State the effect of shape and size of aggregate on strength of concrete.
Shape of aggregate on strength of concrete:- The shape of aggregate influence workability in good measure. The importance of shape of the aggregate will be of great significance in the case of present day high strength and high performance concrete when we use very low w/c in the order of about 0.25.
Size of aggregate on strength of concrete :- The bigger the size of the aggregate the less is the surface area and hence less amount of water is required for wetting the surface and less matrix or paste is required for lubricating the surface to reduce internal friction
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?
What is an air entraining agents? Give some examples. What is efflorescence in concrete structure?
What are the initial and final setting times of cement ? How are they experimentally determined ?
Design concrete mixes of M30 to suit the following data per IS:10262-1982 :
Characteristic cube strength = M-30, type of cement - ordinary Portland, fine aggregate natural river sand conforming to grading zone II of table-4 of IS:383-1970 coarse aggregate-crushed (angular) coarse aggregate of 20 mm maximum size conforming to IS:383 code requirements, specific gravities of cement, sand and coarse aggregate are 3·14, 2·63 and 2·61 respectively. Type of exposure - mild, Degree of quality control - very good. Degree of workability = 0·08. use IS:10262-1982.
What are flaky and elongated aggregates? How can the shape of aggregate influence strength of concrete? Following is the result of a sieve analysis of 500 gm aggregate:
|IS sieve size
|lower than 150 micron
|Weight retained in gm
Find out the 'Fineness Modulus' of the sample