QUESTION 4: MATERIALS AND QUANTITIES
4.1 Name TWO reactions which take place during the hydration process of cement - NSC Civil Technology Civil Services - Question 4 - 2017 - Paper 1
Question 4
QUESTION 4: MATERIALS AND QUANTITIES
4.1 Name TWO reactions which take place during the hydration process of cement.
4.2 Briefly motivate why cement must not be ... show full transcript
Worked Solution & Example Answer:QUESTION 4: MATERIALS AND QUANTITIES
4.1 Name TWO reactions which take place during the hydration process of cement - NSC Civil Technology Civil Services - Question 4 - 2017 - Paper 1
Step 1
Name TWO reactions which take place during the hydration process of cement.
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Answer
The chemical reaction where water combines with the compounds in cement to form calcium silicate hydrate and calcium hydroxide.
The physical binding effect that occurs as the water evaporates, resulting in the hardening of the cement.
Step 2
Briefly motivate why cement must not be stored longer than three months.
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Answer
Cement can absorb moisture from the air, which can alter its chemical properties and result in reduced strength and effectiveness. After three months, its quality may deteriorate, leading to potential structural failures.
Step 3
Name ONE purpose of lime in a mortar mix.
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Answer
Lime improves the workability and plasticity of the mortar, allowing for better adhesion and easier application.
Step 4
Which ingredient is first put into the concrete mixer when concrete must be mixed?
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Answer
Coarse aggregates are typically added to the concrete mixer first, followed by the other ingredients such as fine aggregates, cement, and water.
Step 5
Name THREE methods that can be used for curing concrete.
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Ponding - keeping the surface of the concrete moist by using water-filled forms.
Spraying - applying water directly on the surface at regular intervals.
Using curing compounds - applying a chemical to preserve moisture in the curing concrete.
Step 6
Briefly motivate why the cube test must be performed on concrete.
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Answer
The cube test is essential to determine the compressive strength of concrete. It ensures the material meets required specifications for load-bearing applications and helps predict long-term durability.
Step 7
Name TWO uses of each of the following materials in the construction trade: Copper.
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Answer
Electrical wiring
Plumbing pipes
Step 8
Name TWO uses of each of the following materials in the construction trade: Zinc.
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Answer
Covering for iron and roof sheets
Used in alloys for various construction applications
Step 9
Make a neat sketch to illustrate the profile of channel iron.
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Answer
A sketch can depict a standard channel iron profile, which often resembles the letter 'U', emphasizing the dimensions of the flanges and web.
Step 10
Name THREE properties of a good preservative for wood.
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Answer
It should be readily absorbed by the wood fibers to penetrate deeply.
Should not be harmful or toxic to humans and animals.
Must resist decay and not corrode metals.
Step 11
Briefly describe the composition of plywood.
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Answer
Plywood is composed of multiple layers of thin veneer sheets, glued together with the grain of adjacent layers running perpendicular to each other. This cross-layering provides enhanced strength and durability.
Step 12
Use the quantity list on ANSWER SHEET A and determine the volume of concrete which will be needed for a floor with a length of 6 m, width of 3 m and thickness of 75 mm.
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Answer
To calculate the volume:
Volume = Length × Width × Thickness
= 6 m × 3 m × 0.075 m = 1.35 m³.
Step 13
Use the quantity list on ANSWER SHEET A and determine the number of bricks which will be needed for a cavity wall with a height of 4 m and a length of 2.4 m.
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Answer
First, calculate the area of the wall:
Area = Height × Length
= 4 m × 2.4 m = 9.6 m².
Assuming each brick has an area of 0.002 m², the number of bricks needed is:
Number of bricks = Total area / Area of one brick
= 9.6 m² / 0.002 m² = 4800 bricks.
