Fiber-reinforced Cement Research Articles

5443627 Organopolysiloxane-alkyltrialkoxysilane emulsions for impregnating structural fibre-reinforced cement components

Starting from SiO2–CaO–P2O5–ZnO–CaF2 oxide system, vitroceramic materials were obtained by employing the sol-gel approach, followed by thermal treatment in order to provide, in a controlled manner, the nucleation and growth of crystalline phases in the parent glassy matrix. Thermal analysis, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, selected area electron diffraction and Fourier transformed infrared spectroscopy were employed for the characterization of the resulting samples. The sintered vitroceramics present calcium silicates as crystallized nano-domains and a porosity that decreases with the enhancement of the processing temperature. The assessment of the biological properties was carried out in vitro by simulated body fluid immersion for 14 days, associated with a detailed analysis of the apatitic layer formed on the surface.

Study on the size effect of tensile characteristics of carbon fibre-reinforced cement composites

It is well known that the tensile strength of concrete is affected by the size of the test specimen; this is called the size effect. The tensile and flexural strengths of carbon fibre-reinforced cement composite (CFRC) also exhibit the size effect, i.e. they decrease with increasing specimen size. In this study, flexural tests of CFRC beams of various sizes were performed to investigate the size effect on the tensile and flexural characteristics of CFRC. Flexural analysis of CFRC beams considering the size effect was also conducted. From the test results, it is clear that the size effect becomes larger as the fibre length increases. Reasonable agreement between experimental and analytical results was obtained for the load-displacement relationship of CFRC beams.

Mathematical model for tensile behaviour of hybrid continuous fibre cement composites

A mathematical model has been developed for the tensile behaviour of cement composites reinforced with two types of continuous and unidirectional aligned fibres. The model is based on the theory for single fibre composites proposed by Aveston, Cooper and Kelly. Theoretical curves have been obtained for the tensile properties of the polypropylene/glass fibre-reinforced cement composites by means of substituting parameters into the developed equations, and these curves were compared with experimental results for a limited range of fibre combinations. It is shown that to attain optimum hybrid effects for toughness and the first maximum point of the stress-strain curve, the correct fibre volume combinations should be included.

The effects of centrifugation and titanium fiber reinforcement on fatigue failure mechanisms in poly(methyl methacrylate) bone cement

The contributions to fatigue resistance in poly(methyl methacrylate) bone cement (PMMA) by centrifugation and titanium fiber addition were studied. Three modified bone cements were tested: porosity reduced cement (C-PMMA); titanium (Ti) fiber-reinforced cement (R-PMMA), using a novel method to incorporate fibers; and porosity reduced and Ti fiber-reinforced cement (C-R-PMMA). Specimens of untreated bone cement (PMMA) were included as controls. Non-notched and notched specimens were cyclically loaded in fully reversed bending. For the non-notched specimens, at all stress levels, C-R-PMMA had significantly greater fatigue life than either C-PMMA or R-PMMA (except C-PMMA at 30 MPa). R-PMMA had lower fatigue life than the control at 30 MPa (nominal maximum stress), but higher fatigue life at 20 and 15 MPa. At both 20 and 15 MPa, there was no statistical difference between the fatigue lives of C-PMMA and R-PMMA. Fractography revealed that, at 30 MPa, characteristics of rapid fracture predominated. At 20 and 15 MPa, in contrast, almost the entire fracture surface showed the characteristic fatigue morphology, indicating that subcritical crack growth was predominant. For the notched specimens, C-PMMA showed greater life than PMMA at the highest stress intensity, but the lifetimes converged with decreasing stress intensity. In contrast, the life-times for PMMA and R-PMMA diverged with decreasing stress intensity. The effect of centrifugation appeared to be strongest at higher stress intensities, and diminished with decreasing stress intensity. The reinforcing effect of Ti fiber addition increased the notched fatigue life at high initial stress intensities, and the reinforcing effect increased with decreased stress intensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Concise encyclopedia of composite materials

Aircraft and aerospace applications of composites. Applications of composites: an overview. Artificial bone. Asbestos fibers. Automobile tires. Automobile components: fabrication. Boron fibers. Carbon-carbon composites. Carbon-fiber-reinforced plastics. Carbon fibers. Composite armor. Continuous-filament glass fibers. Creep of composites. Dental composites. Failure of composites: stress concentrations, cracks and notches. Fatigue of composites. Fiber-reinforced cements. Fiber-reinforced ceramics. Fiber-reinforced polymer systems: extrusion. Fibers and textiles: an overview. Fibrous composites: thermomechanical properties. Friction and wear applications of composites. Glass-reinforced plastics: thermoplastic resins. Glass-reinforced plastics: thermosetting resins. Halpin-Tsai equations. Helicopter applications of composites. High-modulus high-strength organic fibers. High-performance composites with thermoplastic matrices. Hybrid fiber-resin composites. In situ composites: fabrication. In situ polymer composites. Joining of composites. Kirchhoff assumption (Kirchhoff hypothesis). Laminates: elastic properties. Long-term degradation of polymer-matrix composites. Manufacturing methods for composites: an overview. Metal-matrix composites. Molded fiber products. Multiaxial stress failure. Multilayers, metallic. Multiple fracture. Nanocomposites. Natural composites. Natural-fiber-based composites. Nondestructive evaluation of composites. Nonmechanical properties of composites. Oxide inorganic fibers. Paper and paperboard. Particulate composites. Percolation theory. Plywood. Polymer-polymer composites. Recycling of polymer-matrix composites. Silicon carbide fibers. Silicon nitride fibers. Smart composite materials systems. Solid fiber composites as biomedical materials. Strength of composites. Strength of composites: statistical theories. Structure performance maps. Thermosetting resin matrices. Three-dimensional fabrics for composites. Toughness of fibrous composites. Whiskers. Wood-polymer composites. Wood strength. Woven-fabric composites: properties

The study of autoclaved cellulose fiber-reinforced cement composites

The effects of individual or combined addition of sodium water glass (SWG), calcite and CaCl 2 into the starting material, consisting of 92 wt.% of Portland cement with sand and 8 wt.% of cellulose fibers, were studied after autoclaving. Bending strength, bending toughness and module of elasticity were determined. The optimal additions were either 26 wt.% of SWG and 10 wt.% of calcite (sample No. 4) or 5 wt.% of CaCl 2 (sample No. 2). Autoclaved products were also investigated by X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). All results were compared to the product obtained without additions.

Improved grades of carbon black

The limitations of the traditional material design approach in driving properties to extreme values and handling multiple design criteria and variables can be overcome by applying the optimization approach. Fiber-reinforced cement based composites based on strong aggregates and exhibiting approximately bilinear fiber pullout behavior are optimized in the present study for a given compressive strength f′c with a view to maximizing their uniaxial tensile strength f′t and fracture energy GF. Relations for the bridging stresses prior to and during fiber pullout are established using fracture mechanics. The mix design leads to nonlinear, single, or multicriterion maximization problems for the objective functions f′t and lch = EGF/f′t2 (characteristic length), subject to an equality constraint on f′c. In this way, optimal values for the microstructural parameters (fracture toughness of paste, length of fiber, and volume fractions and diameters of aggregate and fiber) are obtained.

Fiber-reinforced cement based composites under tensile impact

Abstract In many civil engineering structures, adequate resistance of the material to suddenly applied loads is essential. This article describes the improvements in the impact resistance of cement matrices when reinforced with high volume fractions of carbon, steel, and polypropylene micro-fibers. Tensile briquettes were fractured under a rapidly applied load using a newly designed instrumental impact machine. Strength and fracture energy values were measured. When compared with static test results, considerable sensitivity to stress rate was noted. The composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fiber volume fractions.

Effect of Fiber-Fiber Interaction on the Strength Properties of Short Fiber Reinforced Cements

A general modification to the models used for the study of the effect of fiber volume on the strength properties of short fiber reinforced cements is presented. It considers the composite as a mix of cement paste, fibers, and voids. The matrix contribution to the strength of the composite is expressed as a function of the void and fiber volume fractions. A modification to the strength contribution of the fibers is proposed based on the reduction of interfacial surfaces due to fiber-fiber and fiber-void interactions. Furthermore, the void volume fraction is related experimentally to the fiber volume fraction. The effect of these modifications on the different measures of strength and toughness in fiber-reinforced cements is briefly discussed. The experimentally observed nonlinear variation of the bending strength of wood fiber reinforced cement (WFRC) with fiber volume fraction can be predicted by applying the proposed modifications to the rule of mixtures traditionally used to predict that strength.

Air-cured banana-fibre-reinforced cement composites

In this paper techniques for the fabrication of banana-fibre-cement composites are reported. The physical and mechanical properties of air-cured fibre-reinforced cement composites, containing banana reinforcement prepared by several different methods are discussed. It was found that kraft pulped banana fibre, at a loading of between 8 and 16% by mass, resulted in composites with flexural strengths in excess of 20 MPa. At a fibre loading of 14% by mass, the flexural strength is 24·92 MPa and the fracture toughness value is 1·74 kJm −2, properties adequate for the production of commercially viable building materials. Thus, in countries like India, China, and within South East Asia, where there is a lack of softwood fibre (the natural fibre most preffered as an alternative to asbestos), but in which banana fibre occurs in abundance, a viable alternative fibre resource is available for commercial consideration.

Approaches to improve the properties of wood fiber reinforced cementitious composites

In an attempt to improve the workability, stability, and physical and mechanical properties of wood fiber-reinforced cementitious composites (WFRCs), alkali-activated blended cements have been explored for their compatibility with various wood fibers such as hardwood fiber, recycled newspaper fiber and recycled kraft paper fiber. Methods including high shear mixing, modifying the cement matrix with silica fume, and molding pressure were evaluated as means for further strengthening the wood fiber-reinforced cement composites. Flexural strengths up to 40 MPa. along with enhanced toughness have been achieved.

Non-linear analysis of RC beams using a SIFCON matrix

The results of a non-linear analysis model of reinforced concrete beams using a high-performance fibre-reinforced cement (FRC) based matrix are described and compared with experimental observations. The constitutive relationship of the FRC materials used in both compression and tension and the logical flow chart for the non-linear analysis model are described. Analytical predictions of moment versus curvature and moment versus deflection curves are compared with experimentally observed results of reinforced concrete beams using a SIFCON (slurry infiltrated fibre concrete) matrix. The use of a fibre-reinforced matrix in the compression zone of a reinforced concrete beam allows for other over-reinforced sections to achieve significant increases in structureal ductility while resisting loads close to their ultimate load. Ductility and energy ratios, normalized by the control beam without fibres, ranged from 2.47 to 3.60 and 3.28 to 5.69, respectively; that is several hundred per cent in improvement. The analytical model is shown to predict, with reasonably good agreement, experimental observations of moment-curvature and moment-deflection curves. Thus it can be used to evaluate the effects of various parameters in order to optimize structural performance.

APV Baker twin-screw extruder installed at Wells Plastics

The limitations of the traditional material design approach in driving properties to extreme values and handling multiple design criteria and variables can be overcome by applying the optimization approach. Fiber-reinforced cement based composites based on strong aggregates and exhibiting approximately bilinear fiber pullout behavior are optimized in the present study for a given compressive strength f′c with a view to maximizing their uniaxial tensile strength f′t and fracture energy GF. Relations for the bridging stresses prior to and during fiber pullout are established using fracture mechanics. The mix design leads to nonlinear, single, or multicriterion maximization problems for the objective functions f′t and lch = EGF/f′t2 (characteristic length), subject to an equality constraint on f′c. In this way, optimal values for the microstructural parameters (fracture toughness of paste, length of fiber, and volume fractions and diameters of aggregate and fiber) are obtained.

Blowing agents

The limitations of the traditional material design approach in driving properties to extreme values and handling multiple design criteria and variables can be overcome by applying the optimization approach. Fiber-reinforced cement based composites based on strong aggregates and exhibiting approximately bilinear fiber pullout behavior are optimized in the present study for a given compressive strength f′c with a view to maximizing their uniaxial tensile strength f′t and fracture energy GF. Relations for the bridging stresses prior to and during fiber pullout are established using fracture mechanics. The mix design leads to nonlinear, single, or multicriterion maximization problems for the objective functions f′t and lch = EGF/f′t2 (characteristic length), subject to an equality constraint on f′c. In this way, optimal values for the microstructural parameters (fracture toughness of paste, length of fiber, and volume fractions and diameters of aggregate and fiber) are obtained.

Engineering ductile fracture in brittle-matrix composites

This letter describes a newly discovered phenomenon: ductile fracture in cementitious materials. The brittle nature of materials such as concrete and ceramics has prompted the development of various approaches to enhance their fracture toughness. Fibre reinforcement has been the common focus in the toughening of the brittle materials. Two types of fracture have been observed to date in cementitious materials and ceramics: brittle and quasi-brittle fracture. Brittle fracture can be observed, for example, in hardened cement paste material. It is characterized by a very small microcrack zone at the crack tip (Fig. la), typically of submillimetre scale, low fracture energy of the order of 0.01 kJm -2, and a linear load versus load-point displacement curve from a fracture test. Quasi-brittle fracture can be observed in concrete and in most fibre-reinforced cements or concretes (FRC). It is characterized by a bridging process zone in addition to the small microcrack zone at the crack tip (Fig. lb). The bridging action provides additional energy absorption through aggregate and/or ligament bridging in concrete, and through fibre bridging in FRC, in the wake of the crack front. For quasi-brittle materials the fracture energy extends a large range, from 0.1 kJm -2 in concrete to several kJ m -z in the case of FRC. Correspondingly, the process zone size extends from the mm scale to the cm scale. The load versus load-line displacement curve from a fracture test may involve a small non-linear region near the peak load, with a significant post-peak tension-softening behaviour. Research into quasi-brittle materials in the past decade has been extensive (see, for example [1, 2] for a recent collection of papers on the subject). It must be mentioned that the classification of the fracture characteristics for cementitious materials described above may also be applicable to current monolithic and fibre-reinforced ceramics.

Fiber-reinforced cement composites

Historical developments mechanics of fibers basic concepts of mechanical properties - tension, bending constitutive materials mixture proportions - mixing and casting procedures properties of freshly mixed FRC properties of hardened FRC compression, tension and flexure FRC under impact and fatigue loading creep, shrinkage and long-term performance of FRC plastic drying shrinkage fiber-reinforced shotcrete glass fiber reinforced cement (GFRF) thin sheet products slurry infiltrated fiber concrete (SIFCON) use of FRC in structural components field performance and case studies.

Impedance characterization of microcracking behaviour in fibre-reinforced cement composites

Crack growth behaviour of polypropylene, carbon-fibre and mica-flake reinforced cement composite systems subjected to a compressive load was investigated by an AC impedance technique. Two crack dependent processes appear to be associated with characteristics of the high-frequency arc diameter ratio, R 2/ R 20 versus load ratio, P/ P m curves for cement-based composites. These correspond to microcrack formation and propagation. Evidence indicates that slight increases of the high frequency arc (HFA) diameter in the fibre-reinforced systems as the load increases are a result of the fibre reinforcement impeding the crack formation process. It is suggested that microstructural densification in the vicinity of the fibre boundary influences the crack formation process and leads to a slight increase of the HFA diameter.

Evaluation of interfacial mechanical properties in SiC fiber-reinforced macro-defect-free cement composites

The application of a micro-indentation technique for the measurement of interfacial mechanical properties in a fiber-reinforced cement composite has been examined. The composite was formed by placing aligned SiC fiber tows between macro-defect-free (MDF) cement sheets after which the compact was warm pressed at 6·89 MPa (1000 psi) at 80°C. The interfacial characteristics of the composite were varied by modifying the surfaces of the fibers prior to their incorporation into the matrix. These modifications included either an application of a stearic acid film or 1000°C gas phase treatments in air, oxygen, or nitrogen for one hour. These four fiber surface treatments served as the independent parameter for the mechanical testing analysis. The interfacial characteristics, including the shear, the residual axial fiber, and debond stresses, were evaluated with a mechanical properties microprobe by measuring the force/displacement curves generated during load-unload cycling. Estimates of these three stress values were obtained by matching the experimental force/displacement curves with data predicted from an existing model. For two of the four systems investigated, relatively high residual axial fiber compressive stresses were required adequately to describe the large fiber displacement recovery obtained after complete unloading. The stresses were believed to have resulted from the large differential shrinkage between the fibers and matrix during processing. The shear and debond stress values were highest for those fibers oxidized in air and lowest for fibers coated with stearic acid. The calculated interfacial shear stress value becomes significantly overestimated when the residual axial stress has a large magnitude and is not taken into account in the calculation.

Impact behaviour of corrugated sheets of fibre-reinforced cement

Impact behaviour of corrugated sheets of short fibre-reinforced cement has been studied experimentally on the basis of measured time functions of impact force and structure displacement. These results are compared with those obtained from a newly developed theoretical model which simulates not only the local dynamics of the impact of a rigid spherical object on a thin flat elastic plate but also considers couples membrane modes of motion due to the curvature of the corrugated structure.

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