Past Year Questions: Concrete Technology | Topic wise GATE Past Year Papers for Civil Engineering - Civil Engineering (CE) PDF Download

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Q1: Concrete of characteristic strength $30MPa$30MPa is required. If 40 specimens of concrete cubes are to be tested, the minimum number of specimens having at least $30MPa$30MPa strength should be    [2024, Set-1]
(a) 35
(b) 37
(c) 38
(d) 39
Ans: (c) 
Sol: As per IS456:2000, at least 95% of the specimen should have strength equal to more than the characteristics strength.
∴ Minimum number of specimens  = 0.95 x 40 = 38

Q1: In cement concrete mix design, with the increase in water-cement ratio, which one of the following statements is TRUE?    [2023, Set-1]
(a) Compressive strength decreases but workability increase
(b) Compressive strength increases but workability decreases
(c) Both compressive strength and workability decrease
(d) Both compressive strength and workability increase
Ans: (a)
Sol: As the water-cement ratio increases, the porosity in the hardened concrete increases and hence the strength decreases.
Also, as water-cement ratio increases, ducts higher water availability, the workability increases.
Hence, correct answer is (A).

Q1: It is given that an aggregate mix has 260 grams of coarse aggregates and 240 grams of fine aggregates. The specific gravities of the coarse and fine aggregates are 2.6 and 2.4, respectively. The bulk specific gravity of the mix is 2.3.
The percentage air voids in the mix is ____________. (round off to the nearest integer)    [2022, Set-2]
Ans: 8 to 8
Sol: Given that,
Coarse aggregate = 260 gms
Fine aggregate = 240 gms
G_CA = 2.6
G_FA = 2.4
Bulk specific gravity G_m = 2.3
$Gm=2.3$Percentage air voids in the mix = ?
G_t (Theoretical specific gravity)

V_v = 8

Q2: Match all the possible combinations between Column X (Cement compounds) and Column Y (Cement properties):

Which one of the following combinations is correct?    [2022, Set-2]
(a) (i) - (P), (ii) - (Q) and (T), (iii) - (R) and (S)
(b) (i) - (Q) and (T), (ii) - (P) and (S), (iii) - (R)
(c) (i) - (P), (ii) - (Q) and (R), (iii) - (T)
(d) (i) - (T), (ii) - (S), (iii) - (P) and (Q)
Ans: (a)
Sol: C₃S - Responsible for early age strength
C₂S - Responsible for later age strength and lowest heat of hydration
C₃A - Flash setting and highest heat of hydration

Q3: Which of the following equations is correct for the Pozzolanic reaction?    [2022, Set-1]
(a) Ca (OH)₂ + Reactive Superplasticizers  + H₂O → C - S - H
(b) Ca (OH)₂ +  Reactive Silicon dioxide +  H2O → C - S - H
(c)  Ca (OH)₂ +  Reactive Sulphates + H₂O → C - S - H
(d)  Ca (OH)₂ +  Reactive Sulphur +  H₂O → C - S - H
Ans: (b) 
Sol: $H2O\to C-S-H$
Pozzolanic materials have no cementing properties itself but have the property of combining with lime to produce stable compound.
Pozzolana is considered as siliceous and aluminous materials and when added in cement it have S_iO₂ and Al₂O₃ form.
So, pozzolanic reaction :
 H₂O + Reactive Silicon dioxide +  H2O → C - S - H  gel or Tobermoritegel