Dynamic segregation of self-consolidating concrete : new test method and effects of mix proportions

Abstract

Self-Consolidating Concrete (SCC) is a type of high performance concrete that can fill formworks without external vibration. SCC has three essential workability characteristics which can be described in terms of flowability, passing ability, and segregation resistance. These properties are typically characterized by data that relate to specific testing methods. Of the three unique properties, segregation resistance refers to the ability to retain a homogenous distribution of aggregates. Segregation is categorized as static or dynamic segregations. Cement paste and coarse aggregate tend to separate vertically when the concrete is at rest before setting, this is so-called static segregation. This separation also occurs horizontally in the presence of flow, which refers to dynamic segregation. Normally segregation resistance is achieved by adding finely powdered materials such as fly ash, silica fume, and limestone powder to increase paste viscosity and volume. Poor segregation resistance can cause an uneven distribution of coarse aggregate, blocking of flow around reinforcement, high drying shrinkage and non-uniform concrete compressive strength (Bui, 2002).Therefore, in this thesis, a new experimental approach named flow trough test was developed to test dynamic segregation. The flow trough test was employed to assess the effect of several parameters on dynamic segregation of fresh SCC. Twenty-nine SCC mixes made with various mix proportioning parameters, including aggregate size and gradation, super-plasticizer, paste volume, and slump flow were evaluated. Flow trough tests showed that increasing slump flow or super-plasticizer dosage would increase dynamic segregation and reducing paste volume may increase dynamic segregation. Also a smaller aggregate size and better gradation would reduce dynamic segregation.