What is external sulphates attack?

Concentration of water-soluble sulphates in water _______ ppm for mild exposure.

Strength of concrete show an increase with _____

Approximate ratio of the strength of the cement conc of 7 days to that of 28 days (2/3)?

Concentration of water-soluble sulphates in water _______ ppm for severe exposure.

Approximate ratio of strength of the 30 cm cube to that of 15 cm cube is _________

In order to avoid segregation, the concrete should not be thrown from a height.

For concrete exposed to a very aggressive environment the w/c should be lower than ______