This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Chemical Prestressing”.
1. The chemical pre stressing is also called as ___________
a) Self stressing
b) Whole stressing
c) Half stressing
d) Model stressing
View Answer
Explanation: Self stressing or chemical pre stressing of concrete was made possible by the development of expanding cements by Lossier of France in 1944 and generally expanding cement consist of 75% Portland cement, 15% alumina cement and 10 % gypsum which result in formation of calcium Sulpho aluminate.
2. The linear expansion of the cement in chemical pre stressing is about ___________
a) 5-10%
b) 2-3%
c) 3-4%
d) 6-7%
View Answer
Explanation: The linear expansion of the cement in chemical prestressing is about 3 to 4% Mikhailov has reported that expansive cements have been used for pre stressing purposes in erstwhile in USSR since 1949 and splices are adopted for circular prestressing of tanks and the advantage is that there is no reduction in the strength of wire.
3. The degree of expansion can be controlled by varying the conditions of ___________
a) Bending
b) Bonding
c) Heating
d) Curing
View Answer
Explanation: The degree of expansion can be controlled by varying the curing conditions in expanding cements and when the concrete is subjected to compression the amount and rate of expansion is controlled by controlling the curing conditions of the member.
4. The expansion of the concrete is restrained by ___________
a) High-tensile steel
b) High-strength concrete
c) Precast members
d) Concrete members
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Explanation: concrete is composite material consisting of an aggregate and a binder phase and the binder phase is hardened cement and the expansion of concrete is restrained by high tensile steel wires, the compressive stresses that develop in concrete and steel wires are subjected to tensile stresses.
5. The tensile stresses developed in steel by the expansion of concrete are about ___________
a) 850n/mm2
b) 250n/mm2
c) 600n/mm2
d) 500n/mm2
View Answer
Explanation: Tensile stresses of up to 850n/mm2 were developed in steel by the expansion concrete results of laboratory investigations of several types of chemically pre stressed elements, such as beams, slabs, frames, columns, pipes and hyperbolic parabolic sheets have demonstrated the feasibility of chemical pre stressing.
6. The chemical pre stressing is generally suited for elements like ___________
a) Pre cast beams and columns
b) Bonding elements
c) Breakage elements
d) Tensioning elements
View Answer
Explanation: It has been found that structural elements ideally suited for chemical pre stressing include pipes, thin walls and slabs, shells; folded plates and composite columns as well as pre cast beams and columns.
7. The method of chemical pre stressing is not suited for ___________
a) High degrees of prestress
b) High degrees of compression
c) High degrees of anchoring
d) High degrees of jacking
View Answer
Explanation: In the present state of art, chemical pre stressing can be applied to structural elements and systems in which the optimum amount of pre stress is relatively low and this method is most not suited for high degrees of prestress and high percentages of steel where mechanical pre stressing can be conveniently used.
8. The suitability of post tensioning is good for ___________
a) Long spans
b) Break spans
c) Edge spans
d) End spans
View Answer
Explanation: The suitability of post tensioning is good for medium to long span in situ work, where the cost of tensioning is very less and the major advantage of is the stopped off and curved cables are allowed by which designer can easily differ the prestresss distribution.
9. The long span decks are fabricated by ___________
a) Post tensioning
b) Pre tensioning
c) Thermo electric prestress
d) Chemical prestress
View Answer
Explanation: Post tensioning is ideally suited in concrete construction work involving stage prestressing most of the long span bridge structures are constructed using post tensioning system and long span bridge decks are also fabricated by the use of post tensioning.
10. The concrete dams are constructed using which?
a) Post tensioning
b) Thermo electric pre tensioning
c) Biological pre tensioning
d) Elongation pre tensioning
View Answer
Explanation: Concrete dams, biological shields of nuclear reactors and circular pre stressing of large concrete tanks are strengthened by using post tensioning and high tensile wire is wrapped under high tension using a wire serving machine developed by the inventors.
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