Civil Engineering Materials - Aggregates Quiz

Civil Engineering Materials - Aggregates

• Aggregates are insoluble, non-cementing materials added to mixtures of hydraulic cement and water to reduce cost and modify properties like strength and shrinkage.
• Aggregates must not contain constituents that would affect cement hardening or the durability of the hardened mass.
• Organic matter reduces the hydraulic activity of cement.
• Dust and clay reduce the bond between aggregate particles.
• Aggregates shouldn't contain decomposing or changing constituents.

Types of Aggregates

• Igneous rocks:
  • Intrusive (coarse-grained): Granite, diorite, gabbro
  • Extrusive (fine-grained): Rhyolite, andesite, basalt
  • Volcanic: Ash, tuff, agglomerate
• Sedimentary rocks:
  • Mechanically deposited: Consolidated shale, siltstone, sandstone
  • Chemically deposited: Calcareous (limestone, dolomite), siliceous (chert, opal), coal
• Other relevant aggregates:
  • Natural fibrous rock (asbestos)
  • Wood fibre (low-mass thermal insulation)
  • Steel, glass, polymers (fibers)

Aggregate Properties and Potential Problems

• Relevant properties: Maximum size, grading, texture (crushed or rounded), shape (flakiness, elongation), abrasion resistance (LA test), aggregate crushing value, specific gravity (SSD), bulk density, porosity, and absorption, moisture content.
• Potential problems:
  • Organic impurities (affect cement hydration)
  • Coatings (clay, silt affect bond)
  • Unsound particles (shale, wood)
  • Alkali-aggregate reaction (AAR)

Types of Aggregates (Continued)

• Normal density aggregates:
  • Specific gravity (2.5-3.0)
  • Bulk density (1450-1750 kg/m³)
  • Examples: gravel, crushed rocks, crushed gravel.
• Lightweight aggregates:
  • Porous (natural or man-made)
  • Lower thermal conductivity, density, and strength.
  • Examples: vermiculite.
• High-density aggregates:
  • Used for high-density concrete.
  • Examples: barytes, ferrous metal granules, ferrous ores.

Characteristics and Tests

• Resistance to abrasion and degradation
• Resistance to freezing and thawing
• Resistance to disintegration by sulfates
• Particle shape and surface texture
• Grading
• Bulk unit weight or density
• Specific gravity
• Absorption and surface moisture
• Compressive and flexural strength
• Definition of constituents
• Aggregates constituents
• Resistance to alkali reactivity and volume change

Aggregate Size and Distribution

• Sieve analysis: Determines the proportion of different particle sizes.
• Maximum size: Influences difficulty of placing and filling corners of formwork. Suitable size varies depending on the project.
• Grading: The distribution profile of particle sizes, affects economy, strength, shrinkage, and finishability.

Moisture and absorption

• Varying moisture levels affecting concrete, including oven-dry, air-dry, saturated-surface-dry, water saturated states
• Absorption capacity: measures the maximum water an aggregate can absorb
• Surface moisture and effective absorption important aspects for consideration.

Other key considerations

• Fineness Modulus: A measure of sand fineness, important for proper concrete characteristics.
• Choice of aggregates: Considering factors like source proximity, properties influencing concrete outcome, and quality standards
• Unit Weight: Weight per volume of aggregate. Impacts concrete properties and cost.
• Specific gravity: A dimensionless ratio related to aggregate density and water density. Indicates porosity.
• Bulking phenomena: Aggregate apparent volume increase due to moisture, affecting concrete characteristics.

Test your knowledge of aggregates used in civil engineering materials. This quiz covers types of aggregates, their properties, and considerations when selecting them for construction. Understand the impact of various aggregate types on the durability and performance of cement mixtures.