Q61: If P, Y and Z are weights of cement, fine aggregates and coarse aggregates respectively and W/C is the water cement ratio, the minimum quantity of water to be added to first batch is obtained by the equation:
Difficulty: Hard
A. Only A
B. Only B
C. Only C
D. Only D
Correct Answer: B. Only BSolution:The correct formula for minimum water to be added to the first batch is: 0.3P + 0.1Y + 0.01Z = (W/C) x P. Here the coefficients 0.3, 0.1, and 0.01 represent the water absorbed by cement, fine aggregates, and coarse aggregates respectively per unit weight. The right-hand side (W/C x P) is the theoretical water required by the cement.
Q62: Pick up the correct statement from the following
Difficulty: Easy
A. An increase in water content must be accompanied by an increase in cement content
B. Angular and rough aggregates reduce the workability of the concrete
C. Large size aggregates increase the workability due to lesser surface area
D. All options are correct
Correct Answer: D. All options are correctSolution:All three statements are correct: (A) When water content increases, cement must also increase to maintain the target w/c ratio and avoid strength loss. (B) Angular/rough aggregates increase inter-particle friction, reducing workability. (C) Larger aggregates have less surface area per unit volume, requiring less water to coat them, thus increasing workability for a given water content.
Q63: Which of the below is an example of plasticizer?
Difficulty: Medium
A. Hydroxylated carboxylic acid
B. Fluoro-silicate
C. Gypsum
D. Surkhi
Correct Answer: A. Hydroxylated carboxylic acidSolution:Plasticizers (water-reducing admixtures) include: hydroxylated carboxylic acids and their salts (e.g., gluconic acid, citric acid), lignosulphonates, and hydroxycarboxylic acids. They adsorb onto cement particle surfaces, creating electrostatic repulsion that disperses particles and reduces water demand by 5-15%.
Q64: Pozzolana are rich in:
Difficulty: Medium
A. Silica
B. Silica and alumina
C. Silica, alumina and alkali
D. Silica, alumina, alkali and iron
Correct Answer: C. Silica, alumina and alkaliSolution:Pozzolanas (per ASTM C618 and IS 1344) are naturally occurring or artificial materials rich in silica (SiO2), alumina (Al2O3), and alkali (alkali oxides/reactive siliceous constituents). They have little or no cementitious value alone but react with Ca(OH)2 in the presence of water to form cementitious compounds.
Q65: Find the odd entry among silica fume, rice husk ash, metakaoline and ground granulated blast furnace slag with respect to cement product:
Difficulty: Hard
A. Silica fume
B. Rice husk ash
C. Metakaoline
D. Ground granulated blast furnace slag
Correct Answer: C. MetakaolineSolution:Metakaolin (calcined kaolin) is the odd one out because it is a MANUFACTURED product (produced by calcining purified kaolin clay). The other three — silica fume (by-product of silicon/ferrosilicon production), rice husk ash (agricultural by-product), and GGBS (by-product of iron blast furnaces) — are all INDUSTRIAL or AGRICULTURAL BY-PRODUCTS.
Q66: W1 and W2 are the weights of a cylinder partially compacted and fully compacted. If the compaction factor (W1/W2) is 0.95, the workability of concrete is:
Difficulty: Easy
A. Extremely low
B. Very low
C. Low
D. High
Correct Answer: D. HighSolution:CF = W1/W2 = 0.95. Per IS 7320, CF > 0.92 = High workability. W1 is weight of partially compacted concrete and W2 is weight of fully compacted concrete (cylinder filled to the brim). CF close to 1.0 means the concrete self-compacts almost completely under gravity = very workable/fluid.
