Concrete Technology: Aggregates Overview

Aggregates in Concrete Technology

• Aggregates serve as fillers in mortar and concrete production, constituting 70-80% of concrete volume.
• Essential characteristics of good aggregates include cleanliness, hardness, strength, durability, and appropriate grading.

Source of Aggregates

• Natural Sources: Found in river basins, sea beds, bedrock. Examples include gravel, sand, and crushed rocks like granite.
• Artificial Sources: Man-made from waste materials such as broken bricks, air-cooled blast furnace slag, sintered fly ash, and bloated clay.

Requirements of Good Aggregate

• Strength: High crushing strength is required to withstand stresses from traffic loads.
• Hardness: Should resist abrasion effectively.
• Durability: Capable of withstanding weathering effects, such as rain and temperature variations.
• Workability: Should facilitate easy mixing, transporting, placing, and finishing.
• Shape: An angular shape ensures strong interlocking.
• Texture: Rough texture promotes better bonding in the concrete mix.
• Water Absorption: Should limit absorption to 0.5-1% to maintain a consistent water-cement ratio.
• Purity: Free from organic and inorganic impurities to ensure quality.

Classification of Aggregates by Size

• Coarse Aggregates:
  • Size ranges from 4.75 mm to 80 mm.
  • Sourced from natural disintegration or artificial crushing of rocks.
• Fine Aggregates:
  • Size less than 4.75 mm.
  • Obtained from rivers and crushed stones.
  • Smallest size (sand) is 0.075 mm.
  • Passes through a 4.75 mm sieve and retained on a 75 µm sieve.
  • Functions to fill voids and enhance workability.

Types of Fine Sand

• Coarse Sand: Size between 4.75 mm and 2 mm.
• Medium Sand: Size between 2 mm and 0.425 mm.
• Fine Sand: Typically varies below 0.425 mm, specific classifications may apply.

Aggregates in Concrete Technology

• Aggregates serve as fillers in mortar and concrete production, constituting 70-80% of concrete volume.
• Essential characteristics of good aggregates include cleanliness, hardness, strength, durability, and appropriate grading.

Source of Aggregates

• Natural Sources: Found in river basins, sea beds, bedrock. Examples include gravel, sand, and crushed rocks like granite.
• Artificial Sources: Man-made from waste materials such as broken bricks, air-cooled blast furnace slag, sintered fly ash, and bloated clay.

Requirements of Good Aggregate

• Strength: High crushing strength is required to withstand stresses from traffic loads.
• Hardness: Should resist abrasion effectively.
• Durability: Capable of withstanding weathering effects, such as rain and temperature variations.
• Workability: Should facilitate easy mixing, transporting, placing, and finishing.
• Shape: An angular shape ensures strong interlocking.
• Texture: Rough texture promotes better bonding in the concrete mix.
• Water Absorption: Should limit absorption to 0.5-1% to maintain a consistent water-cement ratio.
• Purity: Free from organic and inorganic impurities to ensure quality.

Classification of Aggregates by Size

• Coarse Aggregates:
  • Size ranges from 4.75 mm to 80 mm.
  • Sourced from natural disintegration or artificial crushing of rocks.
• Fine Aggregates:
  • Size less than 4.75 mm.
  • Obtained from rivers and crushed stones.
  • Smallest size (sand) is 0.075 mm.
  • Passes through a 4.75 mm sieve and retained on a 75 µm sieve.
  • Functions to fill voids and enhance workability.

Types of Fine Sand

• Coarse Sand: Size between 4.75 mm and 2 mm.
• Medium Sand: Size between 2 mm and 0.425 mm.
• Fine Sand: Typically varies below 0.425 mm, specific classifications may apply.