Basic Civil Engineering — Exercise Solutions
Key Concepts Quick Recap
| Material | Use | Key Property |
|---|
| OPC (Ordinary Portland Cement) | Binding in concrete and mortar | Sets by hydration |
| Sand | Fine aggregate | Fills voids; 4.75 mm below |
| Gravel/Stone | Coarse aggregate | 4.75 mm above; provides strength |
| Brick | Walling | Compressive strength, water absorption |
| Steel (TMT bars) | Reinforcement in RCC | High tensile strength |
| Timber | Shuttering, roofing | Lightweight; must be seasoned |
| Lime | Mortar, plastering | Traditional binding agent |
I. Choose the Best Answer (MCQs)
1. The standard size of a modular brick in India is: (a) 240 × 115 × 75 mm (b) 190 × 90 × 90 mm (c) 300 × 150 × 100 mm (d) 250 × 120 × 80 mm
Answer(b) 190 × 90 × 90 mm Modular brick (IS 1077): 190 × 90 × 90 mm. With 10mm mortar joints: effective size 200 × 100 × 100 mm (easy calculation).
2. The ratio of cement:sand:aggregate for M20 concrete is: (a) 1:1.5:3 (b) 1:2:4 (c) 1:3:6 (d) 1:1:2
Answer(a) 1:1.5:3 Concrete mix ratios: M15 = 1:2:4; M20 = 1:1.5:3; M25 = 1:1:2. M20 means characteristic compressive strength of 20 N/mm² at 28 days.
3. Reinforced Cement Concrete (RCC) is used because: (a) Plain concrete is strong in tension (b) Steel reinforcement compensates for concrete's weakness in tension (c) It is cheaper than plain concrete (d) It sets faster
Answer(b) Steel reinforcement compensates for concrete's weakness in tension Plain concrete: strong in compression (~10-40 MPa) but weak in tension (~1/10 of compressive strength). Steel bars: strong in tension. RCC combines both → strong in both compression and tension.
4. In surveying, the instrument used to measure horizontal and vertical angles is: (a) Theodolite (b) Dumpy level (c) Staff (d) Planimeter
Answer(a) Theodolite Theodolite: measures horizontal angles (bearing) and vertical angles (elevation/depression). Used for: setting out buildings, road alignment, triangulation. Dumpy level: only horizontal; used for levelling (differences in height).
5. The foundation transfers loads from the structure to the: (a) Walls (b) Soil (c) Roof (d) Columns only
Answer(b) Soil Foundation: lowest part of structure; spreads superstructure loads to soil safely. Types: shallow (strip, raft, isolated column footing) and deep (pile, well/caisson). Suitable when top soil is weak.
6. The grade of steel most commonly used as reinforcement in RCC is: (a) Fe 250 (b) Fe 415 (c) Fe 200 (d) Fe 600
Answer(b) Fe 415 Fe 415: TMT (Thermo-Mechanically Treated) bars; yield strength 415 N/mm². Commonly used in residential and commercial construction. Fe 500: stronger; used in high-rise buildings and heavy structures.
7. Which type of road surface is most commonly used in India for highways? (a) Gravel road (b) Water-bound macadam (WBM) (c) Bituminous (asphalt) surface (d) Concrete pavement (PQC)
Answer(c) Bituminous (asphalt) surface Bituminous roads: most common for Indian highways. Flexible pavement. Layers: subgrade → granular sub-base → base course → bituminous wearing course. Cement concrete roads (rigid pavement) used for city roads, expressways, airport runways.
II. Short Answer Questions
Q1. What are the types of foundations and when are they used?
Answer
Shallow foundations (depth < width):
- Isolated column footing: One footing per column; for light loads, good soil.
- Combined footing: Two or more columns share one footing; when footings overlap.
- Strip foundation: Continuous under walls; for load-bearing masonry.
- Raft/Mat foundation: One large slab under entire building; for poor soil or heavy loads.
Deep foundations (depth > width):
- Pile foundation: Long slender columns driven into soil; transfers load to deeper, stronger stratum.
- Well foundation (caisson): Used for bridges over rivers; large diameter, sunk into river bed.
Q2. What is the difference between mortar and concrete?
Answer
| Feature | Mortar | Concrete |
|---|
| Components | Cement + Sand + Water | Cement + Sand + Coarse aggregate + Water |
| Coarse aggregate | Absent | Present (gravel/crushed stone) |
| Uses | Joining bricks/blocks, plastering | Columns, beams, slabs, foundations |
| Strength | Lower | Higher (especially with reinforcement) |
| Mix ratio | 1:3 to 1:6 (cement:sand) | 1:1.5:3 to 1:3:6 (M20 to M10) |
Exam Checklist
- Modular brick: 190 × 90 × 90 mm (IS 1077).
- Concrete mix M20: 1:1.5:3 (cement:sand:aggregate).
- RCC: steel compensates for concrete's poor tensile strength.
- W/C ratio: lower = stronger; 0.45-0.55 for structural concrete.
- Theodolite: measures angles (horizontal + vertical); Dumpy level: levels only.
- Foundation: transfers superstructure loads to soil.
- Bituminous roads: most common in India (flexible); concrete: rigid.
