Portland Pozzolana Cement (PPC) is also called as fly ash blended cement. The main parameter that makes an ordinary portland cement (OPC) differ from PPC is the fly ash content. Lets discuss each and every feature of PPC in simple explanation.

Ingredients of Portland Pozzolana Cement (PPC)


The main ingredients of PPC manufacture are:

  1. High Quality Portland Cement Clinkers (65 to 80%)
  2. Gypsum (3-5%)
  3. Pozzolanic Materials (15 to 35%)
All the above mentioned ingredients are blended in required proportions and are grinded thoroughly to produce PPC. 

As per IS: 1489, Part I, the fly ash used must be not less than 15 percent and not greater than 35%, by mass of PPC.

Pozzolana in PPC

The pozzolana used in PPC can either be natural or artificial material. In natural form it is clay & shale, volcanic tuffs, diatomaceous earth. Artificial forms of pozzolana are fly ash and rice husk.

The most commonly used pozzolana are fly ash. Fly ash is a fine material which is not a cementicious material, but it undergoes reaction with lime in the presence of water under ambient conditions to give a similar products and hydrated structure to that of ordinary portland cement concrete or mortar.

Hydration Reaction of Portland Pozzolana Cement (PPC)

We know, the important hydration products of OPC mortar or concrete are C-S-H Gel. The reaction results in excess amount of calcium hydroxide Ca (OH)2. These unreacted calcium hydroxide when formed in PPC, reacts with fly ash material and produce C-S-H gel. Hence, Ca (OH)2 is not wasted in PPC.

Hence, quality production of C-S-H gel give a compact structure to PPC concrete. This hence increases the durability of concrete and strength over a period of time.

Benefits of Pozzolanic Reaction in PPC Concrete


1. Pozzolanic reaction in PPC cement undergoes  continued hydration. This provides, higher long term strength, reduced heat of hydration and improved resistance to chemical attack.

2. Pozzolanic reaction consumes less water compared to OPC hydration reaction. It consumes around 7.5 to 4 percent water hence reducing bleeding issues, shrinkage and creep issues and permeability issues.

3. Pozzolanic reaction facilitates cohesion within the mixture. Cohesion thus improved can reduce segregation and issues faced during concrete placement.

How Pozzolana Reaction Improve Concrete Strength?


Fine Size of Pozzolana Improve Concrete Strength

One important feature of fly ash or pozzolana are their fine particle size. As they are finer than cement particles, they have larger surface area to perform hydration reaction. Hence, there is reduction of amount of trapped water between the cement particles, as major water get reacted.

Pozzolana Reaction Products in PPC
Pozzolana Reaction Products in PPC

Particle Packing Effect of Pozzolana Improves Concrete Strength

The fine size of pozzolana have the ability to fill the voids, thus reducing the overall voids in concrete. Fly ash is hence an efficient void filler compared to OPC. This will also reduce the amount of water content to obtain given consistency.

Ball Bearing Effect in Pozzolana Particles in PPC

The fly ash particles posses spherical shape, that reduces inter-particle friction. This facilitates mobility of mix and improves rheology of concrete.