Shear Strength and Durability Testing of Adhesive Bonds in Cross-laminated Timber

Abstract

The paper addresses the quality of the interface and edge bonded joints in layers of crosslaminated timber (CLT) panels. The shear performance was studied to assess the suitability of two different adhesives, Polyurethane (PUR) and Phenol-ResorcinolFormaldehyde (PRF), and to determine the optimum clamping pressure. Since there is no established testing procedure to determine the shear strength of the surface bonds between layers in a CLT panel, block shear tests of specimens in two different configurations were carried out, and further shear tests of edge bonded specimen in two configurations were performed. Delamination tests were performed on samples which were subjected to accelerated aging to assess the durability of bonds in severe environmental conditions. Both tested adhesives produced boards with shear strength values within the edge bonding requirements of prEN 16351 for all manufacturing pressures. While the PUR specimens had higher shear strength values, the PRF specimens demonstrated superior durability characteristics in the delamination tests. It seems that the test protocol introduced in this study for crosslam bonded specimens, cut from a CLT panel, and placed in the shearing tool horizontally, accurately reflects the shearing strength of glue lines in CLT.

The Influence of Panel Lay-Up on the Characteristic Bending and Rolling Shear Strength of CLT

“…This is thought to be associated with the conservative value of 50 N/mm 2 , assumed for the rolling shear modulus, G R [9]. When comparing the different panel configurations, the highest mean values of approximately 36 N/mm 2 were obtained for the thinnest samples (B- [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], and the lowest of approximately 29 N/mm 2 for the thickest (B-3-40). Based on these results, there is a general tendency that the thicker the CLT panel, the lower the bending strength.…”

“…All of the panels were manufactured using a one-component PUR adhesive (PURBOND HB S309), with a spreading rate of 160 g/m 2 , and a pressure (face bonding only, no edge bonding) of 0.6 N/mm 2 . These manufacturing parameters are based on the adhesive qualification testing undertaken by Sikora et al [4]. The pressure was applied using steel plates, tightened with M20 steel bolts to provide the required compressive force, and maintained for a period of 120 min.…”

“…In general, the guidelines and requirements of the adhesive manufacturers must be followed in the manufacture of CLT panels. It must be stated that some parameters, such as the bonding pressure, the quantity of applied adhesive, and the moisture content of adherends, are based on experience with glulam production [3][4][5][6][7].Many studies have examined CLT and its uses in the timber construction industry. Its excellent in-plane and out-of-plane strength, rigidity, and stability have allowed larger and taller buildings to be built [3,[8][9][10][11][12].…”

“…In general, the guidelines and requirements of the adhesive manufacturers must be followed in the manufacture of CLT panels. It must be stated that some parameters, such as the bonding pressure, the quantity of applied adhesive, and the moisture content of adherends, are based on experience with glulam production [3][4][5][6][7].…”

Investigation of epoxy‐based wood adhesives

“…By definition, the cold‐set adhesive can cure by itself at room temperature in the absence of extra heat energy. The cold‐set wood adhesives that can be used for the production of thick wood‐based composite panels include resorcinol–formaldehyde (RF), phenol–RF (PRF), MUF, and polyurethanes (PURs) . RF, PRF, and MUF are formaldehyde‐based adhesives and typically contain residual carcinogenic formaldehyde that is emitted during the production and use of the panels .…”