This set of Repair and Rehabilitation of Structures Multiple Choice Questions & Answers (MCQs) focuses on “Principal Causes of Building Cracks”.
1. Initial shrinkage of concrete structures occurs only once in a lifetime.
a) True
b) False
View Answer
Explanation: Initial shrinkage occurs in the concrete or mortar only once in lifetime at the time of manufacturing or construction, when the moisture used in the process of manufacturing or construction dries out.
2. Greater the water quantity used in the mix ___________ is the shrinkage.
a) greater
b) lesser
c) remains unchanged
d) twice
View Answer
Explanation: When the water content increases, the rate of evaporation increases leading to greater shrinkage which ultimately results in formation of shrinkage cracks.
3. With the use of largest possible, maximum size aggregate in concrete with good grading the shrinkage decreases.
a) True
b) False
View Answer
Explanation: By using the maximum size aggregate the requirement of water for desired workability is reduced with consequent decrease in shrinkage on drying due to reduction in porosity.
4. Concreting done in mild winter have ____________ cracking tendency than the concreting done in hot summer months.
a) greater
b) less
c) moderate
d) no changes in cracking tendency
View Answer
Explanation: With the reduction in the ambient temperature the requirement of water for the same slump/workability is reduced with the subsequent reduction in shrinkage. And so concreting done in mild temperature have less cracking tendency in comparison with those concreting done in hot temperature.
5. The process in which cracks occurs on the surface of the freshly laid concrete cement, before it has to set is called as ______________
a) initial shrinkage
b) plastic settlement cracks
c) elastic shrinkage
d) plastic shrinkage
View Answer
Explanation: When the concrete surface loses water at the rate faster than the bleeding rate then the shrinkage of top layer of concrete occurs and the concrete which in plastic state leads to plastic shrinkage. In this plastic state, the concrete cannot withstand any tension and thus leading to the formation of cracks on upper surface of concrete.
6. The extent of plastic shrinkage depends on ___________
a) maximum size, grading and quality of aggregate
b) curing
c) exposure to the heat from sun radiation
d) water content
View Answer
Explanation: The exposure to the heat, from sun radiation influences the rate of evaporation which in turn leads to the formation of plastic shrinkage. And remaining are the governing factors of initial shrinkage.
7. Plastic settlement cracks are normally observed in _____________
a) narrow column and walls
b) expansion joints
c) shear joints
d) mid span of elements
View Answer
Explanation: Plastic settlement cracks are mainly observed in narrow column and walls due to obstacles to the sedimentation action of concrete due to narrow pathway. These obstructions leads to the breakage of back concrete leading to the formation of voids under their belly.
8. Expansion of cement mortar and concrete as almost ___________ of the bricks and brick work.
a) thrice
b) twice
c) four times
d) same
View Answer
Explanation: Expansion due to thermal movement in concrete and cement mortar caused due to heat of hydration in concrete which is absent in bricks. And so expansion in cement mortar and concrete is twice that of bricks and brick work.
9. The component more liable to cracking due to thermal variations are _____________
a) internal walls
b) intermediate floors
c) external walls and roof
d) expansion joints
View Answer
Explanation: Mainly the external walls and roofs are always exposed to direct solar radiation and are more liable to cracking. The remaining components are not subjected to intense thermal variations.
10. What component of the building undergoes elastic deformation?
a) Sub-structure
b) Super structure
c) Structural elements
d) Foundation
View Answer
Explanation: Dead and super imposed live loads in the structural components of the building leads to elastic deformation in accordance with hook law. The amount of deformation also depends upon other factors like elastic modulus, magnitude of loading and the dimension of the component.
11. When two materials, having different elastic properties are built, shear stress is set up at the ________ of the two materials.
a) interface
b) corner
c) edge
d) base
View Answer
Explanation: Shear stress is set up the interface of two materials, under the effect of load, when two materials having different elastic materials are built up side by side, resulting in the formation of cracks at the junction. Such a situation is commonly encountered in the construction of RCC framed structure and brick masonry panel and partition walls.
12. Creep in brickwork with weak mortar is generally ___________
a) lesser
b) higher
c) poor
d) unaffected
View Answer
Explanation: Creep in brickwork with the weak mortar is generally higher because the creep in brick work depends on stress/strength ratio. For example: For same quality of brick, creep of brick work in the ratio 1:1:6 mortar is 2 to 3 times that of brick work in the ratio 1:1:3 mortar.
13. What component of the building undergoes sulphate attack?
a) Sub-structure
b) Super structure
c) Structural elements
d) Foundation
View Answer
Explanation: Concrete and masonry in foundation and plinth and masonry and plaster in super structure are more liable to sulphate attack. The sulphate attack on these building components will result in weakening of their structural strength and in course of time it leads to unequal settlement of the foundation.
14. Factors which contribute to corrosion of reinforcement in concrete are __________
a) formation of cracks in concrete
b) permeability of concrete and mortar
c) use of admixtures and pozzolonas
d) relative humidity
View Answer
Explanation: When the reinforcement steel gets corroded, it increases the internal stress in concrete. In course of time cracks occurs in the direction of reinforcement, later on causing spalling of concrete thereby allowing the water to enter into the component, which later leads to corrosion of reinforcement.
Sanfoundry Global Education & Learning Series – Repair and Rehabilitation of Structures.
To practice all areas of Repair and Rehabilitation of Structures, here is complete set of Multiple Choice Questions and Answers.
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