Pozzolana Portland cement is mainly used in hydraulic construction.
It has no cementing or binding properties but as a microscopically grounded, it reacts with calcium hydroxide to form compounds with cement properties.
Here we will learn about Portland pozzolana cement, types of Portland pozzolana cement & much more.
Introduction to Portland pozzolana cement:
The Pozzolana component should be within 10 to 25 %, the combination of Pozolana component and OPC should be very intensive.
Fineness should not exceed 5% residue through a 90-μm sieve.
For the manufacture of PPC, pozzolana materials such as diatomaceous earth, opaline shales, tuffs, volcanic ash, pumice stone, fly ash are used.
Properties of Portland Pozzolana Cement:
- Initial setting time = 30 min (minimum).
- Final setting time = 600 min (maximum).
- At three days 13MPa (minimum).
- At 7 days 22 MPa (minimum).
- In 28 days 33 MPa (minimum).
- Drying shrinkage should not be greater than 0.15%.
- Fineness should not be lower than 300 m2/kg.
- The initial strength of the PPC is very low, but the final strength is equal to the 28-day strength of the OPC.
- PPC has a lower rate of strength development than OPC.
Types of Pozzolana Portland cement:
Fly ash, silica fume, rice husk, blast furnace slag.
Burnt clay, pumicite, diatomaceous Earth.
Manufacture Process of portland pozzolana cement:
- The primary raw materials used for manufacturing this cement are limestone and clay.
- Rocks are loaded into trucks and transported to crushers, where they’re crushed and turned into fine particles.
- Fine particles of clay and limestone are fed into air-swept ball mills in the desired proportions as required and are mixed very well before being sent to silos for storage.
- This mixture is then pre-heated to 800–1000 c where calculations from CACO3 to CaO.
- The preheated mixture is sent to the kiln, where the mixture is heated to 1450C in a rotary kiln.
- The modules formed by the burning process are called clinkers.
- This clinker is now blended with gypsum and pozzolana materials within the required proportions and thus PPC is obtained.
Advantages of Portland Pozzolana Cement:
- It is an environmentally friendly cement because the materials used in construction are made from natural recycled waste.
- It is very good cement so is very good when it is used for plastering works.
- Pozolana has silica content that makes it cheaper and therefore reduces the cost of cement.
- Pozolana cement has a very good resistance against sulfate attack hence it is used in hydraulic structures, marine structures, seashore structures, dam structures, etc.
- PPC is used in pre-stressed and post-stressed concrete members.
- This makes it environmentally friendly by reducing carbon monoxide emissions from concrete.
- Since pozzolana material is very fine, it can fill the gaps between reinforcement and aggregation, thus reducing shrinkage, honeycomb formation and bleeding, thereby increasing the strength and durability of the concrete.
Disadvantages of Portland Pozzolana Cement:
- The initial strength is low, which affects the de-shattering of the initial support.
- Since it contains more fine material, it is difficult to handle the concrete.
- The OPC setting time is less as compare to PPC.
- Reduction in alkalinity & corrosion resistance of steel reinforcement
- As the strength of this solid gain gradually, the curing process is very important. Any errors in this can cause stability problems.
Uses of Portland Pozzolana Cement:
- PPC is used in hydraulic constructions, marine constructions, seashore constructions, dam constructions, and so on.
- It is used in pre-stressed and post-tensioned concrete members.
- Additionally, used in masonry mortars and plastering.
- As it gives a better surface finish, used in decorative and art structures.
- It is used in the manufacture of precast sewage pipes.
- Also, used under harsh concreting conditions.
Pozzolana is a very old building material that was also used in Roman times.
Portland Pozzolana cement is a type of low heat cement because it produces much less heat of hydration, it has better resistance to an aggressive water attack.
This reduces the leaching of calcium hydroxide when used in hydraulic constructions.