Aggregate

Pro tip: A well-graded aggregate (mix of sizes) reduces voids and requires less cement, cutting both cost and CO₂.

Quick Definition

Aggregate is any hard, inert particulate material that—when bound together by a cementing matrix such as Portland cement, epoxy, or bitumen—forms a composite with enhanced strength and dimensional stability.

Major Types

CategoryTypical Size RangeCommon SourcePrimary Uses
Coarse Aggregate4–40 mmCrushed rock, gravelStructural concrete, road base
Fine Aggregate75 µm – 4 mmNatural sand, manufactured sandMortar, plaster, terrazzo matrix
Lightweight Aggregate4–20 mmExpanded clay, pumiceLightweight concrete panels
Decorative Aggregate2–15 mmPolished marble, glass chipsTerrazzo, exposed-aggregate slabs
Recycled Aggregate4–40 mmCrushed concrete wasteEco-concrete, sub-base layers

Good to know: Recycled concrete aggregate often displays higher water absorption—adjust your mix design accordingly.

Key Properties

  • Gradation: Continuous particle-size distribution improves packing density.
  • Shape & Texture: Angular particles raise strength but lower workability.
  • Specific Gravity: Heavier aggregates increase unit weight of concrete.
  • Cleanliness: Silt & clay films inhibit bond; ASTM C33 limits < 3 % fines.
  • Moisture Content: Impacts water-cement ratio—always correct for SSD state.

Role in Composite Materials

  1. Concrete

    60–80 % by volume; provides compressive strength and bulk.

  2. Mortar & Render

    Fine sand controls shrinkage and surface finish.

  3. Terrazzo

    Decorative chips visible after grinding; size #0–#3 most common.

  4. Asphalt Pavements

    Aggregate skeleton resists rutting; bitumen merely coats.

Selection Guidelines

  1. Meet the spec: Follow ACI 211 or local mix-design codes.
  2. Compatibility: Ensure chemical inertness with binder (e.g. no alkali-silica reactive silica).
  3. Local availability: Cuts transportation cost and embodied energy.
  4. Sustainability: Prefer recycled or industrial by-products where performance allows.

Where to Use

  • Structural concrete – beams, slabs, foundations
  • Architectural finishes – exposed-aggregate façades, terrazzo floors
  • Landscaping – drainage layers, decorative gravel paths
  • Rail ballast & road base – coarse crushed stone distributes loads

Sustainability Angle

  • Replacing 30 % of natural coarse aggregate with recycled concrete can lower embodied energy by ~10 %.
  • Industrial by-products such as copper slag or steel furnace slag divert waste from landfills while matching conventional performance.

FAQs

Does aggregate size affect concrete strength?

Yes. Smaller maximum sizes increase surface area, demanding more paste but often delivering higher compressive strength and better finish.

Can I use beach sand in concrete?

Generally not—salt contamination accelerates steel corrosion. Wash thoroughly or avoid altogether.

Related Terms

References

  1. ASTM C33 / C33M-18 : Standard Specification for Concrete Aggregates.
  2. ACI 211.1-19 : Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete.
  3. Mehta & Monteiro, Concrete – Microstructure, Properties and Materials, 4th ed., 2014.