What is concrete ?
What is concretes?
An overview of concrete as a material is difficult at this stage because we
must refrain from discussing specialized knowledge not yet presented, so
.that we have to limit ourselves to some selected .features of concrete
Concrete, in the broadest sense, is any product or mass made by the use of a cementing medium . Generally, this medium is the product of reaction between hydraulic cement and water. But , These days, even such a definition
would cover a wide range of products : concrete is made with several types of cement and also containing pozzolan, Fly ash, blast-furnace slag, micro-silica.
Additives, recycled concrete aggregate, admixtures, polymers, fibres-
and so on ; and these concretes can be heated, steam-cured, autoclaved, vacuum-treated, hydraulically pressured. shock-vibra ted, .Extruded, And sprayed,
This immediately begs the question what is the relation between the constituents of this mixture? There are three possibilities. First, one can view the cementing medium, i.e. The products of hydration of cement, as the essential building material, with the aggregate .fulfilling the role of a cheap, or cheaper, dilutant.
Second, one can view the coarse aggregate as
a sort of mini-masonry which is joined together by mortar, i.e. By a mixture of hydrated cement and line aggregate. The third possibility is to
recognize that, as a first approximation, concrete consists of two phases hydrated cement paste and aggregate, and, as a result, the properties of
concrete are governed by the properties of the two phases and also by the presence of interfaces between them.The second and third view each have some merit and can be used to
explain the behavior of concrete. The first view, that of cement paste diluted by aggregate, we should dispose of. Suppose you could buy cement more cheaply than aggregate-should you use a mixture of cement and water alone as a building material? The answer is emphatically no because the so-called volume changes’of hydrated cement paste are far too large
shrinkage 2 of neat cement paste is almost ten times larger than shrinkage of concrete with 250 kg of cement per cubic metre. Roughly the same
.applies to creep