Standards (NS & IS) and tests for civil engineering materials

Laboratory tests check whether materials delivered to site meet the specified quality. In Nepal, the Nepal Bureau of Standards and Metrology (NBSM) issues Nepal Standards (NS), and where an NS is missing Indian Standards (IS) are widely followed in specifications and in the Department of Roads/DUDBC norms. This note covers the standard tests on bricks, cement, sand and reinforcing steel that are listed in the NEC syllabus: what each test measures, how it is done and the typical acceptance values.

Key concepts

Tests on bricks

Water absorption test

1. Dry the bricks in an oven at 105–115 °C to constant mass ($W_1$).
2. Immerse in clean water for 24 hours (cold-water method) at room temperature.
3. Wipe surface and weigh ($W_2$).

• Water absorption = $(W_2 - W_1)/W_1 \times 100$.
• Limits: should not exceed 20% for first-class bricks (up to 25% for lower classes in many specifications).

Compressive strength test

1. Remove irregularities, fill frogs with 1:1 cement mortar, store under damp sacks 24 h, then immerse in water for 3 days.
2. Test in a compression machine with load applied at about 14 N/mm² per minute, frog upward.
3. Strength = maximum load ÷ area of bed face.

• Common classes: ≥ 3.5 N/mm² (minimum common brick), first-class about 10.5 N/mm² or more.

Other brick tests: efflorescence (soaking and drying — nil/slight acceptable), dimension tolerance (20 bricks laid together), hardness and soundness (field tests).

Tests on cement

Normal (standard) consistency – Vicat apparatus with 10 mm plunger.

• Percentage of water that allows the plunger to penetrate to 5–7 mm from the bottom of the Vicat mould.
• Typically 26–33% for OPC. Used as basis for other tests.

Setting time – Vicat apparatus with needles, paste at $0.85P$ water ($P$ = consistency).

• Initial setting time: time when 1 mm² needle fails to penetrate beyond 5 ± 0.5 mm from bottom; ≥ 30 minutes for OPC.
• Final setting time: when annular attachment makes an impression but needle does not; ≤ 600 minutes (10 h) for OPC.

Soundness – checks free lime/magnesia that cause later expansion.

• Le Chatelier method: paste in split brass mould, cured 24 h, boiled 3 h; expansion ≤ 10 mm for OPC.
• Autoclave test: expansion ≤ 0.8% (sensitive to magnesia).

Compressive strength – 1:3 cement–standard sand mortar cubes of 70.6 mm (area 5000 mm²), water $(P/4 + 3)\%$ of combined mass, vibrated, cured and tested at 3, 7 and 28 days.

• For 43-grade OPC: ≥ 23 MPa (3 d), 33 MPa (7 d), 43 MPa (28 d). For 33-grade: 16/22/33 MPa. For 53-grade: 27/37/53 MPa.

Fineness (Blaine air permeability ≥ 225 m²/kg for OPC; or residue on 90 µm sieve ≤ 10%) is also routine.

Test on aggregate — bulking of sand

• Moist sand occupies more volume than dry sand because thin water films keep grains apart. Bulking is maximum (about 20–40%) at around 4–6% moisture, and almost zero when sand is fully saturated (inundated).
• Test: fill a container with loose moist sand to height $h_1$, then flood/inundate it with water and measure the settled height $h_2$.
• Bulking (%) = $(h_1 - h_2)/h_2 \times 100$.
• Importance: in volume batching, extra sand must be added to compensate, otherwise the mix becomes sand-deficient (harsh, weak).

Test on rebar — tensile test

• Bar specimen in a universal testing machine (UTM); load–elongation recorded.
• Results: yield (or 0.2% proof) stress, ultimate tensile strength (UTS), percentage elongation on gauge length $5.65\sqrt{A_0}$.
• IS 1786 requirements (e.g. Fe 500): yield ≥ 500 N/mm², UTS ≥ 545 N/mm² (≥ 1.08 × yield), elongation ≥ 12%; Fe 500D: UTS/YS ≥ 1.10, elongation ≥ 16%.
• Also: bend and rebend tests, mass per metre ($d^2/162$ kg/m, $d$ in mm).

High-yield points

• Brick water absorption after 24 h immersion: ≤ 20% for first class.
• Normal consistency: Vicat plunger 5–7 mm from the bottom; setting-time paste uses $0.85P$ water.
• OPC: initial set ≥ 30 min, final set ≤ 600 min; Le Chatelier expansion ≤ 10 mm; autoclave ≤ 0.8%.
• Mortar cubes 70.6 mm, 1:3, water $(P/4 + 3)\%$; 43 grade: 23/33/43 MPa at 3/7/28 days.
• Bulking of sand is maximum (20–40%) at 4–6% moisture.
• Fe 500 (IS 1786): UTS ≥ 1.08 × yield, elongation ≥ 12%; bar mass $d^2/162$ kg/m.

Formulas

$\text{Water absorption}(\%) = \frac{W_2 - W_1}{W_1}\times100$ $\text{Bulking}(\%) = \frac{h_1 - h_2}{h_2}\times100$ $\%\text{ Elongation} = \frac{L_f - L_0}{L_0}\times100,\qquad \sigma = \frac{P}{A_0}$

Worked example

A 12 mm TMT bar (gauge length 5.65√A₀) yields at 60 kN and breaks at 66 kN. Find yield stress, UTS, and check the Fe 500 ratio.

• $A_0 = \pi\times12^2/4 = 113.1$ mm²
• Yield stress = 60 000/113.1 = 530.5 N/mm² (> 500 ✓)
• UTS = 66 000/113.1 = 583.6 N/mm²
• UTS/YS = 1.10 (≥ 1.08 ✓ for Fe 500)
• Mass per m = 12²/162 = 0.889 kg/m.

Exam tips

• Initial setting ≥ 30 min, final ≤ 600 min for OPC; Le Chatelier expansion ≤ 10 mm.
• Cement mortar cube = 70.6 mm, 1:3 with standard sand; concrete cubes are 150 mm.
• Consistency: plunger 5–7 mm from bottom; setting time paste uses 0.85P water.
• Bulking is maximum at 4–6% moisture and nearly zero for saturated sand.
• Bricks absorb ≤ 20% (good class) after 24 h immersion.

Exam-style questions

From Calmon's question bank, which has 25 questions on this topic.

1. The plunger of the Vicat apparatus used for the standard consistency test of cement has a diameter of

• A. 10 mm
• B. 25 mm
• C. 1 mm
• D. 5 mm

Answer: A. The consistency plunger is 10 mm in diameter and 50 mm long; the 1 mm square needle is used for initial setting time.

2. In the Le Chatelier soundness test, the expansion of ordinary Portland cement should not exceed

• A. 10 mm
• B. 5 mm
• C. 20 mm
• D. 1 mm

Answer: A. IS limits the Le Chatelier expansion of OPC to 10 mm; larger expansion indicates unsoundness due to excess free lime.

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