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In common people, cement milk means a liquid plastic mass consisting of cement and water.
There is an opinion that when pouring foundations into the ground, concreting sites or using leaky formwork without appropriate films - cement the milk can partially go into the ground or through the cracks in the formwork, as a result of which the strength of the finished concrete structure decreases due to the loss binder.
I would like to analyze these moments in the article, dwell on real facts and tell about misconceptions. And let's start with a chemical like cement.
Cement is an artificial binder in the form of a powder, which, when interacting with water, forms a plastic composition, after a while, turns into an artificial cement stone. Its interaction (reaction) with water is scientifically called hydration of cement.
How does hardening come
Upon contact with water, a cement particle already from the first minutes begins to form needle-shaped crystals, which adhere to crystals of neighboring particles.
After 12 hours, the crystals fill the entire volume between the aggregate (sand, screenings, crushed stone) of the concrete structures, representing a monolithic fine-porous material, which is commonly called a cement stone.
The reaction rate is closely related to the ambient temperature; the higher the temperature, the faster the reaction proceeds, but it has been established that at temperatures above 30 ° C the strength of the bonds is lost due to the evaporation of water and its deficiency for the reaction (Therefore, in the heat, the master soaks the tile or brick, and when joining concrete sections, the cold seam is abundantly spilled water). At the same time, despite the recommended proportions (60-70% of water), only 40% of water in units of mass is required for the reaction of cement, the remaining excess water remains in the pores of the stone until it evaporates.
Reaction of cement and water
The initial stage of kneading is wrapping the aggregate with cement glue:
In the course of the reaction, the reacted water and cement grain are inseparable - this mixture is popularly called as "cement milk".
During the kneading process, cement glue (cement laitance) envelops the aggregate (sand, screenings) and due to formed bonds cannot be separated from him, respectively, to break off and go into the ground - the task for him is not by forces. Due to spatial bonds, crystallized cement is so strongly adhered to a particle of sand (crushed stone) that even through a gap in the formwork it does not go anywhere, - the binder will always be around placeholder.
Only free (excess) water that remains unused in the reaction can go into the ground or through a crack, which we actually observe as a displaced liquid with a film formed on top of the laid concrete.
Have you seen some of the spilled concrete falling to the ground or sand? Have you tried to break this cake? If not, then I will say that after hardening it has the colossal strength inherent in concrete. This is because the cement milk did not go anywhere at all.
Have you encountered drilling foundations in the ground? The task is not easy! This proves with a practical example that cement milk, so often mentioned in various forums, does not go anywhere.
The concrete is poured into the formwork, previously covered with a film, for only one purpose - to create a greenhouse effect, to prevent the water from evaporating, which in turn should react with the maximum amount of cement grains. And when concreting foundations in the ground, measures are taken that protect the earth from falling into a trench with in order to avoid mixing of soil and concrete, but not in any way to prevent leakage of cement adhesive ("milk")!
It is important to note that the behavior and properties of the cement glue described in the article correspond to the correct proportions of the components during mixing. With the correct ratio, the necessary plasticity of the mixture is achieved, which an experienced builder can easily assess by taking a certain amount of concrete on a shovel or trowel (trowel). Thus, in the field, foremen approximately understand the parameters of the "cone settlement", i.e. mobility and workability of the mixture.
Of course, if you plump 2 buckets of water per 1 bucket of cement, then there can be no question of the quality of the cement glue, and, accordingly, the cement stone.
That's all, I think, in the article I answered the question! I hope you liked the material.
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