Effect of dynamic segregation of self-consolidating concrete on homogeneity of long pre-cast beams

Self-consolidating concrete (SCC) is a highly flowable concrete mixture which does not need any external source of vibration. Due to its high fluidity, it can flow for considerable distances solely due to gravity, but it is also susceptible to segregation at rest (static) and during flow (dynamic). Extended flow distances for SCC could lead to increased non-homogeneous distribution of constituent elements, which could affect key properties of the concrete once hardened. This paper describes a project where SCC was allowed to flow in beams with 9 m or 18 m length, for which the homogeneity was assessed by means of the ultrasonic through-transmission method, and by evaluating the compressive strength on drilled cores. The largest variability, assessed by both methods, was systematically observed at the bottom of the beams in horizontal direction and at the casting point (at one end of each beam) in vertical directions. Changes in compressive strength in vertical direction related well to the dynamic segregation potential from the tilting box test, while the changes at the bottom of each beam in horizontal direction related well to the plastic viscosity of the concrete, which is a parameter affecting the drag (or lack of it) executed by the mortar on the coarse aggregates.