Ordinary Cement use cases; Pros and Cons

Articles > Ordinary Cement use cases; Pros and Cons

OPC: Things we must know about Ordinary Portland Cement:

There are tens of types of cement, which are aimed at suiting different weather conditions. Some of the cement types are resistant to chemical attack, while others are resistant to those of water and moisture.  Some of the types are specially formulated to get extra hardness and strength. Among all these types of cement, the most common type is OPC. OPC, which is also known as Ordinary Cement is the most common cement all around the world. OPC stands for Ordinary Portland Cement. This is the most ordinary and common cement used all through the globe. However, in some cases, like the construction of underwater structures, construction is severe cold and hot regions, the use of OPC becomes insufficient. There are dozens of varieties of cement in the market, which meet the need of almost all conditions. Keeping in view the limitations and advantages of OPC cement, we started this discussion, which is as under:

Chemical Composition of OPC:

Portland Cement is made from Lime Stone and Shale. Lime Stone is a white-colored, soft, and fine-grained sedimentary rock, while Shale is fine-grained but black/grey colored rock. These two rocks are ground and mixed with each other to prepare Ordinary Portland Cement. The chemical composition of Portland cement is as under:

Compound

Formula

Shorthand form

% by weight

Tricalcium Aluminate

Ca3Al2O6

C3A

10 %

Tetracalcium Aluminoferrite

Ca4Al2Fe2O10

C4AF

8 %

Belite or Dicalcium Silicate

Ca2SiO5

C2S

20 %

Alite or Tricalcium Silicate

Ca3SiO4

C3S

55 %

Sodium Oxide

Na2O

N

 

2%

Potassium Oxide

K2O

K

Gypsum

CaSO4.2H2O

CSH2

5 %

 

Properties of Cement Compounds:
Each composition compound of the cement has its own properties and objective.

?  Tricalcium aluminate (Ca3Al2O6 ):
It has little strength contribution. During the early stage of hydration, it liberates a large amount of heat. But the presence of gypsum slows down the rate of heat production. It also makes the cement Sulfate resistant

?  Tricalcium Silicate (Ca4Al2Fe2O10  ):
The function of Tricalcium Silicate is to harden the structure by means of hydration. The initial setting of Portland cement largely depends on this compound.

?  Dicalcium Silicate (Ca2SiO5 ):
The function of Ca2SiO5 is to hydrate and harden the structure slowly. After one week the structure starts strengthening. This process of strengthening is dependent on pouring water for about 6 days.

?  Ferrite (M2+Fe2 3+O4):
M2+Fe2 3+O4 helps to reduce the melting temperature of the raw material in the kiln. It reduced the melting temperature from 3,000o F to 2,600o F. It hydrates rapidly, but does not contribute to the strength of the concrete/mortar structure.

Preparation of OPC mixture:

OPC mixture is prepared by mixing these compounds (OPC), with water and admixture. Mixing the material well is usable. After the preparation of the structure it is left for about 12-24 hours (depending on weather temperature and moisture in the air), then water is poured on the structure to further hydrate and harden the structure. Water is poured for 3 to 6 six-day.

Grades of OPC:

Grades are the measuring units of the compressive strength of the structure made up of cement concrete. Different level grades give different levels of strength. There are 3 grades of OPC, i.e. OPC 33 Grade, OPC 43 Grade, and OPC 53 Grade. At each grade, the concrete gives different levels of strength.

  1. Structure made of OPC 33 Grade can bear a load of a minimum of 330 kg/sq.cm.
  2. Structure made of OPC 43 Grade can bear a load of a minimum of 430 kg/sq.cm.
  3. Structure made of OPC 53 Grade can bear a load of a minimum of 530 kg/sq.cm.

The minimum age of the structure for attaining full strength is 28 days. After 28 days, the strength of the concrete does not increase further.

Advantages of OPC:

  1. Less costly than many other types of cement, like white cement, rapid hardening cement, hydrophobic cement, etc.
  2. It is sulfate resistance. It is used for moderate sulfate resistance.
  3. It generates low heat of hydration. The heat of hydration means the heat released when the water is added to Cement.
  4. The process of Hydration hardens the structure made up of OPC. The more water is poured on the surface of the cement, the more the structure will be hard and durable.
  5. It is used in all types of ordinary constructions.
  6. Easy to handle and set, if compared to the rest of the types of cement. Not a special type of skill is needed for setting it.
  7. The initial strength of this type of cement is higher than that of PPC.
  8. The curing period of OPC is less than that of the Portland Pozzolana Cement, hence recommended where curing cost prohibited.
  9. The initial setting time of this type of cement is faster than many other types like Portland Pozzolana Cement.

Disadvantages of OPC:

  1. OPC is not recommended for the construction of a mass structure, as it has a high heat of hydration if compared to PPC.
  2. The compressive strength of more than 53 grade is not recommended to be used for plastering because it develops the shrinkage cracks due to its high strength.
  3. Very few cement manufacturers are known to manufacture 33 grade of OPC. 33 grade means that the compressive strength of the cement after 28 days is 33N/mm2 when tested as per US Standards under standard conditions. This grade of cement is used for general construction work under normal environmental conditions.
  4. It is low sulfate resistant; it fails when the sulfate attack is higher.
  5. The durability of concrete structures made up of OPC is lesser than that of PPC.
  6. It is less resistant to aggressive chemical attacks, therefore, the structures of workshops and factories are not recommended to be built of OPC.
  7. The cohesive strength of the concrete made of OPC is weaker than other types of cement.
  8. OPC has a lower fineness and has higher permeability, thus being less durable.
  9. OPC has low workability; therefore admixtures are added to increase its workability.
  10. OPC is costlier than PPC and many other types of cement.

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