Pozzolanic Effect

A pozzolanic reaction occurs when a siliceous or aluminous material get in touch with calcium hydroxide in the presence of humidity to form compounds. The C-S-H gel (Calcium Silicate Hydrate) generated by the hydration of C3S (Tricalcium Silicate) and C2S (Dicalcium Silicate) is the main strengthening constituent. Calcium Hydroxide and ettringite that are crystalline hydration products are randomly distributed and form the frame of the Gel like products. Excess calcium hydroxide can be detrimental to concrete strength, due to tending the crystalline growth in one direction. It is known that by adding pozzolanic material to concrete mix, the pozzolanic reaction will only start when CH is released and pozzolanic/CH interaction exist.

The crystallized compound of C-S-H and C-A-H, which are called cement gel, hardened with age to form a continuous binding matrix with a large surface area and are components responsible for the development of strength.

Pozzolanic Reaction

Pozzolan-Lime reactions are slow, generally starting after one or more weeks. The behaviour of the delayin pozzolanic reaction will result in more permeable concrete at early ages and gradually becomes denser than plain concrete with time. This behaviour is due to two reasons:

  1. Pozzolan particles become the precipitation sites for the early hydration C-S-H and CH that hinders pozzolanic reaction.
  2. The strong dependency of the breaking down of glass phase on the alkalinity of the pore water which could only attain the high PH after some days of hydration. Pozzolan can partially replace cement in concrete mix without affecting strength development. The effect of the pozzolanic reaction produces more cement gel reducing the pore size blocks the capillary and produces denser concrete thus making it stronger and more durable.

Pozzolanic Usage

The use of our product decreases the formed CH by the pozzolanic reaction to produce more C-S-H gel that can improve the strength and durability of concrete. The pozzolanic nature of our product reacts with lime more rapidly. Use of our product accelerates the early hydration of C3S. The increase in the early hydration rate of C3S is attributed to the high specific surface area. This phenomenon specially takes place with fine particles of our product. Finer particles of our product speed up the reactions and form smaller CH crystals.