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.
This research focused on studies of the cross-laminated timber (CLT) construction system and, in particular, on an innovative panel composition of eucalyptus (Eucalyptus grandis) heartwood, which is considered in Brazil as a low-added-value material that is often discarded or used for less noble purposes. The aim of this study was to investigate the thermo-energetic performance of CLT panels for use in low-income housing under several different climate conditions. The research was based on the simulation method of the Brazilian Technical Regulation of Quality for the Energy Efficiency Level of Residential Buildings (RTQ-R). The results, based on 72 parametric simulations, proved that CLT panels made of eucalyptus heartwood have significant potential for thermo-energetic improvement in various housing types under diverse climatic conditions. The simulated envelope combinations showed that in Curitiba (bioclimatic zone 1), it is important to associate 5-layered CLT panels with 10 cm thermal insulation; in São Paulo (bioclimatic zone 3), the envelope should be provided with low solar absorptance and 5-layered CLT panels without thermal insulation; and in Belém (bioclimatic zone 8), in addition to the low solar absorptance in the envelope, the CLT panels should be composed of only three layers and without thermal insulation. It was concluded that the innovative CLT construction system with low-added-value eucalyptus heartwood is a very promising technology for Brazilian dwellings that are more energy efficient, with further studies on mechanical behavior being necessary for its consolidation in the country.