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- Effects of anobiid damage on shear strength parallel to the grain in single step jointsPublication . Lima, Daniel F.; Branco, Jorge M.; Parracha, João Luís; Machado, José S.; Nunes, LinaABSTRACT: Traditional carpentry joints can be found worldwide in many timber truss structures connecting rafter and tie beam. One failure mode of this connection result from shear in the tie beam beyond the notch either due to bad design or deterioration. In this article, the reduction in shear strength of Single Step Joints (SSJ) resulting from biological attack by anobiids was analysed. For this purpose, tests were carried out in non-degraded scots pine (Pinus sylvestris L.) specimens (reference) and compared to artificially degraded specimens with three different levels of degradation. The reduction of shear resistance was analysed in relation to the density of holes drilled during the degradation simulation, the loss of mass, and the reduction of the shear-resistant area. At lower degradation levels, no significant reduction in shear strength was observed. On the other hand, the linear regression shows a trend of resistance reduction with increasing degradation. Despite the relatively low coefficient of determination (r2 = 0.25), the parameter that best correlated with the residual strength was the reduction in the shear-resistant area.
- Insulation Materials Susceptibility to Biological Degradation Agents: Molds and Subterranean TermitesPublication . Nunes, Lina; Duarte, Sónia; Parracha, João Luís; Jones, Dennis; Paulmier, Ivan; Kutnik, MagdalenaInsulation materials are fundamental for decreasing energy losses and guaranteeing thermal and acoustic comfort in buildings, which may significantly contribute to decreasing the energy consumption related with poor thermal building conditions. These insulation materials should have a low susceptibility to biological degradation agents to decrease the risks of degradation of other construction materials, as well as decrease possible health risks related with the development of noxious biological degradation agents regarding indoor air quality, for example, or decrease possible structural risks posed by those agents. The present study aimed at evaluating the susceptibility of several insulation materials to mold growth and subterranean termites’ attack. Insulation materials, including expanded polystyrene (EPS), mineral wool (MW), and expanded cork agglomerate (ICB), were tested against mold development, using maritime pine as a control. Three types of inoculations were made: (1) natural indoor inoculation; (2) artificial inoculation using Aspergillus niger and Penicillium funiculosum; and (3) artificial inoculation using Aureobasidium pullulans. The susceptibility of the insulation materials referred to, plus wood/glass fiber (WGF), was evaluated for two subterranean termite species: Reticulitermes grassei and Reticulitermes flavipes. The expanded cork agglomerate showed a higher susceptibility to molds than the other insulation materials tested. The remaining materials revealed a good performance, showing no growth or traces of growth of molds. All the materials tested showed susceptibility to subterranean termites, with both species being able to cross them to obtain access to the wood. However, wood/glass fiber showed a negative effect, which translated into lower survival rates and attack degrees of the wood. Some tested materials showed a good resistance to the development of biological degradation agents, namely an organic material (coconut fiber), a composite of organic and inorganic materials (WGF), and an inorganic material (EPS). These results indicate that it is possible to pursue the development of innovative and effective insulation materials with a low susceptibility to biological degradation agents, regardless of their organic or inorganic origin.
- Effects of hygrothermal and natural aging on the durability of multilayer insulation systems incorporating thermal mortars with EPS and aerogelPublication . Parracha, João Luís; Veiga, Rosário; Nunes, Lina; Flores-Colen, InêsThis study evaluated the durability of three innovative multilayer insulation systems incorporating thermal mortars with EPS aggregates and silica aerogel granules after hygrothermal accelerated aging and one year of natural aging at an urban site in Portugal. The loss of performance was assessed after the accelerated aging and every three months of natural aging using non-destructive testing. Chemical-morphological analyses were also carried out prior to and after accelerated and natural aging. Results obtained after accelerated and natural aging were compared, thus contributing towards a deeper understanding of possible synergistic effects of several degradation agents and mechanisms on the long-term durability of multilayer insulation systems. The Coffin-Manson equation showed that the accelerated aging procedure (∼13 days of heat/rain cycles and 5 days of heat/cold cycles) adopted herein corresponds to approximately 11 years of natural aging in typical urban conditions. The results show a significant increase in capillary water absorption and drying capacity after aging. Extensive surface microcracking was observed after accelerated aging and after 3 months of natural aging, especially in the systems facing North. Traces of biological growth were detected on both the artificially and naturally aged systems, whereas aesthetic alterations were more pronounced in North-oriented specimens after 3 months of exposure, with significantly lower surface gloss and a darker tone. On the other hand, color change cannot be detected in the artificially aged systems, due to the lack of degradation agents such as pollutants or UV radiation that were not included in the accelerated aging procedure.