Characterizing early-age and seasonal effects on slab response to environmental loads

The focus of this study is to provide a detailed analysis on the strain that develops as a result of environmental loads. This study characterizes slab response immediately after construction (first 72 hours after paving) and also addresses seasonal effects over the first two years following construction. A heavily instrumented test section containing both doweled and undoweled slabs was constructed to help better characterize slab response to environmental loads. Surface profile measurements were also made on these slabs at various times of the day during each season. The magnitude of the built-in gradient was quantified along with the early-age response of the slab to environmental loads. It was found that the equivalent linear temperature gradient at the time of set was 0.12 °C/cm (0.22 °F/in). The largest built-in curvature measured along the diagonal for the doweled and undoweled slabs was 0.0000124 1/m (0.0000408 1/ft) and 0.0000138 1/m (0.0000454 1/ft), respectively. The increase in curvature with an increase in equivalent linear temperature gradient for the undoweled slabs was 7 percent higher than the doweled slabs. While the profile measurements are used to quantify overall slab deformation, strain gages were used to analyze the slab response at localized points within the slab. Using strain gages, it was found that a substantial amount of the drying shrinkage occurred within the first 50 days after construction. Despite that the thermal strain was still found to be twice as high as the drying shrinkage the first winter following construction. A thorough characterization of slab response to gradients in the slab is provided. Variations in drying shrinkage and temperature are characterized not only throughout the depth of the slab but also across the slab surface.