Triaxial behavior of fiber-reinforced cemented sand

In this research, a series of laboratory tests have been performed to investigate the effects of cement and polypropylene (PP) fiber on the triaxial behavior of sand. The cement contents were 0 and 5% by weight of the dry sand. Fiber length and diameter were 18 and 0.023 mm, respectively, were added at 0 and 0.6% by weight of dry sand–cement. Triaxial compression tests were performed at confining pressures of 0.1, 0.25, 0.5, and 1 MPa. The results of the study indicate that the inclusion of PP fiber increases the shear strength and the peak axial strain. The elastic modulus of specimen decreased with increase in fiber content and increased with the increase in cement content. Moreover, the initial stiffness and peak strength increased by increasing cement content.     

高掺量聚丙烯纤维自密实混凝土制备及其性能研究

为了有效提高高掺量聚丙烯纤维自密实混凝土的工作性能,将调整水胶比和砂率进行配制聚丙烯纤维体积掺量为0.5％的自密实混凝土并对其材料性能进行试验研究.研究表明:高掺量聚丙烯纤维的掺入对自密实混凝土的流动性有较大影响,适当调整水胶比和砂率可配制满足工作性能要求的高掺量聚丙烯纤维自密实混凝土;水胶比的增大提高了高掺量聚丙烯纤维自密实混凝土的扩展度,同时也提高了其离析的风险,降低了其抗压强度;砂率的增大对高掺量聚丙烯纤维自密实混凝土的抗压强度基本没有影响,但可提高其拌合物的粘聚性.     

短切纤维增强改性磷酸盐水泥抗折性能研究

分别采用短切碳纤维和短切玻璃纤维对磷酸盐水泥进行了增强改性研究.采用羧甲基纤维素溶液做分散剂使短切纤维在水泥基体中得到了很好的分散;通过凝结时间及抗折强度测试,研究了纤维种类与掺量对磷酸盐水泥性能的影响.结果表明,短切纤维的加入对磷酸盐水泥的凝结时间影响不明显;两种短切纤维的加入都使磷酸盐水泥的抗折强度显著提高,磷酸盐...     

Strength,permeability, and durability of hybrid fiber‐reinforced concrete containing styrene butadiene latex

Hybrid fiber‐reinforced concrete (HFRC) is examined in this study. Two types of synthetic fibers were considered: polyvinyl alcohol fiber/macro synthetic fiber (PVA/MSF) and polypropylene fiber (PP)/MSF. Styrene butadiene latex was added at 0%, 5%, 10%, and 15% of the cement weight. Tests carried out for the study included compressive strength, flexural strength, chloride ion penetration, abrasion resistance, and impact resistance. The results demonstrated that higher latex contents improved the dispersibility of the fibers because of the increased workability of the HFRC and the improved adhesion. Formation of a latex film improved the strength, permeability resistance, abrasion resistance, and impact resistance. PVA/MSF HFRC had better properties than PP/MSF HFRC. This was attributed to stronger hydrogen bonding by the hydrophilic PVA fibers, which led to superior resistance to micro‐cracking and crack propagation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A strategy for the preparation of closed‐cell and crosslinked polypropylene foam by supercritical CO2 foaming

We report the preparation of a closed‐cell polypropylene (PP) foam material by supercritical carbon dioxide foaming with the assistance of γ‐ray radiation crosslinking. Styrene–ethylene–butadiene–styrene (SEBS) copolymer was added to PP to enhance radiation crosslinking and nucleation. Radiation effects on the foaming of the PP/SEBS blend with different ratios were investigated. A significant improvement in the foaming of the crosslinked PP/SEBS blend was achieved as compared to pristine PP. The cell density of the crosslinked PP/SEBS foam greatly increased at a dose of 10 kGy and a high closed‐cell ratio was obtained. The tensile strength of the crosslinked PP/SEBS foams (10 kGy) was improved from 14 to 20.7 MPa compared to pristine PP foam (0 kGy). In addition, the crosslinked PP/SEBS blend exhibited a wider foaming temperature window (10 °C) as compared to the non‐crosslinked ones (4 °C). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45809.     

适于小河流的反滤混凝土配合比优化设计

通过室内试验制备反滤混凝土试块,以碎石、水泥、河砂、SR-3、水为试验因素,选用4因素5水平的均匀设计,探究影响反滤混凝土抗压强度、孔隙率、pH值等的影响因素.通过试验研究对比,得出适用于小河流治理的反滤混凝土配合比范围:碎石、水泥、河砂、SR-3和水用量分别为1546~1578 kg/m3、250~280 kg/m3、80~100 kg/m3、4.7~5.5 L/m3、72.5~109.2 L/m3,为生态混凝土护坡的实际工程应用提供一定的参考价值.     

Effect of polypropylene fibers on thermogravimetric properties of self‐compacting concrete at elevated temperatures

In this study, the effect of polypropylene (PP) fibers on thermogravimetric parameters of self‐compacting concrete (SCC) containing indigenous materials was investigated experimentally and statistically. The mixes containing cement, water, fly ash, fine aggregate, coarse aggregate, and super plasticizer, with the addition of PP fibers (0%, 0.05%, 0.1%, and 0.15%) by volume of the mixtures, were prepared. The physical properties of SCC were determined at elevated temperatures (200, 400, and 600 °C) after cooling in the laboratory. Regression models were developed to determine the responses, and the optimum amount of 0.05% PP fibers by volume was measured. Copyright © 2012 John Wiley & Sons, Ltd.     

High Stiffness Natural Fiber‐Reinforced Hybrid Polypropylene Composites

Abstract

Natural fibers are potentially a high‐performance non‐abrasive reinforcing fiber source. In this study, pulp fibers [including bleached Kraft pulp (BKP) and thermomechanical pulp (TMP)], hemp, flax, and wood flour were used for reinforcing in polypropylene (PP) composite. The results show that pulp fibers, in particular, TMP‐reinforced PP has the highest tensile strength, possibly because pulp fibers were subjected to less severe shortening during compounding, compared to hemp and flax fiber bundles. Maleic‐anhydride grafted PP (MAPP) with high maleic anhydride groups and high molecular weight was more effective in improving strength properties of PP composite as a compatiblizer. Coupled with 10% glass fiber, 40% TMP reinforced PP had a tensile strength of 70 MPa and a specific tensile strength comparable to glass fiber reinforced PP. Thermomechanical pulp was more effective in reinforcing than BKP. X‐ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) were used to aid in the analysis. Polypropylene with high impact strength was also used in compounding to improve the low‐impact strength prevalent in natural fiber‐reinforced PP from injection molding.     

PP/PVA纤维增强硫铝酸盐水泥基快速修补材料试验研究

针对交通压力增大,公路桥梁路面易出现疲劳破坏的问题,提出以聚丙烯(PP)纤维与聚乙烯醇(PVA)纤维提升硫铝酸盐水泥基快速修补材料性能。分别探究了PP纤维与PVA纤维单掺及复掺对硫铝酸盐水泥基快速修补材料流动度、强度以及韧性的影响,并进一步研究了最优复掺比例对修补材料粘结强度及体积稳定性的影响。结果表明:单掺PP纤维对修补材料砂浆流动度影响较小,并且能显著提升抗折强度,掺入0.2%(体积分数,下同)的PP纤维流动度仅下降4%,1 d和28 d抗折强度分别达到了12.8 MPa、15.5 MPa。单掺PVA纤维会大幅减小修补材料砂浆流动度,提升抗压强度,掺入0.2%的PVA纤维流动度下降21%,1 d和28 d抗压强度分别达到了56.6 MPa、84.3 MPa。当PP和PVA纤维按3:1的比例,以0.2%的总体积掺量进行复掺时,两种纤维可以发挥协同作用使修补材料不仅可以获得良好的流动性能、强度与韧性,同时获得较好粘结强度与体积稳定性。28 d时修补材料砂浆的粘结强度达到5.6 MPa,干燥收缩率低至2.73×10^-4,可以更好地满足公路桥梁路面、伸缩缝的快速修补需求。     

On the mechanism of polypropylene fibres in preventing fire spalling in self-compacting and high-performance cement paste

With the increasing application of self-compacting concrete (SCC) in construction and infrastructure, the fire spalling behavior of SCC has been attracting due attention. In high performance concrete (HPC), addition of polypropylene fibers (PP fibers) is widely used as an effective method to prevent explosive spalling. Hence, it would be useful to investigate whether the PP fibers are also efficient in SCC to avoid explosive spalling. However, no universal agreement exists concerning the fundamental mechanism of reducing the spalling risk by adding PP fiber. For SCC, the reduction of flowability should be considered when adding a significant amount of fibres.In this investigation, both the micro-level and macro-level properties of pastes with different fiber contents were studied in order to investigate the role of PP fiber at elevated temperature in self-compacting cement paste samples. The micro properties were studied by backscattering electron microscopy (BSE) and mercury intrusion porosimetry (MIP) tests. The modification of the pore structure at elevated temperature was investigated as well as the morphology of the PP fibers. Some macro properties were measured, such as the gas permeability of self-compacting cement paste after heating at different temperatures. The factors influencing gas permeability were analyzed.It is shown that with the melting of PP fiber, no significant increase in total pore volume is obtained. However, the connectivity of isolated pores increases, leading to an increase of gas permeability. With the increase of temperature, the addition of PP fibers reduces the damage of cement pastes, as seen from the total pore volume and the threshold pore diameter changes. From this investigation, it is concluded that the connectivity of pores as well as the creation of micro cracks are the major factors which determine the gas permeability after exposure to high temperatures. Furthermore, the connectivity of the pores acts as a dominant factor for temperatures below 300 °C. For higher temperatures micro cracks are becoming the major factor which influences the gas permeability.     

Fire resistance of geopolymer concrete produced from Elazığ ferrochrome slag

This paper presents the effect of elevated temperatures up to 700 °C on compressive strength and water absorption of two alkali‐activated aluminosilicate composites (one of them is river sand aggregate geopolymer concrete; the other one is crushed sand aggregate geopolymer concrete) and ordinary Portland cement based concretes. To obtain binding geopolymer material, Elaz?? ferrochrome slag was ground as fine as cement, and then it was alkali activated with chemical (NaOH and Na₂SiO₃). Geopolymer concrete samples were produced by mixing this binding geopolymer material with aggregates. At each target temperature, concrete samples were exposed to fire for the duration of 1 h. Fire resistance and water absorption of geopolymer and ordinary Portland cement concrete samples were determined experimentally. Experimental results indicated that compressive strength of geopolymer concrete samples increased at 100 °C and 300 °C temperatures when compared with unexposed samples. In geopolymer concrete samples, the highest compressive strength was obtained from river aggregates ones at 300 °C with 37.06 MPa. Water absorption of geopolymer concrete samples increased at 700 °C temperature when compared with unexposed samples. However, a slight decrease in water absorption of concrete samples was observed up to 300 °C when compared with unexposed samples. SEM and X‐ray diffraction tests were also carried out to investigate microstructure and mineralogical changes during thermal exposure. Copyright © 2016 John Wiley & Sons, Ltd.     

Fabrication of highly isotactic polypropylene fibers to substitute asbestos in reinforced cement composites and analysis of the fiber formation mechanism

Highly isotactic polypropylene (PP) is currently studied as a cement‐reinforcement fiber that could potentially be substituted for asbestos because of its resistance to prolonged high‐temperature curing. The higher the isotacticity of the PP fiber is, the higher the tensile modulus and breaking strength of the cured fiber are. The PP fiber that exhibits a isotacticity of 99.6% (XI) and draw ratio of 6.0 retains a tensile modulus of 4.23 GPa, even after high‐temperature curing at 175°C for 5 h. PP fiber is cut into 6‐mm lengths and dispersed throughout a cement mixture to prepare a reinforced cement composite. The mixture is cured in an autoclave at 175°C for 5 h. The Charpy impact strength and flexural strength of the obtained cement composite tends to increase with increasing PP isotacticity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 981‐988, 2013     

Flexural properties after exposure to elevated temperatures of a ground granulated blast furnace slag concrete incorporating steel fibers and polypropylene fibers

Experiments were carried out to investigate the flexural properties of fiber‐reinforced ground granulated blast furnace slag (GGBFS) concrete after exposure to high temperatures. On the basis of experimental observation, the effect of GGBFS content, the steel fiber dosage, the polypropylene (PP) fiber dosage, and the strength grade on the residual strength of concrete after exposure to elevated temperatures were systematically examined. Test data indicate that exposure to high temperatures causes deterioration in the flexural strength of concrete; inclusion of GGBFS, PP fibers, and steel fibers, all effectively improve the residual flexural strength of concrete after fire. The optimum amounts of GGBFS, PP fibers, and steel fibers are identified respectively for better fire resistance of concrete. The strength losses of concretes characterized by different strength grades are very close to one another. Equations are proposed to predict the residual flexural strength of concrete incorporating GGBFS, PP fibers, and steel fibers after being heated to temperatures up to 800°C. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of spalling resistance of high performance concrete with polypropylene fiber contents and lateral confinement

This paper presents an experimental study on the spalling resistance of high performance concrete with polypropylene (PP) fibers and fabric or sheet material for lateral confinement subjected to fire. According to the test results, spalling occurred on all specimens that did not contain PP fiber in the concrete mixture. However, spalling did not occur on specimens containing PP fibers above 0.05% by volume. A metal fabric showed beneficial effect on spalling resistance, but glass or carbon fiber fabrics do not show the same effect on the spalling resistance due to reduction of bond strength at high temperatures. Spalling did not occur on all specimens in which PP fibers and metal fabric were applied at the same time, and hence spalling resistance performance was significantly improved. The residual compressive strength was maintained at about 90% of its original strength, and this can be considered as an improved performance against fire damage.     

Influence of fibers on bond strength of concrete exposed to elevated temperature

Concrete is a building material having good fire resistance and the resistance depend on many factors including the properties of its constituent materials. Fiber Reinforced Concrete (FRC) apart from improving mechanical properties has better fire resistance than conventional concrete. Bond strength of concrete is one of the important properties to be considered by structural engineers while designing reinforced concrete cements. In this research, an experimental investigation has been carried out to determine the effect of fibers on the bond strength of different grades (M20, M30, M40 and M50) of concrete subjected to elevated temperature. Different types of fibers such as Aramid, Basalt, Carbon, Glass and Polypropylene were used in the concrete with a volume proportion of 0.25% to determine the bond strength by pull-out test. Prior to the pull-out test, the specimens were kept in a furnace and subjected to elevated temperatures following standard fire curve as per ISO 834. Based on the test results of the investigations, type of fiber, grade of concrete and duration of heating were found to be the key parameters that affect the bond strength of concrete. The contribution of carbon fiber in enhancing the bond strength was found to be more significant compared to other fibers. An empirical relationship has been developed to predict the bond strength of FRC at a slip of 0.25?mm. This empirical relationship is validated with experimental results.     

Amino‐functionalization of carbon fibers through electron‐beam irradiation technique

Amino‐functinonalized carbon fibers were achieved via electron‐beam (EB) irradiation in Diethylenetriamine (DETA) solution and triethylene tetramine (TETA) solution at 200 kGy. Different graft monomer concentrations were investigated to find the optimal concentration of each graft monomer. X‐ray photoelectron spectroscopy, scanning electron microscopy, and Raman spectroscopy were applied to investigate chemical composition and functional groups, topography and disorder degree of amino‐functionalized carbon fibers surface. Meanwhile, adsorption ability and interfacial adhesion between modified carbon fibers and epoxy resin were determined by TGA and interlaminar shear strength (ILSS). It is found that amino‐functionalized carbon fibers which had rougher and more active surface performed better adsorption ability on epoxy resin than untreated fibers. The optimal ILSS values of carbon fiber (treated with DETA and TETA) reinforced composites were 21.37 MPa and 18.28 MPa, which were much higher than that of untreated fiber reinforced composites. The comprehensive results demonstrated that in this condition, the optimal grafting concentrations of both DETA and TETA were 1.5 mol/L. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40274.     

桥梁伸缩缝超高性能混凝土关键性能的研究与应用

基于不同纤维混杂效应设计原理,利用PVA纤维或聚丙烯纤维与钢纤维二元混杂优化,制备了一种常温养护桥梁伸缩缝超高性能混凝土(UHPC),并探讨了其在实际工程中的应用.研究结果表明,采用这种方法所制备的混杂纤维增强UHPC不仅具有较高的强度且抗裂性好.当用掺量为20 kg/m的聚丙烯纤维与钢纤维混杂时,UHPC常温养护2 d时的抗折强度和抗压强度可分别达到13.6 MPa和40.9 MPa,28 d时可分别达到51.3 MPa和138.5 MPa,且无明显的收缩开裂现象.工程实践表明,利用该混杂纤维增强UHPC对桥梁伸缩缝混凝土的病害进行整治时,不仅可以达到技术性能使用要求,而且可实现快速恢复交通,具有广阔的推广应用前景.     

Flax fiber surface modifications: Effects on fiber physico mechanical and flax/polypropylene interface properties

This study arises on the opportunities of using flax fibers as reinforcement for polypropylene (PP) matrix composites. For this purpose, untreated flax fiber bundles obtained by a retting process have been used. For improving compatibility between flax fiber bundles and PP matrix, fiber surface treatments such as maleic anhydride, maleic anhydride polypropylene copolymer, and vinyltrimethoxy silane have been carried out. On the other hand, alkali treatment has also been carried out for fiber modification. The effect of surface modification on tensile properties of single fibers and also on fiber‐matrix interfacial shear strength (IFSS) has been analyzed. Finally, both optical microscopy and atomic force microscopy have been used for characterizing flax fiber microstructural features. The current study completes previous results to elucidate the influence of treatments on fiber surface and flax fiber‐PP interface. POLYM. COMPOS. 26:324–332, 2005. © 2005 Society of Plastics Engineers.     

A homogenization approach to macroscopic strength criterion of steel fiber reinforced concrete

The present study aims to investigate the strength properties of the fiber reinforced concrete (FRC) by means of a micromechanics approach combining the static approach of limit analysis and the homogenization theory. The macroscopic strength criterion for FRC can be theoretically obtained from the knowledge of the strength properties of the individual constituents, namely, concrete matrix and fibers. Adopting a Drucker–Prager failure condition for the concrete matrix and assuming a simplified geometrical model for fiber orientations and length, an approximate static-based model is formulated for the overall strength properties. Explicit analytical expressions have been derived emphasizing the reinforcing contribution of fiber addition.Additionally, numerical solutions are computed by means of finite element tool implementing an elastoplastic step-by-step algorithm. The main objective of the numerical approach is twofold: qualify the relevance of the analytical results and investigate the influence of real fiber morphology on the composite strength properties.     

纤维打团效应对纤维混凝土抗拉性能的影响

针对纤维在混凝土中存在的打团效应引入了纤维均分系数,并建立了六种纤维打团模型。基于复合材料的力学理论,分析了纤维打团效应对纤维混凝土(FRC)抗拉性能的影响。结果表明:纤维均分系数随打团纤维根数的增大而减少;纤维打团效应的存在导致纤维临界体积掺加率有一定程度的增大,FRC的抗拉强度有不同程度的减小;FRC抗拉强度的损失与纤维临界体积掺加率均随纤维打团含量的增大而增大;考虑纤维打团效应的FRC拉伸强度计算值与试验值较为接近。