Portland Pozzolanic Cement

The term Pozzolan is derived from the name of the town Pozzuoli, Italy. It is situated near Mt. Vesuvius and is the place where the Romans more than 2,000 years ago mined the ashes deposited by the occasional eruptions of this volcano. Definition and Use of Pozzolans: A "Pozzolan" is defined as "a siliceous or siliceous and aluminous material, which in itself possesses little or no Cementing property, but will in a finely divided form - and in the presence of moisture - chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing Cementitious properties."

Benefits of Pozzolans

Pozzolans not only strengthen and seal the concrete, they have many other beneficial features you will realize the moment you purchase them or add them to the mix. All of the below benefits apply to fly ash and rice hull ash, and most of them to silica fume as well.

• Spherical Shape: Fly Ash (FA) and Rice Hull Ash (RHA) particles are almost totally spherical in shape, allowing them to flow and blend freely in mixtures.
• Ball Bearing Effect: The "ball-bearing" effect of FA and RHA particles creates a lubricating action when concrete is in its plastic state.
• Economic Savings: Pozzolans replace higher volumes of the more costly Cement, with typically less cost per volume.
• Higher Strength: Pozzolans continue to combine with free lime, increasing structural strength over time.
• Decreased Permeability: Increased density and long-term Pozzolanic action, which ties up free lime, results in fewer bleed channels and decreases permeability.
• Increased Durability: Dense Pozzolan concrete helps keep aggressive compounds on the surface, where destructive action is lessened. Pozzolan concrete is also more resistant to attack by sulfate, mild acid, soft (lime-hungry) water, and seawater.
• Reduced Sulfate Attack: Pozzolans tie up free lime that otherwise could combine with sulfate to create destructive expansion.
• Reduced Shrinkage: The largest contributor to drying shrinkage is water content. The lubricating action of FA and RHA reduces the need for water and therefore also drying shrinkage.
• Reduced Volume: As Pozzolans can in certain cases substitute for up to four times the mass of Cement, besides making the same amount of concrete harder than without Pozzolans, less voluminous structures are able to bear the same load.
• Reduced Alkali Silica Reactivity: Pozzolans combine with alkalis from Cement that might otherwise combine with silica from aggregates, which would cause potentially destructive expansion. Read more . . .