Prestressed Concrete Structures Multiple Choice Questions on “High Strength Concrete”.
1. The developments in the field of concrete mix design gave compressive strength ranging between ___________
a) 30-70
b) 70-100
c) 35-45
d) 30-80
Answer: b
Clarification: Recent developments in the field of concrete mix design have indicated that it is now possible to produce even ultra high strength concrete, of any desired 28 day cube compressive strength ranging from 70-100n/mm2 without taking resource to unusual materials.
2. High strength concrete resists ___________
a) Levelling
b) Bursting
c) Tangent moments
d) Trapezoidal moments
Answer: b
Clarification: The concrete in a prestressed concrete member is subjected to high bearing stresses due to anchoring at its ends and hence, high strength concrete is required to safely resist the bursting stresses at the end of the beam.
3. In high strength concrete, high modulus of elasticity in the beam is due to ___________
a) Elastic and creep strains
b) Principle tensile stresses
c) Reinforced beams
d) Vibration
Answer: a
Clarification: Low shrinkage, minimum creep characteristics and a high value of young’s modulus are generally deemed necessary for concrete used for prestressed members and the loss of prestress in steel reinforcement is minimum because the elastic and creep strain are very small due to high modulus of elasticity.
4. Which of the following is one of the standard codes used for designing high strength concrete mixes?
a) BS 8110-1985
b) BS 883-1974
c) BS 8113-1986
d) BS 886-1976
Answer: a
Clarification: The various methods adopted for designing high strength concrete mixes are Erntroy and Shack lock’s empirical method, American concrete institute method, British DOE method, Indian standard code and British code BS 8110-1985 stipulates that not more than 5 percent of the test results should fall below 28 days characteristic strength.
5. Which of the following is the Indian code used for high strength concrete mixes?
a) IS 1343-1980
b) IS 10263-1982
c) IS 384-1980
d) IS 457-1979
Answer: a
Clarification: Indian standard code IS 1343-1980 and IS 456-1978 stipulates that only controlled concrete should be used for prestressed concrete construction and the exact specifications with regard to the acceptance criteria for concrete generally vary from one code to another.
6. The cube strength of concrete required for both pre tensioning and post tensioning according to Indian standard codes are ___________
a) 30 and 20
b) 15 and 25
c) 40 and 30
d) 45 and 35
Answer: d
Clarification: The minimum 28 day cube compressive strength prescribed in the Indian standard code IS 1343-1980 is 45n/mm2 for pretensioned members and 35n/mm2 for post tensioned members with the development of vibration techniques in 1930, it became possible to produce without much difficult, high strength concrete having 28 day compression strength in the range of 30-70n/mm2.
7. The full form of ACI method for mix design proportion is ___________
a) American committee institute
b) American council institute
c) American concrete institute
d) American cement institute