SSC · Concrete Technology and RCC practice

Correct answer: C

M stands for mix and the number is the characteristic strength (5 percent failure probability) of 150 mm cubes at 28 days.

Correct answer: C

IS 456 prescribes M20 as the minimum for RCC in mild exposure. M15 is allowed only for plain concrete.

Correct answer: C

IS 456 gives Ec = 5000√fck. The expression 4700√fck belongs to the American code.

Correct answer: B

IS 456 recommends at least 40 mm (or the bar diameter, if larger) for columns. Slabs usually have 20 mm and beams 25 mm in mild exposure.

Correct answer: A

The limiting depth of neutral axis ratio is 0.53 for Fe 250, 0.48 for Fe 415 and 0.46 for Fe 500.

Correct answer: A

IS 456 assumes 0.0035 in bending. The value 0.002 is the strain at the peak stress for axial compression.

Correct answer: A

The partial safety factor is 1.5 for concrete and 1.15 for steel.

Correct answer: C

Slump is insensitive for stiff mixes. The Vee-Bee time (in seconds) measures the effort to remould a slumped cone into a cylinder under vibration.

Correct answer: C

The minimum curing period is 7 days for OPC concrete and 10 days where mineral admixtures or blended cements are used.

Correct answer: C

IS 456 limits the spacing of vertical stirrups to 0.75d or 300 mm, whichever is smaller, so that every potential diagonal crack is crossed.

Correct answer: D

When ly/lx > 2, nearly all load is carried in the short direction, so the slab is designed as one-way.

Correct answer: A

The minimum steel ensures that the beam does not fail suddenly when the concrete cracks. With fy in N/mm², As,min = 0.85 bd / fy.

Correct answer: A

emin = L/500 + D/30 = 3000/500 + 300/30 = 6 + 10 = 16 mm, but it must be at least 20 mm, so 20 mm governs.

Correct answer: A

Factored load = 1.5 × (20 + 10) = 45 kN/m. M = wL²/8 = 45 × 36 / 8 = 202.5 kN·m.

Correct answer: A

Strength decreases as the water-cement ratio increases, provided the concrete is fully compacted.

Correct answer: C

Ld = φσs / (4τbd) with σs = 0.87 × 415 = 361.05 N/mm². Ld = 16 × 361.05 / (4 × 1.92) = 5776.8 / 7.68 ≈ 752 mm (about 47φ).

Correct answer: C

IS 456 treats a column as short if both Lex/D and Ley/b are below 12; otherwise it is slender and additional moments are added.

Correct answer: A

Strains from creep and shrinkage are fixed amounts. With a high initial stress the effective stress left after these losses stays large.

Correct answer: A

The limits are 2.8 for M20, 3.1 for M25, 3.5 for M30, 3.7 for M35 and 4.0 for M40 and above. If τv exceeds this, the section size must be increased.

Correct answer: D

M20 corresponds to 1:1.5:3. The nominal mixes are M5 (1:5:10), M7.5 (1:4:8), M10 (1:3:6), M15 (1:2:4) and M20 (1:1.5:3).