Civil Engineering Today

  Classification of Pozzolanas Pozzolanas are classified as natural and artificial : 1. Natural pozzolanas -  All pozzolanas are rich in silica and alumina and contain only a small quantity of alkalis .  The following are some of the naturally occurring pozzolanas: ·  Clays and shales which must be calcined to become active. ·   Diatomaceous earth and opaline cherts and shales which may or may not need calcination ·  Volcanic tuffs and pumicites. Fine grained ashes form better pozzolana. However, tuffs solidified volcanic ash-may be ground to desired fineness for use. ·  Rhenish and Bavarian trass.   2.  Artificial Pozzolanas - Artificial pozzolanas is a man-made material that is a byproduct of industrial processes, such as burning organic materials like coal in furnaces to reclaim ash.  Some of the examples of artificial pozzolanas are: 1 . Fly ash 2.  Surkhi (burnt clay pozzolana) 3 . Rice husk ash 4 . Ground...

  Pozzolana The term pozzolana is derived from Pozzuoli , a town in Italy on the Bay of Naples near Mount Vesuvious . The sand (volcanic dust) around this town when mixed with hydrated lime was found to possess hydraulic properties . Pozzolana may be defined as a siliceous material which  itself possessing no cementitious properties, either processed or unprocessed and in finely divided form, reacts in the presence of water with lime at normal temperatures to form compounds of low solubility having cementitious properties. Pozzolanas may be natural or artificial , fly ash being the best known in the latter  category. Before the advent  of cement these were used with lime to make concrete.   THE ACTIVITY OF P0ZZOLANA - When mixed with ordinary Portland cement the silica of the pozzolana combines with the free lime released during the hydration of cement. This action is called pozzolanic action . The pozzolanic activity is due to the presence of finely divid...