The early age behaviour of concrete industrial ground floor slabs

This thesis is concerned with the early-life behaviour of concrete industrial ground floors. Advances in construction methods are placing increased demands on the performance of industrial floors and pushing the limits of the current design guidance. Uncertainties about the true behaviour of industrial floors have been addressed by a programme of in-situ monitoring. An in-situ instrumentation methodology has been developed to monitor the slab and the local climate. Vibrating wire strain gauges and demecs were used to collect concrete shrinkage and joint performance data, whilst thermocouple arrays and thermistors in the strain gauges recorded the slab temperature. This allowed the effects of the cement hydration and the impact of ambient conditions on the slab to be assessed. The use of an automated data collection system allowed the timing as well as the magnitude of the movements to be measured helping identify cause and effect. Floor slabs covering long strip and large area pour construction, jointed and jointless detailing and mesh fabric and fibre reinforcement have been investigated. The data has shown the strong thermal influence on the behaviour of the slabs. Initial joint opening was found to be triggered by the cooling of the slab, whilst the effects of seasonal temperature changes in the first couple of months after construction could be as large if not larger than the drying shrinkage. Frictional resistance was found to reduce the measured movement, whilst the restraint arising from adjacent pours was also found to be significant. Finite element models of the temperature development have been produced using material property data found in the literature. Calibration and verification were carried out using the temperature data collected from site with good agreement. Structural models were then developed using the temperature and degree of hydration output from the thermal analysis as input. These models were used to determine the theoretical stress distribution in slabs at early-ages, and to conduct a parametric study. This demonstrated that the warping stresses present in a slab are generally greater than those from frictional restraint. The thesis concludes with recommendations for the design and construction of industrial ground floors.