When cement is fixed with water to a plastic mass called cement paste, hyderation reaction begin, resulting in the formation of gel and crystalline product. The interlocking crystals finally bind the innert particles of the aggricated into a compact rock like material. The process of solification comprises of :
1) Initial Setting
2) Final Setting
3) Hardening
Initial Setting: When cement is mixed with water, the hydrolysis process for setting do not take place for about an hr. So we can mold the plastic mixture in any form. But with time the jellification start further it is not distrubuted until it attains certain stiffness.
Final Setting: After few hrs. of mixing the mixture attains such a stiffness that it cannot be molded further.
Harding: On further hydraulics it increases its strength. The hardening process continuous till it kept moist and may continue for year. The reaction in the whole process are given bellow…..
At first, in one day. Hydration of tricalcium aliminate and tetracalcium alimino ferrite takes place
3CaO.Al2O3 + 6H2O ---> 3CaO.Al2O3.6H2O 6 Heat
4CaO.Al2O3.Fe2O3 + 7H2O ---> 3CaO.Al2O.6H2O + CaO + Fe2O3.H2O + Heat
In 24hrs the hydration of tricalcium silicate start and completed in 7 days.
2[3CaO.SiO2] + 6H2O ---> 3CaO.2SiO2.3H2O + 3Ca (OH)2 + Heat
The aluminate start crystallizing and decalcium silicates gets hydrated In 7-28 days. Even hydration of tricalcium silicate also complated.
