PSI - Issue 11

Gabriela Lotufo Oliveira et al. / Procedia Structural Integrity 11 (2018) 242–249 Gabriela Lotufo Oliveira, Fabiana Lopes de Oliveira, Sérgio Brazolin / Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction According to ANSI/APA 320 (2018), Cross Laminated Timber (CLT) panels are a prefabricated engineered wood product, made of at least three orthogonal sawn lumber layers. The panels have been developed first in Austria during the 1990’s. Currently, the product is well established in Europe and, over the last years, its use has increased in other continents, such as North America and Oceania. In South America, the panel production started in Brazil in 2012. Some of the countries where CLT has recently been implemented have tropical climates, with high temperatures and humidity. Consequently, wood structural components located in those regions are more susceptible to building pathologies caused by biodeterioration, than they are in dry or cold climates (Scheffer, 1971). Wood is susceptible to both abiotic (chemicals, fire and sunlight damage, for example) and biotic deterioration agents (Morrell, 2006). Biotic agents are living organisms that use wood as food supply, provoking undesirable changes in wood elements. Microorganisms, as fungi and bacteria, insects, such as termite and wood-boring beetles, and marine borers are among these organisms. Nearly all decay biotic agents require oxygen. Another factor necessary for the phenomenon is adequate temperatures. Although organisms have a variety of temperature requirements, the perfect range temperature for their survival is from 5°C to 40°C (Morrell, 2006). Furthermore, for decay caused by microorganisms to occur, the wood moisture content must be higher than the fiber saturation point, which is around 30%. When this level is reached, free water present in wood enables the transportation of the enzymes produced by the microorganisms to the wood cell polymers, among other purposes. The enzymes are responsible for decomposing those polymers and the molecules resulting from this process are transported back to the microorganism through water (Oliveira et al, 1986). Consequently, most organisms are unable to cause damage once the wood moisture content drops below 30%. In a tropical country, the occurrence of termites and beetles in wood buildings and heritage is significant. The termites are the main problem with native and exotic species (Oliveira, et al, 1986). Milano and Fontes (2002) estimated losses at US$ 10,000 per year for treatments, repairs and replacements of deteriorated wood components. However, some wood species have natural resistance, since they produce chemicals that inhibit or are toxic to xylophagous organisms. As for the species that do not produce those extractives, and therefore have low natural resistance, one of the remaining strategies to protect them is the preservation treatment. Preservation treatments improve wood resistance, by means of impregnation of chemicals that are toxic to decay agents (Lelis et al, 2001). Those treatments strongly increase the useful life of a wood product by 20 to 40 times that of untreated wood (Morrell et al, 2006). Since CLT panels are mostly produced of softwoods, whose natural resistance to deterioration is low, their use in tropical locations, such as Brazil, Australia and some parts of the USA, must be associated to preservation methods to avoid the decay of the structural components. Therefore, this paper aims to discuss preservation treatment used in the mentioned countries, where CLT buildings have recently been assembled, by comparing the standards adopted in each one. Additionally, a case study was conducted. Hence, samples of pinewood from the south region of Brazil and treated with CCB (copper, chromium and boron solution) were tested to identify the penetration and retention of the preservative. 2. Potential wood decay in tropical climates Considering the influence of climate conditions on the wood biodeterioration process, Scheffer (1971) developed a climate index to estimate potential for decay in wood structures above ground, in order to evaluate the need for protective measures. The climate index value proposed by Scheffer is calculated from local weather data by the following equation: Climte index = � [(� − 2)(� − 3)] 16,7 ���. ���. (1)