Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Recall key terminology for concrete, bricklaying, and surveying.
• Solve practical problems involving mix ratios and quantity calculations.
• Explain the importance of quality control in construction.
• Identify tools and equipment for concrete, bricklaying, and surveying.

Lesson summary

This week is dedicated to solidifying your understanding of key concepts covered in Grade 10 Civil Technology thus far, in preparation for upcoming assessments. Civil Technology skills are crucial for building and maintaining our infrastructure, from houses to roads to water systems. A strong grasp of the fundamentals will not only help you succeed in this course but will also open doors to various career paths in South Africa's growing construction sector. We will be focusing on a general review, with specific emphasis on concrete technology, bricklaying and basic site surveying.

Lesson notes

2.1 Concrete Technology Definition: Concrete is a composite material made up of cement, aggregates (sand and gravel), water, and sometimes admixtures. It is a fundamental building material due to its strength, durability, and versatility.

Constituents and Their Roles: Cement: The binding agent that hydrates and hardens, holding the aggregates together. Ordinary Portland Cement (OPC) is the most common type.

Aggregates: Provide bulk and strength to the concrete. Sand (fine aggregate) fills the voids between the gravel (coarse aggregate).

Water: Essential for the hydration process of the cement. The water-cement ratio (w/c ratio) significantly affects the concrete's strength and durability. A lower w/c ratio generally results in stronger concrete, but too low can hinder workability.

Admixtures: Added to modify concrete properties such as workability, setting time, and durability. Examples include plasticizers (increase workability), retarders (delay setting), and accelerators (speed up setting).

Concrete Mix Design (Nominal Mixes): A concrete mix design specifies the proportions of cement, aggregates, and water needed to achieve the desired properties. In South Africa, common nominal mixes are expressed as ratios (e.g., 1:2:4), representing cement:sand:gravel by volume. The water is then adjusted to achieve the correct workability.

Example 1: Calculating Material Quantities A contractor needs to prepare 5 cubic meters of 1:3:6 concrete. Estimate the quantity of cement, sand, and gravel required. Assume a bulking factor of 1.2 for sand and 1.1 for gravel.

Step 1: Calculate the total mix proportion: 1 + 3 + 6 = 10 Step 2: Determine the volume of each component per cubic meter of concrete (unbulked): Cement: 1/10 = 0.1 m³ Sand: 3/10 = 0.3 m³ Gravel: 6/10 = 0.6 m³ Step 3: Apply bulking factors: Sand (bulked): 0.3 m³ 1.2 = 0.36 m³ Gravel (bulked): 0.6 m³ 1.1 = 0.66 m³ Step 4: Calculate total quantities for 5 cubic meters: Cement: 0.1 m³ 5 = 0.5 m³ (Convert to bags: approximately 14 bags of cement as 1 bag is about 0.035 m³)

Sand: 0.36 m³ 5 = 1.8 m³ Gravel: 0.66 m³ 5 = 3.3 m³ Example 2: Water-Cement Ratio If a 1:2:4 mix requires 50 kg of cement and the desired water-cement ratio is 0.5, how much water is needed?

Step 1: Calculate the required water: Water = Water-Cement Ratio Cement Quantity Water = 0.5 50 kg = 25 kg. Since 1 kg of water is approximately 1 litre, you need 25 litres of water.

Quality Control: Proper mixing, placing, compaction, and curing are crucial for producing durable concrete. Curing involves keeping the concrete moist for several days to allow proper hydration. 2.2 Bricklaying Definition: Bricklaying is the art and science of constructing structures using bricks bonded together with mortar.

Brick Types: Common brick types include clay bricks, concrete bricks, and face bricks. Clay bricks are commonly used in South Africa.

Mortar: Mortar is a mixture of cement, sand, and water that binds the bricks together.

A typical mortar mix ratio is 1:6 (cement:sand).

Bricklaying Bonds: Different bricklaying bonds, such as stretcher bond, header bond, and English bond, affect the appearance and strength of the wall. Stretcher bond is commonly used for single-skin walls.

Brick Quantity Calculation: Calculating the number of bricks required for a wall is essential for cost estimation and material procurement.

Example 3: Brick Quantity Calculation Calculate the number of bricks needed for a wall 5 m long, 2 m high, and one brick thick (110mm), assuming a brick size of 220 mm x 110 mm x 75 mm and a mortar joint thickness of 10 mm.

Step 1: Adjust brick dimensions for mortar: Adjusted length: 220 mm + 10 mm = 230 mm = 0.23 m Adjusted height: 75 mm + 10 mm = 85 mm = 0.085 m Step 2: Calculate the number of bricks per row: Bricks per row = Wall length / Adjusted brick length Bricks per row = 5 m / 0.23 m = 21.

7

4. Round up to 22 bricks.

Step 3: Calculate the number of rows: Number of rows = Wall height / Adjusted brick height Number of rows = 2 m / 0.085 m = 23.

5

3. Round up to 24 rows.

Step 4: Calculate the total number of bricks: Total bricks = Bricks per row Number of rows Total bricks = 22 24 = 528 bricks. Add extra 5%-10% for wastage and breakages. So final bricks needed approximately is between 554 and 580 bricks.

Tools and Equipment: Bricklaying tools include trowels, levels, plumb bobs, brick hammers, and line and pins. 2.3 Basic Site Surveying Definition: Surveying is the process of determining the relative positions of points on or near the Earth's surface. This is crucial for setting out buildings correctly.

Levelling: Levelling is the process of determining the relative elevations of different points. This can be done with levels (dumpy or laser) and levelling staff.

Instruments: Dumpy Level: A traditional optical instrument used for levelling.

Laser Level: A more modern instrument that projects a laser beam to establish a horizontal plane.

Levelling Staff: A graduated rod used to read elevations.