4.1 Name TWO reactions which take place during the hydration process of cement - NSC Civil Technology Civil Services - Question 4 - 2017 - Paper 1

Cement has a limited shelf life due to its propensity to absorb moisture from the air. If stored for more than three months, it may become lumpy or harden, losing its hydraulic properties and resulting in compromised strength and workability in concrete mixes.

Lime in a mortar mix improves workability and plasticity, making it easier to handle and apply. This is particularly beneficial when sand particles are insufficient, ensuring smoother application and better adhesion.

The first ingredient typically added to the concrete mixer is aggregates, such as gravel or stone, to provide the bulk of the concrete mix.

1. Retaining formwork: Keeping the formwork on the cast concrete to retain moisture.
2. Covers: Using wet burlap or plastic sheeting to cover the concrete to minimize moisture loss.
3. Ponding: Creating ponds of water on the surface of the concrete to ensure continuous hydration.

The cube test is performed to determine the compressive strength of concrete. This test ensures that the concrete mix has been properly formulated and cured, and helps verify that the concrete will perform adequately under load.

1. Electrical wires: Used for wiring systems due to its excellent electrical conductivity.
2. Water pipes: Utilized in plumbing for its anti-corrosive properties.

1. Alloy material: Used to strengthen other metals in various structural applications.
2. Roofing sheets: Employed in construction for roofing, providing durability and weather resistance.

(Insert a sketch here) The channel iron typically resembles a 'C' shape, which provides strength and support in construction applications.

1. Easily absorbed: The preservative should penetrate the wood fibers effectively.
2. Non-toxic: It should not pose harmful effects to humans or the environment.
3. Resistant to water: The preservative should help protect wood from moisture damage and decay.

Plywood is composed of multiple layers, or 'plies', of thin veneer sheets that are glued together. The direction of the grain in each layer is alternated to enhance strength and stability, reducing the risk of warping.

To find the volume of concrete needed:

$ext{Volume} = ext{Length} imes ext{Width} imes ext{Thickness}$

Converting thickness into meters: 75 mm = 0.075 m.

Thus:

$ext{Volume} = 6 imes 3 imes 0.075 = 1.35 ext{ m}^3$

To find the number of bricks needed, first calculate the area of the wall:

$ext{Area} = ext{Height} imes ext{Length} = 4 imes 2.4 = 9.6 ext{ m}^2$

Assuming standard brick size is approximately 0.2 m²:

ext{Number of bricks} = rac{ ext{Area}}{ ext{Area of one brick}} = rac{9.6}{0.2} = 48 ext{ bricks}