Flexural and direct tensile tests have been carried out on cement mortar sheets reinforced with continuous polyolefin films. This new type of composite, developed at the university of surrey and called netcem, has potential applications as combined permanent shuttering and surface reinforcement to simplify construction and to improve the durability of concrete bridge decks. The techniques used for fabricating and testing three forms of netcem are described. Most of the tests were on composites containing polypropylene film, but a few tests were made using high modulus polyethylene. The principal findings were: (i) composites based on open network polypropylene film were nearly twice as strong as those based on a woven mesh. In both cases failure strains were about 7 per cent. Tensile strengths of at least 20 mn/m2 were achievable. (ii) neither prolonged immersion in water nor exposure to ultra-violet radiation caused any deterioration in properties. Limited tests on a composite containing a high modulus polyethylene film indicated an increased load-carrying capacity at a given strain but the strain at failure was slightly less than for the polypropylene composites. Closely spaced fine cracks developed in the cement matrix under load, typical crack spacings being about 1 mm and 3 mm for composites containing 9 per cent by volume of open network film and woven mesh respectively. Preliminary tensile tests on axially reinforced concrete prisms incorporating side panels of netcem suggest that this type of composite material shows considerable promise for the control of surface cracking in concrete structures. (Author/publisher)
Abstract