Part II — Building Materials & Construction

Chapter 2: Building Materials

2.1 Cement

Ordinary Portland Cement (OPC) is manufactured by grinding clinker (produced by heating a mixture of limestone/calcareous material and clay/argillaceous material to about 1450°C in a kiln) with a small percentage of gypsum (added to control/retard the setting time). The four major compounds in cement clinker, known as Bogue's compounds, are: Tricalcium Silicate (C3S) — contributes to early strength gain; Dicalcium Silicate (C2S) — contributes to later/long-term strength; Tricalcium Aluminate (C3A) — contributes to early setting and heat of hydration but low strength contribution; and Tetracalcium Aluminoferrite (C4AF) — contributes to cement colour, minimal strength contribution. Initial setting time of OPC (as per IS 269) should not be less than 30 minutes, and final setting time should not exceed 600 minutes (10 hours). Common cement types include OPC (33, 43, 53 grade), Portland Pozzolana Cement (PPC) (used where lower heat of hydration and better resistance to sulphate attack is needed, e.g., mass concreting and marine structures), and Portland Slag Cement (PSC).

2.2 Aggregates

Aggregates are classified by size into fine aggregate (passing 4.75 mm IS sieve, e.g., sand) and coarse aggregate (retained on 4.75 mm IS sieve, e.g., gravel/crushed stone). Fineness Modulus (FM) is calculated as the sum of cumulative percentage retained on standard sieves divided by 100; a higher FM indicates coarser aggregate. Good aggregate should be hard, strong, durable, chemically inert, and free from harmful impurities like clay, silt, and organic matter. Bulking of sand refers to the increase in volume of sand due to the presence of moisture (surface tension of water films around sand particles pushes grains apart), which is highest at around 5–8% moisture content and must be accounted for when batching concrete by volume.

2.3 Bricks

A standard modular brick in India (as per IS 1077) has nominal dimensions of 190mm × 90mm × 90mm (with mortar joint, giving actual/modular size of 200mm × 100mm × 100mm). Good bricks should have a minimum compressive strength of 3.5 N/mm² (for common building bricks, Class designation varies with strength grade), low water absorption (generally not exceeding 20% of dry weight after 24-hour immersion, per IS 3495), and should give a clear metallic ringing sound when struck.

2.4 Timber

Timber is classified as softwood (from coniferous/needle-leaved trees, e.g., pine, deodar — generally lighter, easier to work) and hardwood (from broad-leaved trees, e.g., teak, sal — generally denser, more durable). Seasoning of timber (controlled drying to reduce moisture content) is essential before use, to prevent shrinkage, warping, and fungal decay; common methods include natural (air) seasoning and artificial (kiln) seasoning, the latter being faster and more controlled.

2.5 Practice Set — Building Materials (16 MCQs)

1. Ordinary Portland Cement is manufactured by heating a mixture of limestone and clay to approximately:
   (a) 900°C (b) 1450°C (c) 2000°C (d) 500°C
2. Gypsum is added during cement manufacture primarily to:
   (a) Increase strength (b) Control/retard the setting time (c) Reduce cost (d) Add colour
3. Which Bogue's compound in cement contributes most to early strength gain?
   (a) Tricalcium Silicate (C3S) (b) Dicalcium Silicate (C2S) (c) Tricalcium Aluminate (C3A) (d) Tetracalcium Aluminoferrite (C4AF)
4. Which Bogue's compound contributes to later/long-term strength development?
   (a) C3S (b) C2S (c) C3A (d) C4AF
5. As per IS 269, the initial setting time of OPC should not be less than:
   (a) 10 minutes (b) 30 minutes (c) 60 minutes (d) 90 minutes
6. As per IS 269, the final setting time of OPC should not exceed:
   (a) 300 minutes (b) 450 minutes (c) 600 minutes (d) 720 minutes
7. Portland Pozzolana Cement (PPC) is particularly preferred for:
   (a) Mass concreting and marine structures, due to lower heat of hydration (b) High early-strength precast elements (c) Cold-weather concreting exclusively (d) Decorative plastering only
8. Fine aggregate is defined as aggregate that:
   (a) Is retained on the 4.75 mm IS sieve (b) Passes the 4.75 mm IS sieve (c) Passes the 20 mm IS sieve only (d) Is retained on the 10 mm IS sieve
9. Fineness Modulus is calculated as:
   (a) Sum of cumulative percentage retained on standard sieves divided by 100 (b) Sum of percentage passing divided by number of sieves (c) The finest sieve size through which all aggregate passes (d) The average particle diameter in mm
10. Bulking of sand refers to:
    (a) A decrease in volume due to compaction (b) An increase in volume due to moisture content (c) A change in colour due to weathering (d) A decrease in density due to heating
11. Bulking of sand is typically maximum at approximately what moisture content?
    (a) 1–2% (b) 5–8% (c) 15–20% (d) 25–30%
12. The nominal size of a standard modular brick in India (as per IS 1077) is:
    (a) 190mm × 90mm × 90mm (b) 200mm × 100mm × 100mm (c) 230mm × 110mm × 75mm (d) 250mm × 120mm × 80mm
13. A good building brick, when struck, should produce:
    (a) A dull thud (b) A clear metallic ringing sound (c) No sound at all (d) A cracking sound
14. As per IS 3495, water absorption of a good building brick after 24-hour immersion should generally not exceed:
    (a) 10% (b) 20% (c) 30% (d) 40%
15. Timber from broad-leaved trees such as teak and sal is classified as:
    (a) Softwood (b) Hardwood (c) Plywood (d) Laminated wood
16. Seasoning of timber is primarily carried out to:
    (a) Increase its weight (b) Reduce moisture content and prevent shrinkage/warping/decay (c) Change its colour (d) Increase its flexibility permanently

Answer Key

1.(b)

2.(b)

3.(a)

4.(b)

5.(b)

6.(c)

7.(a)

8.(b)

9.(a)

10.(b)

11.(b)

12.(a)

13.(b)

14.(b)

15.(b) 16.(b)