Building Material (Part-III) (GENERAL ENGINEERING) (SSC JE)

Soda-Potash has lowest % in OPC because it is harmful ingredient of cement. [0.2 - 1%].
• It causes efflorescence and undergo reaction with aggregates.

Electrochemical corrosion–If wet electrochemical corrosion occurs damage is caused by two types of electro-chemical reaction on the surface of the steel. Oxidation reaction and reduction with oxidation reaction, otherwise termed metal dissolving reaction, metallic atoms enter into solution as metal ions, while electrons remain in the metal. In steel, the iron (Fe) dissolves as follows–  Fe = Fe ²⁺ + 2e⁻

Refractoriness–is defined as the ability of molding sand to withstand high temperatures without breaking down or fusing thus facilitating to get sound casting. It is a highly important characteristic of molding sands.

Low heat cement (IS 12600-1989)– Formation of cracks in large body of concrete due to heat of hydration has focused the attention of the concrete which produces less heat, at a low rate during the hydration process.

A low heat evolution is achieved by reducing the contents of C₃S and C₃A which are the compounds evolving the maximum heat of hydration and increasing C₂S.

Silica (SiO₂) [17%-25%]
• It imparts strength to cement
• If it is in excess, strength of cement is increased but it also increases the setting time of cement.

Comparison of gain in strength of concrete, when portland pozzolona cement compared to ordinary portland cement will give after 28 days is equal compressive strength but the concrete prepared with portland pozzolana cement gains strength at a slower rate earlier and reaches the designed strength in 28 days gaining strength of all concrete depends on age factor.

Note–In this question most precise answer is option (c) but commission is considered as option (b) is right.