Trrl Lr 947

Tests were made on composite reinforced concrete beams incorporating a surface layer of glass reinforced cement (grc) to investigate the effect of local surface reinforcement on serviceability behaviour. The grc was in the form of 6mm thick shallow channel sections moulded into the tension surface of the test beams, which were 3.5 m long and were tested in four-point bending on a simply supported span of 3m. On beams which had been kept dry, the grc surfacing had a significant effect in reducing the size of cracks in the concrete at the design working load but had no effect on deflection; no visible cracks appeared on the surface of the grc until the steel had yielded, at a load well above the design ultimate. Some beams were subjected to artificial ageing before test, by immersing them in hot water to represent natural expose of the grc surfacing rendered it virtually ineffective in controlling cracks in the concrete. The observed behaviour compares well with predictions made from a knowledge of the relevant material properties. Considerable improvements in performance could be expected from newer developments in fibre cement composite technology and by using deeper sections for the surface reinforcement. A logical development, which is likely to have economic advantages, is to use suitable sections of rigid fibre reinforced sheet as permanent formwork for reinforced concrete members