Question 1

Water is used in concrete mixes to&#10;A) Increase the strength of the concrete&#10;B) Reduce the strength of the concrete&#10;C) Enable the cement to set&#10;D) Enable the aggregates to bond with the cement&#10;E) Reduce the heat generated during the setting process

Accepted Answer

C

Question 2

Fine aggregates are used in concrete mixes to&#10;A) Enable the concrete to be poured easily&#10;B) Fill the voids between the coarse aggregate particles&#10;C) Provide increased strength to the concrete&#10;D) Soak up the excess water in the concrete&#10;E) Provide colour to the concrete

Accepted Answer

Fine aggregates, also known as sand, are typically used in concrete mixes to fill the gaps between the coarse aggregate particles. This helps to create a more uniform surface, increase the density and durability of the concrete, and improve workability during placement.

Question 3

Rapid Hardening Portland Cement differs from Ordinary Portland Cement in that it&#10;A) Is more finely ground&#10;B) Contains more limestone&#10;C) Contains more iron oxide&#10;D) Contains more silica&#10;E) Is made at higher temperatures

Accepted Answer

Rapid Hardening Portland Cement is more finely ground than Ordinary Portland Cement, which allows it to hydrate more quickly and gain strength faster.

Question 4

Fine aggregates are distinguished from coarse aggregates in that they A) Have a strength of less than 5 N/mm² B) Have a strength greater than 5 N/mm² C) Have particle sizes of less than 5mm D) Have particle sizes of greater than 5mm E) Are synthetic

Accepted Answer

Fine aggregates have particle sizes of less than 5mm, while coarse aggregates have particle sizes of greater than 5mm. The strength is not a distinguishing factor between fine and coarse aggregates. Synthetic aggregates are not commonly used in construction.

Question 5

Sintered pulverised fuel ash lightweight aggregate is made by&#10;A) Fusing furnace clinker into lumps and then crushing it&#10;B) Spraying molten slag with water&#10;C) Heating shale to cause it to exfoliate&#10;D) Firing moistened burnt coal residue to form pellets&#10;E) Crushing volcanic lava

Accepted Answer

Sintered pulverised fuel ash lightweight aggregate is produced by firing moistened burnt coal residue to form pellets. This process involves the use of coal ash, a byproduct of coal combustion, which is moistened and then fired in a kiln to create lightweight, porous pellets suitable for use as aggregate in construction.

Question 6

Concrete can be made more durable by&#10;A) Increasing the amount of cement used in the mix&#10;B) Increasing the amount of water used in the mix&#10;C) Increasing the amount of fine aggregate used in the mix&#10;D) Reducing the amount of coarse aggregate used in the mix&#10;E) Reducing the number of air voids in the mix

Accepted Answer

Reducing the number of air voids in the mix makes concrete more durable by decreasing permeability and increasing resistance to freeze-thaw cycles and other environmental factors.

Question 7

An excessive amount of water in a mix can&#10;A) Weaken the concrete&#10;B) Reduce the drying shrinkage in the concrete&#10;C) Reduce the drying time&#10;D) Reduce the setting time&#10;E) Increase the fire resistance of the concrete

Accepted Answer

An excessive amount of water will weaken the concrete because it dilutes the cement paste, which is the bonding agent in concrete. This can lead to a lower compressive strength and less overall durability.

Question 8

A 1:3:6 concrete mix contains&#10;A) 1 part cement to 3 parts coarse aggregate to 6 parts fine aggregate&#10;B) 1 part cement to 3 parts fine aggregate to 6 parts coarse aggregate&#10;C) 1 part fine aggregate to 3 parts cement to 6 parts coarse aggregate&#10;D) 1 part coarse aggregate to 3 parts cement to 6 parts fine aggregate&#10;E) 1 part fine aggregate to 3 parts coarse aggregate to 6 parts cement

Accepted Answer

In a 1:3:6 mix, the sum of the ratios is 1+3+6 = 10. This means that for every 10 parts of the mixture, 1 part is cement, 3 parts are fine aggregate, and 6 parts are coarse aggregate. In option B, the ratio listed is exactly that - 1 part cement to 3 parts fine aggregate to 6 parts coarse aggregate. Therefore, B is the correct choice.

Question 9

Proportions of materials in a mix are more correctly specified by weight than volume because&#10;A) Water weighs more than cement&#10;B) Coarse aggregates weigh more than fine aggregates&#10;C) Segregation affects the volume of coarse aggregates&#10;D) Bulking affects the volume of fine aggregates&#10;E) Dense aggregates have a greater volume than lightweight aggregates

Accepted Answer

Bulking affects the volume of fine aggregates, making weight a more accurate measure for proportions in a mix.

Question 10

For every 1 kg of cement used in a mix having a water:cement ratio of 0.52 A) 0.26 litres of water should be added B) 0.39kg of water should be added C) 0.52 litres of water should be added D) 0.65m³ of water should be added E) 0.78kg of water should be added

Accepted Answer

The water:cement ratio is given as 0.52, meaning for every 1 kg of cement, 0.52 kg of water is needed. Since 1 kg of water is approximately equal to 1 litre, 0.52 kg of water is approximately 0.52 litres.

Deck 6: Concrete