Youjiang Wang

Effect of inclining angle, bundling and surface treatment on synthetic fibre pull-out from a cement matrix

Abstract In an experimental investigation of synthetic fibre pull-out at an angle, it was generally observed that the force and energy of fibre pull-out increase with the inclination angle, but such increases are limited by the strength of the cement matrix at high angles due to matrix spalling. Studies were also conducted on the effects of fibre bundling and surface treatment on the pull-out behaviour. It is suggested that for effective use of the reinforcing fibres, fibre bundling should be minimized and the fibre/matrix bond property should be controlled.

A MICROMECHANICAL MODEL OF TENSION- SOFTENING AND BRIDGING TOUGHENING OF SHORT RANDOM FIBER REINFORCED BRITTLE MATRIX COMPOSITES

Abstract A micromechanical model has been formulated for the post-cracking behavior of a brittle matrix composite reinforced with randomly distributed short fibers. This model incorporates the mechanics of pull-out of fibers which are inclined at an angle to the matrix crack plane and which undergo slip-weakening or slip-hardening during the pull-out process. In addition, the random location and orientation of fibers are accounted for. Comparisons of model predictions of post-cracking tension-softening behavior with experimental data appear to support the validity of the model. The model is used to examine the effects of fiber length, snubbing friction coefficient and interfacial bond behavior on composite post-cracking tensile properties. The scaling of the bridging fracture toughening with material parameters is discussed.

Modelling of fibre pull-out from a cement matrix

Abstract Theoretical analyses of fibre pull-out from a matrix reported in the literature are briefly reviewed. The effects of Poissons ratio, elastic-frictional bond strengths, and bond strength variation with slippage distance on the pull-out relation are discussed. A theoretical model motivated by observations of fibre surface abrasion is developed to predict the pull-out force versus displacement relationship. The model takes into consideration the variation of the frictional fibre-matrix bond strength with fibre slippage distance. Good agreement is achieved between model predicted pull-out behaviour and experimental pull-out curves for nylon and polypropylene fibres. For these synthetic fibres, the bond strength increases with the slippage distance during the process of pull-out. The model also predicts reasonably well the pull-out behaviour of steel fibres for which the bond strength decreases with the slippage distance.

An experimental study of synthetic fibre reinforced cementitious composites

Fibre reinforcement is one of the effective ways of improving the properties of concrete. However, current studios on fibre -reinforced concrete (FRC) have focused mainly on reinforcements with steel and glass fibres. Thin paper reports on an experimental programme on the properties of various synthetic fibre reinforced cementitious composites and the properties of the reinforcing fibres. Acrylic, polyester, and aramid fibres were tested in uniaxial tension, both in their original state as we!! as after ageing in nerO*nL Samples of these fibres were found to lose varying amounts of strength with time, depending on the ageing temperature. Two different test methods were used to measure the fibre-cement interfacial bond strength. The tensile properties of concrete reinforced with acrylic, nylon, and aramid fibres, in the form of random distribution or unioxial alignment, were studied by means of three different tests: compact tension, flexural, and splitting tensile tests. The properties of concrete, particularly that of apparent ductility, were found to be greatly improved by the inclusion of such fibre reinforcement.

Properties of fibre reinforced concrete using recycled fibres from carpet industrial waste

A study was carried out to evaluate the use of recycled fibres from carpet industrial waste for reinforcement of concrete at 1 and 2 vol% fractions. Compressive, flexural, splitting tensile and shrinkage tests were performed. Significant increases in shatter resistance, energy absorption and ductility were observed. This paper reports on the experimental programme and compares the effectiveness of such recycled fibres with that of virgin polypropylene fibres specially made for fibre reinforced concrete (FRC). The paper also discusses the benefits of using such FRC for construction applications and possible ways to further enhance the performance of such FRC.

TENSILE PROPERTIES OF SYNTHETIC FIBER REINFORCED MORTAR

Abstract This paper reports on an experimental study of synthetic fiber reinforced mortar. The fibers used included aramid, high-strength high-modulus polyethylene, and polypropylene, and they were randomly mixed in the matrix at volume fractions below 3%. Tensile properties of the composites were measured by the direct tensile test under both monotonic and cyclic loading. Workability and the drying shrinkage of the composites are also reported.

Experimental Determination of Tensile Behavior of Fiber Reinforced Concrete

With reported improvements in tensile behavior of concrete due to fiber reinforcement, considerable interest has been generated in tensile testing techniques for cementitious composites. Such methods are reviewed and a novel method for direct tensile tests on fiber reinforced concrete (FRC) is described. The method requires only a simple loading fixture yet gives satisfactory test results. The results of tensile measurements are reported for various synthetic FRC with mortar matrix. It is expected that direct tensile test of FRC can be widely performed by using this method.

Characterization of the longitudinal tensile behavior of pultruded I-shape structural members using coupon specimens

Abstract Durable, lightweight, and low cost pultruded structural composites are suitable materials for construction applications. An experimental program has been carried out to characterize the tensile behavior of pultruded composite I-shape structural members using coupon specimens of different widths cut from different locations. Results of material strength, modulus, and failure mechanisms are reported. It was observed that the specimen width and original location had significant effects on the variation of the test data. However the average strength and modulus values were not significantly affected by these factors. Recommended methods for specimen selection and for estimation of material property data for structural design are discussed.

A statistical tensile model of fibre reinforced cementitious composites

Abstract A statistical model has been developed to predict the tensile constitutive relationship of frc from fibre and matrix properties and geometries. This tensile relation for frc is also used to predict the load-deformation relations for the compact tension test and the flexural test configurations. Theoretical load-deformation relations of frc were compared with results from these tests and good qualitative agreement was obtained for different frc . There still exists a difference between the magnitudes of the theoretical and the experimental data. Possible sources of this discrepancy are discussed as a basis for ongoing theoretical and experimental studies aimed at reducing this discrepancy.

Tensile failure mechanisms in synthetic fibre-reinforced mortar

The ultimate tensile behaviour of fibre-reinforced cementitious composites is closely related to its failure mechanisms which in turn are dependent on reinforcement parameters such as fibre characteristics and the fibre/matrix interface properties. Based on the direct tensile tests of mortar specimens reinforced with various synthetic fibres, this paper attempts to explain such relationships and to indicate directions towards more effective fibre reinforcement.