无石棉维纶纤维水泥板的工艺原理与特性

研究用高模量维纶纤维与改性维纶纤维代替石棉制造无石棉纤维水泥板。这两种纤维的弹性模量虽显著低于石棉,但与水泥基体间有较好的界面粘结,故仍起增强作用。探讨了用抄取法制作无石棉维纶纤维水泥板的工艺原理,其中主要有维纶纤维的均匀分散、减少过滤过程中水泥粒子的流失、控制纤维水泥浆的过滤速率、调正抄取机的工艺参数、板坯的补充加压,采取合宜的蒸养制度等。所制成的维纶纤维水泥板具有以下主要特性:(I)横、纵向抗折强度与弹性模量低于石棉水泥板,但变形能力高于后者。(2)抗冲击强度高于石棉水泥板。(3)容重低于石棉水泥板。(4)与石棉水泥板一样,具有较好的不透水性、抗冻性、不燃性、耐热水性与机械加工性。     

Asbestos-free technology with new high toughness polypropylene (PP) fibers in air-cured Hatschek process

After almost 70 years of experience in the fiber–cement production in Brazil, Saint-Gobain Brasilit started the non-asbestos production using polyvinyl alcohol (PVA) fiber technology in 2002.Due to PVA costs and availability problems, efforts were done to develop a local high toughness polypropylene (PP) fiber, with improved frictional interface and better dispersion and affinity to Portland Cement matrix.In the last 5 years, more than 1.6 million tons of asbestos-free corrugated and flat sheets have been produced and commercialized representing about 200 million square meters.This paper reviews the alternative fibers for replacing asbestos and the reinforcing model in cement based products. It also presents the Brasilit high toughness polypropylene fibers properties, its manufacturing process and its mechanical performance and improved impact resistance behavior comparing to fiber–cement products available in the Brazilian market.     

Asbestos: world concern,involvement and culpability

The general population is exposed to asbestos fibers stemming from a massive number of consumer products and from environmental pollution. Asbestos bodies are present in the lungs of many urban dwellers who do not work with the mineral. Heavy occupational exposure to asbestos is known to cause asbestosis, pleural calcification, pleural plaques, lung cancer, and pleural and peritoneal mesotheliomas. The ingestion of asbestos fibers may increase the risk of gastrointestinal tract cancer. At the present time, little is known about the hazards of chronic low‐level exposure to asbestos. However, the use of asbestos fibers should be curtailed whenever possible, more pathogenicity data should be collected and evaluated, and the health risk to the general public should be reassessed and updated with progressing research.     

Flexural responses of hybrid steel–polyethylene fiber reinforced cement composites containing high volume fly ash

Strain hardening and multiple cracking behavior of hybrid fiber reinforced cement composites containing different hybrid combinations of steel and polyethylene (PE) fibers under four-point bending are reported. The total volume fraction of fibers was kept constant at 2.5% to maintain a workable mix. Effects of increase in fly ash content as partial replacement of cement beyond 50%, such as 60% and 70% on the flexural response of hybrid steel–PVA (polyvinyl alcohol) and steel–PE fiber composites are also evaluated here. Among composites with different volume ratios of steel and PE fibers, the composite with 1.0% steel and 1.5% PE was found to show the highest flexural strength and that with 0.5% steel and 2.0% PE exhibited highest deflection and highest flexural toughness. Generally, the steel–PE hybrid composites exhibited lower flexural strength but higher deflection capacity than steel–PVA hybrid composites. The rate of strength loss after peak load in steel–PE hybrid composites was found low compared to steel–PVA hybrid system. The 50% replacement of cement by fly ash is found to be an optimum fly ash content in hybrid fiber composites.     

Self-levelling cement mortar containing grounded slate from quarrying waste

The aim of this research is to obtain a low density self-levelling cement mortar containing grounded slate from quarrying waste that could be used as a substrate levelling layer for flooring purposes. An experimental research was carried out on the design and development of a self-levelling cement mortar substituting up to 75% of the cement by grounded slate from quarrying wastes. In a first stage, the formation of stable reactive binding products of slate–cement pastes was confirmed, using Vicat needle test and Scanning Electron Microscopy and Energy Dispersive Spectroscopy analysis (SEM/EDAX). In addition, mortar mixtures with different amounts of grounded slate have been studied. Fresh state consistency, shrinkage measurements in wet and dry conditions and physical and mechanical properties in the hardened state of these mortars have been assessed. Finally, mortar shrinkage was controlled according to the selected application, including admixtures and glass fibers in the mortar composition, to achieve the flowability and strength required, without segregation.Grounded slate acts as binder, jointly with the cement, confirming that the inclusion of the slate wastes implies a waste valorisation and not a waste disposal. The use of admixtures and short fibers allows to develop a self-levelling mortar.     

Properties of polymer-modified mortars using epoxy and acrylic emulsions

Water based polymer systems are often used for improvement in the properties of plain cement mortar or concrete. Presently, latexes of a single or combinations of polymers like polyvinyl acetate, copolymers of vinyl acetate–ethylene, styrene–butadiene, styrene–acrylic, and acrylic and styrene butadiene rubber emulsions are generally used. One of the limitations of these polymer systems is that they may re-emulsify in humid alkaline conditions. To overcome this problem, an epoxy emulsion based polymer system has been developed. In this paper the properties of the cement mortar modified with this newly developed epoxy emulsion are compared with those of the acrylic-modified mortar. The results showed that the mortars with the newly developed system have superior strength properties and better resistance to the penetration of chloride ions and carbon dioxide.     

An appropriate vacuum technology for manufacture of corrugated fique fiber reinforced cementitious sheets

This paper reports the experiences of making Portland cement based corrugated roof sheets with the reinforcement of a Colombian natural fiber, named fique. The sheets were manufactured by a vacuum forming process. The raw material components of the sheets are given. The average flexural load to failure reported 2875 N/m at 14 curing days, which it is considered appropriate for a roofing sheet. Corrugated sheets produced with asbestos fibers using the same variables of processing reported 2400 N/m. Column permeability tests showed satisfactory results for the tried composites. The vacuum cylinder forming process for manufacture of corrugated sheets at the level of small scale production is promissory because is an environmental friendly low cost appropriate technology that does not need skilled labor.     

混杂纤维布加固钢/聚丙烯短纤维增强混凝土构件技术研究

对采用杜拉纤维和钢纤维混杂改性的混凝土梁外贴碳纤维布和玻璃纤维布（CFS／GFS）进行混杂加固抗弯试验与有限元对比研究，并对构件加固后刚度变化进行对比分析，结果表明，掺入杜拉纤维和钢纤维，可以延缓混凝土构件微裂缝的出现，有效地控制裂纹扩展，提高混凝土材料的强度，这种混杂纤维混凝土梁表现出比单一纤维混凝土梁更优良的材料性能。     

Comparative characterization of particle emissions from asbestos and non-asbestos cement roof slates

The first aim of this study was to characterise total and size-fractionated particulate matter (PM) aerosol, including fibres, released from the processing operations of cement roofing slates. The second aim was to compare particle emissions from asbestos-cement and non-asbestos cement sheets, with respect to total and size-fractionated particulate matter as well as fibres emissions. Asbestos and cellulose-based cement sheets were compared during slate treatment processes, namely crushing, rubbing, rasping and scrubbing. Generated PM and fibres were classified by a variety of methods (PM_2.5 and PM₁₀ cyclones, aerodynamic particle spectrometer and optical particle counter). A substantial variation in the mass of generated particles has been noticed, both within each PM fraction and between different treatment processes. The PM₁₀/PM_total concentration ratio ranged from 70 to 98% and PM_2.5/PM_total ratio equalled to ∼20%. The new generation non-asbestos sheets produced three times higher PM emissions than asbestos-cement sheets during crushing operation. Particle size distribution of number concentrations was mostly bimodal (two modes at 0.5 and 2.5 μm). With respect to fibres, the release of cellulose fibres from non-asbestos slates was from 1.8 to 13 times lower in comparison with asbestos fibres. At the same time, cellulose fibre length was 1.4–1.6 times lower. Hence, new generation non-asbestos roofing slates were proved to be less hazardous from the point of view of fibre release, but more hazardous with respect to total particle release.     

The detection and analysis of particulates in municipal water supplies by transmission electron microscopy

The analysis of particulates in municipal water supplies utilizing the electron microscope and a simple drop transfer technique is illustrated in a study of particulates in the Albuquerque, New Mexico water distribution system. The majority of particles are observed to be crystalline and to have a mineral origin. Asbestos fibers are identified and measured to be less concentrated than previously recorded for many other major cities in the United States, and there is no evidence of asbestos pick up in water that flows through asbestos-cement pipe in the Albuquerque water distribution system.     

Mechanical properties of steel,glass, and hybrid fiber reinforced reactive powder concrete

This study examines the properties of fiber-reinforced reactive powder concrete (FR-RPC). Steel fibers, glass fibers, and steel-glass hybrid fibers were used to prepare the FR-RPC. The non-fibrous reactive powder concrete (NF-RPC) was prepared as a reference mix. The proportion of fibers by volume for all FR-RPC mixes was 1.5%. Steel fibers of 13 mm length and 0.2 mm diameter were used to prepare the steel fiber-reinforced RPC (SFR-RPC). Glass fibers of 13 mm length and 1.3 mm diameter were used to prepare the glass fiber-reinforced RPC (GFR-RPC). The hybrid fiber-reinforced RPC (HFR-RPC) was prepared by mixing 0.9% steel fibers and 0.6% glass fibers. Compressive strength, axial load-axial deformation behavior, modulus of elasticity, indirect tensile strength, and shear strength of the RPC mixes were investigated. The results showed that SFR-RPC achieved higher compressive strength, indirect tensile strength and shear strength than NF-RPC, GFR-RPC, and HFR-RPC. Although the compressive strengths of GFR-RPC and HFR-RPC were slightly lower than the compressive strength of NF-RPC, the shear strengths of GFR-RPC and HFR-RPC were higher than that of NF-RPC.     

Performance of fiber reinforced asphalt concrete under environmental temperature and water effects

This paper studies the reinforcing effects and mechanisms of fibers for asphalt concrete (AC) mixtures under the environment temperature and water effects. Four typical fiber types – polyester, polyacrylonitrile, lignin and asbestos – are studied. Laboratory tests were conduct on the fiber reinforced AC (FRAC) to measure its strength, strain and fatigue behavior. Results show that fibers have significantly improved AC’s rutting resistance, fatigue life, and toughness. The flexural strength and ultimate flexural strain, and the split indirect tensile strength (SITS) at low temperature have also improved. The polymer fibers (polyester and polyacrylonitrile) have improved rutting resistance, fatigue life, and SITS more significantly than lignin and asbestos fibers, which may be primarily due to their greater networking function; while lignin and asbestos fibers result in greater flexural strength and ultimate flexural strain, which may be primarily due to their greater asphalt stabilization effect. However, fiber’s effect under the water freezing–thaw effect does not seem promising, and the SITS of FRAC with lignin and asbestos fibers even reduces to some extent under this effect. It is also found that a fiber content of 0.35% by mass of mixture achieves the optimum performance outputs of rutting resistance and SITS for polyester fiber.     

Performance of slash pine fibers in fiber cement products

Cellulosic fibers produced by the kraft pulping process from slash pine trees (Pinus elliottii), a softwood from the south-eastern US, have been evaluated in fiber cement products. These fibers are longer and coarser than most wood fibers and have been found to provide many benefits in fiber cement applications due to their high modulus and high fiber strength. Lignin levels can be finely controlled ranging from 0% to 4%. Laboratory preparations of multiple formulations of fiber cement products have been carried out incorporating these fibers. High modulus of rupture, high fracture energy (toughness), excellent dimensional stability, and low water absorption were observed. Accelerated aging tests were also run and high performance mix designs showed the most strength retention after aging. Recently conducted plant trials with these fibers have confirmed laboratory findings.     

不同尺寸钢纤维混杂增强水泥砂浆的力学性能

研究了不同尺寸（微细、中等）钢纤维混杂增强水泥砂浆的力学性能．结果表明：在钢纤维体积分数一定的情况下,混杂钢纤维对水泥砂浆力学性能的改善作用可优于单一直径钢纤维;不同尺寸钢纤维的混杂对水泥砂桨抗折强度的提高具有明显的混杂效应;集胶比是影响混杂钢纤维水泥砂浆力学性能的重要因素,集胶比越大,最优钢纤维混杂所需中等直径钢纤维的体积分数也应越大;2种不同直径钢纤维的混杂对水泥砂浆断裂能及断裂韧性的提高有协同效应．     

On the problem of measuring and analysis of chemically changed mineral fibers in the environment and in biological materials

Chemical and physical microanalysis of asbestos and glass fibers obtained by environmental sampling (air, water), and from human and animal tissue have shown chemical and crystalline changes in these particles. Scanning electron microscopy, electron microprobe analysis and mass spectroscopic analysis were used in these investigations. Also chemical and physical changes of asbestos and glass fibers after application of different milling procedures were observedA partial or a total leakage could be assessed. The leakage of elements in fibers is of statistical nature. Some fibers rested chemically unchanged, in some fibers elements were partially leached and in some fibers the majority of metalic elements were leached.     

The need to control asbestos fibers in potable water supply systems

Occupational studies have shown that asbestos is a human carcinogen. Becausemany inhaled asbestos fibers deposited in the lung are cleared and swalloed workers are also exposed through ingestion. Of the millions of current and former workers who have been heavily exposed to asbestos, one in ten will die from cancer of the gastrointestinal tract. A number on the order of 1 in 1,000 ingested asbestos fibers penetrate the digestive tract and ingested fibers have been recovered in such tissues as kidney, intestine, liver, and urine. One animal study showed tumor production related to ingestion of asbestos-containing material but, in general, the results of seven animal feeding studies have been inconclusive. A statistically significant relationship between male lung and stomach cancer and female peritoneal, gall bladder, and esophageal cancer and asbestos counts in drinking water was determined in one epidemiology study. Increased rates for male stomach and lung, and female pancreatic cancer related to asbestos in drinking water were reported in another study but possible occupational exposure made it difficult to draw conclusions. Data on excess gastrointestinal cancer among occupational groups has been used to estimate that drinking water containing 300,000 asbestos fibers per liter over a lifetime will result in one additional cancer among 100,000 people.     

Analytical and experimental study on flexural performance of WPC–FRP beams

Wood plastic composite (WPC) beams retrofitted with carbon and glass fiber-reinforced polymer (CFRP and GFRP) composites offer an attractive solution to enhance the behavior of wood in terms of strength and ductility, as well as altering the mode of rupture of such structural members. However, very little is known about their performance. Thus, this paper presents a theoretical model based on nonlinear WPC properties, to investigate the behavior of hybrid WPC–FRP beams. In order to calculate the bending moment, the model considers an exponential function in the stress–strain diagram of WPC in both tension and compression parallel to the fibers. A four-point bending test configuration was conducted as short-term experiments to determine the load–displacement relationships of WPC beams with CFRP and GFRP sheets adhered to the tensile side. In order to validate the employed approach, the results obtained from the theoretical model were compared with the experimental results where a satisfactory agreement was achieved.     

高强玻璃纤维布碳纤维布混杂加固混凝土梁柱的试验研究

提出高强玻璃纤维 (SGF)布和碳纤维 (CF)布层间混杂加固混凝土梁、柱的思路并进行试验研究。结果表明 ,相对CF布加固方法 ,SGF CF混杂纤维复合材料 (HFRP)加固法既能在保证承载力的前提下显著提高构件的延性 ,又能显著降低加固成本 ,仅刚度略有下降。     

玻璃纤维增强水泥耐久性研究的进展

玻璃纤维增强水泥(GRC)具有抗拉、抗弯、抗冲击、重量轻等多种优点。但长期性能降低限制其在更大范围内使用。对其长期性能降低的机理,国内外有许多学说,也提出了多种改善其耐久性的措施,例如改变玻璃纤维化学成分、基体改性、玻璃纤维表面涂覆处理、界面改善等。目前,其耐久性研究面对着确定加速老化试验方法及标准、搞清长期潮湿环境下GRC性能降低的机理、降低低碱度水泥的高成本、进一步改善普通硅酸盐水泥经掺合料改性后引起的早期强度降低和玻璃纤维性能等课题。     

Physical and mechanical properties of durable sisal fiber–cement composites

Sisal fiber–cement composites reinforced with long unidirectional aligned fibers were developed and their physical–mechanical behavior was characterized in the present study. Flat and corrugated sheets were cast by a manual lay-out of the fibers in a self-compacted cement matrix and compressed with a pressure of 3 MPa. Direct tensile and bending tests were performed to determine the first crack, post-peak strength and toughness of the composites. Drying shrinkage, capillary water absorption and water tightness tests were performed to characterize the physical properties of the composites. To ensure the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin and calcined waste crushed clay brick to consume the calcium hydroxide generated during Portland cement hydration. The durability of the newly developed composite was determined through accelerated aging conditions using the hot-water immersion test. The developed material presented a multiple cracking behavior under bending, even when subjected to 6 months of hot-water immersion under 60 °C. Scanning Electron Microscopy was used to investigate the micro-structure of the composites before and after aging.