High strength self-compacting concrete - Original solutions associating organic and inorganic admixtures

Self-compacting concrete (SCC) is today a pretty well-known technology. It has been established by several authors, on the basis of numerous engineeri ng achievements, that the main benefit that can be expected from this kind of material is the high speed of casting. Furthermore, the concrete's trans portation and placing down are greatly facilitated by the use of pumps; the extreme fluidity allows the realization of complex pieces and enables the access to difficult casting zones, which leads to an improvement of the str ucture's durability. However, the concrete's formulation remains difficult and sensitive; still too often, in their first approach; some formulators s imply increase the water-to-cement ratio or only adjust the dosage of super plasticizer, which generates some poor-quality concrete. In this paper, we present a new method based on the use of two admixtures : a nanometric, amo rphous: silica SiO2 (for its reactivity with the cement paste), combined wi th a specific polysaccharide (for its suspending ability), both of them use d under a liquid form. We show that one can formulate, at a reasonable cost , a highly fluid concrete, without bleeding or segregation. The setting kin etic is improved, which allows the reduction of the demoulding time; the su rface of the hardened concrete is smooth and homogeneous; and the final str engths values achieved are in line with those attained with high strength c oncrete. (C) 1999 Elsevier Science Ltd. All rights reserved.