what is Hydration of cement in English

 

Hydration of cement

When the water is added to cement, a chemical action starts which is exothermic in nature and produces a big amount of heat. This is often called hydration of cement and therefore the liberated heat has termed the heat of hydration.

The process of hydration isn't direct. Hydration of cement is quicker within the early periods and continues indefinitely at a slower rate. In a couple of month’s time, 85 to 90% of the cement hydrates and also the cement attains almost its full strength. The hydration still continues and cement grows stronger with time.

The process of hydration of cement may be explained as follows:

In a cement paste i.e. a radical mixture of cement and water, chemical change soon starts and after a lapse of it slow, the paste consists of hydrates of assorted compounds, collectively called gel, unhydrate cement, water and residue of the water-filled spaces within the fresh paste. These voids are called capillary pores. Hydration of cement is incredibly important.

The cementing gel consists of thin fibrous crystals which is porous in nature. These pores are called gel-pores. About 23% of water by mass of cement is required for reaction of cement with water and is understood as bound water.

About 15% of water by mass of cement is required to fill the gel-pores and is understood as gel-water. Thus, a complete of 38% of water by mass of cement is required for complete hydration of cement. during this discussion, it's assumed that the reaction takes place in a very sealed container.

The remaining water mixed with cement causes undesirable capillary cavities. If only 38% of water is added, the capillary cavities may be eliminated.

The products of hydration of cement are colloidal and since of this, during hydration, the expanse of solid-phase increased enormously. This absorbs an outsized amount of free water. If the water added is 38%, all the colloids aren't sufficiently saturated, which decreases the ratio of the paste.

This ends up in a lower hydration of cement because the gel is often formed only in water-filled space. this needs a minimum of fifty of water by mass of cement or in other words, a water-cement ratio in way over 0.5 is sufficient for hydration.

In actual conditions, the reaction doesn't occur in an exceedingly sealed container and with lower percentage of water, the concrete mix wouldn't be workable. a combination is workable if it may be easily mixed, placed and compacted at the desired place.

Usually about 50 to 60% of water by mass of cement is added to manufacture the concrete.

The rate of hydration of cement is mainly influenced by the following points

The temperature at which hydration takes place: At high temperatures the reaction is rapid. Only 10 to 15 minutes of hydration at higher temperature is corresponding to 10 to 12 hours of hydration at lower temperatures. it's for this reason that in cold weather, sometimes the aggregates are heated before they're used for creating concrete.

The fineness of cement: The finer the cement, the more rapid is that the reaction. because the hydration starts at the surface of the cement particles, the larger the available surface area, the more rapid is that the hydration. Finer cements have larger surface areas and thus the hydration is rapid. However, a awfully fine ground cement is at risk of air-set and deteriorates earlier.

The ingredients of cement: The reaction may be made rapid or slow by changing the properties of the ingredients of the cement.