The basic components of a concrete mix is aggregate (such as sand), binder (cement) and water. Only those three components are sufficient to produce a concrete mix. Naturally it is also possible to apply specific admixtures and additives that specify properties of the composite. The application of additives is not the only way to determine properties of concrete, because this may also be done by assuring appropriate proportions of its components, which also have specific properties.
Cement is the main ingredient in concrete. As a rule is consists in bakes and ground clinker improved by appropriate additives, such as pozzolan, burnt shale, limestone, silica fluid or volatile ash. Appropriate additives of production technology modify properties of cement, and consequently also those of the entire mix.
On the other hand, aggregate is the elementary filling of concrete mix. It comes up to ca. 80% of its mass and not much less volume. Good aggregate should have the appropriate adherence of hardened cement mass, and should not have a direct impact on the setting of this mass. The most popular aggregates comprise gravel or sand, although in some types of composite also used are such components, as pumice, polystyrene, iron ore or steel granulate.
Naturally water applied for the production of a concrete mix should also meet certain criteria. The purer, the better, and so for example simple potable water is suitable for construction works. A possible low content of sulphur compounds (a maximum of 2000 mg/l) or chlorine (a maximum of 1000 mg/l in reinforced concrete, 4500 mg/l in plain concrete) is also of importance. Also to be borne in mind is the content of phosphates, sugar, ions of lead Pb2+ or zinc Zn2+ (a maximum of 100 mg/l). Also undesired is the presence of fats, oil or topsoil.
One should also bear in mind admixtures and additives. The maximum amounts of admixture in composite may not exceed 5% of cement mass, and of additives – 20%. Admixtures determine among others a reduction in the required water amounts, and may also hasten or delay composite binding, increase its plasticity or change its properties, such as frost and fire resistance. Furthermore, additives may increase the volume of the concrete mass or modify its properties both before and after setting.
