Pozzolana in Cementitious Systems – Typical effects on concrete performance When a suitable pozzolana is added to cement (or used as part of a blended cement), which of the following effects are typically observed in concrete, assuming appropriate mix design and curing?

Introduction / Context:
Pozzolanas (for example, fly ash, silica fume, calcined clay) react with calcium hydroxide liberated during cement hydration to form additional calcium silicate hydrates. The pozzolanic reaction modifies concrete microstructure, influencing thermal, durability, and fresh properties. This question checks your understanding of these typical effects.

Given Data / Assumptions:

• Properly graded aggregates and adequate curing are provided.
• Pozzolana replacement is within recommended limits.
• Comparison is made against plain Portland cement concrete.

Concept / Approach:

Pozzolanas dilute clinker content and react secondarily, generally reducing early heat evolution and peak temperature rise (beneficial for mass concrete). The refined pore structure lowers permeability and bleeding by reducing large capillaries and blocking channels. Because pozzolanic reactions are slower, extended moist curing is beneficial to realize the full potential of strength and durability gains.

Step-by-Step Solution:

Verification / Alternative check:

Performance-based specifications for blended cements often call for longer curing periods and demonstrate improved durability indices (for example, RCPT, sorptivity) compared with plain OPC mixes at later ages.

Why Other Options Are Wrong:

Single selections omit complementary effects; “All” best captures the combined, documented benefits under proper practice.

Common Pitfalls:

Expecting identical early strength to OPC without adjusting curing; overdosing or using poor-quality pozzolana; ignoring temperature effects on set and finishability.

Final Answer:

All of the above