Concrete

Abstract

Concrete based on Portland cement has been a widely used construction material for well over a century. In the past twenty years there has been a dramatic change in concrete technology. 'High performance' concretes of compressive strengths of 120 MPa are now routinely produced. Not only has the strength of concrete been increased four fold but the material is also highly durable and resistant to degradation. A major factor determining concrete's strength and durability is its porosity which can be linked to the water/cement ratio used in the mix. In the past, in order to produce a workable concrete, it was necessary to add water in excess of that required for hydration of the cement. This resulted in the production of capillary pores and voids which contributed to the limitation of strength and durability of set concrete. This limitation was overcome by the incorporation into the wet mix of superplasticisers, which produce a workable mix without the addition of excess water, and the addition of an ultrafine component into the mix which not only increases density but also modifies the microstructure.