Cements of yesterday and today -: Concrete of tomorrow

Concrete, the most widely used construction material; is evolving. Modem concrete is more than simply a mixture of cement, water and aggregates; modem concrete contains more and more often mineral components, chemical admixtures, fibres, etc. Of course the utility market will stay the major market of concrete but niche markets implying the use of a la carte smart concretes will also develop. The development of these smart concretes results from the emergence of a new science of concrete, a new science of admixtures and the use of sophisticated scientific apparatus to observe concrete microstructure and even nanostructure. It is not sure that present cements are far superior to cements made 30 to 40 years ago. A high C3S and C(3)A content, a high Blaine fineness are not needed anymore to make a high-initial-strength concrete, it is simply necessary to lower the water/cement or water/binder ratio. Concrete compressive strength is a function of the closeness of the cement particles as well as cement dosage. In fact, reactive powder concretes testing 200 MPa are preferably made with coarse cements not so rich in C3S and C3A, that is, cements for which it is easy to control the rheology. Present cement acceptance standards that were very safe when 20- to 25-MPa concretes were the most used concretes are not always appropriate to test cements that are to be used in conjunction with superplasticizers to make high-performance concrete. Moreover, up to now too much emphasis has been placed on 28-day compressive strength and not enough on concrete durability. It is very important to design concrete mixtures that keep their 28-day compressive strength over the life of the structure under its peculiar environmental conditions. Finally cement and concrete will have to evolve in the respect of the environment within a sustainable development perspective, which means that more mineral components will be blended with clinker and water/binder ratios will be lowered in order to increase the life cycle of concrete structures and lengthen as much as possible the use of hydraulic binders and aggregates. (C) 2000 Elsevier Science Ltd. All rights reserved.