In a 1:2:4 concrete mix, what is the actual quantity of sand per unit volume of cement if sand undergoes 20% bulking?

Detailed Explanation: Bulking Correction for Sand in 1:2:4 Mix

Why B (2.4) is correct: The mix specifies 2 parts of dry sand per 1 part cement. If sand has 20% bulking, its volume has increased by 20% from the dry state. To measure the correct quantity of dry sand, we must measure MORE bulked sand (to compensate for the extra volume caused by moisture films). The correction is: bulked volume = dry volume × (1 + bulking fraction). Specified dry sand = 2 volumes per unit cement
Bulking = 20% = 0.20

Actual volume of moist sand to measure = 2 × (1 + 0.20)
= 2 × 1.20 = 2.4 volumes

Bulking Correction Formula

Mix Ratio	Bulking	Measured Sand Volume
1:2:4	10%	2 × 1.10 = 2.20
1:2:4	20%	2 × 1.20 = 2.40
1:3:6	15%	3 × 1.15 = 3.45

• Formula: Volume of moist sand to measure = Specified dry volume × (1 + bulking fraction).
• For 1:2:4 with 20% bulking: measure 2.4 volumes of moist sand per unit of cement.