1. Gypsum Plasters (CaSO4.2H2O)
• It is a naturally occurring mineral
• It is the raw material for a no. of cementing materials such as
plaster of Paris, keenes plaster & estrich plaster
• On heating, Gypsum undergoes partial or complete dehydration
to give a series of products
150°C 600°C 800°C
CaSO4.2H2O → CaSO4.1/2 H2O → CaSO4 ↔ CaO + SO3
Hemihydrate Anhydrite
1

2. Plaster of Paris
• PoP is formulated as the hemihydrate (CaSO4.1/2H2O) but
commercial plaster is a mixture of the hemihydrate,
anhydrite & unchanged gypsum
• It is manufactured by calcining Gypsum at 150°C followed
by grinding the product to a fine powder
• It forms a plastic mass on mixing with water & sets quickly
with slight expansion
• Hardening is due to hydration of hemihydrate & anhydrite
to gypsum
• Uses- for making accurate plaster casting moulds, indoor
wall plastering
2

3. Keene’s plaster & Estrich plaster
Keene’s plaster is the anhydrite which is less
soluble in water as compared to the
hemihydrate & sets slowly
– Zinc sulphite, potassium sulphite, alum, sod.
Carbonate are used to quicken the setting process
– USES- for plastering exterior walls and in flooring
Estrich Plaster- It is obtained by heating gypsum
above 800°C. It sets and hardens very slowly
3

4. Cement
 Cement is a lime based product exhibiting adhesive &
cohesive properties
 It is used for binding together coarse aggregates such as
bricks, building blocks and stones
 Portland cement is the most commonly used cement in
the construction industry
 In 1824, Joseph Aspdin from Leeds (UK) coined
"Portland" cement because it produced a concrete that
resembled the color of the natural limestone quarried
(extracted) on the Isle of Portland (US)
4

5. Manufacturing of Portland cement
Manufactured from a mixture of calcareous
materials rich in lime (limestone) and argillaceous
materials rich in silica and alumina (clay)
Three distinct operations
Mixing of raw materials- Dry or wet conditions
Burning
Grinding
The chemical reaction involves the combination of basic
oxide (CaO) derived from lime stone with acidic oxides of
Aluminium, ferric oxide, and silica (from clay) to form Ca-
silicates, aluminates, aluminosilicates etc.
5

6. 6
Rich in silica & alumina
1400-1500°C

7. 7
1400-1500°C

8. 8

9. Chemical composition of cement
• Expressed in terms of the Oxides of Ca, Si, Al, Fe
as it is a mixture of many compounds
• Oxide constituents exist in the form of 4 major
phases-
• Dicalcium silicate, 2CaO.SiO2 (C2S)
• Tricalcium silicate, 3CaO.SiO2 (C3S)
• Tricalcium aluminate, 3CaO.Al2O3 (C3A)
• Tetracalcium aluminoferrite, 4CaO.Al2O3.Fe2O3 (C4AF)
• Free oxides CaO, MgO, Na2O, K2O, TiO2, SO3, H2O, CO2 constitute
the remaining 10%
90%
by weight
9

10. Chemical composition of cement
 As per BIS requirement
• The ratio of percentage of alumina to that of iron
oxide should not be less than 0.66
• Ratio of percentage of lime to those of alumina,
iron oxide and silica (lime saturation factor, LSF)-
should not be less than 0.66 & greater than 1.02
10

11. Setting & Hardening of Cement
• On mixing with half its wt of water (gauging), it forms a plastic
pasty mass which gradually looses its plasticity & ultimately
becomes hard
Setting process occurs in 2 stages
• Initial Setting- recognized based on the ability of a weighed
needle to penetrate the mass to a certain depth (5mm)
under a set of prescribed conditions
• Initial setting time depends on the quantity of water as well as
temp.
• Usually 45 mins for Portland cement (sufficient time for mixing,
transportation & placing between aggregates during construction)
• Final Setting-Occurs over a few hours (10 h for Portland)
11

12. Hardening of Cement
• It is a slow process
• Takes a few days during which crystallization
occurs & the strength of cement aggregate
increases
12

13. Hydration & hydrolysis reactions
• Setting & Hardening of Cement is due to the hydration &
hydrolysis reactions involving its constituents giving rise to
hydrated calc. silicate (CSH) in the form of poorly crystallized
gels called tobermolite gels
• Individual components of C2S, C3S, C3A & C4AF undergo
hydration releasing different amounts of heat of hydration
• Initial setting is attributed to C3S, C3A & C4AF which react
rapidly forming calcium hydroxide saturating the gauging
water.
• C3S is the active hydraulic component of Portland cement.
13

14. 14
Typical Oxide Composition of a General-Purpose Portland Cement
(Mindess and Young, 1981)

15. Types of Cement
Different types based on the composition, properties and uses.
• Natural Cement
(Portland cement)-prepared by calcining naturally occurring mixture of
calcareous and argillaceous materials.
• White Portland cement-
doesn’t contain iron oxide as it is prepared from the material free from
iron oxide
• Pozzolana cement
(Naturally occurring, volcanic origin) 45% of silica, 10-20%alumina, <10%
ferric oxide and oxides of Ca, Mg, Na, K & Ti
– Artificial Pozzolana-is made by burning clay or from fly ash (product of
combustion)
– Pozzolana cement is usually mixed with Portland cement
15

16. Types of Cement
• Water Proof Cement- Obtained by grinding portland cement with
calcium stearate.
• Slag Cement- highly resistant to sea water, obtained from blast
furnace slag (a by-product of iron and steel-making) mixed with
Ca(OH)2 & CaSO4
• Super heated cement & high alumina cement- highly resistant to
sea water but with a decreased rate of hardening
– manufactured from blast furnace slag
• Portland blast furnace cement- Portland+slag mixture
• Barium and Strontium cements- obtained by replacing Ca with
Barium or Strontium salts
– It is used for heavy concrete to serve as radiation shields for X-rays and
nuclear radiations 16

17. 17