Self compacting concrete needs to be flowable and segregation resistant in addition to being able to pass through gaps in reinforcement. Of these properties, the one that is affected significantly by the aggregate characteristics is passing ability. The size and gradation of coarse aggregate, along with the presence of flaky and elongated particles, are factors that affect passing ability, and thus the uniformity, of SCC. In this paper, an attempt has been made to analyze the influence of aggregate characteristics on the passing ability through a probabilistic model. In addition, an experiment studying the flow of SCC through a set of barriers (representing reinforcements) in a beam is also described. The probabilistic model developed in this study allows the mix designer to decide on the maximum allowable coarse aggregate content of a specific maximum size and gradation, for a given blocking tolerance. The results of the experimental study showed that the fraction of larger sized and longer aggregates decreased considerably as the SCC flowed through successive sets of barriers. The density and dynamic modulus of elasticity also decreased; however, the apparently high degree of blocking did not have a significant effect on the compressive strength of the concrete.