Construction Materials and Their Properties
This domain tests whether you can select, store, test and accept cement, aggregates, bricks, steel, timber and mortar, and reject material that would fail in the works.
Cement
OPC grades 33, 43 and 53 give 28-day compressive strengths of 33, 43 and 53 N/mm2. Store bags on timber pallets off the floor and away from walls, about 8 to 10 bags high, and use within 3 months on a first-in-first-out basis. Lumps mean damp; a handful of good cement feels cool, not warm.
Aggregates and bricks
Moist sand bulks up to 20 to 30%, so volume batching over-sands unless you correct for it. Silt test: shake sand in a jar of water; silt should be under about 6 to 8% of the sand layer. A first-class burnt clay brick has sharp edges, rings when struck, absorbs under about 20% water and reaches about 10 N/mm2. The modular brick is 190 x 90 x 90 mm, which becomes 200 x 100 x 100 mm with a 10 mm mortar joint.
Steel and timber
TMT bars are graded Fe415, Fe500 and Fe550 by yield strength. Timber must be seasoned, by air or kiln, to control shrinkage, warp and insect attack; moisture content around 10 to 12% suits joinery.
Worked example
A 1:6 mortar by volume is 1 part cement to 6 parts sand. For 1 m3 of wet mortar the dry volume is about 1.33 m3, so cement = 1.33 x 1/7 = 0.19 m3, about 274 kg or 5.5 bags, and sand = 1.33 x 6/7, about 1.14 m3. The 1.33 factor covers voids and shrinkage.
Traps
Confusing grade with fineness; forgetting bulking of sand; using nominal instead of modular brick size; assuming more cement always means better concrete.