加速腐朽环境下重组竹力学及耐腐性能研究

重组竹作为一种新型工程材料,有着良好的力学性能,为了对重组竹的耐腐性能展开定量评价,利用目测分析、失重率分析、力学性能分析以及扫描电镜分析等方法,进行重组竹耐腐性试验研究。结果表明:重组竹在褐腐菌与白腐菌84 d的作用下,仅表面有轻微腐朽,褐腐菌和白腐菌腐朽试件失重率相差不大,且均小于10%,表明重组竹属于Ⅰ级耐腐; 褐腐菌试样的抗弯弹性模量M_E、抗弯强度M_R分别下降5.17%、8.17%,而抗压强度U基本不变,白腐菌试样的M_E、M_R、U下降幅度分别为10.56%、13%、0.45%,远小于木材; 通过扫描电镜分析,相比毛竹在经历84 d腐朽后,其薄壁细胞中布满菌丝,细胞壁上出现大量孔洞,重组竹表面下2 mm以内的薄壁细胞中仅有少量菌丝,并且在84 d试验内均未造成细胞壁的破坏; 竹材内部可以满足木腐菌生存的条件,但在疏解、炭化、浸胶、重组的过程中,吸水性能降低,限制了真菌生长的水分条件,阻碍了木腐菌侵入重组竹内部,另外酚醛树脂具有一定的抑菌性,使得重组竹成为耐腐性强的材料。     

Oxidative devolatilization kinetics of wood impregnated with two ammonium salts

Motivated by the aim of improving the understanding of reaction kinetics, thermogravimetric measurements (heating rates of 5, 10 and 20 K/min up to a temperature of 873 K) in air have been made of wood impregnated with diammonium phosphate and diammonium sulfate and, for comparison purposes, of untreated wood. Wood devolatilization is always followed by char combustion, but the added salts introduce important changes. Indeed, the former is anticipated at lower temperatures with reduced maximum rates, whereas the latter is significantly retarded. For the interpretation of the measured weight loss characteristics, a mechanism has been developed, consisting of parallel reactions with the usual Arrhenius rates and a linear (devolatilization) or a power-law (combustion) dependence on the solid mass fraction. In all cases, three reactions are sufficient for describing the most important features of the devolatilization process, with activation energies practically invariant with the treatments (106, 226 and 90–104 kJ/mol for the decomposition of the pseudo-components hemicellulose, cellulose and lignin, respectively). The effects and differences of the two salts can be effectively taken into account by variations in the pre-exponential factors and amounts of lumped volatile species produced. However, a wide zone of slow volatile release, preceding char combustion, appears, which requires the introduction of two additional reactions with activation energies of 92 and 115 kJ/mol.     

Some of the properties of wood–plastic composites

In this study some of the important properties of experimentally manufactured wood–plastic composites (WPC) were determined. Specimen having 60% and 80% particle and fiber of radiata pine (Pinus radiata ) were mixed with polypropylene (plastic) and four different additives, namely Structor TR 016 which is coupling agent, CIBA anti-microbial agent (IRGAGUARD F3510) as fungicide, CIBA UV filter coating (TINUVIN 123S), CIBA blue pigment (Irgalite), and their combinations. Based on the initial finding of this work static bending properties of the samples enhanced as above chemicals were added into both particle and fiber-based specimens. Thickness swelling of the samples were also improved with having additives in the panels. Micrographs taken on scanning electron microscope (SEM) revealed that coupling agent and pigment resulted in more homogeneous mixture of wood and plastic together. Two surface roughness parameters average roughness (R_a) and maximum roughness (R_max) used to evaluate surface characteristics of the samples showed that particle based samples had rougher surface characteristics than those of fiber based ones. No significant influence of chemicals added in the samples was found on surface roughness values of the samples manufactured from particle and fiber of radiata pine.     

改性橡胶木力学性能试验研究

经过物理和高压化学处理后,改性橡胶木具有良好的防火和耐腐蚀性能.为促进改性橡胶木在结构工程中的应用,对其进行力学性能试验,研究其在不同加载条件下的破坏模式、材料性能、强度和刚度,并与市面上常见的天然木材和胶合木材的试验结果进行对比.试验结果表明,改性橡胶木具有良好的力学性能,可与天然木材相媲美,为改性橡胶木在木结构工程中的应用提供基础依据.     

Some physical,biological, mechanical,and fire properties of wood polymer composite (WPC) pretreated with boric acid and borax mixture

Wood polymer composite (WPC) was obtained by vinyl monomers such as styrene (ST), methylmethacrylate (MMA), and their mixture (50:50; volume:volume) of treated sapwood of Scots pine (Pinus sylvestris L.). Boric acid (BA) and borax (BX) mixture was impregnated into wood at 1% concentration prior to monomer treatment. Wood polymer composite with and without BA and BX mixture pretreatment was evaluated in terms of some physical, biological, mechanical, and fire properties.Vinyl monomers considerably improved physical properties of wood such as increased antiswelling efficiency (ASE), specific gravity (SG), and reduced water absorption (WA) levels of wood. Modulus of elasticity (MOE) and modulus of rupture (MOR) were also higher than that of untreated control specimens. The treated wood proved to be resistant against decay fungi, Tyromycetes palustris and Coriolus versicolor. Boric acid and borax mixture pretreatment imparted WPC total resistance against both decay fungi. Although, ASE, MOE, and MOR levels of WPC pretreated with BA and BX mixture were reduced in some extent, it improved fire resistance of wood.     

Structural,physical and mechanical properties of modified wood–magnesia composite

The results of research about the structural, physical and mechanical properties of wood–magnesia composites based on magnesium binder (caustic magnesia) and filler of wood sawdust modified with chemical industry waste fluorine anhydrite (fluoranhydrite) are described. It was found that during the hydration of caustic magnesia containing fluorine anhydrite additive in composition with magnesium chloride, magnesium oxychlorides with different morphologies are formed depending on the initial components. The structure examination after 9 years of products maintenance showed the intensive carbonization of caustic magnesia hydration products with the formation of magnesium hydroxycarbonates that caused the increase of the material density, strength, water resistance and decrease of the wood–magnesia constructional beam creeping deformations.     

Effect of wood dust type on mechanical properties,wear behavior,biodegradability, and resistance to natural weathering of wood-plastic composites

The present work reports the inclusion of different proportions of Mango/Sheesham/Mahogany/Babool dust to polypropylene for improving mechanical, wear behavior and biodegradability of wood-plastic composite (WPC). The wood dust (10%, 15%, 20% by weight) was mixed with polypropylene granules and WPCs were prepared using an injection molding technique. The mechanical, wear, and morphological characterizations of fabricated WPCs were carried out using standard ASTM methods, pin on disk apparatus, and scanning electron microscopy (SEM), respectively. Further, the biodegradability and resistance to natural weathering of WPCs were evaluated following ASTM D5338-11 and ASTM D1435-99, respectively. The WPCs consisting of Babool and Sheesham dust were having superior mechanical properties whereas the WPCs consisting of Mango and Mahogany were more wear resistant. It was found that increasing wood powder proportion results in higher Young’s modulus, lesser wear rate, and decreased stress at break. The WPCs made of Sheesham dust were least biodegradable. It was noticed that the biodegradability corresponds with resistance to natural weathering; more biodegradable WPCs were having the lesser resistance to natural weathering.     

废弃木质碎料应用于道路铺装材料的力学性能研究

为充分利用废弃木材,探究新型道路铺装材料,研究养护龄期对不同配合比的水泥基木质碎料道路铺装材料抗压强度的影响。对试件的力学性能进行测试和分析,结果表明:各配合比下试件的抗压强度随养护龄期的增长普遍呈上升趋势且试件具有早强现象,同时发现木质碎料的比例对试件强度随养护龄期变化起到决定性作用。该实验可为废弃木质碎料应用于新型道路铺装材料的进一步研究提供参考。     

Water absorption of wood polypropylene composite sheet piles and its influence on mechanical properties

The water absorption behavior and durability of extruded wood polypropylene composite (WPC) material used in Z-section sheet piles was investigated. An experimental technique to determine percentage water absorption and its effect on mechanical properties was implemented. Water absorption tests were carried out on specimens cut from flanges and webs of the Z-section by immersion in tap water at 21, 45 and 70 °C. Freeze–thaw resistance of saturated composites was studied by cycling temperatures in the range of 21 to ?29 °C. The absorption behavior followed the kinetics of a Fickian diffusion process. This behavior was modeled using an analytical solution based on Fick’s second law of diffusion. Quasi-static bending tests were conducted periodically on specimens immersed in water to assess degradation in flexural properties. A significant decrease in mechanical properties of the water-saturated specimens compared to the dry control was observed. Degradation of flexural modulus was found to be a strong function of water absorption with initial decrement as percentage water absorption increased and finally stabilized as the absorption process approached saturation. However, freeze–thaw cycling did not have any significant effect on mechanical properties of saturated composites. A phenomenological model for moisture intrusion and its effect on mechanical properties was implemented and applied to explain the experimental findings.     

深部岩体力学特性的问题思考

介绍了深部岩体力学特征的研究现状,针对深部岩体工程的概念界定、科学现象及力学特点,对其力学试验进行了研究,并总结了深部岩体力学今后的研究重点及发展方向。     

Bowing of marble slabs: Evolution and correlation with mechanical decay

The bowing phenomenon is frequently a problem for newly constructed buildings, where marble slabs used in façades are usually very thin and have a high slenderness ratio. This kind of rock weathering can mainly be attributed to the intrinsic properties of the slab (petrography, dimensions), the anchorage techniques and the climatic conditions. Previous studies investigated marble with an equigranular-polygonal microstructure (granoblastic) and show they have a higher tendency to bow than those composed of anhedral (irregular) grains surrounded by subgrains (interlobate textures). The aim of this research was to study the correlation between the decrease in mechanical properties and the bowing in three types of marble with different textures and petrographic characteristics. This has been achieved through measurements of the bowing and the flexural strength, the water absorption and the ultrasonic pulse velocity at different stages of artificial ageing. As far as the granoblastic marble, with the progress of the artificial weathering, the tendency curve of bowing shows a sharp initial rise which subsequently proceeds more slowly. At the same time all the three types of marble (including xenoblastic marble, not subjected to bowing) showed a loss in mechanical resistance. Moreover, the flexural strength values matched well with the results of the non-destructive tests.     

废橡胶粉混凝土力学及抗冲耐磨性能试验研究

选取颗粒粒径为8、14、16、28目的橡胶粉,分别按水泥质量的3%、6%、9%、12%、15%掺入混凝土,以评价不同的橡胶粉颗粒粒径和掺量对混凝土力学性能的影响,同时选取8、16目的橡胶粉掺入混凝土进行抗冲耐磨试验.试验发现,混凝土强度、弹性模量随橡胶粉粒径的减小和掺量的增加而降低;橡胶粉的掺入可提高混凝土的抗冲耐磨性能,在掺量一定的前提下,抗冲耐磨强度提高3倍,与同水泥用量的硅粉混凝土相比,抗冲耐磨强度提高2倍.     

竹筋实木组合空心柱的制作与力学性能试验

木材是一种绿色环保建材,木建筑中结构柱使用原生态长和粗的原木取材难、价格昂贵,为解决目前原木尺寸小、抗压强度低、使用受到限制等问题,本文提出了一种竹筋实木组合空心柱,解决了小木头不能用作结构柱的问题,把零碎的木块和竹筋进行结合竹木组合柱试验模型,试验采用结构尺寸和特性基本一致的3个实木柱和3个竹筋实木组合柱,进行了加载受压性能对比试验,得到了两种不同结构板的破坏形态、极限承载力。试验研究结果表明:两种结构柱均发生材料破坏,竹筋组合柱比实木组合柱抗压强度提高11.6%,该研究成果对于竹筋实木组合柱结构设计和木结构工程中的应用提供了一定参考。     

Fire resistance of wood structures

Wood as a building material has the disadvantage of being combustible. Consequently wood structures are seen by many as creating an environment less safe than structures built of noncombustible materials such as steel and masonry. However, experience has shown that some wooden structures have a fire resistance comparable, or greater than that of many noncombustible alternatives. Some statistical figures are given comparing wood with other materials. The fire course and the burning mechanisms of wood are briefly discussed, as is the fire resistance of wood structures from different perspectives. Reference is also made to present research work. Reference: Kai Odeen, Fire Resistance of Wood Structures,Fire Technology, Vol. 21, No. 1, February 1985, p. 34. Note: This paper is a modified version of a paper presented at the International Fire Protection Engineering Institute in Brunnen, Switzerland in February and March 1984.     

Effects of freeze-thawing cycles on the physical and mechanical properties of basaltic and dolomitic rocks evaluated with a decay function model

Bulletin of Engineering Geology and the Environment - Basalts from Çorlu Karatepe and dolomite from Kırklareli subjected to freeze-thawing (F-T) cycles were studied, and the resulting...     

Polysulfone ultrafiltration membranes impregnated with silver nanoparticles show improved biofouling resistance and virus removal

Biofouling and virus penetration are two significant obstacles in water treatment membrane filtration. Biofouling reduces membrane permeability, increases energy costs, and decreases the lifetime of membranes. In order to effectively remove viruses, nanofiltration or reverse osmosis (both high energy filtration schemes) must be used. Thus, there is an urgent demand for low pressure membranes with anti-biofouling and antiviral properties. The antibacterial properties of silver are well known, and silver nanoparticles (nAg) are now incorporated into a wide variety of consumer products for microbial control. In this study, nAg incorporated into polysulfone ultrafiltration membranes (nAg-PSf) exhibited antimicrobial properties towards a variety of bacteria, including Escherichia coli K12 and Pseudomonas mendocina KR1, and the MS2 bacteriophage. Nanosilver incorporation also increased membrane hydrophilicity, reducing the potential for other types of membrane fouling. XPS analysis indicated a significant loss of silver from the membrane surface after a relatively short filtration period (0.4 L/cm²) even though ICP analysis of digested membrane material showed that 90% of the added silver remained in the membrane. This silver loss resulted in a significant loss of antibacterial and antiviral activity. Thus, successful fabrication of nAg-impregnated membranes needs to allow for the release of sufficient silver ions for microbial control while preventing a rapid depletion of silver.     

PTB乳液对水泥砂浆力学性能和抗侵蚀性能的影响

研究了PTB乳液改性水泥砂浆的力学性能、抗氯盐和抗硫酸盐侵蚀等性能.结果表明,掺入PTB乳液对水泥净浆有缓凝作用,大幅延长了水泥净浆的终凝时间;掺入PTB乳液降低了水泥砂浆的抗压强度,但是降低抗压/抗折强度比改善了水泥砂浆的延性,提高了水泥砂浆的综合力学性能.PTB乳液/水泥为0.22时的PTB乳液水泥砂浆在氯化钠、硫...     

5083铝合金焊接接头腐蚀性能及力学性能损失分析

采用浸泡试验和失重法研究了5083铝合金焊接接头腐蚀行为,并对接头进行室温拉伸测试,通过扫描电镜对接头进行微观形貌分析和断口分析。结果表明,5083铝合金焊接接头不同区域腐蚀性能存在显著差异。焊缝区耐腐蚀能力最差,热影响区次之,母材最耐腐蚀。焊缝区成分、组织不均、并存在残余应力,造成此区耐腐蚀性最差。焊接接头经过腐蚀后,断裂方式发生改变,接头强度损失严重。     

内置薄壁H钢木组合梁连接界面受力性能试验研究

为明确内置薄壁H钢木组合梁所采用的抗剪螺钉+环氧树脂粘胶复合连接界面的组合受力机理和受力性能,进行了单纯抗剪螺钉连接、单纯环氧树脂粘胶连接和抗剪螺钉+环氧树脂粘胶复合连接界面的推出试验,以研究三种组合连接界面的破坏模式,获取三种组合连接界面的荷载-位移关系曲线、开裂荷载、极限荷载和有效抗滑移刚度等.分析结果表明,抗剪螺...