What Is Aggregate Processing?

Aggregate is essential to the construction industry.  However, before aggregate can be used, it must be processed.

But what is aggregate processing?  Aggregate processing is the act of taking raw aggregate from a quarry and refining it until it meets the needs and specifications of the end-user.  This process often starts at the quarry itself and ends at an aggregate processing plant. 

As an example, take a quarry that creates rock aggregate for stone driveways. Rocks of various sizes would be excavated from the mine. But, before it can be sold, it needs to be further refined. This is because the rocks won’t be uniform in size and many of the rocks mined could end up being three feet or longer.

These large rocks are placed on-site in jaw crushers where they are crushed to a manageable size. Many jaw crushers take the rocks to under one foot each.

The rocks will then be easier to transport to the aggregate processing plant. They will be further refined at this facility until they meet client specifications.

Can Aggregate Processing Be Done At the Quarry?

Aggregate processing can be done entirely at the quarry, but it can depend on several factors.

Type of aggregate: Some aggregates require little processing; a simple portable crushing machine could be all that is needed to create the final product.  In cases like these, it is easier to do all of the processing at the quarry.

Equipment: Many aggregates need to be further refined, requiring more sophisticated machinery to complete the refining process. Bringing these types of machines to all sites may not be feasible. Some quarries are not suitable for aggregate processing.

Government regulations: Some government agencies require specific permits. For example, the Department of Environmental Conservation in the state of Vermont may require you to obtain an air permit for certain types of crushing activities. This permit might not be obtained in certain areas where the process could be dangerous to human health. In such cases, certain processing activities are needed off-site.

What Is Construction Aggregate?

Construction aggregate is simply aggregate that is used in the construction process.  The aggregate can be anything from stone, to gravel, to sand.  An aggregate used in construction, however, usually consists of a multitude of aggregates combined.

Construction AggregateExamples of commonly used aggregates include:

  • Basalt
  • Granite
  • Gravel
  • Limestone
  • Sand
  • Sandstone

These aggregates are often categorized between coarse and fine aggregates. Sand is an excellent example of a fine aggregate, whereas gravel is a great example of a coarse aggregate. Both coarse and fine aggregates are used independently or in combination with aggregates of either type.

Mixed aggregates can be used in a wide range of construction projects. From simple projects including concrete sidewalks, retention walls, and French drains, to more complex projects; dams, highways, bridges, and tunnels. When combinations of aggregates are used, engineers can take advantage of each type of material to create a final product that meets their needs.

One of the easiest ways to demonstrate construction aggregate is to look at concrete. To create concrete, a mixture of sand, stone, and cement are needed.  Different aggregate mixtures will create different types of concrete.

Aggregate Recycling

Aggregates can be recycled from a variety of areas.  One of the most popular ways of procuring recycled aggregate is to use construction and demolition waste.

For example, when an old brick building is demolished, the brick can be recycled and reused to make another aggregate. This is great for the environment as it avoids sending these materials to a landfill.

The process works by taking old materials and placing them into a crusher to be broken down.  A jaw crusher is used to break up large material. Magnets remove any scrap metal and rebar leftover.

This scrap metal and rebar can then be sent to a recycling scrap metal yard. Upon stripping the metal, the aggregate can be cleaned off using a conveyor belt and water sprayers.

The aggregate, now devoid of any metal, is clean and crushed small enough to be further processed into the finished product. This last step usually occurs off-site at an aggregate processing plant.

Aggregate Processing Equipment

Aggregate processing may require a wide range of equipment. Examples of equipment types are:

  • Aggregate Processing EquipmentAttrition Scrubbers: remove contaminants from granular materials.
  • Belt Filter Presses: separate liquids from solids.
  • Bucket Wheels: remove liquids, often without using as much energy.
  • Classifiers: sort and wash granular solids; can also separate liquids.
  • Filter Presses: remove water from solids.
  • Log Washers: remove dirt and other contaminants from the raw aggregate.

Different processing facilities will use various equipment to process their aggregates. A variety of crushers will be used to bring the raw aggregate to the size and shape the end-user requires.

Aggregate Processing Standards

Aggregate processing is often based on ASTM International standards. Since 1898, this organization has provided technical standards and is well-regarded in the industry.

According to ASTM, they have over 12,500 global standards and more than 30,000 volunteers. They also have people from over 140 countries participating in their organization.

Aggregate Processing Plant Design

The aggregate processing plant design can significantly determine its efficiency. Plant designers generally determine plant design based on market surveys. The surveys are used to determine requirements for capacity and product.

Agg-net.com states that “there should be some well-defined data on the physical and chemical characteristics of the proposed in-feed material.” This helps plant designers select the optimum equipment for the job.

Each plant needs to consider how the aggregate will move through the plant and how it will be stored once the aggregate has been fully processed. It is, therefore, crucial to determine plant capacity requirements before planning the design

Aggregate processing plants can be stationary or mobile. Each type of processing plant has its advantages.

Mobile Aggregate Processing Stationary Aggregate Processing
Advantage

●       Materials need not be moved off-site

●       Reduced fuel cost

●       No separate processing facility

●       Possibly more efficient

●       Machines can often be bigger

●       Does not need special power equipment

Disadvantage

●       Only mobile equipment can be used

●       May need generator

●       Used in areas where there is less control of working conditions and external influence

●       Aggregate needs to be brought in

●       Aggregate needs to be partially processed on-site beforehand

●       Requires that material be crushed at least once

 

Aggregate Processing Solutions

Even quarries not planning to do all of their aggregate processing on-site will still need to do some processing before moving any of their aggregates. Often, turning to other companies specializing in aggregate processing solutions is more profitable.

Crushing companies, for example, can provide solutions; so the quarry doesn’t need to bring in crushers. Some aggregate processing solutions can include full on-site aggregate material processing.

In Summary

Aggregate processing is essential to the construction industry. It takes raw materials from quarries and makes them usable building materials. This processing can be done in many ways and will take different forms and uses a variety of machinery depending on the type of aggregate and the end user’s needs.

Milestone Companies is an experienced civil construction company.  We offer aggregate processing both onsite and offsite, depending on the needs of the project.  We are proud to spearhead construction recycling projects and provide economical and quality results for our clients.