Portland Pozzolana Cement – Advantages, Disadvantages & Uses


What Is Portland Pozzolana Cement?

There are various types of cement available in the market. Each one of them has a different use and consists of different elements in it and the properties of each one of them are different. Portland pozzolana cement is one of them.

Portland pozzolana cement, commonly abbreviated as PPC, is a type of cement that is manufactured by grinding Portland cement clinker and pozzolana or by uniformly blending fine pozzolana and Portland cement.

Puzzolana, added in the Portland cement may be burnt clay, shale, or fly ash. Anyone out of these can be used as puzzolana. But fly ash is mostly preferred for this. An approximate quantity of 10 % to 35% of fly ash by mass of Portland puzzolana cement is added to the mixture to form PPC.

Puzzolanas such as burnt clay, shale, or fly ash alone do not possess any cementing value itself but when they are combined with Portland cement, it produces a stable lime-puzzolana compound which has definite cementitious properties.

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It is also resistant to chemical attack, making it suitable to use for construction where there is a presence of moisture or for marine work.

Composition

The chemical composition of Portland pozzolana cement is as follows:

  • Tricalcium silicate = 7 % by weight.
  • Tetracalcium Aluminoferrite = 5 % by weight
  • Belite or dicalcium silicate = 11 % by weight
  • Alite or tricalcium silicate = 25 % by weight
  • Sodium oxide = 2 % by weight
  • Potassium oxide = 2 % by weight
  • Gypsum = 5 % by weight
  • Puzzolanic Ash or fly ash = 45 % by weight

This is the approximate quantity of elements in PPC. It may vary according to the properties of cement required on-site.

Manufacturing Process

The process of manufacturing Portland pozzolana cement is as follows:

1. Fine particles of clay and limestone are fed into the ball mills in the required amount of quantity and specified proportion.

2. The particles of clay and limestone are thoroughly mixed. Once they are mixed, they are sent to silos for storage.

3. The mixture is pre-heated at a degree of around 800 degree Celsius to 1000 degree Celsius where calcination of CACO3 to CaO take place.

4. The mixture which is preheated is sent to the kiln. In the rotary kiln, the preheated mixture is heated at a temperature of 1450 degree Celsius. This process of heating forms some modules, known as clinker. The clinker obtained as a product by burning is cooled down using a rotary cooler.

5. When the clinker is cooled down, it is mixed with gypsum and puzzolanic materials like fly ash, in a required proportion.

6. Thus, Portland puzzolana cement is formed.

Properties Of Portland Pozzolana Cement

The properties of Portland pozzolana cement are as follows:

Initial & final setting time:

  • Initial setting time – 30 minutes (half an hour).
  • Final setting time – 600 minutes (10 hours).

4. The compressive strength is as follows:-

  • At 3 days 13Mpa ( minimum)
  • At 7 days 22Mpa (minimum)
  • At 28 days 33Mpa (minimum)

The given strengths are minimum at various periods.

4. The dry shrinkage of PPC should be a maximum of 0.15%.

5. The fineness of Portland pozzolana cement should not be lesser than 300 m2 per kg.

6. The strength development rate of PPC is relatively lesser as compared to OPC.

7. The initial strength of PPC is lesser but the final strength should be equal to the strength of OPC.

Advantages

The advantages of Portland pozzolana cement are as follows:

1. Calcium hydroxide which is a soluble compound is converted into an insoluble cemented ingredient. Due to this, the structure is formed impervious and prevents the entry of water.

2. It can be used for marine works due to its properties which help in preventing the entry of moisture.

3. As compared to ordinary Portland cement, the heat of hydration generated by Portland pozzolana cement is lower.

4. Prohibition of formation of microcracks in structure, resulting in maintaining the strength of the structure.

5. This cement is economical due to the replacement of ordinary Portland cement by puzzolanic products like fly ash.

Disadvantages

1. De-shuttering of formwork earlier may be dangerous as it takes more time to harden when compared with OPC.

2. Due to the alkalinity reduction, corrosion may occur in reinforcement steel bars.

3. It takes longer to set and mature when compared with ordinary Portland cement.

Uses

Portland puzzolana cement may be used for the following purposes:

  • Structures in water or hydraulic structures.
  • Bridge piers and dams.
  • Structures near sea shores.
  • Underground basement.
  • Canals and canal falls.

Also Read

Types Of Cement Used In Construction
How To Check The Quality Of Cement

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