Construction Materials and Their Properties
Construction Materials and Their Properties tests whether you can select a material for a job and justify it by its physical and mechanical properties. The exam favours BIS grades, mix proportions, simple site tests and quantity checks.
Core rules
- Cement: OPC 33, 43 and 53 grade; initial setting time not less than 30 minutes, final not more than 600 minutes. Store bags dry, stack no more than 10 high, and use older stock first.
- Aggregates: 20 mm coarse aggregate for normal RCC, 10 mm for thin sections; sand must be clean and free of silt and organic matter. Bulking of sand depends on moisture.
- Bricks: modular size 190 × 90 × 90 mm; with a 10 mm mortar joint the nominal module is 200 × 100 × 100 mm. First-class bricks are well burnt, sharp-edged and have low water absorption.
- Steel: Fe415 and Fe500 TMT bars; check grade, diameter and bendability. Timber must be seasoned; stone must be sound and non-porous.
Worked example
Find cement bags for 1 m³ of 1:6 cement mortar. Wet volume = 1 m³; dry volume = 1.33 m³. Total parts = 1 + 6 = 7. Cement volume = 1.33 ÷ 7 = 0.19 m³. One 50 kg bag = 0.0347 m³, so bags = 0.19 ÷ 0.0347 = 5.48, say 6 bags. This is a material check, not a final estimate; site wastage is added separately.
Traps
Mixing up initial and final setting times; treating 190 mm as the nominal brick length; ignoring bulking when batching sand; accepting rusty or bent steel; and using a richer mix than specified without approval.