Effect of fly ash on differential shrinkage between the outer and inner concrete

Shrinkage strain of concrete containing different amount of fly ash was measured at various depths from the drying surface by using several pairs of LVDT displacement sensors, and only one surface of the concrete specimen was exposed to dry condition during the experiment. Relative humidity development of concrete at various depths from the exposed surface was also studied by using embedded humidity sensors. The results showed that remarkable shrinkage strain and relative humidity difference formed according to the depth from the exposed surface for every concrete, and such differential shrinkage increased with the drying time. At each depth from the drying surface, the addition of fly ash decreased the total shrinkage deformation and shrinkage strain induced by per unit of relative humidity reduction in concrete. The addition of fly ash accelerated the development of differential shrinkage of concrete according to depth from the exposed surface during the first one week of drying, but decreased the final shrinkage difference in concrete.