Effects of CCA and LOSP Preservative Treatments on the Bending Performance of Glulam Timber Beam

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1 Volume 118 No ISSN: (on-line version) url: Effects of CCA and LOSP Preservative Treatments on the Bending Performance of Glulam Timber Beam Lannie Francis a, Siti Zaidah Othman a, Syarifah Hanisah Bt Syed Mokhtarruddin b, Zakiah Ahmad c, Zaidon Ashaari d, Hafizah Bt Muhamad Azlan e a Faculty of Civil Engineering, Universiti Teknologi MARA, Cawangan Sarawak b Faculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam c Institute Infrastructure Engineering and Sustainable Management, Universiti Teknologi MARA, Shah Alam d Faculty of Forestry, University Putra Malaysia, Serdang e Faculty of Civil Engineering, Universiti Teknologi MARA, Cawangan Pulau Pinang *Corresponding Author lannie francis@yahoo.com April 1, 2018 Abstract Manufacturing of glued laminated (glulam) timber can help overcome the limited availability of high density, high grade and large timber. The usage of structural adhesives, such as PRF adhesive, may increase the strength and stiffness of the glulam timber. The use of CCA and LOSP preservative treatment may resolve the durability problems 1

2 of the lower density and low grade timbers for outdoor applications. This paper presents the results on the bending strength properties of CCA and LOSP treated glulam beams manufactured from several selected Malaysian tropical woods, namely, Bintangor and Mengkulang in accordance with MS 758. Tests were carried out on four isolated simply supported beams according to the procedure set forth in ASTM D-198. The bending strength of glulam beams was compared with the permissible strength of the timber under bending in accordance with MS 544 Part 3. The results showed that the glulam timber produced passed the required allowable strength value. 1 Introduction A glulam beam is a construction material that makes use of smaller and less desirable dimensions of timber and is engineered to be stronger and larger than the similarly sized timbers made of solid wood (1). Manufacturing glulam beams with high density and high grade solid timber is not suitable because these timbers are expensive and most importantly difficult to glue due to the high density. With the application of glulam technology and advanced research, timbers with low density can be improved to a higher grade (2-4). However, the usage of low density timbers has never been regarded as a structural material due to their inferior strength when used outdoor. This has led to the treatment of timbers with wood preservatives in order for them to be used sustainably for outdoor structural products. Chromated Copper Arsenate (CCA) preservative treatments have been commonly used in Malaysia for solid timbers for structural application, but the use of Light Organic Solvent Preservative (LOSP) is still limited. CCA treatments are also widely used for glulam preservation in New Zealand and Australia. The studies on the treatment of glulam timbers made from Malaysian tropical timbers are still limited and not well documented. Therefore, the purpose of this study is to determine the bending behaviour of LOSP and CCA on glulam manufactured beams from Malaysian tropical hardwood timbers, namely, Mengkulang and Bintangor. Both timbers are classified under hardwood that belong to Strength Group (SG) 5, based on the Malaysia Standard (MS544, 2001) (5). 2

3 2 Literature Review Understanding and predicting the strength of glulam timber structure is a complex and complicated task since it is a composite timber product, which can be made from same or different pieces of timber of varying grades, strengths and stiffness that are bonded together. A non-naturally durable timber is easily degraded by environmental parameters, such as biological organisms, water, light and chemicals(6). Nevertheless, the problems can be minimized by applying treatments and modifications to the timber (7). There are many preservative methods available either chemical-based (such as boron and CCA) or natural-based products. A timbers strength can be affected when the timber is treated with preservatives that relate to the chemistry system and reaction towards wood properties (8). The reaction of preservatives on glulam timber will be more complicated due to the bonding properties of each lamella layer. The modulus of elasticity (MOE) and modulus of rupture (MOR) are the main bending strength properties of glulam timber. The MOE of glulam timber is directly related to the MOE of its individual laminations. Theoretically, elasticity is a property of timber in which strain or deformation is recoverable after an applied load is removed to a certain level of stress, known as the proportional limit. Below this point, each increment of stress will produce the proportional increment deflection and the timber will return to its original shape once the load is removed. Beyond the proportional limit, each strain increases as failure approaches and removal of stress will only result in partial recovery of the strain as shown in Figure 1 (9). (10) stated that stiffness value can be obtained from the gradient of load-deflection or moment rotation curve at elastic region, which is also recognized as the best predictor of strength (10). In fact, in 1994, Parker stated that the modulus of elasticity is a measurement of timber stiffness (11). 3

4 Figure 1: Typical load deflection curve parallel to grain There are numerous references that provide an extensive review of performance of treated glued timber (12-14). (12) investigated the effects of post-layup ammoniacal copper zinc arsenate (ACZA) treatment on the appearance and flexural properties of Douglas-fir glued laminated beams. They found that ACZA treated glulam beams showed higher MOR, MOE and shear values than the control samples. (13) studied the yellow pine wood treated with three different solutions, namely, CCA, ammoniacal copper quaternary compound (ACQ), and CCA Tanalith in order to determine the effects of wood preservatives on MOE and MOR, which are the criteria for designing wood construction. Based on the three-point bending test results, MOE values of the CCA Tanalith preserved wood were higher with slightly lower MOR values as compared to untreated wood. Other chemicals of this study did not affect the MOE values. In another study, Mengeloglu and Gardner (2000) conducted physical and mechanical tests on CCA treated flakeboards. It was found that wood treatment had a significant effect on MOR and MOE of the flakeboards. In addition, the strength properties were greatly reduced and affected due to the significant losses of preservatives during pressing and a large amount of CCA treated particles penetrated into the glued particleboards (15, 16). Despite the numerous studies that had reviewed the performance of treated glulam timber, only a few studies had been done on the performance of treated glulam beams from Malaysias tropical timbers. Hence, the aim of this study is to evaluate the effects of CCA and LOSP treatments on the bending strength properties of glulam manufactured beams using the Malaysian tropical timbers. 4

5 3 Methodology/Materials 3.1 Timbers Air-dried timbers of Mengkulang and Bintagor were planned into 33 mm in thickness and graded in accordance with MS Once the sawn timbers had been graded, they were divided into the untreated group and the treated group. Prior to the treatment, all the surfaces of the timbers were inspected visually to avoid any paint, polish and other surface finish. Then, they were weighed and measured. 3.2 Preservative Treatment CCA Treatment The Bintagor wood was treated with CCA. The treatment process for CCA followed the Malaysian Standard MS544: Part 10, where the Bethell Full Cell process was selected (17). A CCA Tanalith preservative solution was prepared at 3% concentration based on weight over volume. Then, the timbers were placed in a cylinder, where vacuum pressure was applied to remove the air. After that, the treatment solution was pumped into the cylinder. After the cylinder was filled, the samples were kept in the treatment solution for further 60 minutes. Then, the vacuum was released with 1.38N/mm2 pressure for 2 hours. Next, the preservative solution was pumped out from the cylinder. Once all the solution was removed, the final vacuum was applied for 15 minutes. The timber samples were then taken out from the cylinder and wiped lightly to remove any solution left on the timber surfaces LOSP Treatment The Mengkulang wood was treated with LOPS. The ingredients for the LOSP preservative comprised 1.40% permethrin, 1.05% tebuconazole, 1.05% propiconazole, and water repellent agents (resin/wax), in which all of them were dissolved in a common solvent (i.e. white spirit). 5

6 3.3 Manufacturing of Glulam Timber All and untreated lamella were used to manufacture the glulam timbers at a factory in Malaysia. The manufacturing process was in accordance with MS 758 (18). The adhesive used was Phenol Resorcinol Formaldehyde polymer with liquid resin and a hardener at a mixing ratio of 2.5:1 as recommended by the supplier. The number of glulam beams prepared is shown in Table 1. Table 1: Number of Glulam Beams 3.4 Laboratory Testing Bending Test All timber beams with 100mm in width, 150mm in depth, and 3000mm in length were tested under a four-point loading in accordance with ASTM D198 (2009) (19) with the span-to-depth ratio of 18. The schematic diagram of the test set-up is shown in Figure 2 with the actual set up shown in Figure 3. The test was carried out in a universal testing machine (UTM) equipped with a 2500kN load cell with a loading rate of 0.05mm/min. 6

7 Figure 2: The schematic diagram of the test set-up Figure 3: Specimen Under Load in the Four-Point Bending Test From the load data recorded, the corresponding bending strength properties, namely, Modulus of Rupture (MOR) and Modulus of Elasticity (MOE) were calculated using Equation 1 and Equation 2, respectively: (i) Modulus of rupture, MOR, 7

8 MOR= 3P L, N/mm 2 Equation 1 (ii) Modulus of Elasticity, 2bh 2 MOE MOE= P a(3l 2 4a 2 ),GPa Equation 2 Where, 4bh 2 P = maximum load (N) b = width of the specimen (mm) h = depth of the specimen (mm) P = load at the proportional limit (N) = deflection at the proportional limit (N) L =length of the span (mm) a = distance between the loading point and support (mm) m = P = slope of load-displacement graph 4 Results and Discussions 4.1 Bending Strength Properties The bending strength properties of the glulam treated and untreated beams with CCA and LOSP for both species are given in Table 2. The Modulus of Rupture (MOR) value for the untreated Mengkulang timber was 46% higher than the LOSP treated beam. The MOR value for the untreated Bintangor glulam timber was found to be marginally higher (5.6%) than the CCA treated beam. From the finding, the small reduction of MOR explains that timber preservatives gave a significant effect on strength performance of the glulam timber. Compared to the untreated beam, there was a large reduction of MOE in percentage by 55% for the Mengkulang glulam timber after the treatment. It shows that there was an effect of LOSP treatment on the stiffness of the Mengkulang glulam beam. The high amount of treatment solution that retained in the cell wall had caused swelling, thus reduction in MOE occurred. These findings were consistent with the literature (14, 15, 20-22). However, the MOE for the untreated Bintangor timber was marginally lower than the MOE of the CCA treated beam by 6.8%. There was a slight increase in the MOE value for the CCA treated Bintangor beam, which shows a positive contribution of CCA in protecting the timber in the environment. The bending strengths of CCA and LOSP treated glulam timbers were higher than the control glulam beam. The density of Bintangor was increased by 8

9 7.6% when treated with CCA, while the density of Mengkulang was increased by 47% when treated with LOSP. This shows that Mengkulang was able to absorb more CCA solution than Bintangor. This was reflected in the bending strength of treated beam of Mengkulang, which was higher than the treated Bintangor beam. Mengkulang timber was able to absorb more preservative as compared to the Bintangor timber. The treatment process relies on a chemical reaction to bind the chemical in wood (23, 24). In this process, known as fixation, the metal is reduced to less water soluble forms by oxidizing the wood cell-wall components (8). The addition to heat, during and after treatment, potentially accelerates the hydrolytic reactions, magnifying strength reduction. The strength loss as exposure to elevated temperatures is also magnified by the high moisture content induced by the water solvent in the system. Table 2: Summary statistics of bending strength properties of the glulam timber Bending Behaviour of the Mengkulang and Bintangor Glulam Timbers This section compares the bending behaviour of the untreated and treated beams between Mengkulang and Bintangor. Figure 4 and figure 5 show the effects of treatment on the overall behaviour of the glulam beams for Mengkulang and Bintangor. The graphs for each beam were selected based on the graphs that were very close to the average value. The aim of this section is to show the general behaviour of the different beams under bending. Generally, the behaviour of the graphs for each beam was similar in shape with linear portion to maximum point and then the load decreased abruptly without non linear portion. The value of the maximum load and the slope of the linear portion related to the MOR and MOE of the glulam timbers. The glulam treated timbers with LOSP gave lower values in graph than the untreated LOSP glulam beams. Meanwhile, the glulam treated beams with CCA were uniform in bending 9

10 behaviour until failure occurred as compared to the treated LOSP glulam beam. Figure 4 : The Load Versus Deflection for the Mengkulang glulam beam Figure 5 :The Load Versus Deflection for the Bintangor glulam beam Failure Mode Characteristics This section presents the analysis of the failure mode of CCA and LOSP treated and untreated Bintangor and Mengkulang glulam 10

11 beams under the four-point bending test as shown in Figure 3. From the figures, the cracks originated at the bottom of the tension zone and progressed with the application of load for all untreated and treated glulam beams. The continuous application of load caused cracks to slowly propagate along the timber until it reached the weaker zone of the glulam beam. A typical weaker zone for the glulam timber as at the finger joint areas, as shown in Figure 6a, Figure 6b, Figure 7a and Figure 7b. The crack pattern for the CCA treated Bintangor glulam beam was more critical than the Mengkulang glulam timber, as shown in Figure 7a and Figure 7b, which implies the lower MOR values compared to the untreated samples. A similar observation was also reported in the study conducted by (3, 4). Figure 6: Failure Characteristics of CCA Treated Bintangor Glulam Beam Figure 7: Failure Characteristics of LOSP Treated Bintangor Glulam Beam 5 Conclusion This study was conducted to determine the bending strength of CCA and LOSP treated Bintangor and Mengkulang glulam beams, respectively. The load behaviour, the modulus of rupture (MOR), 11

12 and the modulus of elasticity (MOE) were observed for both groups of glulam timbers. Overall, the Mengkulang glulam beam showed higher MOR as compared to the Bintangor glulam beam after treatment. There was a slight increase in the MOE value for the CCA treated Bintangor beam, which shows the positive contribution of CCA in protecting the timber in the environment. In addition, the failure characteristics of the glulam beam were observed in this study. Hence, it can concluded that the application of treatment could improve the behaviour of the strength properties of the lower strength timber. References [1] Moody RC, Liu JY. Glued structural members [2] Ahmad Z, Al-Mattarneh H, Salleh M, Paridah MT, editors. Strength Characteristics of Full Scale Structural Laminated Veneer Lumber in Tension. The 7th World Conference on Timber Engineering; August 2002; Shah Alam, Malaysia. [3] Bhkari NM, Ahmad Z, Bakar AA, Tahir PM. Assessment in bending and shear strength of glued laminated timber using selected malaysian tropical hardwood as alternative to timber railway sleepers. Jurnal Teknologi. 2016;78(5-5): [4] Mohamad WW, Razlan MA, Ahmad Z. Bending strength properties of glued laminated timber from selected Malaysian hardwood timber. Int J Civ Environ Eng. 2011;11(4):7-12. [5] 2001 MP. Code of Practice for Structural Use of Timber. In: Standard Do, editor. Malaysia2001. [6] Kiguchi M, Evans P. Photostabilisation of wood surfaces using a grafted benzophenone UV absorber. Polymer Degradation and Stability. 1998;61(1): [7] Tomak ED, Viitanen H, Yildiz UC, Hughes M. The combined effects of boron and oil heat treatment on the properties of 12

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