“Cement is a cementations material having adhesive and cohesive properties to bond inert aggregates into a solid mass of adequate strength and durability.”
For making structural concrete hydraulic cements are used exclusively.
(It gains strength by hydration)
Water is needed for the chemical process (hydration) in which the cement power sets and hardens into one solid mass. Setting time of cement is varies under different atmospheric conditions.
Properties of Portland Cement
1) Portland cement was made first time in England in 1824.
2) Portland cement is finely powdered.
3) Its color is grayish material
4) It consists of calcium aluminum and silicate.
Manufacturing of Cement
Raw Material for Portland Cement
The common raw material from which cement is made are lime stone which provide CaO clay or shale which furnish Sio2 and Al2O3. These are ground, blended, fused to clinkers in a kiln and cooled.
Gypsum is added and the mixture is ground to the required fineness. The material is shipped in bulk or in bags containing 94 lb of cement.
Lime stone → Ca
Clay/shale → silicate
Al2O3 → aluminum
CaCO3 Co2 CaO Sio2 C2S CaO C2S + C3S CaO C3S + C2S
700-1000 C0 1200 C0 1300C0 1400C0
Properties of C2S and C3S
C2S → (Cao) 2 sio2
If we increase the amount of C2S in cement the setting time of cement will increase
C3S→ Cao) 3 sio2
If we increase the amount of C3S the early setting time of cement will be decrease
C3S control early setting time
Chemical Composition of Cement
Belite C2S → 10% – 30%
Alite C3S → 45% – 65 %
Aluminates C3A → 5% – 12%
Ferrite C4AF → 6% – 12%
Gypsum CaSo4 → 4% to control setting time
Alkalis Na2O → 0.2 %-0.7%
K2o → 0.5% – 1%
Gypsum CaSo4 decrease the setting time of cement.