Addition of Pozzolana to ordinary Portland cement causes

Explanation:

Addition of Pozzolana to Ordinary Portland Cement

The addition of pozzolana to ordinary Portland cement (OPC) modifies its properties in various ways, as detailed below:

• Decrease in Early Strength:

  • Pozzolana reacts slowly with calcium hydroxide (a by-product of hydration) to form additional cementitious compounds.
  • As a result, the initial rate of strength gain is reduced compared to OPC alone.

• Reduction in Chemical Action with Sulphates:

  • The pozzolanic reaction reduces the quantity of calcium hydroxide in the cement matrix.
  • This decreases the vulnerability of the concrete to chemical attacks by sulphates, enhancing durability.

• Increase in Shrinkage:

  • Pozzolanic cement mixtures are more prone to drying shrinkage due to their finer particles and higher water demand.
  • This increased shrinkage can lead to cracking if not properly controlled during curing.

• All of the Above:

  • All the aforementioned effects (decrease in early strength, reduction in sulphate attack, and increase in shrinkage) are observed when pozzolana is added to OPC.

Analyzing the Given Options

1. "Decrease in early strength" (Correct)

   • As explained above, pozzolana slows down the early strength gain due to its slower reaction rate.

2. "Reduction in chemical action with sulphates" (Correct)

   • By consuming calcium hydroxide, pozzolana reduces the material's susceptibility to sulphate attacks, improving resistance.

3. "Increase in shrinkage" (Correct)

   • Due to higher water demand and finer particles, pozzolanic cement is prone to increased drying shrinkage.

4. "All of the above" (Correct Answer)

   • All the listed options are valid effects of adding pozzolana to OPC, making this the correct choice.