New methodology for designing self-compacting concrete

A new segregation-controlled design methodology is introduced for self-comp acting concrete (SCC). The theory suggests that aggregate segregation is go verned by the yield stress, viscosity, and density of the cement paste matr ix. The concept of a rheological self-flow zone (SFZ) for concrete is intro duced where aggregate segregation is avoided, yet the concrete has a high w orkability. The applicability of the theory is studied by systematically changing the r heology of the cement paste matrix of fresh concrete. The yield stress and viscosity of three different types of pastes incorporating silica fume and a cellulose thickening agent is measured as a function of density. A U-tube apparatus is then used to determine the SFZ for concrete made with the dif ferent cement paste compositions. The results suggest that the new segregat ion control design theory can be used to produce SCC The slump of concrete produced using this new methodology was 29 cm (11 in.), with no segregation of coarse aggregate even at the periphery of the slumped material.