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 engineering achievements, that the main benefit that can be expected from this kind of material is the high speed of casting. Furthermore, the concrete's transportation 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 structure's durability. However, the concrete's formulation remains difficult and sensitive; still too often, in their first approach; some formulators simply increase the water-to-cement ratio or only adjust the dosage of superplasticizer, which generates some poor-quality concrete. In this paper, we present a new method based on the use of two admixtures : a nanometric, amorphous: silica SiO2 (for its reactivity with the cement paste), combined with a specific polysaccharide (for its suspending ability), both of them used under a liquid form. We show that one can formulate, at a reasonable cost, a highly fluid concrete, without bleeding or segregation. The setting kinetic is improved, which allows the reduction of the demoulding time; the surface of the hardened concrete is smooth and homogeneous; and the final strengths values achieved are in line with those attained with high strength concrete. (C) 1999 Elsevier Science Ltd. All rights reserved.