QUESTION 4: MATERIALS AND QUANTITIES 4.1 Name TWO reactions which take place during the hydration process of cement - NSC Civil Technology Construction - Question 4 - 2017 - Paper 1

Cement should not be stored for more than three months because it absorbs moisture from the air, which can lead to clumping and a reduction in its effectiveness. After three months, the chemical properties of cement may degrade, leading to inferior bonding and strength in concrete. Stale cement may also fail to achieve the desired setting and hardening characteristics.

One purpose of lime in a mortar mix is to enhance workability. Lime improves the plasticity of the mortar, making it easier to spread and shape while also providing better adhesion between the bricks or blocks.

The first ingredient that is typically put into the concrete mixer is aggregates, particularly coarse aggregates like gravel or crushed stone. This is followed by sand, cement, and then water, as the order of mixing can affect the concrete's final properties.

Three methods that can be used for curing concrete are:

1. Retaining formwork - Keeping the forms in place to retain moisture in the concrete.
2. Ponding - Creating a small pond or water pool on the surface of the concrete to maintain humidity.
3. Curing compounds - Applying liquid curing agents that form a film to prevent moisture loss.

The cube test is performed on concrete to ensure that it meets the required strength specifications. Testing concrete samples in the form of cubes allows for the assessment of compressive strength over time, which is critical for structural integrity and safety. The results help determine if the mix proportions and curing methods are effective.

1. Electrical wiring - Copper is used extensively for electrical wiring due to its excellent conductivity.
2. Plumbing - Copper pipes are used in plumbing for water supply systems, thanks to their corrosion resistance.

1. Covering for iron and roof sheets - Zinc is applied as a protective layer to prevent rusting in steel structures.
2. Electrical equipment - Zinc is used in various types of electrical equipment for corrosion resistance.

A neat sketch of channel iron typically shows a C-shaped profile with two parallel flanges at the top and bottom connected by a vertical web. This shape provides good structural strength and is commonly used in the construction of frames and supports.

Three properties of a good preservative for wood include:

1. Easily absorbed - The preservative should penetrate well into the wood to provide effective protection.
2. Non-toxic - It should not be harmful to humans and animals, ensuring safe use around living environments.
3. Not corrode metal - A good preservative should not react adversely with metal fixtures associated with wooden structures.

Plywood is composed of multiple layers (or plies) of thin sheets of wood veneer glued together. Typically, an odd number of layers is used to ensure that the grain direction of adjacent veneers runs perpendicular to each other. This construction enhances strength and resistance to warping. Plywood can vary in thickness and type of wood used, resulting in differing properties for various applications.

To determine the volume of concrete needed, use the formula for volume:

$V = L imes W imes H$
where:

• V = Volume
• L = Length = 6 m
• W = Width = 3 m
• H = Thickness = 0.075 m (75 mm converted to meters)

Calculating the volume:

$V = 6 imes 3 imes 0.075 = 1.35 ext{ m}^3$
Thus, 1.35 cubic meters of concrete will be required.

To find the number of bricks required, calculate the volume of the wall:

$V_{wall} = L imes H imes t$
where:

• V_{wall} = Volume of wall
• L = Length = 4 m
• H = Height = 2.4 m
• t = Thickness of the wall (assumed as the standard brick thickness, e.g., 0.1 m)

Calculating the volume of the wall:

$V_{wall} = 4 imes 2.4 imes 0.1 = 0.96 ext{ m}^3$
Now, if one standard brick occupies approximately 0.001 m³, the number of bricks required can be calculated as follows:

Number ext{ of bricks} = rac{V_{wall}}{V_{brick}} = rac{0.96}{0.001} = 960
Thus, 960 bricks will be needed for the cavity wall.