Concrete is an artificial stone that is obtained by hardening a mixture of binder, water and aggregate. The properties of the maturing concrete depend on where and for what the concrete mix is used. On the basis of this is calculated the concrete strength class, suitable aggregates are selected and, if necessary, frost resistance, water tightness, etc., is indicated.

On hardening of the concrete, cement hydration takes place, resulting in the emergence of a solid artificial stone. The reaction is exothermic, i.e., heat is released during the process. During the hardening, processes take place with the concrete mix; the concrete mix solidifies, congeals and hardens.

The concrete mix is usually manufactured from a cement binder (such as Portland cement or oil shale cement) and with normal dense aggregates, such as crushed stone or gravel, sand and water.

Regular concrete or normal concrete

The fine aggregate of regular concrete has sand with a grain size of 0.14 to 4 mm, and it must not contain substances that prevent the hardening of the concrete, reduce persistence or cause corrosion of the reinforcement. The coarse aggregate in normal concrete is rubble or gravel. The water used in the concrete mix must be clean (to meet the requirements of drinking water); seawater can only be used in the concrete if its salt content is less than 2%. Clean water should also be used for concrete irrigation. Normal concrete is used the most in construction, but it finds use everywhere from large construction to use for private houses.

Concrete gelation period

During the gelation period, concrete can be installed; during the hardening period, installation is no longer possible. In the case of regular cement, the average concrete hardening time at a temperature of 20°C is 2-4 hours. During the concrete hardening, process temperatures may not rise above 50°C. When this happens, there is a risk that the concrete may lose up to 30% of its final strength.


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