Question

which one of the following statements is not correct with respect to the properties of cement?

• A. Highly reactive Pozzolanas enhance the early age strength of the composite cement
• B. Pozzolanic activity refines pore structure which decreases electrolytic resistance of concrete
• C. The expansion due to alkali-silica reaction can be controlled by replacement of as high as 60% of OPC with high-calcium Pozzolana.
• D. Such high amounts of replacement cements result in higher accelerated carbonation depths compared to pure use of OPC only

Answer 1

The correct option is A Highly reactive Pozzolanas enhance the early age strength of the composite cement

Ans. (a) : Composite cement made with 60% OPC + 30% fly ash + 5% lime stone powder has higher strength than PPC made with 10% fly ash.
Even in highly reactive pozzolanas, strength gain due to pozzolanic action does not start immediately as $Ca(OH{)}_2$ is needed, which comes from the hydration of $C_{3}S$ and $C_{2}S$.
Expansion is s seldom observed if the alkali content $(N{a}_{2}O+0.658K_{2}O)$ is below 0.6% and generally increase with an increase in alkalinity.