive strength ranging from 55 N/mm2 to 88 N/mm2. However, as the lamina angle increased, so did the compressive properties. As a result, understanding the mechanical properties of laminated bamboo for structural applications is becoming increasingly important. The goal of this study was to investigate the destruction of compression parallel to the grain caused by a fracture of the fibre or matrix, where failure at the fibre-matrix interface resulted in delamination failure. The objective of this study was to analyze the compression MOE, compressive strength, and detailed failure modes for all specimens. The study was investigating how different factors such as species, adhesive and configurations (lay-up and arrangement) effect these properties. The test arrangements and experimental parameters are illustrated in Fig. 1. In this study, 288 laminated bamboo specimens were tested in compression parallel to the grain and the influence factors on bamboo material type, such as composition pattern, layer thickness, and lamina lay-ups type were comprehensively considered. Then, the performance of compression parallel to the grain of laminated bamboo was tested, which provided a basis for the material selection for prestressed laminated bamboo.
Fig. 1. The specimen for compression parallel to the grain test arrangements
EXPERIMENTAL
Material Preparation
This study focused on two bamboo species, G. scortechinii and G. levis, which are often utilized in Malaysia for the production of laminated bamboo board. These species were chosen due to their abundant availability and remarkable strength. This was based on the results of the authors’ previous studies on the physical and mechanical properties of the bamboo strips of the selected species (Yusof et al. 2023). The harvested matured bamboo culms with an average age 3–5-year-old were cut to 2,000 mm and split to 22 mm width. Splits were trimmed to 20 mm width and 5 mm thickness were obtained. Prior to laminated bamboo manufacturing, bamboo strips were treated for 24 h with 5% boric acid to provide short-term protection against biodeterioration agents. The bamboo was harvested in Kedah, Malaysia.
Laminated bamboo from G. scortechinii and G. levis using phenol resorcinol formaldehyde (PRF) and polyurethane (PUR) adhesive were fabricated. Adhesive were supplied by AkzoNobel Sdn. Bhd., Petaling Jaya. The glue spread rate was 250 g/cm² for PRF and 200 g/cm² for PUR. The bamboo strips were arranged in a horizontal, vertical and mixed arrangement with two lay-up patterns namely parallel and perpendicular. Laminated bamboo was pressed for 4 hours at 75 kg/cm2 for edge bonding and 125 kg/cm2 for face bonding using a laboratory hydraulic press (Carver CMG 100H-15, Ontario, NY, USA). The test apparatus of the compression parallel to the grain tests used according to the European standard BS EN 408 (2010) and ISO/TC 165 N1242 (2024) was referred to for the bamboo structures. This standard is certified for determining the stiffness and strength properties of laminated wood based on the BS EN 16351 (2015) standards. A total of 288 specimens (12 samples × 2 species × 2 adhesives × 6 configurations) was tested. The test was performed on Instron Universal Testing Machine 8802 and 5582 (250 kN and 100 kN). All the strengths were adjusted at 12% moisture content according to EN 384 (2016). The chosen adhesive was based on its superior mechanical, bonding physical properties, and cost effectiveness which are criteria frequently used in the production of laminated boards.
Fig. 2. Dimensions of compression parallel to grain for laminated bamboo
This section examines the effects of species, adhesive, and configurations (direction: parallel and perpendicular; arrangements: vertical, horizontal, and mixed) on compression and compressive strength of three-layer laminated bamboo boards.
Specimen Preparation
Figure 2 shows the size of the specimen was 6h with different thicknesses of 54 mm, 27 mm, and 13 mm.
Test Method
The test pieces were full cross sections and length of six times (6 × h) the smaller cross-sectional dimension. The end-grain surfaces were accurately prepared to ensure that they were aligned and parallel to one another and perpendicular to the axis of the piece. The MOE and MOR calculations were based on the measurement values from the gross cross-section of tested samples according to BS EN 408 (2010).
The test pieces were loaded concentrically using spherically seated loading heads or other devices, where the compressive load was applied without inducing bending. The load was applied at a constant rate and the rate of movement of the loading head shall be not greater than 0.00005 l mm/s.
Load was applied at a constant loading head movement and the maximum load is reached within (300 ± 120 s). The time to failure of each test piece was recorded and its average reported. Any single piece diverging more than 120 s from the target of 300 s was reported. The MOR and MOE for compression were calculated using the following Eqs. 1 and 2,
(1)
where Fmax is the maximum load, N; A is the cross-sectional area, mm2, and
(2)
where F2 ˗ F1 is an increment of load on the straight-line portion of the load deformation curve (N); W2 – W1 is the increment of deformation corresponding to F2 ˗ F1 (mm); l1 is the gauge length for the determination of modulus of elasticity (mm); and A is the cross-sectional area (mm²).
Statistical Analysis
The data were tested for potential differences in group mean characteristics of the compression parallel to the grain for laminated bamboo that had eventually been analyzed using the Analysis of Variance (ANOVA).
Meanwhile, mean separation was carried out using the Least Significant Difference (LSD) method. The level of significance (α) was set for all the statistical tests at 0.05 so that probability values less than 0.05 were taken as indicatives of statistically significant difference.
RESULTS AND DISCUSSION
Analysis of Variance
The analysis of variance (ANOVA) of the effects of species, adhesive, and lay-up in the different arrangements on compression parallel to the grain MOE and compressive strength is shown in Table 1. The results showed that lay-up had the greatest impact on both compression MOE and compressive strength. Aside from that, with the exception of mixed arrangements for values compression MOE and compressive strength, both vertical and horizontal arrangements had a significant effect in species. Meanwhile, only horizontal arrangement had a significant effect on compression MOE in adhesive. In compressive strength, horizontal arrangement was found to be significantly affected by adhesive types in both values, followed by vertical arrangement. Except in mixed arrangements, there was an interaction effect between the species and the adhesive on vertical and horizontal arrangements for compression parallel to the grain for both values. Table 1 shows the results of further analysis of these effects using the least significant difference (LSD) method.
Table 1. ANOVA for the Effects of Species, Adhesive, Direction, and Configurations for the MOE in Compression and Compressive Strength of Laminated Bamboo
Notes: ns p > 0.05; * Significantly different at p < 0.05; ** Significantly different at p < 0.01; *** Significantly different at p < 0.001
Compression MOE and Compressive Strength of Laminated Bamboo
The value of compression parallel to the grain in three different arrangements of laminated bamboo samples from this study is tabulated in Table 2. The evaluation included the compression MOE and compressive strength. The average values for MOE and compression strength in parallel lay-up was 20% higher compared with perpendicular lay-up irrespective of strips arrangement. This is due to the layer of parallel lay-up connecting three longitudinal layers, which offer sufficient compression capacity (Wei et al. 2019). Table 2 displays the highest and lowest values from 24 types (6 configurations × 2 bamboo species × 2 adhesive types) of laminated bamboo boards. Despite being 4.2 times thinner than that of the vertical arrangement, laminated bamboo made by arranging the strips horizontally exhibited strength two-thirds to three-quarters of the former mostly in the compressive strength.
Table 2. MOE in Compression and Compressive Strength of Laminated Bamboo Boards Fabricated with Different Configurations
Note: *Adjusted at 12% moisture content;; BPA- Beting PRF parallel; BUA- Beting PUR parallel; BPB- Beting PRF perpendicular/ cross; BUB- Beting PUR perpendicular/ cross; SPA- Semantan PRF parallel; SUA- Semantan PUR parallel; SPB- Semantan PRF perpendicular/ cross; SUB- Semantan PUR perpendicular/ cross; Mean followed by the same letters in the same column are not significantly different at p ≤ 0.05 according to LSD; Values in parenthesis are standard deviation
All samples were adjusted at 12% moisture content based on BS EN 384 (2016) (Eq. 2). Based on the Table 2, the mean compression MOE and compression strength was 5,240 to 9,300 N/mm², 46.6 to 54.4 N/mm² (G. levis parallel), 2,130 to 7,010 N/mm², 16.0 to 74.8 N/mm² (G. levis perpendicular), 4,850 to 10,900 N/mm², 44.7 to 54 N/mm² (G. scortechinii parallel), 2,130 to 8,480 N/mm², and 16.5 to 34.3 N/mm² (G. scortechinii perpendicular), respectively. The highest value in parallel (A) lay-up from vertical arrangements from G. scortechinii with 11,300 N/mm² and 59.2 N/mm² and the lowest was perpendicular (B) lay-up from mixed arrangements from G. levis with 2,090 N/mm² and 16.3 N/mm².
The compression results were primarily influenced by the density of the laminated bamboo. Table 3 provides a summary of the density of laminated bamboo boards made from two species (G. scortechinii and G. levis), two types of resin (PRF and PUR), two lay-up (parallel and perpendicular), and three strip arrangements (vertical, mixed, and horizontal). The density ranged from 665 to 793 kg/m³ for G. scortechinii and from 651 to 803 kg/m³ for G. levis. These ranges apply to different parallel and perpendicular lay-up arrangements, as well as vertical, horizontal, and mixed arrangements. The densities were adjusted to 12% moisture content.
Table 3. Density of Laminated Bamboo Boards Fabricated with Different Configurations
Note: BPA- Beting PRF parallel; BUA- Beting PUR parallel; BPB- Beting PRF perpendicular/ cross; BUB- Beting PUR perpendicular/ cross; SPA- Semantan PRF parallel; SUA- Semantan PUR parallel; SPB- Semantan PRF perpendicular/ cross; SUB- Semantan PUR perpendicular/ cross; Mean followed by the same letters in the same column are not significantly different at p ≤ 0.05 according to LSD; Values in parenthesis are standard deviation
In comparison to the adhesive types, the effect of the bamboo species parameters appears to be influenced by the arrangements, particularly in vertical arrangement. In both parameters, G. scortechinii performed better than G. levis (lay-ups and adhesive types). However, when bonded with PRF adhesive, G. levis surpassed G. scortechinii in both horizontal and mixed arrangements. In contrast, laminated bamboo bonded with PUR adhesive produced the opposite result for horizontal and mixed arrangement. The density of laminated bamboo was comparable to Malaysian medium hardwood categories, with an average density of 720 to 880 kg/m³. In MOE compression, the density of G. levis was higher compared to G. scortechinii values of horizontal and mixed arrangement, but compressive strength was closely related for both species. In all parameters (species, lay-up, and arrangements), laminated bamboo bonded with PRF adhesive produced better results and density than PUR. The compression strength parallel to the grain of laminated bamboo was significantly affected by the lay-up patterns in all arrangements.
In comparison to Malaysian wood strength classification (Table 4), the compression strength parallel to the grain value of laminated bamboo was comparable to wood strength group (SG) A for vertical in parallel lay-up (A), and SG C for perpendicular lay-up (B). Meanwhile, except for perpendicular lay-up (B) laminated bamboo bonded with PUR, horizontal arrangement was mostly in SG B. Despite having a lower density than heavy hardwood (800 to 1,120 kg/m3), laminated bamboo had a higher compression strength in both species, adhesive, and arrangements. Most medium hardwood timber belongs to either SG B or SG C, with a few exceptions in SG A. Light hardwood timber (400 to 720 kg/m³) is typically found in strength groups C and D. However, despite having a high-density value, some laminated bamboo had the weakest compression strength parallel to the grain. Particularly, this was true for mixed arrangements in perpendicular lay-up (B) for both species and adhesive in SG D. Meanwhile, for laminated bamboo in mixed arrangement for parallel lay-ups in SG B it was significantly higher than that of mixed arrangements in perpendicular lay-up.
Table 4. Strength Grouping Table