Free Concrete Technology MCQs with Answers

• A. Calcium silicate hydrate gel
• B. Calcium hydroxide crystals
• C. Calcium sulphate dihydrate
• D. Unhydrated clinker minerals

Explanation: Calcium silicate hydrate, commonly called C-S-H gel, forms the main binding structure in hydrated cement paste.

• A. Volume of water to volume of cement
• B. Mass of water to mass of cement
• C. Mass of cement to mass of aggregate
• D. Volume of cement to volume of water

Explanation: The water-cement ratio is normally calculated by dividing the mass of mixing water by the mass of cement.

• A. Reducing cement hydration
• B. Increasing aggregate size
• C. Increasing cement fineness
• D. Increasing the volume of entrapped air

Explanation: Finer cement particles provide greater surface area for hydration, so strength develops more rapidly at early ages.

• A. Slump value and air content
• B. Aggregate impact value and abrasion value
• C. Cement fineness and initial setting time
• D. Standard deviation and a statistical margin

Explanation: Target mean strength is set above the characteristic strength by an allowance based on production variability, commonly expressed using…

• A. Hardening involves strength gain after setting
• B. Hardening occurs before water is added
• C. Hardening refers only to loss of workability
• D. Hardening is caused only by evaporation

Explanation: Setting marks the transition from a fluid or plastic state to a rigid state, while hardening is the continuing development of strength…

• A. Moisture correction
• B. Volume
• C. Absolute volume
• D. Specific gravity

Explanation: Mass batching gives more reliable control over the quantities of cement, water and aggregate.

• A. A reduction in aggregate surface area
• B. A lower cement content at constant paste volume
• C. A greater proportion of angular aggregate
• D. The use of saturated surface-dry aggregate

Explanation: Angular and rough-textured aggregate has greater surface area and interparticle friction, so more water is needed for the same…

• A. 5 percent
• B. 10 percent
• C. 15 percent
• D. 20 percent

Explanation: Characteristic strength is statistically defined so that not more than about 5 percent of properly conducted results are expected to fall…

• A. Low-heat Portland cement
• B. Rapid-hardening cement
• C. High-alumina cement
• D. Quick-setting cement

Explanation: Low-heat Portland cement is formulated to release heat more slowly and is useful in massive concrete where thermal cracking is a concern.

• A. Higher density and strength
• B. Reduced compressive strength
• C. No change in strength
• D. Greater resistance to all chemical attack

Explanation: Entrapped air creates voids that reduce the effective load-bearing area and therefore lower compressive strength when it is not…

• A. To determine aggregate absorption capacity
• B. To measure aggregate resistance to impact
• C. To determine aggregate particle-size distribution
• D. To measure aggregate surface moisture

Explanation: Sieve analysis separates aggregate particles into size ranges and gives the grading curve.

• A. Become completely resistant to sulphate attack
• B. Require no water for normal consistency
• C. Produce less heat during hydration
• D. Hydrate more rapidly and gain early strength faster

Explanation: Finer cement has a greater surface area in contact with water, so hydration proceeds more rapidly and early strength usually increases.

• A. Loss of moisture from the cement paste
• B. Expansion of aggregate particles in water
• C. Chemical attack by atmospheric oxygen
• D. Increase in the volume of entrained air

Explanation: Drying shrinkage occurs when moisture leaves capillary pores in the hardened cement paste, producing contraction.

• A. Long compared with their average diameter
• B. Thin compared with their length and width
• C. Easily crushed under a compressive load
• D. Porous because of internal voids

Explanation: Flaky particles have a small thickness compared with their other dimensions.

• A. More resistant to abrasion and impact
• B. More angular and likely to improve workability
• C. More porous and likely to take up mix water
• D. Less affected by changes in moisture condition

Explanation: High absorption usually indicates connected pores within the aggregate, allowing it to draw water from the concrete mixture.

• A. The slump of concrete before placing
• B. The initial setting time of freshly mixed cement paste
• C. The grading of fine aggregate in a stockpile
• D. The in-place condition and strength of hardened concrete

Explanation: A drilled core provides a physical sample of hardened concrete for examination and, when properly tested, an estimate of in-place…

• A. Refining pores and reducing permeability
• B. Increasing the size of capillary pores
• C. Replacing all cement hydration products with air
• D. Preventing aggregate particles from absorbing water

Explanation: Silica fume reacts pozzolanically and fills or refines pores in the cement paste, producing a denser microstructure.

• A. The aggregate grading is slightly different from the design grading
• B. Temperature differences develop between its interior and surface
• C. The concrete surface is finished with a wooden float
• D. The cement paste contains no entrapped air

Explanation: Hydration heat can make the interior of a large member hotter than its surface.

• A. Add dry coarse aggregate without changing other ingredients
• B. Add water freely until the original slump is restored
• C. Remix it without adding water unless the specification permits adjustment
• D. Allow it to set and then compact it by heavy vibration

Explanation: Remixing may restore uniformity, but adding unapproved water raises the water-cement ratio and can reduce strength and durability.

• A. Nominal maximum aggregate size only
• B. Aggregate particle shape and texture
• C. Fresh concrete temperature only
• D. Strength and impermeability

Explanation: The gel-space ratio compares hydrated cement products with the total space available in the paste.