A. Peled, S. Sueki ,and B. Mobasher, "Mechanical Properties of Hybrid Fabrics in Pultruded Cement Composites," 16th European Conference of Fracture (ECF16), Special Symposium Measuring Monitoring and Modeling Concrete Properties Alexandroupolis, Greece, July, 2006 Mechanical Properties Of Hybrid Fabrics In Pultruded Composites Alva Peled1, Barzin Mobasher2, and Sachiko Sueki2 1Structural Engineering Department, Ben Gurion University, Beer Sheva, Israel, 2Department of Civil and Environmental Engineering, Arizona State University, Tempe, AZ, USA ABSTRACT Cement based composites were developed with a combination of fabric types using cast (hand lay up) process and pultrusion (impregnated) method. The influences involved with the impregnation process using the pultrusion technique was studied by pullout and tensile tests. Hybrid composite laminates with combination of low modulus PE or PP fabrics with high modulus AR glass fabric were developed and tested in tension. The effect of various fabric types in suppressing the localization and crack bridging mechanisms were studied as well as the microstructure of these composites. It was found that the processing methods and fabric type significantly affect the bond as well as the tensile performance of the composite. Hybrid composites combining low modulus and high modulus fabrics found to influence the mechanical performance of the composite. Combinations of PE and Glass fabrics gave composite with better ductility than a single glass and with greater strength than the PE single composite. Key words: cement composites; fabric; processing; pultrusion; hybrid; tensile; pullout 1. INTRODUCTION There is a growing interest in the use of fabrics as reinforcement for thin sheet cement composites. In addition to ease of manufacturing, non-linear geometry of individual yarns within the fabric results in excellent bond development and mechanical anchorage. These characteristics result in improved strength due to strain-hardening behavior even though the reinforcing yarns have a low modulus of elasticity1,2. The wide variety of fabric production methods such as: weaving, knitting, breading and non-woven allows great flexibility in fabric design. This flexibility enables controlling of fabric geometry, yarn geometry and orientation of yarns in the fabric in various directions as well as yarns material combinations (hybrid). Hybrid systems with two or more fiber materials are being used to combine the benefits of each fiber into a single composite product. Optimized performance of hybrid thin sheet composite in the hardened state, with respect to strength and toughness, has been studied by several investigators using combination of different fiber types with low and high modulus of elasticity3-6. The use of hybrid fiber reinforcement is particularly promising in fabric-cement composites. Fabrics allow several ways to combine different yarn types in a composite, i.e. different yarns in x direction, y direction or in both directions. Various contents of each yarn type at each direction are also possible. Moreover, one can combine several fabrics layers in one composite where each layer is made from a different single material. Pultrusion process is an efficient way to produce fabric-cement composites laminates. This method is based on a relatively simple set up using low cost equipment and results in uniform production7. In this study cement based composites were developed with a combination of different layers of single fabric types. The composites were prepared by the cast (hand lay up) process and pultrusion (impregnated) method. The influences involved with the impregnation process using the pultrusion technique was studied by pullout and tensile tests. Composite laminates with combination of low modulus fabrics PE or PP with high modulus AR glass fabric were developed and tested in tension. The effect of various fabric types in suppressing the localization and crack bridging mechanisms were studied as well as the microstructure of these composites. 2. EXPERIMENTAL PROGRAM 2.1 Fabric types Three different fabrics were used for this study made from high modulus AR Glass, low modulus polypropylene (PP) and low modulus polyethylene (PE). The AR Glass was a bonded fabric in which perpendicular set of yarns (warp and weft) was glued together at the junction points, having 4 yarns per cm in both directions of the fabric. The entirefabric was coated with sizing. The PP was a weft insertion warp knitted fabric in which the yarns in the warp direction were knitted into stitches to assemble together straight yarns in the weft direction which were the reinforcing yarns in the composite. This fabric was made from multifilament yarns with 8 yarns per cm in the reinforcimg direction (weft yarns) and 0.8 stitches per cm in the perpendicuar direction (warp yarns). The PE was a woven fabric, where the warp and the fill (weft) yarns pass over and under each other, made from monofilament with 22 yarns per cm in the reinforcing direction (warps) and 6 yarns per cm in the perpendicular direction (fills). The properties and geometry of the yarns made up the fabrics are presented in Table 1. Table 1. Properties and geometry of yarns made up the fabrics Yarn type Yarn nature Tensile strength, MPa Modulus of elasticity, MPa Filament size, mm Bundle diameter, mm PE Monofilament 260 1760 0.25 0.25 PP Bundle 500 6900 0.04 0.40 AR-Glass Bundle (coated) 1360 78000 0.0135 0.80 2.2 Composite Preparation 2.2.1 Pullout tests The specimens for pullout tests were produced by hand lay up of a single layer of fabric in the center of the cement matrix, along the specimen length. The pulled out yarns in the fabrics were the same as the reinforcing yarns in the tension specimens. The length of the specimen was equal to the embedded length of the fabric in the cement matrix: 12.7 mm long (0.5 inch) for all fabrics PE, AR Glass, and PP. Two sets of specimens were prepared for the PP and glass systems. In the first set, "clean" fabrics without cement were embedded in the cement matrix. In the second set, the fabrics were first impregnated in the cement bath using the pultrusion process; then the impregnated fabrics were embedded in the cement matrix. Table 2 presents the different tested systems. 2.2.2 Tensile tests Composite laminates were prepared by the cast and pultrusion process. In the pultrusion method the fabrics were passed through a slurry