PPC cement, also known as Portland Pozzolana cement, is a type of integrated cement that is produced by blending pozzolanic materials with OPC cement in a specific ratio. This results in a cement that possesses unique properties and characteristics.
The manufacturing process of PPC cement involves the use of materials such as fly ash, volcanic ash, and calcined clay, which are added to the OPC cement in precise proportions. The combination of these materials leads to the formation of a high-quality cement that is known for its durability and strength.
PPC cement offers several advantages, including enhanced workability, reduced heat of hydration, and resistance to sulfate and chloride attacks. It is also more environmentally friendly than other types of cement, as it makes use of waste materials that would otherwise be discarded.
Despite its numerous advantages, PPC cement does have some disadvantages as well. It tends to have a slower rate of strength development compared to other types of cement, and it may require longer curing times. Additionally, the use of pozzolanic materials can sometimes result in a lower early strength of the cement.
Overall, Portland Pozzolana cement is a versatile and widely used type of cement that offers many benefits in terms of durability, sustainability, and resistance to certain types of damage. Its production and use are likely to continue to increase as more people become aware of its unique properties and advantages.
What is pozzolana or pozzolanic material?
Pozzolana is a type of volcanic powder that is commonly found in Italy near Mount Vesuvius. It is classified as a pozzolanic material, which can either be natural or artificial and contains silica and aluminous in a reactive form. Initially, pozzolanic materials do not possess any cementitious properties, but when mixed with water, moisture, or lime, they undergo a chemical reaction with calcium hydroxide. This reaction results in the formation of compounds that possess cement-like properties.
Pozzolana is known for its ability to enhance the durability and strength of cement when used as an additive. It has been used since ancient Roman times as a key component in the construction of various structures, such as aqueducts, bridges, and buildings. Pozzolana has become increasingly popular in modern times due to its cost-effectiveness, environmental sustainability, and superior performance compared to other cement additives.
The use of pozzolana has also been linked to the reduction of carbon emissions in the construction industry. Its production process requires less energy and emits fewer greenhouse gases than traditional cement production methods. In addition, the use of pozzolana reduces the amount of cement required in construction projects, further reducing carbon emissions. These factors have made pozzolana a popular choice for sustainable construction projects around the world.
Fig 1: Use of PPC in marine structure.
Types of pozzolana materials :
1. Artificial pozzolana
These are four common materials used in construction and manufacturing processes. Fly ash is a byproduct of coal combustion and is often used in concrete production to improve its strength and durability. Silica fume, on the other hand, is a fine powder that is a byproduct of the production of silicon and ferrosilicon alloys. It is also used in concrete to increase its strength and reduce permeability.
Rice husk is the outer layer of rice grains and is often considered waste. However, it can be used as a source of fuel and energy, as well as a raw material in the production of various products such as insulation materials and biofuels. Additionally, rice husk ash can be used as a pozzolan in concrete, which improves its strength and reduces permeability.
Blast furnace slag is a byproduct of iron production and is often used in cement production as a replacement for Portland cement. It can also be used as a raw material in the production of aggregates and concrete. Blast furnace slag has many advantages over traditional cement, including higher strength, improved durability, and reduced environmental impact.
2. Natural pozzolana
Burnt clay, pumicite, and diatomaceous Earth are all types of natural materials with a variety of uses. Burnt clay, also known as terracotta, is a material made by heating clay in a kiln until it hardens. It is often used to make pottery and bricks. Pumicite, on the other hand, is a volcanic rock that has been fragmented into tiny pieces. It is often used as an abrasive in cleaning products and as an ingredient in lightweight concrete. Diatomaceous Earth, also known as diatomite, is a sedimentary rock that is composed of the fossilized remains of tiny aquatic organisms called diatoms. It has a variety of uses, including as a natural insecticide, a filtering agent in swimming pools and aquariums, and as a component in some types of cat litter.
Manufacture of Portland pozzolana cement
Cement manufacturing involves using limestone (CaCO2) and clay (SiO2, AI2O3, Fe2O3) as the primary raw materials. These rocks are transported in trucks and crushed into fine particles before being fed into air-swept ball mills in the desired proportions. The resulting mixture is thoroughly mixed before being sent to storage silos.
Next, the mixture is pre-heated to temperatures between 800-1000C, which leads to the calcination of CACO3 into CaO. The pre-heated mixture is then transferred into a kiln where it is heated to a temperature of 1450C in a rotary kiln. As a result of the burning process, clinker modules are formed. The clinker is then cooled using a rotary cooler.
To produce Portland Pozzolana Cement, the clinker is mixed with gypsum and pozzolana materials in the required proportion. This process results in the final product, which is ready for use.
Properties of Portland Pozzolana Cement
To ensure the quality of Portland Pozzolana Cement (PPC), several parameters need to be met. The initial setting time of the cement should not be less than 30 minutes, and the final setting time should not exceed 600 minutes. This ensures that the cement has enough time to set properly and achieve the desired strength.
The strength of the PPC is also a crucial parameter, and it should attain a minimum strength of 13 MPa at 3 days, 22 MPa at 7 days, and 33 MPa at 28 days. These values ensure that the cement is strong enough to withstand various forces and stresses that it may encounter during use.
Another essential factor to consider is the drying shrinkage of the cement. This should not exceed 0.15%, as excessive shrinkage can lead to cracking and other forms of damage to the structure.
The fineness of the cement is also critical, and it should not be less than 300 m2/kg. This ensures that the cement has a large surface area, allowing it to react more effectively with water and other components in the concrete mix.
It’s worth noting that PPC has lower initial strength compared to Ordinary Portland Cement (OPC). However, its final strength is equal to the 28-day strength of OPC. Additionally, PPC has a lower rate of development of strength than OPC, meaning that it takes longer for the cement to achieve its full strength potential.
Uses of Portland Pozzolana Cement
Reinforced concrete is a popular construction material that finds extensive use in hydraulic and marine structures, construction near the sea shore, and dam construction. Its superior strength and durability make it an ideal choice for such applications where the structure is exposed to the harsh environment of water and weathering.
Another advantage of reinforced concrete is its ability to be used in pre-stressed and post-tensioned concrete members. These structures are designed to handle high loads and require high strength and durability, which reinforced concrete can provide.
Apart from its structural applications, reinforced concrete is also widely used in masonry mortars and plastering. It is known for providing a better surface finish, making it suitable for decorative and art structures where aesthetics play an important role.
In the manufacture of precast sewage pipes, reinforced concrete is the material of choice due to its resistance to harsh chemicals and extreme conditions. It is also used in concrete structures that require exceptional durability and strength under harsh concreting conditions.
Overall, reinforced concrete is a versatile and reliable construction material that has found its place in various industries and applications due to its exceptional strength, durability, and resistance to harsh environments.
Advantages of Portland Pozzolana Cement
Pozzolana cement is a type of eco-friendly cement that is manufactured using natural recycled waste materials. This cement is very fine in texture, making it ideal for use in plastering works. Additionally, its main component, pozzolano, is composed of silica material, which makes it cost-effective and economical to use.
One of the most significant advantages of pozzolana cement is its excellent resistance to sulphate attack, making it ideal for use in hydraulic and marine structures, construction near the sea shore, dam construction, and other similar applications. It is also commonly used in pre-stressed and post-tensioned concrete members.
Moreover, pozzolana cement is considered environmentally friendly as it reduces the emission of carbon monoxide from the concrete. This feature makes it a popular choice in construction projects that prioritize sustainability and eco-friendliness.
Finally, the fine texture of pozzolana cement allows it to fill gaps between reinforcement and aggregate, reducing shrinkage, honeycomb formation, and bleeding. This feature, in turn, increases the strength and durability of the concrete, making it an attractive option for a wide range of construction projects.
Disadvantages of Portland Pozzolana Cement
The strength of PPC concrete initially obtained is relatively lower compared to other types of concrete, which can have an impact on the early de-shuttering of supports. This is due to the higher content of fine materials in the mix, making it more challenging to handle during construction. Additionally, when compared to Ordinary Portland Cement (OPC), PPC has a shorter setting time, which requires careful monitoring during the mixing and pouring process.
Another factor to consider is that the reduction in alkalinity in PPC can result in reduced resistance to corrosion of steel reinforcement. This means that special attention needs to be paid to the selection of materials and construction techniques to ensure the durability of the structure over time.
Finally, it’s essential to note that PPC concrete gains strength more slowly than other types of concrete, which makes the curing process critical for its long-term performance. Any errors in the curing process can lead to durability problems, emphasizing the importance of proper handling and maintenance during and after construction.