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
The first reaction is the formation of calcium silicate hydrates (C-S-H) which contributes to strength development.
The second reaction is the formation of Calcium Hydroxide (Ca(OH)₂), which helps in the setting process.
Step 2
Briefly motivate why cement must not be stored longer than three months.
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Answer
Cement should not be stored longer than three months because it can absorb moisture from the air, leading to clumping and a decrease in its effectiveness. This moisture can reduce the workability and strength of the concrete mix.
Step 3
Name ONE purpose of lime in a mortar mix.
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Lime is used in a mortar mix to improve the workability and plasticity, making it easier to spread and adhere to 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 put into the concrete mixer is usually the coarse aggregate (gravel or crushed stone).
Step 5
Name THREE methods that can be used for curing concrete.
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Retaining formwork to keep the moisture in.
Covering the surface with wet burlap or plastic sheeting.
Applying curing compounds that form a moisture-retaining film.
Step 6
Briefly motivate why the cube test must be performed on concrete.
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The cube test is performed to ensure the concrete mix meets strength specifications. It provides an indication of the quality and durability of the concrete, which is crucial for structural integrity.
Step 7
Name TWO uses of each of the following materials in the construction trade: Copper.
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Electrical wiring in buildings.
Plumbing systems for water supply and drainage.
Step 8
Name TWO uses of each of the following materials in the construction trade: Zink.
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Covering for roofs and exterior wall cladding.
Used in the production of various alloys, including brass.
Step 9
Make a neat sketch to illustrate the profile of channel iron.
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A neat sketch should include a cross-section view of channel iron, showing its 'C' shape, with dimensions labeled for height, base, and thickness.
Step 10
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.
Effective in preventing decay and insect infestation.
Step 11
Briefly describe the composition of plywood.
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Plywood is made of thin layers of wood veneer that are glued together with adjacent layers having their wood grains in perpendicular directions to enhance strength and reduce shrinkage.
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
Convert the thickness from mm to m: 75 mm = 0.075 m.
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 length of 4 m and a height of 2,4 m.
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First, calculate the area of the wall: Area = length × height = 4 m × 2.4 m = 9.6 m².
Assuming each standard brick has an area of approximately 0.002 m², the number of bricks needed would be:
Number of bricks = Area / Area of one brick = 9.6 m² / 0.002 m² = 4800 bricks.
