Pozzolanic materials react with calcium hydroxide to form cementitious compounds.

• A. True
• B. False
• C. Not always
• D. Sometimes

Answer: (A)

Pozzolanic materials are reactive siliceous or aluminous substances that, in a cementitious system, use the calcium hydroxide produced during cement hydration to form additional cementitious binding phases. When cement hydrates, calcium hydroxide (portlandite) is released. The silica or alumina in pozzolanic materials reacts with this calcium hydroxide in the presence of water to form compounds like calcium silicate hydrates and related hydrates. These reaction products fill pores and develop strength over time, improving durability and reducing the amount of free calcium hydroxide in the paste. The process requires water and alkaline conditions provided by the cement paste, and it tends to occur progressively as the concrete cures, which is why blended cements with pozzolanic materials often gain strength at later ages.