Aggregate is the general name for granular materials such as sand, gravel, chippings and crushed stone used in building materials like concrete, asphalt, mortar, road fill and railway ballast. Aggregate makes up most of the volume of concrete, so a structure’s strength, durability and cost depend to a large extent on the quality of the aggregate used.
In this guide we explain what aggregate is, the types of aggregate, aggregate properties and bulk density, what aggregate quarries and plants are, and where aggregate is used.
Types of Aggregate
By Origin
| Type | Source | Feature |
|---|---|---|
| Natural aggregate | River beds, sand and gravel pits | Rounded particles; prepared by washing and screening (sand and gravel guide) |
| Crushed aggregate | Quarries (limestone, basalt, granite, etc.) | Angular particles; produced by crushing |
| Artificial aggregate | Industrial processes (e.g. blast furnace slag, expanded clay) | Lightweight or special-purpose aggregates |
| Recycled aggregate | Construction and demolition waste | Produced by crushing concrete and brick waste (recycling guide) |
By Particle Size
- Fine aggregate (sand): Particles generally below 4 mm; natural sand or manufactured sand.
- Coarse aggregate: Gravel and chippings fractions above 4 mm (types of chippings).
- All-in aggregate: Material containing both fine and coarse particles, used in road sub-base.
Limit values may vary with the relevant standard and application; technical specifications define fractions as “d/D” (lower/upper sieve).
By Density
- Normal-weight aggregate: Most natural and crushed aggregates.
- Lightweight aggregate: Such as pumice and expanded clay; for lightweight concrete and insulation.
- Heavyweight aggregate: Such as barite and magnetite; for radiation-shielding concrete.
Aggregate Properties
| Property | What It Affects | How It Is Measured |
|---|---|---|
| Grading (particle size distribution) | Concrete workability, void ratio, cement demand | Sieve analysis |
| Particle shape | Workability, asphalt strength | Flakiness and shape index |
| Fines content | Water demand, strength, bond | Washed sieve analysis, methylene blue test |
| Wear resistance | Durability in roads and asphalt | Los Angeles abrasion test |
| Water absorption | Freeze–thaw resistance, mixing water | Water absorption test |
| Particle density | Mix design, concrete unit weight | Density test |
| Harmful substances | Alkali–silica reaction, organic matter, clay lumps | Chemical and petrographic tests |
For test methods and quality categories see our aggregate standards guide, and for the link between particle shape and crusher selection our aggregate quality guide.
Aggregate Bulk Density
The weight of aggregate depends on the density of the particles and the voids between them. Common values:
- The particle density of normal aggregate is mostly around 2.5–2.8 t/m³.
- Loose bulk density of sand and chippings is mostly around 1.4–1.7 t/m³.
- In sand, moisture can change bulk density significantly (bulking).
For sales, stock and truck load calculations, the values the quarry measures for its own products should be used.
What Are Aggregate Quarries and Aggregate Plants?
An aggregate quarry is the site where aggregate raw material (rock or sand and gravel) is extracted. An aggregate plant is the crushing and screening plant where this raw material is crushed, screened and, if needed, washed. A typical crushed aggregate plant consists of:
- Feed hopper and grizzly feeder (feeder types),
- Primary crusher (usually a jaw crusher),
- Secondary and tertiary crushers (cone, impact or VSI),
- Vibrating screens (vibrating screen guide),
- Sand washing equipment if needed (sand screw washer),
- Belt conveyors and a stockyard (belt conveyor guide).
For plant planning see our crushing and screening plant set-up guide.
Uses of Aggregate
| Field | Use |
|---|---|
| Concrete | Ready-mix, precast, concrete pipes and elements |
| Asphalt | Most of a hot bituminous mix is aggregate |
| Road building | Sub-base, base and fill layers |
| Railways | Ballast and substructure |
| Mortar and plaster | Fine sand |
| Drainage and filtration | Clean, single-size coarse aggregate |
| Landscaping | Decorative gravel and chippings |
Points to Consider When Choosing Aggregate
- The standard and quality category the application requires,
- Consistency of the source and quality control records,
- Stable grading (segregation in stock must be prevented),
- Fines and clay content,
- Haul distance and total cost.
Frequently Asked Questions
Are aggregate and chippings the same thing?
Chippings are a type of aggregate. Aggregate is a general term covering all granular building materials such as sand, gravel, chippings and crushed stone.
What is the difference between fine and coarse aggregate?
Fine aggregate is sand-sized (generally below 4 mm); coarse aggregate is the gravel and chippings fractions above that.
Is crushed or natural aggregate better?
It depends on the application. Crushed aggregate interlocks better with its angular faces; natural aggregate improves workability with its rounded particles. Both are used successfully when produced to the standards.
Why is aggregate washed?
To remove clay, silt and organic matter and so protect concrete strength and binder adhesion.
The Role of Aggregate in Concrete
Aggregate forms the skeleton of concrete. Cement paste fills the spaces between the particles and binds them together. Therefore:
- Well-graded (continuously graded) aggregate reduces voids and lowers cement demand,
- Clean aggregate lets the cement paste bond well to the particles,
- Strong, durable particles increase the abrasion and freeze–thaw resistance of concrete,
- Suitable particle shape improves workability and reduces water demand.
Aggregate quality categories for concrete and asphalt are defined in the relevant product standards (aggregate standards).
Quality Control Plan in Aggregate Production
| Check | Suggested Frequency (example) | Purpose |
|---|---|---|
| Sieve analysis | Daily or per shift | Keeping grading stable |
| Fines / methylene blue | At regular intervals | Clay control |
| Flakiness and shape index | Weekly or on setting changes | Particle shape |
| Los Angeles, water absorption, density | Periodically | Strength and durability |
| Visual stockpile check | Every day | Segregation and contamination |
Frequencies should be set according to the product, customer specification and factory production control system.
Field Example
Suppose a ready-mix concrete plant notices that sand from the same quarry causes a higher water demand in concrete on some days. Investigation at the quarry shows that the clay content rises on rainy days and the washing line’s capacity is insufficient. When a sand recovery unit with hydrocyclones is added and fines are measured regularly, sand quality becomes stable.
Glossary
- Grading: The particle size distribution of an aggregate.
- d/D: The lower and upper sieve sizes of an aggregate fraction.
- Fines: Material generally passing 0.063 mm.
- All-in material: Unprocessed material of mixed sizes.
- Aggregate quarry: The site where aggregate raw material is extracted.
More Questions
Are an aggregate quarry and a stone quarry the same thing?
Quarries producing crushed aggregate are aggregate quarries; sand and gravel pits are natural aggregate quarries.
Can recycled aggregate be used in concrete?
When properly processed, and in the proportions allowed by the relevant standard and specification, yes.
What determines the unit price of aggregate?
Rock type, processing (crushing, screening, washing), fraction, quality class and haul distance are the main factors.
CSP Mühendislik Support
CSP Mühendislik designs and manufactures crushing, screening, washing and material handling plants for aggregate production, and supports operators with wear part and spare parts supply and service, maintenance and repair. See our products page for our equipment.
