Process parameters of cross-laminated timber (CLT) fabricated with Japanese larch were evaluated. The process parameters were designed by using an orthogonal test including pressure, glue consumption, and adhesive. Both delamination and block shear tests were conducted on CLT in accordance with GB/T 26899 (2011). The results showed that the optimum process parameters were A2B3C2 including pressure (1.2 MPa), glue consumption (200g/m2), and amount of sdhesive (one-component plyurethane). The weight loss and moisture absoption increased when the temperature increased, but the block shear strength decreased as the temperature was raised from 20C to 230C.
The feasibility of manufacturing cross-laminated timber (CLT) from southern yellow pine (United States grown) treated with micronized copper azole type C (MCA-C) preservative was evaluated. Lumber (2x6 visually graded no. 2 boards) was treated to two retention levels (1.0 and 2.4 kg/m3 ), planed to a thickness of 35 mm, and assembled along with an untreated control group using three adhesive systems following product specifications: melamine formaldehyde (MF), resorcinol formaldehyde (RF), and one-component polyurethane (PUR). Block shear and delamination tests were conducted to examine the bonding performance in accordance with ASTM D905 and ASTM D2559 Standards, respectively. One-way analysis of variance and Kruskal-Wallis H test were conducted to evaluate the effects of preservative retention and adhesive type on block shear strength (BSS) and wood failure percentage (WFP). Regardless of adhesive type, the 1.0 kg/m3 retention treatment significantly lowered BSS compared to the untreated control. CLT composed of the laminations treated at 2.4 kg/m3 maintained BSS when PUR and RF were used but not MF. The average WFP of each CLT configuration ranged from 89% to 99%. The untreated CLT specimens did not experience any delamination under accelerated weathering cycles. The delamination rates of the treated specimens assembled using MF and RF increased with the preservative retention level, while PUR provided delamination rates less than 1% to the laminations treated at both levels. These combined data suggest that, under the conditions tested, PUR provided overall better bonding performance than MF and RF for MCA-C treated wood.
Eucalyptus is one of the most important plantation species in south China. The need of alternate applications of plantation grown hardwood species including eucalyptus is concerned because of the sharp decrease of the demands from pulp and paper industry. The feasibility of manufacturing cross-laminated timber (CLT) using fast-grown small diameter eucalyptus wood (Eucalyptus urophylla × Eucalyptus grandis) was evaluated here. The effects of adhesives, priming treatment, adhesive spread rate, pressure, and pressing time duration on block shear strength (BSS), wood failure percentage (WFP), and rate of delamination (RD) of CLT via block shear tests and cyclic delamination tests. The results indicated that eucalyptus CLTs made of small diameter lumbers with four types of EP, EPI, PRF, and PUR adhesives could qualified bonding and mechanical requirements according to ANSI/APA PRG 320-2012. The maximum wood failure percentage (WFP) and block shear strength (BSS) values at dry stage condition were 85.2% and 3.51 MPa obtained from specimens bonded with PUR adhesive meanwhile those values at wet stage condition were 58.2% and 1.62 MPa obtained from specimens bonded with EPI and PUR adhesives, respectively. The minimum rate of delamination (RD) value was 7.6%, which was obtained from specimens bonded with PUR adhesive. The optimal pressing parameters were adhesive spread rate 160 g/m2, pressure 0.8 MPa, and pressing time duration 200 minutes when one-component polyurethane adhesive was used to manufacture eucalyptus CLT. The values of MOEs and MORs in the major and minor direction were 11,466 MPa, 24.5 MPa, 681 MPa, and 8.6 MPa, respectively. The values of transverse shear moduli and interlaminar shear strength in the major and minor strength were 91.8 MPa, 1.3 MPa, 241.6 MPa, and 0.5 MPa, respectively. The mechanical properties of eucalyptus CLT were equivalent to those of commercial CLT made of traditional softwoods available in market. Generally, HMR priming treatment was effective to enhance bonding performance and mechanical properties of eucalyptus CLTs. It is safe to conclude that fast-grown small diameter eucalyptus lumber was feasible to manufacture CLT for structural applications.
Cross laminated timber (CLT) has been developed to a worldwide well-known and versatile useable building material. Currently increasing rates in production volume and distribution can be observed. In fact CLT, thanks to its laminar structure making it well suited for use in construction, provides new horizons in timber engineering, in areas which had until now been the realm of mineral building materials like concrete and masonry.
After a short introduction, this paper aims to demonstrate current production processes used for rigid CLT. In section 2 the process steps are described and essential requirements, as well as pros and cons of various production techniques, are discussed. Latest results of R & D and of development and innovation in production technology are presented. In section 3 test and monitoring procedures in the area of the internal quality assurance, known as factory production control (FPC), are presented. Diverse regulations, in the form of technical approvals for CLT as well as in the CLT product standard prEN 16351 , are discussed. Additionally, some technological aspects of the product, CLT, together with a comparison of geometrical and production relevant parameters of current technical approvals in Europe are provided in section 4. In the final and main part of the paper, production and technology is presented in a condensed way. The outlook for current and future developments, as well as the ongoing establishment of the solid construction technique with CLT, is given. The product, CLT, comprises an enormous potential for timber engineering as well as for society as a whole. Standardisation and further innovation in production, prefabrication, joining technique, building physics and building construction make it possible for timber engineering to achieve worldwide success.