Construction Materials and Their Properties
Domain 1 covers Construction Materials and Their Properties: what each material is, the standard that governs it, the test that checks it, and the location in a building where it is the correct choice. Questions are short and factual, so a wrong IS number or a confused property loses the mark outright.
Core rules
- Bricks (IS 1077): burnt clay bricks are graded by compressive strength from 3.5 to 30 N/mm²; a class 10 brick carries roughly 10 N/mm² (about 100 kg/cm²). Water absorption should stay under about 20% for ordinary classes. A sharp metallic ring when struck and a uniform, well-burnt colour indicate good quality; the frog (indentation) faces up to hold mortar.
- Cement (IS 269, IS 8112, IS 12269): OPC 33, 43 and 53 grade. Initial setting time not less than 30 minutes, final not more than 600 minutes; soundness is checked with the Le Chatelier apparatus. Store bags on timber at least 150 mm off the floor, not more than 10–12 bags high, and use within three months.
- Aggregates (IS 383): sand must be free of silt and clay (jar test silt layer below about 5%); coarse aggregate of 20 mm nominal size suits RCC, 40 mm suits mass concrete.
- Steel (IS 432, IS 1786): Fe415 and Fe500 TMT bars; ribs improve bond with concrete.
- Mortar and concrete: masonry mortar 1:4 to 1:6, plaster 1:4 to 1:6, M20 nominal mix 1:1.5:3 with water-cement ratio near 0.5.
Worked example
A truck of sand arrives. The mason shakes a sample in a jar: a 12 mm silt layer sits over 150 mm of sand, about 8%. Reasoning: silt coats the grains, raises water demand and reduces strength and bond. The sand is rejected or washed; adding extra cement is not a substitute.
Traps that cost marks
- Confusing cement grade (43 grade) with concrete grade (there is no standard M43 nominal mix).
- Assuming a richer mix is always better; it increases shrinkage and cost.
- Judging brick quality by colour alone instead of sound, absorption and strength.