Fresh and hardened properties of self-consolidating concrete

Self-consolidating concrete, (SCC) is a new technology and the market share of its products is rapidly growing because of the economic opportunities and improvements of the quality of the concrete and the working environment. In view of the potential number of ingredients, SCC is a complex system that is usually proportioned with one or more mineral admixtures and one or more chemical admixtures. A key factor for a successful formulation is a clear understanding of the role of the various constituents in the mix and their effects on the fresh and hardened properties. The fundamental rheological properties of SCC are based on low yield stress, moderate viscosity and retention of the kinetic energy of the flowable mix by reducing the volume fraction of coarse aggregate. These measures are necessary for imparting the requested fluidity, segregation resistance and prevention of interparticle collision and blocking. A low yield stress is attained by incorporation of adequate contents of superplasticizer. The flow characteristics are further modified by changing the aggregate volume fraction, coarse-to-fine aggregate volume, and the composition of the other ingredients. The viscosity is controlled by the contents of the free water, superplasticizer, and the volume fraction of the solids in the mix. The two strategies for maintaining a moderate viscosity are based on either incorporation of high amounts of powder; i.e. total content of cementitious materials (referred to as powder type SCC) or addition of viscosity modifier agents (referred to as VMA type SCC). By analogy to the Powers and Brownyard gel-space ratio, the compressive strength can be approximated by calculating the binder-space ratio. One of the main challenges is to impart the required rheological properties that allow desired flow and filling ability characteristics whilst retaining dynamic and static stability. With this respect, the density of the matrix and maximum size of aggregate cannot be overlooked as, within the range of practical attainable viscosities that allow a free-flow, their effects on the resistance to segregation are as high or even greater than that of the effect of viscosity. Attention is also drawn to the higher shrinkage values of SCC, especially the inherent higher shrinkage associated with the powder type SCC.