Civil Engineering Drawing Multiple Choice Questions on “R.C.C. Work and Amount”.
1. Reinforced cement concrete work is usually estimated under ________ items.
Clarification: The concrete work including centering and shuttering, and binding of steel bars in position is taken under one item in cu m (cu ft) and the steel reinforcement and its bending is taken under one item in (cwt).
2. The density of steel may be taken as _______________
a) 68.5 quintal per cu m
b) 9.85 grams per cu m
c) 390 lbs per cu ft
d) 78.5 quintal per cu m
Clarification: The density of steel may be taken as 78.5 quintal per cu m or 7.85 grams per cu m, 390 lbs per cu ft. The percentage of steel reinforcement depends on the design of the structure.
3. In R.C.C. work the end or side covers for steel bar may be taken as ____________
a) 4cm to 5cm
b) 7cm to 9cm
c) 6cm to 9cm
d) 3cm to 7cm
Clarification: In R.C.C. work the end or side covers for steel bar may be taken as 4cm to 5cm (1 1/2” to 2”) and the bottom and top covers may be taken as 1.2 cm to 2 cm(1/2” to 3/4”) for slab and 2.5 cm to 5cm (1” to 2”) for beams.
4. Concrete reinforced with fibers (which are usually steel, glass, or plastic fibers) is less expensive than hand-tied rebar, while still increasing the tensile strength many times.
Clarification: A thin and short fiber, for example short, hair-shaped glass fiber, is only effective during the first hours after pouring the concrete (its function is to reduce cracking while the concrete is stiffening), but it will not increase the concrete tensile strength. A normal-size fiber for European shotcrete (1 mm diameter, 45 mm length—steel or plastic) will increase the concrete’s tensile strength.
5. Resistant to weak acids and especially sulfates, this cement cures slowly and has very low durability and strength.
Clarification: Resistant to weak acids and especially sulfates, this cement cures quickly and has very high durability and strength. It was frequently used after World War II to make precast concrete objects. However, it can lose strength with heat or time (conversion), especially when not properly cured. After the collapse of three roofs made of prestressed concrete beams using high alumina cement, this cement was banned in the UK in 1976. Subsequent inquiries into the matter showed that the beams were improperly manufactured, but the ban remained.
6. The coefficient of thermal expansion of concrete is similar to that of steel, eliminating large internal stresses due to differences in thermal expansion or contraction.
Clarification: An average value for the coefficient of thermal expansion of concrete is about 10 millionths per degree Celsius (10×10-6/C), although values ranging from 7 to 12 millionths per degree Celsius have been observed.
7. If a material with high strength in tension, such as steel, is placed in concrete, then the composite material, reinforced concrete, resists not only compression but also bending and other direct tensile actions.
Clarification: A reinforced concrete section where the concrete resists the compression and steel resists the tension can be made into almost any shape and size for the construction industry. FRP composites and Construction Parameters.
8. Another, cheaper way of protecting rebars is coating them with calcium sulphate.
Clarification: Another, cheaper way of protecting rebars is coating them with zinc phosphate. Zinc phosphate slowly reacts with calcium cations and the hydroxyl anions present in the cement pore water and forms a stable hydroxyapatite layer.