Explain Kelly Ball to measure the workability of concrete. Mention the limitation of the test.
KELLY BALL TEST:-
This is a simple field test consisting of the measurement of the indentation made by 15 cm dia. metal hemisphere weighing 13.6 kg when freely placed on fresh concrete. The test has been devised by Kelly and hence known as Kelly Ball Test. The advantage of this test is that it can be performed on the concrete placed in site and it is claimed that this test can be performed faster with a greater precision than slump test. The minimum depth of concrete must be at least 20 cm and the minimum distance from the centre of the ball to nearest edge of the concrete 23 cm.
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?
Write notes on Mixing and Mixer machines of concrete.
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.