Learn : Pozzolana, Natural Pozzolanas, Artificial Pozzolana,Clay pozzolana,cement sand mortars, Pozzolana when added to lime make it hydraulic and the resulting mortar will be stronger.
POZZOLANAS
These are siliceous materials having siliceous material but no binding values within themselves, will chemically react with Calcium hydroxide at ordinary temperatures and in the presence of moisture to form compounds possessing binding properties.
Pozzolanas when added to lime make it hydraulic. The resulting mortar will be stronger than the ordinary lime mortar.
Pozzolanas are divided into :
(a) Natural Pozzolanas.
(b) Artificial Pozzolanas.
(a) Natural Pozzolanas.
These are natural clay or siliceous volcanic materials having Pozzolanic properties. These occur in Pozzuoli near Vesuvins, south east France; the Azores; Canary islands; Germany, Grecian islands etc.
(b) Artificial Pozzolana.
There include powdered bricks, tiles, burnt clay (surkhi) and fly ash.
Clay pozzolana have the folliwing advantages :
- Clay pozzolana replace cement to the extent of 20 per cent in cement concrete and mortars without affecting the strength and also constitute 20 to 30 per cent of the Pozzolana cement. A cement sand mortar of 1:6 mix can be better replaced by a mortar made by mixing one part of hydrated lime, two parts of clay pozzolana and eight parts of sand.
- In conjunction with the standard quality dry hydrated lime, these can be used for preparation of mortar and plasters having the same strength as that of cement sand mortars.
- Lime pozzolana mortars are cheaper as compared to cement sand mortars.
- These give improved workability.
- These give increased water tightness.
Uses
Pozzolana is abundant in certain locations and is extensively used as an addition to Portland cement in countries such as Italy, Germany, Kenya, Turkey, China and Greece. Compared to industrial by-product pozzolans they are characterized by larger ranges in composition and a larger variability in physical properties. The application of pozzolana in Portland cement is mainly controlled by the local availability of suitable deposits and the competition with the accessible industrial by-product supplementary cementitious materials. In part due to the exhaustion of the latter sources and the extensive reserves of pozzolana available, partly because of the proven technical advantages of an intelligent use of pozzolana, their use is expected to be strongly expanded in the future