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What is pozzolana and why is it used in cement?

Pozzolana is an ingredient in cement

One of the core ingredients of cement is pozzolana, or pozzolanic ash. It is a natural material that comes from volcanic ash and it contains silica, which gives pozzolana cementitious properties. This means that pozzolana can react with certain elements to form a hard, binding material.

Volcanic ash was first used by the ancient Greeks as a building material as early as 500 BC. However, it was the Romans that really pioneered the use of pozzolana as a binding agent to hold stones together. This allowed the Romans to build tall buildings and underwater structures, some of which still stand today, more than 2100 years later.

The substance is widely used in the manufacture of cement, including at LafargeHolcim Tanzania’s Tembo cement facility in Mbeya. Pozzolana has a number of physical properties that make it perfectly suited to creating cement, which we will outline below:

Properties of pozzolana

Pozzolana is used in cement for a number of reasons. When water is added to cement, it produces lime, or calcium hydroxide. Pozzolana reacts with this lime to form a strong bond with the other materials. On its own, lime does not contribute to the strength of concrete. The reaction between these two elements produces calcium silicate hydrate which is a strong bonding material.

By reacting with lime, pozzolana increases the strength of concrete. It also makes the concrete more dense, which is good for a structure’s durability. This reaction also decreases the efflorescence of concrete – the migration of salts to the surface of the concrete. Pozzolana is an important material for numerous reasons

Pozzolana can include the following elements:

  • Fly ash
  • Slag
  • Silica fume
  • Metakaolin
  • Vitrified calcium alumino-silicate

Of these elements, fly ash is the least reactive to lime and silica fume is the most reactive. This reaction determines the curing time of the concrete. These elements help to give cement it’s fine, powdery texture which is what makes it a good bonding agent when added to water and aggregates.

Other uses of pozzolana

Pozzolanic substances have a range of uses in construction, including the following:

  • Used in the manufacture of Portland Pozzolana cement (PPC).
  • Used as a soil-stabilisation material.
  • Used as a filler mineral in asphalt roads, helping to fill voids in the tar.
  • Used as a component in geopolymers, such as ceramics.
  • Used in roller-compacted concrete dams.
  • Used in the manufacture of concrete bricks.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 

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LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

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At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

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