There are several important characteristics of cement which need to be considered upon purchase of this binding. The complex of its properties is expressed by the brand of product. Therefore for different works choose certain grades of cement.
1. Cement – the most popular binding without which any construction does not do. There are several brands which designate complex of its properties and according to them define the field of its application. The grade of cement reports about its durability on compression. The valid durability is called active. For example, at strength indices of compression of 44 MPas, the activity will be equal to 440 kgfs/cm2, therefore cement grade – M400.
2. Binding with these characteristics it is everywhere used in the course of production of concrete for filling of the bases, masonry units, paving slabs. M500 brands apply in production of high-strength concretes to casting of reinforced concrete constructions above.
3. One of the most important properties of cement is the speed of its hardening. It is expressed in accumulation of durability for certain period and depends on mineralogical structure binding, its microstructures and fractions of grinding. From portland cements the most quick-hardening is sulfate-resistant. It has higher resistance to influence of the liquids containing sulfates. The concrete made on the basis of rapid-hardening cement have low heat transfer coefficient.
4. Upon purchase of cement it is necessary to pay attention to its ability to hold moisture. This property call "water keeping". It defines uniformity of concrete mix and adhesive strength binding with filler and the reinforcing material. If the ability holds water of insufficient, there can be stratification of concrete structure or product. In due measure portland cements of M400, M500, M600 brands have this property.
5. One more important property of cement – uniformity of change of volume. The standard indicator accepted as the construction standard in many countries – expansion of portland cement from 0.5% to 1.3%. For example, in the USA the admissible expansion is equal to 0.8%, in China – 1.3%. In the course of hydration of cement there is heat production. It is one more property of this binding which has drawn attention for the reason that concrete temperature at its laying often considerably increases. It causes growth of tension connected with uneven cooling of the top and base layers of structure that can lead to cracking of finished product.
6. Normal density of cement - indicator of amount of water which is necessary for receiving solution of certain consistence. Mean value of density of binding – 22-27%. It raises by introduction to composition of cement of the tonkomoloty additives having property of water absorption (bergmeal, flask, etc.). The normal density is lower, the less it is necessary waters for receiving quality concrete. And its quantity leads reduction to reduction of consumption of cement. Therefore in production of concrete products use cements with the lowered normal density.