Civil Engineering - Concrete Technology - Discussion

Let’s analyse each option carefully concerning pozzolana (such as fly ash, silica fume, volcanic ash) when added to cement, typically forming Portland Pozzolana Cement (PPC):

1. Decreases workability:
Actually, pozzolana increases workability due to its finer particles and smooth surface texture. So this statement is false.

2. Increases strength:
Pozzolana contributes to long-term strength, but initial strength is lower than Ordinary Portland Cement (OPC). So this statement is partially true, but not generally correct in early stages.

3. Increases heat of hydration:
Pozzolanic materials reduce the heat of hydration, making PPC suitable for mass concreting. So this is false.

4. Decreases curing time :
Pozzolana increases the time required for strength gain, so curing time should be longer, not shorter.

Hence, none of these options are correct as per how pozzolana behaves.

The increase in strength is in comparison to the ordinary cement. In case of Pozzolana Portland Cement, the rate of increase in strength is slower. It is therefore that it has the property of emitting less heat of hydration thereby reducing shrinkage cracks. At site it is advisable to use PPC instead of OPC if you have the advantage of time.

Addition of pozzolana to cement make the following statement:

1. Increasing strength.

2. Delay setting of cement.

3. Decreasing heat of hydration (the reacting between cement and water).

4. Increasing durability and serviceability.

5. Decreasing porosity of concrete.

So; the choose number B is correct.

Pozzolana cement concrete.

-> Less heat of hydration.

-> Used in dams, thick structures, retaining walls, abutments, foundation etc where more concrete is to be placed.

-> Low strength for first 28 days. After 28 days it gains strength equals to OPC.

-> Responsible for ultimate strength.

The strength of the concrete is increased, its density is increased.

Efflorescence is decreased.

The propensity for alkali-silica reaction (reaction with glass) is decreased or even virtually eliminated.

The addition of pozzolana to ordinary Portland cement increases shrinkage but reduces the permeability of the concrete.

Advantages: It increases the workability. It can reduce permeability.

Pozolonic cement increases strength but it has originally less quantity of cement (10 to 30%) so strength of OPC and pozzolona approx same.

Pozzolana Cement is a option of OPC cement It having near about similar strength as OPC but not greater than OPC. So option E correct.

Addition of pozzolana to cement increase shrinkage and which is not in the option So option E should be the correct answer.

It increase the long term strength due to forming CSH which is stronger, and through better backing of concrete.