Tropical species are widely used in construction, and their physical and mechanical properties have been important characteristics with direct impact on the design of structures, especially the ...strength and stiffness of wood applied in them. Tests to obtain both parameters are conducted under ABNT NBR 7190 (1997) guidelines in Brazil, being rarely found in some research centers because of the higher costs of testing equipment. For instance, the toughness test depends on equipment with a pendulum, whose device requires accuracy and maintenance for reliable analyses. This paper aims to estimate toughness through another property more easily found, given by the compression strength parallel to the grain. For this, 20 tropical wood species of the South American region were used to obtain initial values of these properties. The characteristic values of the compression strength parallel to the grain as well as linear and quadratic regression models were obtained. Statistical analysis was performed and confirmed that a linear model gave better predictions than a quadratic model.
This research examined the influence of the compositions between coconut fiber (Cocos nucifera) and wood particles (Pinus taeda L. and Eucalyptus saligna) on physico-mechanical properties of ...homogeneous particleboards. The exploratory study was carried out under Tukey’s contrast test of means, at 5% significance level, with the following compositions: 100% coconut fiber (F100 P0 E0); 50% coconut fiber, 25% pine particles, and 25% eucalyptus particles (F50 P25 E25); and 50% of pine particles and 50% of eucalyptus particles (F0 P50 E50), with particle moisture content between 0% to 2% and 10%, in mass, of polyurethane-castor oil (PU-Castor) resin. Three panels were produced for each composition. The physico-mechanical properties such as density, moisture content, swelling in thickness after 24 h of immersion in water, perpendicular tensile strength, static bending strength, and modulus of elasticity were evaluated using standard methods. The results obtained indicated the potential for using coconut fiber for the production of homogeneous particleboards in view of the minimum criteria required by the normative documents, with emphasis on the physical property of swelling after 24 hours, which obtained a statistically equivalent average relative to the treatment that contained only wood particles.
Display omitted
The aim of this research was to evaluate the influence of the curauá or polypropylene fibers on rheological properties of fresh cementitious paste. The variables were the percentage ...of fiber content 1 wt% or 2 wt% and the length of the curauá or polypropylene fibers: 6 or 10 mm, but it was also prepared paste without fibers as reference. Squeeze flow and ram extrusion tests were carried out to analyze the flow of the pastes. The hardened paste was evaluated by X-ray microtomography to observe the orientation of the fibers inside the paste. Curauá fiber led to higher force of extrusion and lower displacement of the fresh cement paste at the squeeze flow test and increased the pressure at the ram extrusion test in relation to polypropylene fibers, independently of the content and length. However, length of the same fiber presented higher influence on mixture flow than fiber content.
In order to contribute to the dissemination of lignocellulosic residues in the composite materials manufacturing, this study aimed to investigate the influence of a soaking in the presence of natural ...bacteria and fungi on the resistance to axial traction of açaí fibers (Euterpe oleracea Mart.). The stipulated factors and levels were the source of water, i.e., Rio Guamá, Pará Sanitation Company COSANPA and Cassava, as a catalyst and the mass concentration of water on the açaí cores, i.e., 2%, 4%, 6%. In this way, 9 different experimental conditions were performed, together with the reference condition, i.e., açaí fibers without the soaking. In all, 200 specimens were cast, with 10 of each composition. The analysis of variance results revealed that the individual factors were not significant in obtaining the axial tensile strength, providing equivalent results regardless of the concentration and type of water. However, the interaction between the factors was considered significant, showing that the best treatment for the fibers came from the use of 2% cassava scraps. The axial tensile strength was 47% greater than the axial tensile strength obtained from the reference sample. Furthermore, 59% surpassed the reference sample, showing the efficiency of the soaking in the presence of natural bacteria and fungi treatment.
Wood is a natural material with properties that are strongly influenced by anatomical characteristics, so studies that aim to correlate properties through empirical equations in search of ...simplification to obtain the values of their characteristics are essential. In this context, this work aims to generate multiple regression models to estimate the properties of shrinkage and compression parallel and normal to the grain of Brazilian tropical woods as a function of the values of porosity, density, and for both properties, with porosity being obtained by mercury intrusion porosimetry. As a result, the radial (RRT) and total tangential (RTT) shrinkage could be estimated through porosity. However, it was not possible to estimate them considering only density as an independent variable. All the models that were used were able to accurately estimate the modulus of resistance and modulus of elasticity values (fc,0, Ec,0, fc,90, and Ec,90).
In Brazil, standard ABNT NBR 7190 (1997) prescribes the determination of strength (fM) and modulus of elasticity (EM) in static bending from specimens measuring 5 cm × 5 cm × 115 cm. Thus, the ...relationship between the test span (L) and the specimen height (h) greater than or equal to 21 (L/h ≥ 21) is respected, ensuring that the effect of shear in the calculation of displacements is negligible (Euler Bernoulli Theory). Considering the expressive number of tree species cataloged in the Brazilian Amazon Forest, any procedure that aims to facilitate the realization of experimental tests is highly desirable because it provides the knowledge of unusual species. These wood species may potentially replace woods that have been traditionally used and historically exploited. Using five hardwood species, this research aimed to verify, while maintaining constant L/h ≥ 21 ratios, the influence of specimens dimensions in the determination of fM and EM. For all species studied, the statistical analysis found equivalence in the values of fM and EM determined as a function of the sample sizes. Therefore, respecting the ratio L/h ≥ 21, the size of the specimens does not influence the determination of strength and stiffness in static bending.
As wood is an orthotropic and natural material, there are several properties required for its use in civil construction. The apparent density has been used to estimate physical and mechanical ...properties of wood, as it is easy to determine experimentally, unlike other determinations, which involve the use of equipment available only in large research centers. Using the Brazilian standard ABNT NBR 7190 and linear and non-linear regression models, this research aimed to evaluate their accuracy in estimating the compressive strength parallel to the fibers (fc0) as well as their characteristic value (fc0,k). This study considered 72 tropical wood species from native forests that were divided into the 4 strength classes of this standard. For the set formed by all species, the linear polynomial model was the best fit, resulting in a determination coefficient of just over 70%.
► Density, porosity and modulus decreased, whereas strength increased with polymer addition larger steatite particles. ► An interaction effect was found for the porosity. ► The material colour was ...similar to soapstone being useful for restoration works.
Cement mortars prepared with steatite particles have been investigated for restoration of sculptures and other craftworks. This work investigates the addition of a thermoset polymer into cement-based composites reinforced with residues of steatite particles in order to seal the open pores, reduce water penetration and thus enhancing the material's lifetime. A full factorial design of 2
14
1 type was carried out to investigate the effect of the steatite particle size and polymeric fraction on the physical and mechanical properties of the composite materials, such as bulk density, apparent porosity, elastic modulus and compressive strength. Scanning electron microscopy (SEM) was used to reveal features in the microstructure that are related to the physical properties. Results have shown that highest compressive strength (43
MPa) and lowest apparent porosity (0.19%) are achieved when steatite particles are coarser (ranging from 1.41
mm to 0.42
mm) and 40% of polymeric phase is employed. The composite with best performance also presented texture and colour quite similar to the surface characteristics of the natural soap-stone, which makes it suitable for restoration purposes.
To reduce dependence on wood and deforestation, alternative materials have been considered. This research evaluated particleboards panels of Pinus elliotti mixed with residues of polyethylene ...terephthalate (PET) in flakes with 50% of each material, glued with 10% of castor oil-based polyurethane resin (PUR). The temperature during board production was varied to evaluate its influence on the physical and mechanical properties of the boards. The study concludes that the increase in temperature did not result in a significant improvement in the particleboard properties, but their results showed application potential according to the normative standards.
The fiber saturation point (FSP) is an important parameter of wood material, related to dimensional stability and variations of mechanical performance. This paper investigated the FSP values of 15 ...tropical Brazilian wood species covering all strength classes of the Brazilian standard code. An additional goal was to estimate FSP value based on the wood’s apparent density. The FSP values were determined by measuring the wood specimen dimensions during moisture content reduction from the saturated state. Wood densities at 0% and 12% moisture contents and basic density were determined according to the Brazilian standard code. The average FSP for all wood species was 21.6% moisture content. Among density values, good correlations were observed, and a multivariate regression model for FSP estimation based on wood densities presented a coefficient of determination equal to 13.07%. There was no correlation between FSP and wood densities, suggesting that this parameter is almost constant regardless of the wood species.
PDF
