What is hydration of cement and heat of hydration,Hydration of cement in concrete,in this article we know about what is hydration of cement and heat of hydration and hydration of cement in concrete and heat of hydration for cement. We know that hydration of cement is exothermic process, when cement is mixed with water its liberates more amount of heat energy with hydrate product which letter get hydrated and harder and thicker.
You know that concrete is composite material which are made of two major component” filler “and “binder“. The Binder component is paste of cement mix with water which is act as “glues “for filler component to held together. So major constituents used for Binder is water and cement and filler component is fine aggregate and coarse aggregate. Let us discuss about Portland cement.
What is portland cement and its constituent
Ordinary Portland cement is nature of compound made by burning of limestone and clay together at very high temperature ranging between 1400 to 1600 ℃. Production of Portland cement which consists of various steps in first step limestone and clay Shale mix together and going for Quarrying and crushing process.
And their mixture is heated in kiln and product which is obtained is known as marble size pieces known as clinker and now some amount of gypsum material is added with clinker and again it is crushing and grounded in ball mill to make heterogeneous mixture of powder of OPC cement.
You should also visits:-
What is hydration process of concrete
The hardening of concrete and their strength through the process of hydration. Concrete is mix of cement sand aggregate and water.
In which paste of cement and water act as Binder component and sand and aggregate are act as filler component. Hydration is a chemical process and reaction in which the major component of concrete its cement form chemical bond when react with water molecules and becomes hydrates and form hydrate product.
And aggregate and sand are chemically inert solid bodies are held Together by paste of cement.
Cement + water = paste of cement +energy
Reaction of cement with water is exothermic process liberates high amounts of energy.
Five major component of cement
1) tricalcium silicate 3CaO.SiO2 and it is represented by C3S and their weight percentage is about 50%
2) dicalcium silicate 2CaO.SiO2 and it is represented by C2S and their weight percentage is about 25%
3) tricalcium aluminate 3CaO.Al2O3 and it is represented by C3A and their weight percentage is about 10%
4) tetracalcium aluminoferrite (4CaO.Al2O3.Fe2O3) and it is represented by C4AlF and their weight percentage is about 10%
5) Gypsum CaSO4.2H2O and their weight percentage is about 5%
Role and importance of water in cement hydration
Concrete is prepared by mixing cement water sand and aggregate together to make workable paste. When water is added to cement in concrete each of the major component of cement undergoes hydration reaction and contribute to the final product that is known as hydrates product. The water need to be pure in order to prevent side reaction with some Alkalies present in polluted water. Polluted water weaken the strength of concrete and role of water is important because the water cement ratio is the most critical factor in the production of perfect concrete.
Little of water increase concrete strength and less workability and vice versa more water decrease the concrete strength and more workability so water and cement ratio in very important and adequate amount of water is added to concrete mix for high strength and workability.
Product formed during cement hydration process
When tricalcium silicate ,dicalcium silicate ,tricalcium aluminate, tetracalcium aluminoferrite and Gypsum react with water it undergoes exothermic reaction and formed product of hydrate of calcium silicate and Calcium Hydroxide with the Liberation of higher amount of energy.
1) C3S + H2O = hydrates of calcium silicate + calcium hydroxide
2) C2S +H2O = hydrates of calcium silicate + calcium hydroxide
3) C3A H2O = hydrates of calcium aluminate + calcium hydroxide
4) C4AlFe + H2O = hydrates of calcium aluminate + calcium hydroxide
Out of four of major product formed during hydration of cement only hydrates of calcium silicate contribute and responsible for increase the strength and for hardening of concrete.
Hydrate of tri calcium silicate is responsible for early strength and most of early 7 days. And hydrates of dicalcium silicate which react more slowly and contribute only to the strength of concrete at later time.
Hydration reaction of tricalcium silicate with water
Tricalcium silicate + water = hydrates of tricalcium silicate +calcium hydroxide +heat
2Ca3SiO5 + 7H2O = 3CaO.2SiO2.4H2O + 3Ca(OH)2 + 173.6 KJ
After adding of water in cement its major component tricalcium silicate rapidly react to form hydrates of tricalcium silicate and release calcium Ca+2 and Hydroxide ion (OH_) and large amount of heat. The pH quickly Rises to over 12 because of release of Hydroxide ion and this initial stage of hydrolysis gradually Slow Down quickly after it starts resulting in decrease in heat evolved and the reaction slowly continues producing calcium ion and Hydroxide Ion until the system becomes saturated.
Production of hydrate of tricalcium silicate and calcium hydroxide crystal make seed upon and grow more thicker and making it more difficult for water molecules to reach unhydrated tri calcium silicates.
Hydration reaction of dicalcium silicate with water
Dicalcium silicate when mix with water react slowly and contributes only to the strength of concrete at later times.dicalcium silicate also affect the strength of concrete more slowly and the heat in the exothermic process is released less than released in reaction of water with tricalcium silicate.
Dicalcium silicate + water = hydrate of calcium silicate + calcium hydroxide + heat
2Ca2SiO4 + 5H2O = 3CaO.2SiO2.4H2O + Ca(OH)2 + 58.6 KJ
Note:- other major component of Portland cement like tricalcium aluminate ,Tetra calcium aluminoferrite and Gypsum also react with water because of complex reaction do not contribute significantly to increase the strength of concrete so their reaction is not discuss in this article.
Heat of hydration of cement in concrete
When Cement in concrete is mix with water heat is evolved due to the breaking and making of chemical bond during hydration process this is known as heat of hydration it is actually exodothermic process. Heat of hydration of cement generally divided into five stage
1) pre – induction ( zone 1)
2) dormant induction (zone 2)
3) acceleration (zone 3)
4) deacceleration (zone 4)
5) steady stage ( zone 5)
1) pre induction ( zone 1) :- in Pre induction stage hydrolysis of cement compound occurs rapidly with rising of temperature increased to several degree. It’s take time for 0 to 15 minute.
2) dormant phase ( zone 2) :- it is known as dormancy period of heat of hydration in which the evolution of heat gradually slow down and dramatically in this stage. And the dormancy period of concrete can last from 1 to 3 hours. during in this period concrete is in plastic stage which allows the concrete to transport and placed without any major difficulty and it is easy to transfer it at job site that is ready mix concrete.
3) Acceleration phase ( zone 3) :- in this stage concrete start to Harden and the heat evolution increases due to primary hydrolysis of tricalcium silicate and dicalcium silicate with water and it is lasting upto 36 hours.
4) deaccelreation (zone 4) :- in this phase hydrolysis of tricalcium silicate and dicalcium silicate is gradually decrease and release less amount of heat energy and hydrate product. It will be undergoing and last for 3 to 5 days.
5) steady stage ( zone 5) :- in this phage there is slow formation of hydrate products occurs and continue as long as water and unhydrated silicates are present. And it will be undergoing and last for 6 to 10 days.