Frequently Asked Questions - Aggregates

Q1: What are aggregates used for?
A1: Aggregates play a crucial role in construction, providing materials for drainage, load-bearing, surface protection, foundation building, filling, and decorative purposes. They are also key components in mixing mortar and other construction materials, and are widely used in building, landscaping, and infrastructure projects.

Q2: What is an aggregate in construction?
A2: Aggregates are granular materials like crushed stone, sand, slag, and gravel, sourced either naturally or through recycling for use in construction. These materials can range from fine to coarse and are available in various sizes. Aggregates are the most-extracted natural resources globally, making them essential for construction.

Q3: What are the four main types of aggregates?
A3: The four primary types of aggregates are gravel, crushed stone, sand, and concrete. These can be sourced as freshly-mined raw materials or recycled from old construction projects, offering an eco-friendly option.

Q4: What are some examples of aggregates?
A4: Common examples of aggregates include sharp sand, gravel, crushed stone, and crushed concrete. Other varieties include slate, ballast, MOT (a type of road sub-base), slag aggregates, natural coarse aggregates, grano dust, and recycled aggregates.

Q5: What are the most commonly used aggregates?
A5: River gravel and sharp sand are the most frequently used aggregates in construction, followed by crushed stone and concrete. Type 1 MOT is popular for road building and sub-bases, while topsoil is commonly used for landscaping. Geosynthetic aggregates are preferred for specialized engineering applications.

Q6: What size aggregate should I use for concrete?
A6: The size of the aggregate greatly influences the strength of the concrete. For mid-strength concrete, 40mm aggregates are generally recommended, while 20mm aggregates are better for high-strength concrete applications.

Q7: What are fibre cement products made of?
A7: Fiber cement is made from Portland cement, cellulose fibers, sand, and water. Cement binds the materials, fibers add reinforcement, sand provides weather resistance, and water activates hardening. Some manufacturers may add extra chemicals to improve durability.

Q8: What are some examples of recycled aggregates?
A8: Recycled aggregates include materials like gravel, sand, crushed stone, asphalt, bricks, blocks, slags, and recycled concrete. Recycled concrete aggregates (RCA) are processed from crushed construction and demolition waste, making them suitable for reuse in new projects.

Q9: What types of aggregates should be avoided?
A9: Certain aggregates should be avoided, including soft or porous materials prone to splitting, certain types of "chert" that degrade easily, smooth-textured materials, those containing organic impurities, clay lumps, friable materials, and aggregates smaller than 75 micrometers.

Q10: Is recycled aggregate more cost-effective?
A10: Yes, using recycled aggregates can reduce construction costs. Since they do not require fresh quarrying, recycled aggregates are generally more affordable. Additionally, materials sourced locally can lower transportation expenses.

Q11: Is recycled concrete as strong as traditional concrete?
A11: Recycled concrete offers similar strength to traditional concrete, with the added benefits of being cost-effective and eco-friendly. While most construction companies report little difference, some have noted that recycled concrete may be 10-25% weaker than concrete made from natural coarse aggregates, depending on the project’s specific requirements.

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