Q1: Which property of concrete makes it advantageous for construction of bridges?
Difficulty: Easy
A. Low thermal conductivity
B. Low durability
C. High compressive strength
D. Low tensile strength
Correct Answer: C. High compressive strengthSolution:Bridges are primarily compression-dominant structures. Concrete’s high compressive strength (20–80 MPa) makes it ideal for piers, abutments, arches, and deck soffits. Combined with reinforcing steel (to handle tension), reinforced concrete efficiently carries all bridge loads. Durability and excellent formwork flexibility are additional advantages.
Q2: Which precaution is followed in COLD weather concreting and NOT in hot weather concreting?
Difficulty: Medium
A. Sprinkling formwork with cooled water
B. Use of an air-entraining agent
C. Cooling of aggregates
D. Covering finished concrete with impermeable sheet
Correct Answer: B. Use of an air-entraining agentSolution:Air-entraining agents introduce microscopic air bubbles that absorb ice expansion during freeze-thaw cycles — a protection needed only in cold weather. Options A (sprinkle cooled water) and C (cool aggregates) are hot-weather precautions to lower mix temperature. Option D is used in both conditions for different reasons.
Q3: Precautions required for concreting in sub-zero temperatures: (i) Pre-heating (ii) Economical heating (iii) Anti-freezing admixtures (iv) Electrical heating
Difficulty: Medium
A. Only (i) and (ii)
B. (i), (ii), (iii), and (iv)
C. Only (i)
D. Only (i), (ii), (iii)
Correct Answer: B. (i), (ii), (iii), and (iv)Solution:All four precautions are required for sub-zero concreting. Pre-heating raises the initial temperature; economical heating manages costs; anti-freezing admixtures lower the pore water freezing point; electrical heating maintains concrete temperature during curing. No single measure is sufficient at sub-zero temperatures.
Q4: For cold weather concreting, cement containing ________ should be selected.
Difficulty: Medium
A. Lower C₃S and higher C₂S
B. Higher C₃S and lower C₂S
C. Lower C₃S and lower C₂S
D. Higher C₃S and higher C₂S
Correct Answer: B. Higher C₃S and lower C₂SSolution:C₃S (Tricalcium Silicate) hydrates rapidly, generates high heat of hydration, and develops high early strength — all critical in cold weather to prevent freezing before the concrete gains strength. C₂S (Dicalcium Silicate) is slow-hydrating and contributes minimal heat and early strength. Rapid Hardening Portland Cement (high C₃S) is ideal for cold weather.
Q5: Effects of cold weather on concrete: (i) Delay in setting and hardening (ii) Freezing at early age (iii) Alternate Freezing and Thawing
Difficulty: Easy
A. Both (ii) and (iii)
B. Both (i) and (ii)
C. Only (i)
D. (i), (ii), and (iii)
Correct Answer: D. (i), (ii), and (iii)Solution:All three effects are caused by cold weather: delayed setting (hydration slows below 10°C), early-age freezing (damage if water freezes before concrete gains ≥3.5 MPa), and freeze-thaw cycling (long-term surface scaling and microcracking). Each is a distinct and well-documented cold weather effect.
Q6: Underwater concreting methods: (i) Pumping (ii) Hydro valve (iii) Toggle bags (iv) Bagged concrete method
Difficulty: Medium
A. Only (i)
B. Only (i), (ii), (iii)
C. (i), (ii), (iii), and (iv)
D. Both (i) and (ii)
Correct Answer: C. (i), (ii), (iii), and (iv)Solution:All four are recognised methods for placing concrete underwater. The Tremie method (most common) was not listed. Each method addresses the key challenge: concrete must not fall freely through water. Pumping and tremie keep concrete submerged in itself; toggle bags and bagged concrete are placed by divers for smaller-scale applications.
Q7: Freezing of freshly laid concrete results in strength loss due to:
Difficulty: Medium
A. Formation of ice lenses in capillary cavities
B. High workability of the mix
C. Endothermic reaction in the mix
D. Air-entraining agents in the mix
Correct Answer: A. Formation of ice lenses in capillary cavitiesSolution:When freshly placed concrete freezes, water in capillary cavities turns to ice with ~9% volumetric expansion. These ice lenses exert enormous internal pressure on the weak nascent cement gel matrix, rupturing it before it gains any meaningful strength. The result is a permanently disrupted structure with severe strength loss.
Q8: Which of the following statements about pumped concrete is/are true?
Difficulty: Medium
A. Pipe diameter ≤ 30 cm only
B. Slump between 5 cm and 8 cm only
C. w/c ratio between 0.5 and 0.65 only
D. All of these
Correct Answer: D. All of theseSolution:All three specifications are correct for pumped concrete: pipeline diameter typically 100–200 mm (not exceeding 300 mm); slump 50–80 mm (medium workability for pumpability); w/c ratio 0.5–0.65 (fluid enough to pump; cohesive enough to resist segregation). All three must be satisfied simultaneously for effective pumping.
Q9: High temperature on concrete:
Difficulty: Easy
A. Increases the strength of concrete
B. Decreases the strength of concrete
C. Has no effect on the strength of concrete
D. None of these
Correct Answer: B. Decreases the strength of concreteSolution:High temperatures (>38°C) reduce concrete strength. Rapid initial hydration produces coarser, less dense C-S-H gel microstructure with larger pores. Accelerated evaporation of mixing water creates more capillary voids. Plastic shrinkage cracks form at the surface. The net result is 10–20% or more reduction in 28-day and ultimate compressive strength versus concrete placed at 20–27°C.
Q10: The resistance of an aggregate to the effect of hydration of cement and weather is called:
Difficulty: Easy
A. Soundness
B. Crushing strength
C. Abrasion resistance
D. Impact value
Correct Answer: A. SoundnessSolution:‘Soundness’ specifically describes an aggregate’s ability to resist disintegration due to weathering (freeze-thaw, wet-dry cycles, temperature changes) and volume instability from chemical reactions with cement hydration products. It is tested by IS 2386 Part 5 using sodium or magnesium sulphate immersion cycles. Crushing strength, abrasion resistance, and impact value measure different mechanical properties.
Q11: The Leaching action in concrete is an example of:
Difficulty: Medium
A. Crystallisation
B. Creeping
C. Chemical reaction
D. Decomposition
Correct Answer: C. Chemical reactionSolution:Leaching is a chemical deterioration process where water dissolves calcium hydroxide [Ca(OH)₂] from the cement paste and carries it out through capillary pores. The dissolution reaction Ca(OH)₂ → Ca²⁺ + 2OH⁻ is a chemical reaction. The visible white deposit (efflorescence) forms when dissolved Ca²⁺ reacts with atmospheric CO₂ to form CaCO₃ at the surface.
Q12: Low temperature during concrete laying:
Difficulty: Hard
A. Increases strength
B. Decreases strength
C. Has no effect on strength
D. Depends on other factors
Correct Answer: A. Increases strengthSolution:(SSC JE Official Answer) Low non-freezing temperatures result in slower cement hydration, which produces a denser, more uniform C-S-H gel microstructure with fewer defects. This ultimately yields higher final compressive strength compared to concrete cured at higher temperatures. Note: while early-age strength (7-day) is significantly lower at low temperatures, the long-term ultimate strength is higher than the standard reference (20–27°C curing).
