What is the standard length of glue line need to be examined for delamination tests?
Abstruse
Glued laminated timber (glulam) is a wood-based production with frequent use in timber construction. Maritime pino (Pinus pinaster Ait.) is a species suitable for glulam production and is available with abundance in Portuguese forests. This study assessed the influence of the phase in which the preservative handling is applied in the surface bonding operation. Several elements were produced considering different treatment scenarios: timber without handling, timber treated before gluing, and timber treated after gluing. The bonding quality was tested by both shear force and delamination tests, following the indications given in EN 14080 (2013). Glulam elements treated after gluing (TAG) presented less delamination when compared with the ones treated before gluing (TBG). All the same, TBG elements presented college shear strength values than TAG elements. Despite the recorded differences, all the considered sets performed adequately both for delamination and shear strength tests.
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Influence of the Treatment Phase on the Gluing Performance of Glued Laminated Timber
André Chiliad. A. Dias,* Carlos Due east. J. Martins, and Alfredo M. P. G. Dias
Glued laminated timber (glulam) is a wood-based product with frequent utilize in timber structure. Maritime pine (Pinus pinaster Ait.) is a species suitable for glulam production and is bachelor with abundance in Portuguese forests. This written report assessed the influence of the phase in which the preservative handling is practical in the surface bonding performance. Several elements were produced because different treatment scenarios: timber without handling, timber treated before gluing, and timber treated after gluing. The bonding quality was tested by both shear forcefulness and delamination tests, post-obit the indications given in EN 14080 (2013). Glulam elements treated after gluing (TAG) presented less delamination when compared with the ones treated before gluing (TBG). Notwithstanding, TBG elements presented college shear strength values than TAG elements. Despite the recorded differences, all the considered sets performed adequately both for delamination and shear strength tests.
Keywords: Pinus pinaster Ait.; Glued Laminated Timber; Preservative treatment; Delamination; Shear forcefulness
Contact information: ISISE, Department of Civil Engineering, Academy of Coimbra, R. Luis Reis dos Santos 290, 3030-790 Coimbra, Portugal; *Corresponding author: andre.dias@educatee.dec.uc.pt
INTRODUCTION
Timber has been used for structural applications since the beginning of humankind, and significant advances have been observed in its utilise for indoor applications and, in contempo decades, more often for outdoor applications. However, there are some important limitations, such as the susceptibility to decay, which significantly affects the performance of the structures and in many cases is the cause of failures and malfunction (Freemanet al. 2003). At that place are dissimilar approaches to mitigate this problem; chemical preservative treatments are some of the almost effective.
Almost species used for glulam are slightly/moderately durable to fungi attack and susceptible to termites orHylotrupes bajulus attacks, every bit measured by EN 350-2 (1994). The consideration of preservative products is an alternative to improve the low natural durability of species such as maritime pine.
Co-ordinate to Nuneset al. (2016), carbolineum (anthracene oil) was the first preservative product used in Portugal every bit early on every bit 1900. For applications in exposed conditions, mainly railway sleepers, telephone and telegraph poles, preservatives such as copper naphthalene and pentachlorophenol were used and later replaced with creosote, chromated copper arsenate (CCA), chromated copper borate (CCB), and other products (Nuneset al. 2016).
Since 2000, the European Matrimony has approved new regulations with specific restrictions on preservative products that accept been used in Europe for many years, including creosote, CCA, and CCB (Coggins 2008). New organic preservative products were developed based on copper. TANALITH E and CELCURE are the most common ones in Portugal, as reported by 23 companies from a total of 33 product plants with an autoclave installed for preservation past impregnation (Nuneset al. 2016).
Glulam is one of the most used engineered wood products. However, its application in exterior conditions (Service Form three) requires the adoption of protecting measures such equally coatings. The bonding performance of preservative-treated wood has been examined for decades, considering several wood species, adhesives, and preservative products (Truaxet al. 1953; Selbo 1957, 1959; Raknes 1963; Miyazaki and Nakano 2003). The use of primers was too considered to improve the resistance to delamination by Vick (1995, 1997) and Lorenz and Frihart (2006).
Maritime pine is the dominant softwood species in the Portuguese National Wood and has been considered for glulam production in previous studies (Costa 1978; Cruz 1985; Sousa 1990); it is one of the species covered by EN 14080 (2013). Maritime pine can be impregnated and therefore is a expert culling for uses in Service Form 3 (Use Classes 3 or 4). Gasparet al. (2009) assessed the bonding performance on maritime pine preservative treated with TANALITH E 3492 glued with PRF adhesive, confirming the good bonding operation through delamination and shear strength tests. The delamination was always college than in untreated woods. However, the bonding functioning of preservative-treated maritime pine in the natural ageing process revealed inadequate performance after ix months of exposure. The bonding performance of maritime pino (untreated and preservative treated) glued with primer solutions has been tested. Lampreia (2010) carried out a written report to assess the influence of using a hydroxymethylated resorcinol (HMR) based primer on the bonding performance of treated maritime pine with TANALITH Eastward 3492 and TANALITH E NB. However, the PRF agglutinative (resin – Prefere 4040 and hardener – Prefere 5839) showed an adequate bonding operation even without the use of primer and for both preservative products.
Silva (2010) investigated the delamination performance of railway sleepers in ii conditions: untreated timber and timber treated with creosote subsequently bonding (Use Course 4). Scots pine (Pinus sylvestris 50.) and maritime pine (non-structural elements) were glued with ii types of adhesives (PRF and MUF). The authors observed that the delamination was college within the specimens tested after handling, being approximately 35% and lx% college for maritime pine (PRF and MUF, respectively). For Scots pine, the divergence was fifty-fifty higher (> 3 times) despite the lower average values of delamination (1.viii% for untreated and v.nine% for preservative-treated) compared to maritime pine (6.3% untreated and 10.1% preservative-treated), both glued with MUF adhesive.
Several studies have evaluated the bonding performance of glued preservative-treated wood, in some cases mentioning the advantages and disadvantages of applying the treatment before or after gluing. Despite that, in that location accept been no studies that accept compared the consequence of the treatment stage (before and later bonded) on bonding performance of glulam. Treated maritime pino is a good culling for other European softwoods in glulam production. This report assessed the surface bonding quality of glulam elements treated before or later on gluing with the TANALITH E 8001 product.
EXPERIMENTAL
Materials
Two samples of maritime pine were considered: i) untreated boards (S1) and preservative treated boards with TANALITH E 8001 (S2). Each board was weighed and measured in its cross-sectional dimensions and length to determine its density. S1 had a nominal density at 12% moisture content of 623 ± fifty kg/m3, whereas S2 had 638 ± 46 kg/m3. The timber boards of both samples had the nominal dimensions of 40 x 110 ten 2500 mm3. The moisture content of each board was measured with an electrical moisture meter according to EN 14080, Addendum G (2013), resulting in a mean value of 13.1 ± 0.viii% for sample S1 and 17.eight ± 1.iv% for sample S2.
TANALITH E 8001 (Lonza, 2020) is a commercial water-based product for wood preservative treatment by impregnation and is composed of copper and organic biocides. The composition of TANALITH E 8001 product is presented in Table 1.
Table ane. TANALITH E 8001 – Active Compounds and Quantities
The gluing process was washed with two commercial adhesives of type I, namely, phenol-resorcinol formaldehyde (PRF) and melamine-urea-formaldehyde (MUF). The agglutinative mixture of both adhesives was based in a ratio resin/hardener of 100/20.
The PRF adhesive was considered previously on untreated and preservative-treated maritime pine glulam (Lampreia 2010). According to Jianget al. (2014), a subtract in the use of PRF adhesives was noticed due to its chocolate-brown colour. MUF adhesives are interesting alternatives due to their white color. There are no previous tests performed on maritime pino glulam glued with MUF adhesives that ensure its performance in delamination and shear strength tests. For both adhesives, the technical information sheets (TDS) were considered to define the corporeality of adhesive, clamping pressure, and pressing time used for the assembly process.
Glulam Elements Production
To accomplish the intended objectives, three different gluing sets were considered: i) glulam elements of untreated boards (MP); ii) glulam elements from preservative-treated boards (TBG); and 3) glulam elements from untreated boards and treated by impregnation after the gluing procedure (TAG). These sets were considered for both adhesives. In total, 22 elements were produced in a laboratory: 6 elements for MP set (3 per adhesive), eight elements for TBG set (4 per adhesive), and viii elements for TAG set (4 per adhesive). Each chemical element comprised 4 lamellas of 30 mm of thickness and 1 m length. The final cantankerous-department after planing was approximately 110 mm in width and 120 mm in tiptop.
Planning, assembly and force per unit area
The production of all glulam elements began with the planing of the boards to the last thickness (30 mm). The agglutinative mixture was prepared immediately before being applied in one surface of adjacent lamellas. A manual spreader was used to uniformly distribute the agglutinative, which was the amount applied controlled by weighing. The amount of adhesive considered was the value in betwixt the interval divers in the TDS of the adhesive, which was 350 g/thouii for PRF adhesive and 400 1000/m2 for MUF adhesive.
The clamping pressure was based on the results of Cruzet al. (2018) for untreated maritime pine glulam elements and within the interval defined in EN 14080 (2013) for softwoods. The values of 0.eight and 0.half-dozen MPa were adopted for clamping pressure for the PRF and MUF adhesives, respectively. The pressing time considered followed the TDS of each adhesive, namely 240 min for PRF and 540 min for MUF. The associates was performed in controlled weather (20 °C and 65% relative humidity), and afterwards that, the glulam elements were kept in the controlled conditions to ensure the curing process of the adhesives for at least 7 days.
Treatment process
From the assembly procedure, 22 glulam elements were obtained (14 made from untreated maritime pine and 8 from preservative-treated maritime pino). The preservative product considered for the sample S2 was the TANALITH E 8001. From the 14 untreated glulam elements, 8 of them were subjected to the treatment process with the referred treatment production used in sample S2 (TAG).
The treatment procedure was based on the total-cell process, which is also designated as the Bethell Process. The treatment was practical to place the timber in a pressure vessel and adding the treatment production diluted with water. The impregnation of the preservative product in the wood was made applying consecutive cycles of vacuum and pressure in a vessel. Both glulam elements of TBG and TAG were submitted to identical handling with the same preservative production. The product retention was approximately 31 kg/m3, which met the requirements of Apply Grade 4 and consequently the utilise of the elements under Service Class 3.
After the handling procedure, the glulam elements from TAG set were stored in outdoor conditions for 2 weeks, and the wet content was estimated based on the initial moisture content (adamant based on the boilerplate moisture content of lamellas), the weight before being treated, and the retention of the product within the treatment procedure. The estimated moisture content of all glulam beams was college than xviii%, and it was decided to dry the elements in a climatic sleeping room with controlled conditions of temperature and relative humidity to dry out the glulam elements to moisture contents closer to 12%. The temperatures and relative humidity were defined to achieve an equilibrium moisture content of 10 to 12% (USDA 2010). During the drying process, the elements were weighed, and the estimated moisture content was adamant. Afterwards 28 days, 7 in viii elements had an estimated average moisture content of 13.3%, and only i element (TAG_PRF_1) had an estimated value of 21.2%.
Test Methods
The bonding quality of all glued elements manufactured in this report was assessed through delamination and shear strength tests, following the specifications of EN 14080 (2013). For the delamination tests, a total of vii specimens per glulam chemical element were obtained and tested. In relation to shear strength tests, fourteen specimens were obtained from each glulam chemical element beingness divided past glue line tests (x specimens per glulam element) and lamellae tests (iv specimens per glulam element). The number of delamination and shear specimens and tests per set is given in Table ii.
Table 2. Number of Delamination and Shear Specimens and Tests Per Set
Delamination tests
Delamination tests consist of the introduction of a moisture gradient into the specimens, which causes internal stresses perpendicular to the glue lines. The examination protocol followed the specifications of Annex C of EN 14080 (2013). From Annex C, two methods (Method A and Method B) could be considered to assess the bonding quality of glued elements intended to be used in Service Grade 3. Based on previous studies performed with maritime pino (untreated and preservative treated), Method A was used. The delamination was measured at the terminate of 2nd and 3rd cycle, and the total delamination and maximum delamination were determined.
Every bit the treatment penetration is higher in fibers direction, the specimens can exist sealed during the delamination tests, equally reported past Liet al. (2018). The sealing prevents moisture transfer in the management of the fibers. To ensure the comparability of delamination tests results with literature results for maritime pino, the wood elements were not sealed.
Shear strength tests
Shear force tests are based on loading consecutive lamellas in such a fashion that shear stresses are introduced in the gum lines until the failure occurs. For each specimen 3 glue lines were tested. It was also considered to perform shear tests in lamellas to assess the efficiency of the mucilage line, with 4 tests being performed per specimen. The test procedure is indicated by Addendum D of EN 14080 (2013).
A constant rate of displacement of 0.006 mm/s was considered. After each test, the wood failure pct (WFP) and the maximum load were recorded. To hands identify the failure by wood, a mixture (50/l) of phloroglucinol (2%) with chloridric acid solution (10%) was used to highlight the lignin of wood and distinguish the failure within the wood from the failure within the adhesive.
RESULTS AND DISCUSSION
Delamination and Shear Strength Tests
The results from delamination tests are presented in Table 3 for both PRF and MUF adhesives. For each treatment phase, and for both exam cycles, the mean values of total delamination are presented, together with the mean of maximum delamination values. The maximum values registered by fix are presented in brackets. Effigy 1 presents the shear strength results for each glue line test and the respective wood failure percentage (WFP) for each treatment phase and adhesive considered.
Fig. 1.Shear force and wood failure percentage – private values
In terms of total delamination, both adhesives showed a adept performance in terms of hateful values, with slightly higher values observed with MUF agglutinative for TBG set up. As expected, an increment of values was recorded from the 2nd cycle to the 3rd bike. Some TBG specimens presented higher full delamination than the established limits given in EN 14080 (2013) (5% – twond cycle and 10% – 3rd cycle). All the glue lines had a maximum delamination lower than the limit of 30% proposed past EN 14080 (2013).
The private values of glue line shear forcefulness and WFP showed adequate performance ensured by both adhesives, with all tests fulfilling the minimum limits established past the standard (minimum of 4MPa if the WFP is 100%). However, the PRF gum lines had lower WFP than glue lines of MUF, and the mucilage lines of the TAG set had lower shear strength when compared with TBG and MP.
Influence of Handling Stage
The influence of treatment phase was assessed past comparing the delamination and shear strength results per treatment set and adhesive. The boxplot methodology was used for the comparison of delamination results afterward the 3rd exam wheel (Fig. 2). From the PRF adhesive results, similar values were plant between MP and TAG elements. Slightly higher delamination values were institute within TBG elements being negligible the negative effect of the preservative treatment applied before gluing, as observed past Lampreia (2010).
However, elements glued with MUF agglutinative were clearly not influenced by the awarding of preservative treatment afterwards the gluing process (TAG), presenting slightly lower values on delamination compared to MP set. On the reverse way, the elements that were treated before gluing (TBG) had a significant increase in total delamination (mean values). Excessive delamination (higher than 10%) was registered in 4 specimens (from a total of 28) later the 3rd test bicycle of TBG_MUF specimens. A detailed assay showed that the four specimens with excessive total delamination belonged to the aforementioned glued element.
Table 1. Summary of Full Delamination (Mean Values) and Maximum Delamination (Hateful Values) After Both Test Cycles of Delamination – PRF and MUF Adhesives
Note: Parentheses indicate the maximum value for each set
Fig. two.Total delamination (%) of each treatment fix afterward the 3rd test cycle
Because the possible factors that could influence the delamination operation, the possible influence of density, wet content, and other parameters related to gluing process was not considered. Most delaminations occurred in the glue lines whose side by side lamellas presented growth rings displayed tangentially to the mucilage lines and wider compared to the lamellas of other elements (Fig. 3).
Fig. 3. Broad and tangential almanac rings (left) and delamination occurred later on the tertiary test wheel (correct)
Tabular array two. Summary of Mean Shear Forcefulness Test and WFP Results – PRF & MUF
The shear strength and WFP results are presented in Table 4. All the specimens fulfilled the limits of WFP and shear strength established by EN 14080 (2013) (6 MPa with a minimum WFP of xc% for mean values) . The best performance on shear strength of mucilage lines was establish in the MP set for both adhesives. The application of a preservative treatment decreased shear strength wherever the phase which the handling is applied; it was more considerable in TAG elements of both adhesives (16.1% for PRF and 14.8% for MUF) in comparing to TBG elements (6.seven% for PRF and seven.4% for MUF). Regarding the shear strength of the lamellas, there was a relevant decrease merely in TAG elements glued with PRF adhesive. This decrease was undoubetly influenced by the college moisture content of the TAG_PRF_1 element specimen compared to the other sets. The mean values from WFP did not prove considerable differences between the considered phases of preservative handling.
Exterior Analysis of Treated Elements
The visual label of treated elements proposed in this work consisted of two unlike analysis: i) superficial delaminations subsequently the drying procedure, and ii) the percent of treatment in cantankerous-department. During the drying procedure, the TAG elements exhibited some superficial delaminations in lateral glue lines, and their quantification was made by dividing the total length of the delaminations by the total length of the glue line. Regarding the superficial delamination the values varied between ane.08% and 6.23% for PRF adhesive and from 0.20% to 2.60% for MUF agglutinative.
The analysis of the pct of treatment in the cross-section (TAG and TBG elements) was made at the specimens obtained for delamination tests (prior testing). The percentage of cantankerous-section without preservative treatment was then quantified in relation to the total area of the cross-section through the difference in color. Co-ordinate to EN 350-2 (1994), maritime pino heartwood is extremely hard to treat and sapwood is like shooting fish in a barrel to care for, which is a reason why office of the cross section from TAG and TBG elements did not receive preservative treatment (Fig. 4). From the external analysis of the boards used for MP and TAG elements, information technology was not possible to distinguish the presence of heartwood. In contrast, the TBG elements that were planed before gluing showed some untreated surface area.
The percentage of handling in cross-section was determined through the mean values of the presence of treatment in the specimens collected from both ends of the elements. The presence of handling was accounted past the percent of handling in cross-section, using the software AutoCad, where the total expanse of the cross-section was determined and divided by the expanse of treatment (dark-green colour – Fig. 4) in cantankerous-department.
This analysis demonstrated a considerable departure betwixt the TBG_MUF elements (92% of handling in cross-section) and the remaining elements of TBG_PRF (44% of treatment in cross-section) and TAG (48% and 66% of treatment in cantankerous-section, for MUF and PRF, respectively). Thus, the inadequate bonding performance constitute for TBG elements glued with MUF adhesive could be clearly related to the higher content of sapwood (preservative treatment area) inside the cross-section compared with TBG elements glued with MUF adhesive and TAG (both adhesives).
Effigy 4 presents two specimens showing the difference of retentivity of preservative product in TBG and TAG elements. The retention of treatment in TBG elements was mainly influenced by the presence of heartwood in its cross-department, identified by the contrast between the light-green colour of treated wood and the natural colour of the untreated forest expanse. The retention of treatment in TAG elements was influenced by the presence of heartwood and by the glue lines, which represented a barrier for treatment penetration. An example was the TAG element presented in Fig. 4 showing role of sapwood that did not receive handling because of the heartwood presence and glue lines barriers.
Fig. 4. TBG cross section after gluing (left) and TAG cross section afterwards treatment (right)
Before delamination tests, the delaminations that result from the drying process in TAG elements were measured. From the eight glulam elements belonging to TAG set, the initial delamination was balance with mean values ranging between 0.0% and 0.7% (TAG_PRF_1), which ways that the drying process after the preservative treatment did not take a considerable influence on the mucilage lines.
CONCLUSIONS
- In general, improve performance in delamination was achieved with treated after gluing (TAG) elements compared with treated before gluing (TBG) elements, for which some specimens with excessive delamination were observed (melamine-urea-formaldehyde MUF elements).
- The untreated elements (MP) glued with phenol-resorcinol-formaldehyde (PRF) had similar functioning to the previous results obtained past Lampreia (2010).
- The untreated elements (MP) glued with MUF presented good performance for both delamination and shear force tests, which validates the glulam elements of maritime pine.
- The shear forcefulness of glue lines was afflicted past the preservative treatment, and it was more than evident inside the elements of TAG.
- The choice of the boards to be used should have a full cross-department of sapwood to ensure an effective preservative treatment, especially for TAG elements, where the identification of sapwood is harder.
- For TAG elements, the efficiency of a preservative treatment depends on the absence of heartwood on boards and on the glue lines that were considered barriers to the preservative product penetration.
- The application of preservative treatment afterward bonding is followed by a drying process, which leads to superficial delaminations, cracks on lamellas and dimensional variations that could be considered a disadvantage compared to TBG elements.
- The production of glulam with previously treated boards (TBG) has the inconvenient of generating a considerable amount of sawdust that contains the preservative production.
- The authors recommend the analysis of the influence of glue lines on the treatment of timber later on gluing (TAG) and the influence of sapwood and heartwood of glulam treatability equally targets of future works.
ACKNOWLEDGMENTS
This work was financed by: FEDER funds through the Competitiveness Factors Operational Programme – COMPETE; national funds through FCT – Foundation for Scientific discipline and Technology within the telescopic of the Project UIDB/04029/2020 – ISISE and the Project POCI-01-0145-FEDER-007633; and by the Regional Operational Programme for the Centro Region (Centro 2020) within the telescopic of the Projection SUSpENsE – CENTRO-01-0145-FEDER-000006.
The authors wish to thank Foundation for Scientific discipline and Applied science for the PhD grants (PD/BD/135159/2017) given to André Dias and (PD/BD/52656/2014) given to Carlos Martins in the frame of EcoCoRe doctoral program, and to Dynea Equally and ColquÃmica Adhesives for providing the adhesives and finally to Pedrosa Irmãos for the collaboration given with the raw fabric.
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Article submitted: February 24, 2020; Peer review completed: April 26, 2020; Revised version received and accepted: May thirty, 2020; Published: June 3, 2020.
DOI: 10.15376/biores.15.3.5725-5736
Source: https://bioresources.cnr.ncsu.edu/resources/influence-of-the-treatment-phase-on-the-gluing-performance-of-glued-laminated-timber/
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