MCQs on Ingredients of Concrete
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Q46: Pick up the correct statement from the following
Difficulty: Medium
Solution:
All the given statements are correct. The angularity number correlates with the percentage of voids in excess of 33%, angular aggregates offer superior interlocking strength, and surface texture is an inherent rock property.
Q47: The flakiness index of aggregates is the percentage by weight of particles in it whose thickness is less than
Difficulty: Easy
Solution:
The flakiness index is defined as the total percentage by weight of aggregate particles whose least dimension (thickness) is less than 0.6 times (or 3/5ths of) their mean sieve dimension.
Q48: The bulk density of aggregates depends upon its :
Difficulty: Easy
Solution:
The bulk density of aggregates (mass per unit volume) is highly dependent on how the particles pack together, which is determined by their shape, grading, and the degree of compaction applied.
Q49: If aggregates completely pass through a sieve of size 75 mm and are retained on a sieve of size 60 mm, the aggregates will be known as elongated aggregate if its length is not less than
Difficulty: Medium
Solution:
Mean dimension = (75 + 60) / 2 = 67.5 mm. An aggregate is elongated if its longest dimension exceeds 1.8 (or 9/5) times its mean dimension. Minimum length for elongated classification = 1.8 x 67.5 = 121.5 mm.
Q50: Calculate the proportion (in percentage) of the fine aggregate in combined aggregate so that the fineness modulus of the combined aggregate becomes 6.4. The fineness modulus of coarse aggregate and fine aggregate in the concrete mix is 7.6 and 2.8 respectively.
Difficulty: Hard
Solution:
Using the fineness modulus blend formula: P = [(FM_coarse – FM_combined) / (FM_combined – FM_fine)] x 100 = [(7.6 – 6.4) / (6.4 – 2.8)] x 100 = (1.2 / 3.6) x 100 = 33.33%.
Q51: The size of the fine aggregates does not exceed:
Difficulty: Easy
Solution:
By definition, fine aggregates are those that essentially pass through a 4.75 mm IS sieve. Therefore, their size generally does not exceed 4.75 mm.
Q52: The most useless aggregate is one whose surface texture is:
Difficulty: Easy
Solution:
A glassy surface texture develops an extremely poor mechanical bond with the cement paste, making it the least desirable or ‘most useless’ aggregate for achieving concrete strength.
Q53: The aggregate which is obtained from the seashore or rivers and produces minimum voids in the concrete is known as ……..
Difficulty: Easy
Solution:
Rounded aggregates (typically river or seashore gravels) pack closely to produce the minimum percentage of voids (about 32-33%), meaning they require less cement paste for a given workability.
Q54: If fineness modulus of sand is 2.5 it is graded as ..
Difficulty: Medium
Solution:
The standard fineness modulus ranges for sand are: Fine sand (2.2 – 2.6), Medium sand (2.6 – 2.9), and Coarse sand (2.9 – 3.2). A value of 2.5 falls squarely in the fine sand category.
Q55: According to IS : 382-1963, a good aggregate should be ………
Difficulty: Easy
Solution:
For concrete to be strong and stable, the aggregates used must be hard, durable, sufficiently strong to resist loads, and chemically inert so they don’t react adversely with cement.
Q56: An aggregate is known as cyclopean aggregate if its size is more than ………
Difficulty: Easy
Solution:
Cyclopean aggregates refer to exceptionally large aggregates (boulders or large cobbles), typically classified as those exceeding 75 mm in size, used in massive unreinforced structures.
Q57: The aggregate containing moisture in pores and having its surface dry is known as ……..
Difficulty: Easy
Solution:
When an aggregate’s internal pores are fully saturated with water but its outer surface is completely dry, it is referred to as being in a Saturated Surface Dry (SSD) condition.
Q58: Grading of aggregate in a concrete mix is necessary to achieve :
Difficulty: Medium
Solution:
The primary technical goal of grading an aggregate (mixing different particle sizes) is the reduction of voids. Minimizing voids indirectly leads to higher density, better durability, and requires less cement paste.
Q59: Quick sand is
Difficulty: Medium
Solution:
Quick sand is not a distinct material or type of sand; rather, it is a hydraulic flow condition that occurs in cohesionless soils (like fine sand) when upward seepage forces overcome the effective stress.
Q60: If aggregates completely pass through a sieve of size 75 mm and are retained on a sieve of size 60 mm, the particular aggregate will be flaky if its minimum dimension is less than ……….
Difficulty: Medium
Solution:
Mean dimension = (75 + 60) / 2 = 67.5 mm. An aggregate is flaky if its minimum dimension is less than 0.6 (or 3/5) of the mean dimension. So, (3/5) x 67.5 = 40.5 mm.