Variations of Sorptivity with Rheological Properties of Concrete Cover in Self-Consolidating Concrete

Transport properties of the concrete cover can influence the durability of concrete. Concrete cover of conventional vibrated concrete has greater porosity because of the looser packing density of coarse aggregate against the surface of the formwork, which is referred to as the "wall effect". In the case of self-consolidating concrete (SCC), the volume of coarse aggregate is lower, and the packing density of the aggregate can depend on the flow properties of the SCC under its own weight. The extent of the wall effect on the quality of the concrete cover can vary with the rheological properties of the concrete. The work presented in this paper seeks to evaluate the effect of changes in rheological properties of SCC on the sorptivity of the concrete cover that can be affected by the degree of consolidation of the SCC near formed surfaces as well as changes that can result from water migration and changes in the packing of solid particles in the vicinity of formed surfaces. The sorptivity of the concrete cover is also compared to that of the bulk concrete. In total, 17 SCC mixtures covering a wide range of rheological properties were investigated. Good correlation between initial plastic viscosity of SCC determined by the modified Bingham model and the sorptivity measured during the first 6 h of testing is established. It is likely that the initial plastic viscosity has a marked influence on the volume of the largest capillary pores of concrete, which can significantly affect transport properties and durability. Test results indicate that the sorptivity of the concrete cover in SCC is similar to that obtained in the interior bulk concrete.