Скачать или смотреть Concrete Technology Hindi| How concrete works| How cement Harden| CSH gel formation| Ettringite form

This video gives a basic idea regarding modern concrete and its mechanism.

Concrete..!
What is concrete? Why is concrete? What hardens concrete? What are the compositions of cement and do they look like? What are hydrates, and how do they look like and how do they form? What are the roles of aggregates in concrete? Why aggregates are called silent killer of concrete?
Welcome friends In this episode I have brought for you the mechanism of How concrete works.
Concrete mix design is a scientific approach of choosing an economic proportion from available materials to get desired workability, durability, strength, cohesiveness etc.
Human beings are using concrete for last 1000s of years, but their ingredients may vary as per the availability of material resource in their respective region.
Today we make concrete of primary materials like cement, water, coarse aggregates and fine aggregates.
Human being can make amorphous powder from hard rock with the help of some machineries in few hours, but naturally it takes more than 10 thousands of years to make hard rock from powder.
Each ingredient in concrete has some specific role to play, Cement is a magical product which converts mobile concrete into an artificial rock in just few hours, which can also be moulded into different shape & sizes during its plastic state.
Concrete gets hard in few hours but hydration continuous for week or even years after placement.
Coarse aggregates are used as the replacement of cement for making it cost effective but in most of the cases CA is mainly used for the purpose of providing strength because in normal grade concrete the high w/c ratio makes the mortar weak which doesn’t give desired strength to the concrete; In general, coarse aggregates are also used reducing the thermal cracks, shrinkage.
Fine aggregates are nothing but the finer version of CA and it is used as the filler to fill the gap between CA.
Water is used for workability and hydration process.
The more you add water to the concrete, more the workability you will get but this added workability comes at a cost to the concrete strength. The most important thing you get from mix design is how much water is to use for the mix.


Cement and water forms glue for binding the non-binding materials in concrete. Cement is composed of oxides because the earth’s crust is mainly composed of 8 & 7 are associated with oxygen to form oxides. A number of tests had been carried out to check whether which oxides reacts better to give cementitious property.
In 2 alkali-oxides of Na and K, their ions do not precipitate they do not become rigid hence they are found to be unable to hold the cement grains together which contradicts the property of hard concrete hence can’t be used for making the hard concrete.
Iron oxide and magnesium oxide have found to be redundant part as they have very low mobility in the alkali solution of concrete. They don’t harm the solution but also they don’t move from its mean position means they don’t contribute much in hardening the structure. MgO doesn’t even fill the space between the grains.
So finally we have end up with these three oxides which gives cementitious properties on reacting with water. We make cement using CaO and SiO because cement could have also been made from CaO and Alumina which would give better result due to less emission of carbon dioxide but unfortunately the raw material for alumina is bauxite which is also used for the production of aluminium which makes it expensive material for making concrete. Hence cement is essentially made up of CaO and SiO which is also known as lime and clay.
Cement chemistry,
When lime & clay get mix together, they don’t react with water but when you provide heat of 1450 degree C, the oxides react to become compound. This compounds have been given scientific name called nomenclature.
A picture of micro structure of cement grains which show C3s, C2S, C3A.
When water is added to cement the cement grains float in water, this is the plastic state of concrete. The cement grains keep dissolving which reduces the grain size & thus their ions of Ca, Si, Al, OH, ooze out of the grain. These ions react with water (H2O) and form needles and crystals which are actually the precipitates which makes rigid structure around the cement grains. Red colour rigid part is called hydrates. This reaction is popularly known as C-S-H gel formation. The volume of rigid and crystals increases and when these coatings of needles and crystals impinge, holds the other cement grains and stop the cement grain movement, setting occurs, Thus making the concrete hard.
Basic idea of hydration we have seen where mobile concrete turns to an artificial hard rock in just few hours. Concrete is very vast topic to understand.
In my next video we will be exploring some other hidden secrets of concrete. Till then take care.