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
4.1 Name TWO reactions which take place during the hydration process of cement.
4.2 Briefly motivate why cement must not be stored longer than three months.
4.3 Na... show full transcript
Worked Solution & Example Answer: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
Chemical reaction: The primary chemical reaction involves tricalcium silicate (3CaO·SiO2) reacting with water to form calcium silicate hydrate (C-S-H) and calcium hydroxide.
Physical reaction: Cement also undergoes a physical binding process, where the cement particles bind together to form a solid mass as water evaporates.
Step 2
Briefly motivate why cement must not be stored longer than three months.
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Answer
Cement must not be stored longer than three months because it can absorb moisture from the air, leading to clumping or caking, which decreases its effectiveness. Additionally, it can undergo hydration prematurely, making it unusable for construction purposes.
Step 3
Name ONE purpose of lime in a mortar mix.
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One purpose of lime in a mortar mix is to improve workability, allowing for easier application and better bonding between masonry units.
Step 4
Which ingredient is first put into the concrete mixer when concrete must be mixed?
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The first ingredient that should be added to the concrete mixer is the aggregate, typically coarse aggregate, as it provides the bulk of the concrete mix.
Step 5
Name THREE methods that can be used for curing concrete.
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Retaining formwork: Keeping the forms in place to retain moisture.
Covering: Using wet burlap or plastic sheeting to keep the surface damp.
Ponding: Creating a small pond of water on the surface to maintain moisture.
Step 6
Briefly motivate why the cube test must be performed on concrete.
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The cube test is essential for testing the compressive strength of concrete. It ensures that the concrete mix used in construction meets the required strength specifications, which is crucial for the safety and durability of structures.
Step 7
Name TWO uses of each of the following materials in the construction trade:
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4.7.1 Copper:
Electrical wiring.
Plumbing pipes.
4.7.2 Zinc:
Coating for iron and roof sheets to prevent rust.
Used in alloys to enhance corrosion resistance.
Step 8
Make a neat sketch to illustrate the profile of channel iron.
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Answer
A neat sketch should include the typical U-shape of channel iron with dimensions clearly labeled, indicating the depth, width of flanges, and thickness.
Step 9
Name THREE properties of a good preservative for wood.
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Easily absorbed into the wood fibers.
Non-toxic to humans and animals.
Resistant to mold and decay.
Step 10
Briefly describe the composition of plywood.
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Plywood is composed of multiple layers of thin wood veneer glued together with the grain of each layer running perpendicular to the adjacent layers. This cross-grain construction enhances strength and stability, minimizing warping.
Step 11
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 of concrete needed:
Volume = Length × Width × Thickness.
Converting thickness from mm to m: 75 mm = 0.075 m.
Thus, the volume is:
V=6extmimes3extmimes0.075extm=1.35extm3
Step 12
Use the quantity list on ANSWER SHEET A and determine the number of bricks which will be needed for a cavity wall with a length of 4 m and a height of 2.4 m.
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To find the number of bricks:
Calculate the wall area:
Area = Length × Height = 4 m × 2.4 m = 9.6 m².
Assuming each brick has a standard size of 0.19 m × 0.09 m:
Area of one brick = 0.19 m × 0.09 m = 0.0171 m².
Number of bricks = Total area / Area of one brick:
