Hydration of Concretes

Concrete is a building material which originates by mixing, laying, compacting and treating the mix containing the cement (binders), aggregates, water, ingredients and admixtures. Under certain conditions this mix obtains in time mechanical properties. The set of all chemical, physical and mechanical reactions which are effective at the same time and whose resultant is permeated, is called hydration. There exist a long term efforts to penetrate deep into the knowledge of hydration processes. There are known many theories, many a partial knowledge. It is not the purpose of this paper to give their detailed summary. However, it is possible to generalize that the prevailing part of explanations supposes that the dominant factor is that of the reaction cementing materials and water. This reaction lies in progressive dissolution of the cementing materials ( we do not mean cement only, but possible active aggregates or mixes of various cementing materials, etc. ) and through the complicated process of heterogeneously forming gel and metastabile crystalloid structure.

Considerably differences exist in the opinions about the fact, what sort of gel and metastabile crystalloid stages are continuously created, about their kinetics of origin and perishing, about what may be considered as a final product of hydration and about the period of duration of hydration processes. In this respect most easily are accepted the opinions being possible much general enabling wide interpretation.

Energetic Model of Hydration

Energetic model of hydration is based on the condition that the sufficiently general description including both physical and mechanical acts must be put on the base being common for everybody. One of the possibilities is that of consumption of energies ( work ).

On the base of the laws of quantum physics it is valid that no act is passing in nature unless there is given a reason for it. The reason for it is the imbalance of energies. Energy is meant in a complex way, not only as an outer impulse, but first of all by the so called balanced state. If the environment or its energetic stability are changed, there arises also a newly defined balanced state of the internal energy. The sensitivity of these changes is not continuous, it moves in very small jump values, the so called quanta.

According to these principles the resulting product of hydration may be reached in different ways. The resulting state may theoretically be, but really already need not be identical. E.g. by a chemical reaction there originates a new compound, by the physical reaction the body is cooled or rewarmed and by the mechanical reaction there appears just a small crack.

As far as this process is applied on the hydration processes, then let us have for the entrance condition for the system:

• hydration is conditioned by the presence of at least the cementing

material ( cement ) and water;

• the cementing material is progressively dissolved into water;

• from the dissolved mix of cementing material in water is reversely

created a new stage, i.e. crystalloid or a gel one.