What is an air entraining agents? Give some examples. What is efflorescence in concrete structure?
Air entraining concrete is made by mixing a small quantity of air entraining agent or by using air entraining cement. These air entraining agents incorporate millions of non-coalescing air bubbles, which will act as flexible ball bearing and will modify the properties of plastic concrete regarding workability, segregation, bleeding and finishing quality of concrete. It also modifies the properties of hardened concrete regarding its resistance to frost action and permeability.
The following types of air entraining agents are used for making air entrained concrete:
Efflorescence:- Efflorescence is caused when soluble salts and other water dispersible materials come to the surface of concrete and mortars. Its induced by low temp. moist conditions, condensation, rain, dew and water added to the surface of fresh concrete to assist troweling.
What are the initial and final setting times of cement ? How are they experimentally determined ?
Short notes on :
Introduce Flow table test. How can sulphate attack be controlled?
Discuss the role of Gel-space ratio. How can it be determined? Calculate the gel-space ratio and theoretical strength of a sample of concrete made with 500gm of cement with 0.5 w/c ratio on full hydration and 40% partial hydration. Discuss the factors which influence creep in concrete?