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Past Questions — 2025
What is the compressive strength of M20 grade concrete at 28 days?
A)
10 MPa
B)
15 MPa
C)
20 MPa
D)
25 MPa
In concrete technology, the designation 'M' stands for 'Mix' and the number following it represents the characteristic compressive strength of the concrete. According to IS 456:2000 (the Indian Standard code for Plain and Reinforced Concrete), the grade of concrete is defined as the characteristic compressive strength of 150 mm cubes at 28 days. Therefore, for M20 grade concrete, the '20' explicitly denotes a characteristic compressive strength of 20 N/mm² (which is equivalent to 20 MPa) when tested after a curing period of 28 days.
- Option (a) 10 MPa corresponds to M10 grade concrete.
- Option (b) 15 MPa corresponds to M15 grade concrete.
- Option (d) 25 MPa corresponds to M25 grade concrete.
A concrete beam is designed for a compressive strength of 30 MPa. What is its approximate tensile strength?
A)
1.5 MPa
B)
3.8 MPa
C)
4.5 MPa
D)
6.2 MPa
For normal concrete, the tensile strength is much lower than the compressive strength and is commonly estimated by the empirical relation f_t \approx 0.7\sqrt{f_{ck}} (in MPa). For f_ck = 30 MPa, f_t \approx 0.7\sqrt{30} \approx 0.7 \times 5.48 \approx 3.8 MPa. Hence option (b) is correct.
Why the others are incorrect: (a) 1.5 MPa is too low for 30 MPa concrete; (c) 4.5 MPa is somewhat high; (d) 6.2 MPa is far too high and is closer to the square root of 30 without the usual reduction factor.
Which test is commonly used to measure the workability of fresh concrete?
A)
Compressive strength test
B)
Slump test
C)
Soundness test
D)
Impact test
Workability of fresh concrete refers to the ease with which it can be mixed, placed, consolidated, and finished without segregation.
1. **Slump Test (Option b):** This is the most common field test used to measure the consistency and workability of fresh concrete. It involves filling a conical mold (Abrams cone) with concrete and measuring the vertical subsidence (slump) after the mold is removed. A higher slump generally indicates higher workability.
2. **Compressive Strength Test (Option a):** This is performed on hardened concrete (usually using cubes or cylinders) to determine its load-bearing capacity, not its workability in the fresh state.
3. **Soundness Test (Option c):** This test is typically performed on cement (using the Le Chatelier or Autoclave method) to ensure that the cement does not undergo excessive volume change after setting, which would cause cracking.
4. **Impact Test (Option d):** This is an aggregate test used to determine the resistance of aggregates to sudden shock or impact, which relates to the toughness of the material, not the workability of the concrete mix.
What does the term “plinth area” refer to in construction?
A)
The total cost of the project
B)
The total area covered by the building at the ground level
C)
The total area of all floors combined
D)
The roof area
In civil engineering and estimation, the 'Plinth Area' is defined as the built-up covered area of a building measured at the floor level of the plinth. It is calculated by taking the external dimensions of the building (including the thickness of the walls) at the plinth level.
- Option (a) is incorrect because the total cost is the 'Project Cost' or 'Estimated Cost'.
- Option (c) is incorrect because the total area of all floors combined is referred to as the 'Total Floor Area'.
- Option (d) is incorrect because the roof area is specifically the 'Roof Area' or 'Slab Area', which may differ from the plinth area if there are overhangs or projections (chajjas).
A road has a width of 6m and an average thickness of 20 cm. The length of the road is 1 km. What is the total volume of material required?
A)
1000 m³
B)
1200 m³
C)
1500 m³
D)
1800 m³
To find the total volume of material required for the road, we use the formula for the volume of a rectangular prism: Volume = Length × Width × Thickness.
1. **Identify and Convert Units to Meters (m):**
- Length (L) = 1 km = 1,000 m
- Width (W) = 6 m
- Thickness (T) = 20 cm = 20 / 100 = 0.2 m
2. **Calculate the Volume:**
- Volume = 1,000 m × 6 m × 0.2 m
- Volume = 6,000 m² × 0.2 m
- Volume = 1,200 m³
Comparing this result to the given options:
- Option (a) 1000 m³ is incorrect.
- Option (b) 1200 m³ matches our calculation.
- Option (c) 1500 m³ is incorrect.
- Option (d) 1800 m³ is incorrect.
Why are under-sluices provided in weirs and barrages?
A)
To divert excess water during floods
B)
To control the movement of fish in the river
C)
To remove sediment from the riverbed and prevent silting
D)
To allow boats and ships to pass through
Under-sluices are gated openings provided at the lower level of a weir or barrage, typically located adjacent to the canal head regulator. Their primary engineering purpose is to create a 'scouring' effect. By opening these gates, water flows at a high velocity along the riverbed, which flushes out accumulated silt and sediment (sediment exclusion). This prevents the riverbed from rising (aggradation) and ensures that the water entering the canal is relatively free of sediment.
Analysis of other options:
- Option (a) is incorrect because excess floodwater is typically handled by the main spillway or crest gates of the barrage, not specifically by the under-sluices.
- Option (b) is incorrect because structures designed for fish movement are called 'fish ladders' or 'fish ways'.
- Option (d) is incorrect because structures allowing boats to pass are called 'locks'.
Why is river training necessary in hydraulic engineering?
A)
To increase the river’s flow velocity
B)
To control river meandering and prevent erosion
C)
To reduce the depth of the river channel
D)
To increase sediment deposition in floodplains
Option B is correct: To control river meandering and prevent erosion.
A spillway is designed for a peak flood discharge of 2000 (cumecs or m³/s). If the velocity of flow over the spillway is 8 (m/s) and the depth of flow is 2 meters, what is the required width of the spillway?
A)
100m
B)
125m
C)
200m
D)
250m
Option A is correct: 100m.
What is the compressive strength of M20 grade concrete at 28 days?
A)
10 MPa
B)
15 MPa
C)
20 MPa
D)
25 MPa
Option A is correct: 10 MPa.
What is the main role of admixtures in concrete?
A)
Reduce curing time
B)
Improve workability, strength, and durability
C)
Increase the setting time
D)
Replace aggregates
Option B is correct: Improve workability, strength, and durability.
Which of the following is the primary binding material in concrete?
A)
Sand
B)
Cement
C)
Water
D)
Aggregates
Option B is correct: Cement.
Which test is commonly used to measure the workability of fresh concrete?
A)
Compressive strength test
B)
Slump test
C)
Soundness test
D)
Impact test
Option B is correct: Slump test.
What is the ideal water-cement ratio for normal-strength concrete?
A)
0.2-0.3
B)
0.4-0.6
C)
0.7-0.9
D)
1.0-1.2
Option B is correct: 0.4-0.6.
What is the purpose of curing concrete?
A)
Improve workability
B)
Prevent moisture loss and enhance strength
C)
Increase slump value
D)
Reduce setting time
Option B is correct: Prevent moisture loss and enhance strength.
If the slump value of a concrete mix is 100 mm, what is the workability level?
A)
Low
B)
Medium
C)
High
D)
Very high
Option B is correct: Medium.
Why is an ogee spillway preferred in high dams?
A)
It increases the flow velocity significantly
B)
It allows better aeration of water
C)
It reduces water pressure and improves flow conditions
D)
It requires less construction material compared to other spillways
Option C is correct: It reduces water pressure and improves flow conditions.
Which test is used to determine the fineness of cement?
A)
Slump test
B)
Vicat apparatus test
C)
Sieve analysis
D)
Le Chatelier test
Option C is correct: Sieve analysis.
Which type of dam is best suited for a narrow valley with strong rock foundations?
A)
Earthen dam
B)
Gravity dam
C)
Arch dam
D)
Buttress dam
Option B is correct: Gravity dam.
What is the primary chemical compound responsible for early strength gain in cement?
A)
Tricalcium silicate (C₃S)
B)
Dicalcium silicate (C₂S)
C)
Tricalcium aluminate (C₃A)
D)
Tetracalcium aluminoferrite (C₄AF)
Option A is correct: Tricalcium silicate (C₃S).
What is the unit of stress in the SI system?
A)
N/m
B)
N/m²
C)
N/m²
D)
N
Option B is correct: N/m².
Which type of special concrete is used for lightweight construction?
A)
Self-compacting concrete
B)
High-performance concrete
C)
Aerated concrete
D)
Fiber-reinforced concrete
Option C is correct: Aerated concrete.
Why do we consider shear stress variation in beams?
A)
Because shear stress is constant throughout the beam
B)
Because shear stress varies across the cross-section, being maximum at the neutral axis
C)
Because shear stress is maximum at the top and bottom of the beam
D)
Because shear stress only affects the length of the beam
Option B is correct: Because shear stress varies across the cross-section, being maximum at the neutral axis.
A concrete mix has a water-cement ratio of 0.5. If the cement content is 400 kg/m³, how much water is required?
A)
150 kg
B)
180 kg
C)
200 kg
D)
220kg
Option C is correct: 200 kg.
Why is energy dissipation important in hydraulic structures?
A)
To increase water velocity
B)
To prevent scouring and structural damage caused by high-velocity water
C)
To store excess water for later use
D)
To reduce sediment deposition
Option B is correct: To prevent scouring and structural damage caused by high-velocity water.
Why are masonry dams preferred in narrow valleys?
A)
Because they are cheaper to construct than earthen dams
B)
Because they require strong abutments for stability
C)
Because they allow seepage through the structure
D)
Because they can store more water than concrete dams
Option B is correct: Because they require strong abutments for stability.