Though a longtime major aim of the concrete industries has been to provide the least expensive material possible, these industries have also been concerned with constantly improving their product. New vanguard producers of ready mixed concrete are directing their promotion efforts toward commercialization of high-strength concretes (9000 psi and more). High-strength concretes offer a technological breakthrough in the building of columns, beams and shear walls because, with concrete two or three times as strong as ordinary, the concrete cross-sectional area or the amount of steel can be reduced, thus lessening the dead weight of the building, relieving the strain on the lower columns and foundations, and reducing costs.
Before trying to improve the compressive strength of a concrete, it is worth observing the different possible forms of rupture of a specimen of hardened concrete subjected to a compression test. The specimen will rupture when the shear tension or strains induced by the uniaxial compression load reach a critical value in one of the three following zones: in the hydrated cement-sand mortar; along the interface between coarse aggregate and hydrated cement-sand mortar; in the coarse aggregate. Consequently, in order to make a high-strength concrete we must improve the concrete strength in these three zones.
This article specifies the main points on which research work and quality control should be based for the production of concrete of 9000 psi and higher. We hope to help concrete producers who are willing to launch into such an enterprise and at the same time show the most skeptical of them that after all it is not difficult to make such a concrete when you know how to manage it.