Pozzolana is a globally popular word and mostly used in construction industries nowadays. It is the most common construction material which is either natural or artificial.
The word pozzolana comes from the town Pozzouolinear Naples, where there are still extensive beds of pozzolanic materials, and also around Rome.In ancient times, pozzolanas were used to enhance the properties of lime, mortar and concrete.
Pozzolanas contains siliceous and aluminous mineral substance which itself possesses little or no little cementitious properties.
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Pozzolana material can be divided into two categories according to the source of origin.
01. Naturally Occurring Pozzolanas:
Natural pozzolanas come from the volcanic mineral deposits and sedimentary origin.
a) Clays and Shales
- Montmorillonite Types
- Kaolinite Types
- Illite Types
b) Opaline Materials
- Opaline Shales
- Diatomaceous Earths
c) Volcanic Tuffs and Pumicites
- Rhyolitic Types
- Andesitic Types
- Phonolitic Types
- Basaltic Types
Most natural pozzolanas require grinding to a high degree of fineness to make them suitable for use in concrete and particularly with cement. Pumicites are an exceptional pozzolanic material which has a high degree of fineness.
Natural pozzolana can be further improved by the addition of chemicals such as alkalis during the calcining process.
02. Artificial Pozzolanas:
Artificial pozzolanas are by-products or wastage from the industries. It includes
- Fly Ash
- Silica Fume
- Powdered Brick
- Burnt Oil Shale
- Blast Furnace Slags
- Rice Husk Ash
Pozzolana is a finely divided reactive powder form. In the presence of moisture, it chemically reacts with lime at an atmospheric temperature to form compounds possessing cementitious properties.It is essential that pozzolana be in a finely divided state. Smaller the particle size, higher the reactivity.
Pozzolanas are mostly used as a cement replacement rather than the addition of cement. This cement is known as Pozzolana Portland Cement. The amount of cement varies depending upon the reactivity of pozzolana. A high reactive pozzolana has more cementitious strength value than a lower reactive pozzolana.