This document discusses the composition and hydration process of ordinary Portland cement. It begins by outlining the major components of cement and the physical and chemical processes involved in hydration. The key points are: - Cement is produced by burning limestone, clay, and other materials at high temperatures, forming clinker which is then ground with gypsum. - The main compounds in cement are tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. - Hydration involves physical and chemical changes as the cement sets and hardens over time. Hydration produces heat and results in a solid material. - Gy

1. GENERAL OUTLINE
 Cement and its components.
 Physical and chemical processes
during hydration.

2. CEMENT
 It is produced by burning calcium carbonate
found in lime stone and silica, alumina and
iron oxide found in clay or shale at 1400 °C.
 The material which is formed by burning is
partially fused to form clinker.
 Clinker is cooled and grounded to fine powder
with some Gypsum resulting in the formation of
Ordinary Portland Cement.

3. OXIDE COMPOSITION OF CEMENT
Oxide Content (in %)
CaO 60 - 67
SiO2 17 - 25
Al2O3 3 - 8
Fe2O3 0.5 - 6
MgO 0.1 - 4
Alkalies (NaO, KaO) 0.2 - 0.3
SO3 1 - 3

4. COMPOUND COMPOSITION
Main compound composition in OPC
Name Of Compound Oxide Composition
Tricalcium Silicate (C3S) 3CaOSiO2
Dicalcium Silicate (C2S) 2CaOSiO2
Tricalcium Aluminate (C3A) 3CaOAl2O3
Tetracalcium Alumino Ferrite (C3AF) 4CaOAl2O3Fe2O3

5. HEAT OF HYDRATION
Compound Heat Of Hydration (Joules
/Kg)
C3S 502
C2S 260
C3A 867
C3AF 419

6. HYDRATION: PHYSICAL CHANGE
Cement (Powder Form + H2O)
Paste (Plastic)
Dormant Period
Solid State
10 Hours
Further Solidification Take Place Become Fully Solid
Final Setting (28 Days)
Stiffen
Hardening
Rigid Solid

7. PHYSIOCHEMICAL CHANGES
 Y-axis shows amount.
 X-axis shows the time or age after just mixing the water.
 C3A will react fast and give the impression which is known
as “Flash Set”.
 It mean C3A reacts and stops. Elevate the reaction of all
other material.

8. In order to control the settling process, we
have to add some amount of Gypsum.
Gypsum is calcium sulphate. This have high
affinity of C3A.
C3A + Gypsum Calcium Sulphur Aluminate
(Ettringite)

9. WHAT IS ETTRINGITE
 It is a rod like crystals form in the early stages of reaction.
 They are gradually replaced by monosulphate because
the ratio available of alumina to sulphate increases with
cement hydration and C3A is contained inside cement
grains with no initial access to water. Continued hydration
releases Alumina and proportion of Ettringite decreases as
that of monosulphate increases.

10. CHEMICAL REACTION
2C3S + 6H C3S2H2 + 3CH
(Tricalcium Silicate) (Water) (C-S-H Gel) (Calcium
Hydroxide)
2C2S + 4H C3S2H2 + CH
(Dicalcium Silicate)
C3S is responsible for giving early strength.
C2S is responsible for giving long term
strength.

11. HEAT EVOLUTION CURVE
It give the rate at which mineral are reacting by monitoring the rate at which heat is
evolved.
 There are three characteristic peaks for ordinary Portland cement. The initial heat burst
corresponds to the instantaneous high rate of heat evolved when cement is brought into
contact with water. This is due to the heat of wetting (Heat of wetting = Surface energy –
Energy required for interface creation). Hydration of C3S and C3A also contribute to this
peak.
 The initial burst is followed by a slowdown of the heat evolution rate. The rate does not
become negative or zero at any stage, implying that although slowly, the reactions do
continue. This is termed as the ‘dormant’ or the ‘induction’ period. This period is followed
by the main peak of cement hydration, which is associated with the rapid dissolution of
C3S to form CSH and CH, and formation of ettringite (AFt) from C3A.
 A slowdown of the hydration process beyond the main peak leads to lower rates of heat

12. FORMATION OF C-S-H GEL

13. THANK YOU