Reinforcement of cementitious matrices by warp knitted fabrics

The efficiency of knitted fabrics for reinforcing cementitious composites was studied. Weft insertion warp knitting fabrics of controlled structure were especially produced for this work consisting of high modulus (Kevlar and Polyethylene) and low modulus (Polypropylene) polymers. The performance of the fabrics was studied by evaluating the flexural properties of the composites and the bond to the matrix. The performance of the knitted fabrics was compared to that of the straight yarns from which the knitted fabrics were made, as well as comparison with woven fabric reinforcement. It was concluded that: (i) in the knitted fabric reinforcement greater efficiency was achieved in fabrics consisting of high modulus polymer yarns, which are made of bundles consisting of a smaller number of filaments, (ii) the reinforcing effect of the knitted fabric is smaller than that of the individual straight yarns, (iii) the reinforcing efficiency of woven fabric reinforcement is better than that of the knitted fabric, due to the crimped structure of the yarns in the woven fabric. In view of these conclusions, it might be stated that the use of weft insertion warp knitting fabric for cement reinforcement is advantageous in the sense that the fabric can provide the means by which a composite can be produced with continuous and aligned yarns. However, with this kind of fabric some of the reinforcing efficiency of the individual yarns is lost. In contrast, the use of woven fabric can provide all of the above, with the added advantage of enhanced reinforcing efficiency over the straight yarns, induced by their crimping in the woven fabric.