CHEMICAL ENGINEERING: CEMENT !!! Part I

By no means complicated , cement is simply a material to hold together materials !!! Technically speaking , Cement is the generic name of all those materials which initially have plastic flow , but when it is mixed with water or any other suitable liquid , forms a rigid - continuous mixture which solidifies on standing and when solidified has the capability to resist high compressive strengths .

The most common type of cement is PORTLAND CEMENT !!! Way back in 1824 , an Englishman named JOSEPH ASPDIN patented portland cement . He obtained it by the calcination of an argillaceous limestone . He named it PORTLAND as synonymous to a type of rock found at the Isle Of Portland , famous for it's strength . One to think that this was the start for mankind's construction glue :P is wrong , cause centuries ago Romans built the famous "Colosseum" using a cement like material called POZZOLANS !!! pretty impressive huh ;)

Basically , Cement can be summerised as a mixture of finely ground calcium silicates and aluminates of varying compositions , which decide the properties of that particular variety of cement . The main constituents of cement can be summed up into four varieties :
1) C₂S
2) C₃S
3) C₃A
4) C₄AF
Where ,
C = CaO
S = SiO₂
A = Al₂O₃
F = Fe₂O₃

Varying these % 's can lead to different types of Portland cements namely :-

A ) TYPE - I : REGULAR
   It has the following composition :
   55% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 2.8% MgO, 2.9% (SO₃), 1.0% Ignition loss,
   and 1.0% free CaO.
   It is used for general construction purposes . It gains it's full strength in 28 days .

B ) TYPE - II : MODIFIED
      It has the following composition :
   51% (C₃S), 24% (C₂S), 6% (C₃A), 11% (C₄AF), 2.9% MgO, 2.5% (SO₃), 0.8% Ignition loss,
   and 1.0% free CaO.
   The higher C₂S composition makes the cement moderately sulfate resistant and also
   it has a moderate heat- of-hydration value .
   It is used specifically in places where the sulfur content in the soil is high .

C) TYPE - III : HIGH EARLY STRENGTH
      It has the following composition :
   57% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 3.0% MgO, 3.1% (SO₃), 0.9% Ignition loss,
   and 1.3% free CaO.
   It has the ability to attain the strength of Type - I cement in just 3 days , but due
   to the high % of C₃S and C₃A " together" can be devastating and can cause high
   values of Heat-of-Hydration , thus long-time strength has to be sacrificed . Thus , it
   is useless for massive construction works .
   Used only for emergency  constructions where we do not have much time to wait
   for it to stand to gain strength .

  D) TYPE - IV : LOW HEAT
   It has the following composition :
   28% (C₃S), 49% (C₂S), 4% (C₃A), 12% (C₄AF), 1.8% MgO, 1.9% (SO₃), 0.9% Ignition loss,
   and 0.8% free CaO.
   Notice the lower % of C₃S and C₃A , which are the major contributors of heat-of-
   hydration . Consequently , the % of C₄AF and other aggregates have to be increased.
   Only drawback is that the time required to gain full strength is high when compared
   to normal cement .
   It is used for massive construction works like dams , etc .

E ) TYPE - V : SULFATE RESISTANT
     It has the following composition :
     38% (C₃S), 43% (C₂S), 4% (C₃A), 9% (C₄AF), 1.9% MgO, 1.8% (SO₃), 0.9% Ignition loss,
   and 0.8% free CaO.
   This kind of cement has the highest % composition of C₂S , thus making it highly
   sulfate resistant .
   Used in places nearby to the sea , as it resists sea contact very well .