Air-dry Density Research Articles

Exploring the potential of rigid polyurethane foam waste in structural lightweight concrete

The structural lightweight concrete is gaining significant interest in the research community due to its reduced dead load. The reduction in the self-weight not only lowers the gravity load but can also lower the seismic demands for the structural members and hence can potentially reduce the overall cost. This study examines the feasibility of developing a sustainable structural lightweight concrete by utilizing rigid polyurethane foam waste as coarse aggregates (5–10 mm). The silica fume was incorporated as a cement replacement to enhance the compressive strength of the mix. A total of three composite mix formulations consisting of polyurethane foam, cement-coated polyurethane foam, and pumice (control specimens) as coarse aggregates were tested. The testing was performed for workability, compressive strength, flexural strength, elastic modulus, absorption, permeable voids, chloride-ion penetration, freeze and thaw resistance, and drying shrinkage. The results achieved for elastic modulus, chloride ion penetrability, and drying shrinkage, were meeting the minimum requirements of the standards making this composite suitable for the structural application. The results revealed that uncoated polyurethane based lightweight aggregate concrete resulted in an air-dry density of 1829 kg/m3 with the corresponding compressive strength of 19.5 MPa and flexural strength of 2.78 MPa at 28 days. Besides, the polyurethane-based lightweight concrete also showed lower internal structure damage against freeze and thaw action, along with improved thermal conductivity.

Enhanced thermal insulation and structural health monitoring with ultra-lightweight ECC incorporating air entrainment and cenospheres

This study presents an approach to produce multifunctional ultra-lightweight engineered cementitious composites (ULW-ECCs) spanning an air-dried density ranging from 1398 to 572 kg/m³ utilizing air-entraining agents (AEA) and fly ash cenospheres. The multifunctional ULW-ECCs combine exceptional mechanical properties with enhanced thermal insulation, self-sensing and self-healing functions. Variation of the AEA content results in compressive strengths ranging from 65.92 to 2.82 MPa, tensile strengths from 5.75 to 0.84 MPa, tensile strain capacities of 6.67 %–2.92 %, and flexural strengths of 14.41 to 3.64 MPa. Thermal insulation properties, including conductivity (20 °C: 0.73–0.20 W/(mK); 800 °C: 0.289–0.065 W/(mK)) across different temperatures, effusivity and volumetric heat capacity, were systematically tested. The small-scale thermal insulation test confirms the outstanding performance of ULW-ECCs in thermal insulation. Furthermore, ULW-ECC exhibits excellent self-sensing ability under tension and bending. Resonant frequency and impedance testing results affirm the self-healing ability. Microstructural analysis using an optical microscope, scanning electronic microscope (SEM), and mercury intrusion porosimeter (MIP) reveals that high-speed mixing, cenospheres, AEA and long polyethylene fibres are crucial for achieving porous structures, low-density and multifunctionality. This novel ULW-ECC holds promising applications in structural retrofitting, enhancing energy efficiency, thermal insulation, fire resistance and enabling simultaneous structural health monitoring.

Physical, mechanical, and thermal properties of heat-treated poplar and beech wood

Air-dried density, weight loss (WL), impact bending strength (IBS), Shore-D hardness, and thermal conductivity values were determined for heat-treated poplar (Populus nigra L.) and beech (Fagus orientalis Lipsky) wood and compared with those for untreated samples. The test samples were heat-treated at 140, 160, 180, and 200 °C for 2 h. The results showed that density decreased and WL increased with increasing temperature for all temperatures. Additionally, during the heat treatment, the IBS increased in beech wood samples at 140 °C, but at higher temperatures, these values gradually decreased in both wood species. The highest decline in IBS values, found at a temperature of 200 °C, was 66.5% for beech and 55.7% for poplar. The Shore-D hardness of both wood species increased after heat treatment and regarding beech wood, the hardness increasing rate at temperature at 140 °C, 160 °C, 180 °C and 200 °C, 8.94%, 14.19%, 8.27% and 11.7%, respectively according to control samples. Regarding poplar wood, hardness increasing rates were 6.20% at 140 °C, 4.41% at 160°C, 5.88% at 180°C and 5.31% at 200°C according to control samples. The thermal conductivity of poplar and beech wood samples decreased after heat treatment, except for samples heat treated at 160 °C.

Effects of thermal treatment on air-dried density, color change, average surface roughness, and sound absorption capacity of Scots pine

This study was conducted to investigate some characteristics of thermally treated Scots pine (Pinus sylvestris L.) wood specimens such as air-dried density, color change, average surface roughness, and sound absorption capacity. Heat treatment of Scots pine wood was performed at atmospheric pressure at 140, 160, 180, and 200 °C for 2 h. As a result, the air-dried density values of the thermally treated wood decreased as the temperature of the thermal treatment increased. With the increase of thermal treatment temperature, an increase in total color change values was detected on the surfaces of the samples and the color of the samples became darker. The average surface roughness (Ra) value of samples improved due to thermal treatment conditions and the highest value was determined in thermally treated samples at 200 °C as 3.59 μm. At 140 °C the value of maximum sound absorption coefficient was observed to be 0.48 at 2500 Hz and the highest sound transmission loss value, which was 36.7 dB, was measured at 6300 Hz and at 200 °C.

Wood Quality of Young Tectona grandis L. f. Trees and Its Relationship with Genetic Material and Planting Site in Mato Grosso, Brazil

Tectona grandis L. f. (teak) is highly valued in the international market, but its volume and properties vary depending on its genetic material and planting site. Evaluating these factors is crucial for promoting new plantations. Therefore, this study aimed to assess the impact of genetic material (clones TG1 and TG3 and seminal material) and planting site (Nova Maringá and Água Boa, Mato Grosso, Brazil) on morphological parameters (heartwood, sapwood, bark, pith proportions, and pith eccentricity), physical properties (shrinkage and air-dry density), and mechanical properties (static bending strength—fm, compressive strength—fc0, Janka hardness—fH90, and shear strength—fv0). For this purpose, we sampled five trees aged 13 years per genetic material from commercial plantations. In Nova Maringá, trees exhibited, on average, 56.07% heartwood, while in Água Boa, this value was less than 50%. Seminal material showed the lowest percentage of heartwood (49.2%). The pith percentage was significantly greater in Água Boa than in Nova Maringá, regardless of the genetic material. We observed the highest standard deviation (5.61) in pith eccentricity for the seminal material. Both the planting site and genetic material influenced the air-dry density (~12% moisture content), which ranged from 0.535 to 0.618 g·cm−3. Trees grown in Nova Maringá produced wood with higher dimensional stability than those from Água Boa, exhibiting a 14% lower radial shrinkage and a 6% lower volumetric variation. In Nova Maringá, the wood from the seminal material exhibited greater resistance. On the other hand, in Água Boa, that material showed lower resistance (fv0, fm, and fc0), or there was no significant difference (fH90) compared to the clonal materials. When comparing the clonal materials (TG1 and TG3) at each planting site, they demonstrated similar mechanical properties. The variability in physical and mechanical properties among different genetic materials and planting locations highlights the need to select appropriate teak genetic materials for each region. We concluded that more productive teak clones can be selected without compromising the physical and mechanical properties of the wood.

Phloem Sap and Wood Carbon Isotope Abundance (δ13C) Varies with Growth and Wood Density of Eucalyptus globulus under Nutrient Deficit and Inform Supplemental Nutrient Application

Eucalyptus globulus, commonly known as blue gum or southern blue gum, is a tall, evergreen tree endemic to southeastern Australia. E. globulus is grown extensively in plantations to improve the sustainability of timber and fibre production across Australia. Sustainable forest management practices necessitate the consideration of ‘off-site’ carbon and ecological footprints. Pursuing optimal supplemental nutrient application and maximum growth rates is therefore critical to the establishment of a sustainable timber and fibre production industry. Biological indicators that can predict growth responses are therefore of extreme value. We investigated the carbon isotope abundance of wood cellulose (δ13Ccel) in E. globulus to determine potential relationships with the carbon isotope abundance of phloem sap (δ13Cphl) where the trees were subjected to different level of nutrient availability. This study also sought to determine the effect of nutrient additions on the growth of the E. globulus and to quantify the relationship between the volumetric growth of wood and δ13Ccel. Phloem sap and wood cores were collected from trees within study plots which were subjected to seven nutrient treatments over a two-year period in a monoculture E. globulus plantation in South Australia. Phloem sap was collected using the razor blade technique and wood cores were collected using a stem borer. The carbon isotope abundance (δ13C) of phloem sap and wood grown in the radial direction of the stem were determined. The basic and dry densities of wood were determined, and their relationships with phloem and wood δ13C were established. The δ13Cphl was significantly correlated with δ13Ccel. The relationship between δ13Ccel and the wood density of the respective wood sections was significant but did not consistently show the same pattern. There was no significant variation in basic density observed along the radial direction of the stem wood of the short-rotation E. globulus trees. A positive correlation was observed between δ13Ccel and the wood basic density, but the relationship was not consistent along the radial direction of the stem. However, positive correlations were observed between δ13Ccel and the air-dry density of respective wood sections. The relationship between phloem and wood δ13C and the relationship between δ13C and wood density along the radial direction of the stem needs to be considered while monitoring forest growth under nutrient- and water-limited conditions.

Relationship Between Wood Properties and Drying Qualities at Three Age Groups of Mindi (Melia azedarah L) Tree for Furnitur Materials

All wood based products should have been dried to ensure their stable dimension. Indicators of stable dimension can be figured-out from wood physical properties, especially ratio of tangensial shrinkage to radial shrinkage (T/R ratio) and wood drying properties at high temperature. From those two indicators could be predicted the drying quality of wood as a basic to determine minimum – maximum of drying temperature. This research aimed to look-into the relationship between wood properties of wood and drying quality of mindi (Melia azedarach L)wood at their 5, 9, and 13 year-old trees. The preparing of test samples, and testing methods on wood physical properties covered moisture content, air-dry density, and shrinkage in tangential and radial direction, which referred to the BS 1957. Meanwhile, drying properties followed the modified Terazawa’s method. Five classes of wood drying qualities could be derived from the analysis of T/R ratio and drying property at each tree age group. Results revealed that wood density ranged about 0.46 – 0.58 g/cm3. Drying quality of each wood (except the portion near the pith) belong to B (good) for 13 years old, C (fair) for 9 years, and D (poor) for 5 years old. Related to the drying quality, the minimum – maximum temperature for 13 years mindi wood was 55–85 oC; for 9 years was 50–80 oC; and for 5 years was 40–65 oC. Supported by the performance of wood surface, especially at 13 years old, mindi wood was suitable for wooden furniture.

Effect of Precursor Blending Ratio and Rotation Speed of Mechanically Activated Fly Ash on Properties of Geopolymer Foam Concrete

This research used fly ash and slag to create geopolymer foam concrete. They were activated with an alkali, resulting in a chemical reaction that produced a gel that strengthened the concrete’s structural integrity. The experimental approach involved varying the fly ash content in the precursors at incremental percentages (10%, 30%, 50%, 70% and 90%) and subjecting the fly ash to mechanical activation through a planetary ball mill at distinct rotational speeds (380, 400, 420 and 440 rpm). The investigation discerned that the fly ash content and particle structure exert a discernible influence on macroscopic properties, including flowability, air generation height, compressive strength, dry density and microstructural characteristics such as pore distribution and hydration product arrangement in the geopolymer foam concrete. Employing analytical techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM), it was deduced that diminishing the fly ash content correlates with an enhancement in compressive strength. Furthermore, the specific strength of the geopolymer foam concrete reached a peak of 0.041 when the activated fly ash in the planetary ball mill rotated at 420 rpm, manifesting a lightweight and high-strength outcome.

The Characteristics of Ancient Residence Wood from the Qing Dynasty in Yunnan Province

This study takes the wooden components of the different parts of the ancient buildings at the site of the Zhuangzishang Conference as the object of study, and investigates the deterioration state of the different wood components. To assess their degree of degradation, the wood anatomy, basic density (BD), maximum water content (MWC), cell wall major components, X-ray diffraction (XRD), infrared spectroscopy (IR), and thermogravimetry (TG) were used to compare the samples of new and old wood from the same species. The window (W) was identified by microscopic characterization as cypress (Cupressus sp.), the footing beam (FB) and the weatherboard (WB) as pine (Pinus spp.), the purlin (P) and the column (C) as Chinses fir (Cunninghamia spp.), and the floor (F) as spruce (Picea sp.). In terms of their physical properties, the old wood had a lower basic density of 2.58%–38.19%, a lower air-dry density of 2.87%–39.81%, and a higher maximum moisture content of 8.52%–41.38% compared to the reference wood. The degradation of the FB, which has been subjected to moisture and sunlight, and the P, which has been subjected to termite damage, was greater than that of their conspecifics. The integrated holocellulose of the ancient wood was 3.34%–16.48% less, and the hemicellulose was 1.6%–21.92% less compared to that of the reference wood, and the lignin was 1.32%–25.07% more. The XRD results showed that the crystallinity of the cellulose was greater in the different species of ancient wood compared to the control wood, which was caused by the decrease in the amorphous zones of the hemicellulose and cellulose in the ancient wood. The IR indicated that the degradation of cellulose and hemicellulose occurred in the old wood of all species, from the new lignin uptake peaks in the UV-exposed W, FB, and WB compared to the control timber. The pyrolytic behavior of the ancient and control timber is mainly related to the degradation of the tree species and the ancient wood holocellulose. These results show that the differences in the wooden components of the different parts of the ancient buildings at the Zhuangzishang Conference site are mainly related to the species of trees used in the components, and are secondly related to the location of the ancient wood members, which provides useful information for the protection and repair of the ancient buildings at the site.

Emprenye ve Isıl İşlemin Ahşap Malzemenin Bazı Fiziksel ve Mekanik Özelliklerine Etkileri

The aim of this study was to determine some physical and mechanical properties of spruce (Picea orientalis) wood, which was impregnated with aqueous solutions of valonia (valex) (the extract of Quercus ithaburensis), pine bark powder (pinex) (Pinus brutia Ten.) and gallnut powder (galex) (Quercus infectoria Oliver) as a pre-treatment and then heat treated. Test specimens were prepared from sapwood of spruce wood and impregnated with 10% tannin solutions before heat treatment base on ASTM D 1413-76. After pre-impregnation processs, specimens subjected to heat treatment at 150 °C, 175 °C and 200 °C for 2 h. The effect of impregnation process and heat treatment temperature on the air-dried density, compressive strength paralell to the grain (CS), bending strength (MOR) and modulus of elasticity in bending (MOE) were analyzed. As results, impregnation solutions showed positive effects on mechanical strength in unheat-treated samples and determined that mecnaical strength loses due to heat treatment slightly limited at low temperatures. However, strength loses increased with increasing temperature. The highest strength loses were also determined in impregnated samples with galex extract and heat-treated samples at 200 °C.

Evaluation of some physical and mechanical properties of Acacia hybrid BV10 planted in Quy Chau, Nghe An

This study aimed to evaluate some major physical and mechanical properties of 7 year old Acacia hybrid BV10 planted in Quy Chau district, Nghe An province. Small specimens with dimensions of 20 (Radial) × 20 (Tangential) × 320 (Longitudinal) mm3 were cut near the pith and near the bark at breast height from each sample tree, then placed in a standard laboratory setting until their weights reached a constant value. The resulting mean air-dry density (AD), stress wave velocity (SWV), static modulus of elasticity (MOE) and modulus of rupture (MOR) were 0.53 g/cm3, 4,241 m/s, 10.00 GPa, and 82.17 MPa, respectively. Statistical analysis showed that SWV and these wood properties examined near the bark were always higher than those values measured near the pith. Stress wave technology can be used to predict MOE and MOR; however, AD is still a more reliable indicator for predicting mechanical properties since it showed a strong correlation with MOE (r = 0.86; P < 0.001) and MOR (r = 0.80; P < 0.001).

Research on Gluing Properties of Thick Bamboo–Wood-Oriented Strand Boards

This study investigated the effects of adhesive resination and bamboo strand content on the physical and mechanical properties of thick bamboo–wood-oriented strand board (BWOSB), such as the air dry density (ADD), internal bond strength (IB), water absorption thickness swelling (TS), modulus of rupture (MOR), modulus of elasticity (MOE), and gluing properties. The raw materials used included large strands prepared from Chinese fir (Cunninghamia lanceolata), bamboo (Phyllostachys edulis), and modified isocyanate resin (PMDI). In this study, BWOSB specimens with different adhesive resination and bamboo strand content were fabricated, and their physical–mechanical properties were examined. It was found that the physical and mechanical properties of BWOSB with 8% PMDI resination were better than those with 5%, and their gluing damage was mostly in the form of the tearing of the raised vascular bundles of bamboo strands and the wood-breaking damage of wood strands. With the increase in the proportion of bamboo strands, the internal bonding strength and the short-span shear strength of BWOSB showed a tendency to decrease at first and then increase. The swelling rate of the water absorption thickness showed a tendency to decrease, and the other properties of BWOSB did not show a clear correlation with the change in the proportion of bamboo strands. The unique gluing interface between the bamboo and wood strands, which either used the “keyway” type of gluing effect or the “nail” type of gluing effect, determined the gluing performance of BWOSB, and the proportion of bamboo and wood strands influenced the gluing interface and gluing type of BWOSB, which ultimately affected the gluing performance of BWOSBs. The proportion of bamboo and wood strands also affected the gluing properties of BWOSBs by influencing the gluing interface and gluing type. This study provides a reference for the development of the production process of thick BWOSB and its application in the field of heavy load construction.

Termo–mekanik yoğunlaştırma işleminin ahşap malzemenin fiziksel özellikleri üzerine etkisi

It can be made into high strength, and valuable products by compacting low density, and low commercial value wood species. In this study, black pine (Pinus nigra) and Uludağ fir (Abies nordmanniana subsp. bornmulleriana) tree species were densified by using Thermo-mechanical (TM) method, which is an environmental modification method, at 140 oC and two different ratios of 25% and 50% (in the radial direction). Compression ratio in air-dry moisture, spring-back ratio after densification, and physical properties of air-dry densities were determined. The obtained data were subjected to statistical analysis in the MSTAT-C program. According to the results, wood type, densification type, and all their interactions were found to be effective on the compression ratio, and spring-back ratio in air dry moisture. The compression ratio in air-dried moisture was lower in Uludağ fir (Uludağ fir: 0.40 gr/cm³, black pine: 0.49 gr/cm³) compared to black pine due to the spring-back effect. While the volumetric recovery (spring-back) rates were 15.44% in Uludağ fir, it was determined as 19.40% in black pine. After the condensation process, the air-dry density value increase was lower in black pine compared to Uludağ fir, and it was determined as 35.94% in Uludağ fir and 34.53% in Black Pine

Production of Lightweight Three-Layered Particleboards Using Waste Tire Rubbers

The aim of the study is to investigate the production possibilities of particleboard by using waste tirerubbers with different properties as fillers and find a solution to a serious environmental pollution problem caused by waste tires. For this purpose, waste summer and winter tires were ground, rubber powders were obtained by separating rubber materials from other materials, and particleboards with different properties were produced using this sawdust in different percentages. The oven-dry density, air-dry density, and equilibrium moisture content at (65±5) % RH and (20±2) ºC, thickness swelling (TS, 2 hours and 24 hours), water absorption (WA, 2 hours and 24 hours) characteristics, bending strength, modulus of elasticity, and internal bond strength were determined according to the applicable European standards. The hydrophobic nature of the tire rubber enhanced the water absorption ratios of particleboards. In addition, mechanical performance of groups was affected by tire content, and it was mainly determined that the values decreased dramatically with increasing tire content. It was especially observed that this decrease was more pronounced when subtracting 30 % to 20 % waste tire content. The groups including winter waste tire rubber achieved better performance than summer waste tire groups. The use of waste rubber in boards resulted in a decrease in the equilibrium moisture content and mechanical strength of the samples.

Predicting the air-dry density of black walnut based on NIR analysis

Abstract The combination of computer technology and non-destructive testing technology can facilitate the development of forestry in a more intelligent direction. In this paper, a Shapley additive explanations (SHAP)-based method is used to analyse the importance of band features in the near-infrared spectrum of black walnut wood, which ranges from 900 to 1650 nm. The spectral data from the SHAP analysis are fed into an integrated framework of machine learning algorithms based on four different theories. In the comparison tests, three different pre-processed NIR spectral data are entered into the integrated framework. The result of the SHAP analysis shows that the wavelengths that are positively correlated with the air-dry density of black walnut are 1354.59, 1400.23, 1341.51, 1426.26, 1413.25 nm. The model predictions show that the SHAP-treated spectral data outperformed the other two treatments for each model. For the SHAP-treated spectral data, the KNN model gives the best results with an R 2 of 0.947 and an MSE of 0.0010.

Determination of some physical and mechanical properties of parallel-strand lumber manufactured with bamboo (Phyllostachys bambusoides)

Parallel-strand lumber was manufactured with bamboo (Phyllostachys bambusodies). A polyol compound was added to modify the adhesive (pMDI). Bamboo culms were used to manufacture strands 3 mm thick, 19 mm wide, and 65 cm long. Adhesive was applied to the strands at 200 g/m2 with pressing at 110 °C, 15 kg/cm2, and 30 min. Panels were made with width 600 mm, length 600 mm, and thickness 20 mm. Some physical properties (oven-dry density, air-dry density, moisture content, thickness swelling, and water absorption percentage) and mechanical properties (bending resistance, modulus of elasticity, impact resistance, screw-holding capacity in tangential, radial, and transverse directions) of parallel-strand lumber for both adhesive types were determined. Both resin types improved some physical and mechanical properties of parallel-strand lumber. Additionally, the modulus of rupture and flexural modulus of elasticity of the test specimens using pMDI+5%MP adhesive were higher than those of the test specimens using pMDI. The average screw-holding capacity values of the test specimens were affected by the fiber aspect of the specimens rather than the adhesive type. Parallel-strand lumber produced from both pMDI and pMDI+5%MP adhesives can be used in structural applications, especially in places exposed to the disturbing effects of weather.

The Effect of Different Types of Aggregate and Additives on the Properties of Self-Compacting Lightweight Concrete

The major aim of this research is study the effect of the type of lightweight aggregate (Porcelinite and Thermostone), type and ratio of the pozzolanic material(SF and HRM) and the use of different ratios of w/cm ratio(0.32 and 0.35) on the properties of SCLWC in the fresh and hardened state. SF and HRM are used in three percentage 5%,10%, and 15% as a partial replacement by weight of cement for all types of SCLWC. The requirements of self-compatibility for SCC are fulfilled by using the high performance superplasticizer (G51) at 1.2liter per 100 kg of cement. The values of air dry density and compressive strength at age of 28 days within the limits of structural lightweight concrete. The air dry density and compressive strength at age of 28 days for w/cm ratio(0.32) for SCLWC of Porcelinit aggregate are 1964 kg/m3 and 29.57 MPa, respectively. The corresponding values for the SCLWC of Thermostone aggregate are 1820 kg/m3 and 25.75 MPa, respectively. The results show that the HRM performance which is locally available is better than SF in production of SCLWC.

Properties of heat-treated beech laminated veneer lumber reinforced with carbon fiber fabric

Carbon fiber fabric reinforced laminated veneer lumber (RLVL) pieces were prepared by using heat-treated beech (Fagus orientalis Lipsky) veneers with polyurethane (PU) adhesive as the binder. Carbon fiber fabric was tested in three different locations with solid material and non-reinforced samples (on the bottom adhesive line, upper adhesive line, and upper and bottom adhesive lines-symmetrical). Prior to the manufacture of LVL and RLVL, heat treatment was conducted in a laboratory oven at three temperatures. These temperatures were 150, 170, and 190 °C. Tests were performed on LVL and RLVL to determine their air-dried density, modulus of rupture (MOR), and modulus of elasticity in bending (MOE). Experimental test results showed that reinforcement with carbon fiber increased the air-dried density, MOR, and MOE. In addition, carbon fiber fabric placed symmetrically close to bottom and upper surfaces gave the highest MOR and MOE values. However, locating the carbon fiber fabric closer to the bottom surface tended to give higher mechanical properties for the reinforced LVL.

Ultraviolet light and natural weathering vs. the compression strength of laminated wood

Effects of protective measures were evaluated relative to the compression strength in the direction parallel to the grain of laminated veneer wood (LVL). For this purpose, laminated panels were prepared from Scots pine, Oriental beech, Castanea sativa, and sessile oak wood veneer by gluing them with Desmodur vinyl trie ketonol acetate (D-VTKA), polyvinyl-acetate (PVAc) dispersion D4 adhesive, resorcinol formaldehyde (RF), and melamine formaldehyde (MF). The samples were impregnated with a mixture of wax, linseed oil, and coated with a synthetic-based translucent varnish. The control samples (without the treatment described above), impregnated samples, and varnished samples were kept in the external environment for 1 y and in an ultraviolet (UV) environment for 240 h. The samples were tested to determine the air-dried density, retention amount, and compression strength. The results indicated that, in terms of outdoor conditions, the varnished proceeding provided better protection compared to the impregnated proceeding. The best result for compression strength was obtained on the Oriental beech samples with RF and MF glues. The ratio of the UV environment to represent the external environment was 89%.

Shear and Flexural Behavior of Lightweight Concrete Beams Containing Hybrid Fibers

Abstract Due to the low density of lightweight concrete, work has been done in this research to develop it by adding fibers of more than one type to improve its properties. Basic tests were conducted to determine the properties of concrete before and after the addition of fibers. The variables of the models were beams in two groups (shear and flexural). The variables of these two groups included the type of fibers (steel and polypropylene) and the size of the added fibers 0 %, 0.05 %, 0.1 % for polypropylene fibers 0 %, 0.75 %, 1 % for steel fibers. This study presented an examination of 18 beam specimens and discussed the results, which included mechanical properties (air dry density, slump test, compressive strength, modulus of elasticity, flexural strength, and splitting tensile strength). The results showed that the addition of fibers had an effective effect on the compressive strength, and this led to an increase in the resistance to shear forces and flexural forces, as the highest load capacity was shown by adding polypropylene fibers at a rate of 0.1 % in both groups, and the fibers played an important role in reducing the width of cracks and controlling their spread due to modulus of elasticity of the fiber.