Visualizing and simulating flow conditions in concrete form filling using pigments

Flow variation at surfaces and reinforcement during form filling was visualized with grey and black SCC. The border between grey and black (pigmented) SCC was captured as frozen images on hardened sawn- and formwork surfaces in a flow box experiment. Maximum velocity occurred at the centre of the closed box, and lowest velocity near the formwork, particularly with reinforcement parallel to formwork. Smooth formwork gave shorter flow profiles (higher surface velocity) than rough formwork. The pigmented mixes had similar workability though somewhat increased yield stress. Flow pattern depended on mix rheology, surface roughness and reinforcement: one mix showed plug flow between reinforcement and smooth vertical formwork whereas most mixes mainly had sheared flow. Numerical simulations mostly agreed with observed flow profiles and could be used to model flow at varying formwork surface roughness with a slip velocity. Future investigations should study the conditions causing plug- and wavetype flow, lubrication and surface finish.