Effects of adding pozzolana to cement — select the correct impact When a pozzolanic material is blended with Portland cement (e.g., in Portland-pozzolana cement), which of the following listed effects is correct in general construction practice?

Introduction / Context:
Pozzolanic materials (fly ash, calcined clay, silica-rich ashes) react with calcium hydroxide to produce additional cementitious hydrates. Their effects on fresh and hardened properties drive selection for durability and temperature control, especially in mass concrete and aggressive environments.

Given Data / Assumptions:

• Typical Portland-pozzolana blends used in structural concrete.
• Normal curing and placement practices.
• Comparison with ordinary Portland cement of similar strength class.

Concept / Approach:

Pozzolana generally reduces heat of hydration (beneficial for thermal cracking control), often improves workability (spherical fly ash particles, improved packing), may reduce early-age strength but can improve later-age strength and durability. It does not reduce the required curing time; good curing remains critical. Therefore, the listed statements (a)–(d) are not correct as general truths, making “None of these” the correct choice.

Step-by-Step Solution:

Verification / Alternative check:

Concrete practice texts note reduced temperature rise, improved impermeability, and enhanced sulphate resistance with pozzolanas, balanced against slower early strength gain.

Why Other Options Are Wrong:

• Each statement misstates the typical effect of pozzolanas in general use.

Common Pitfalls:

• Expecting rapid early strength with high fly-ash contents.
• Reducing curing duration because of improved later-age strength potential.

Final Answer:

None of these.