POZZOLANS

POZZOLANS

Pozzolans as materials that contains receptive aluminic and silia which have little or no binding properties but in presence of water when mix with lime, will hardened and set like cement. In similar definition by (Lea and Howlett, 2009) the term pozzolans has two distinct meanings. The first one is the pyroclastic rocks that is essentially glassy and sometimes zeolitised, which occur in the neighborhood of pozouli.

The seconds includes all organic materials, either artificial or natural, when mix with material that can released calcium hydroxide (clinker) or mixed with calcium hydroxide (lime) which hardened in water.

History of Pozzolana

The Romans and Greeks were the first to use pozzolans in mortar lime. Crushed pottery, tiles and bricks which formed the first artificial pozzolans but also found that some of the volcanic soils were good for production of hydraulic mortar.

All this materials are used by the Romans and other countries. Nowadays, different variety of aluminum or siliceous materials are used to produce pozzolans, agricultural residue such as rice husks ash, volcanic ash, fly ash are common materials that are calcined from clay. In construction, cement market has been dominated or cowered by one product, OPC and cement or some form of binding agent is vital element.

In many developing countries in the world, OPC is sometimes scarce commodity, factor and is expensive which limited the construction at houses that are affordable. Although with the growth of the use of pozzolanes in USA and Europe, there are growing numbers of developing countries using more pozzolanes now, in combination with lime or OPC, (Howtopedia, 2006).

Importance of Pozzolana

This importance use of pozzolanic materials in concrete is stated below by (Matawal, 2005) as;
– Technological
– Economical
– Environmental

Technological: Pozzolan can change the form of the characteristic properties of cement, by decreasing or increasing its compressive strength or durability and resistance to aggressive agents and lime.

Economical: This is economically active additions and reduces the quantity of cement required.

Environmental: Bringing such addition bring about a waste material that is laid on different ashes.

(Matawal, 2005) further outlined other advantages of using pozzolanic material for partial replacement of cement in concrete production as:
– Improved workability, assessment of fresh concrete as consideration.
– Improvement of sulphate resistance in freezing and thawing.
– Increased cohesiveness or bonding strength of concrete.
– Reduction in hydration uses.
– Reduction in permeability of water tightness.
– High resistance to alkaline aggregate reactions.
– Reduction content of water, mortar and concrete mix, resulting in less shrinkage and cracking.

These outline advantages are not universal because they vary from one pozzolanic material to another. More knowledge is gain by taking one pozzalana like Rice Husk Ash