Aggregates are extremely useful materials for concrete projects. They make up around 60% to 75% of the volume of concrete, and also help determine the functional properties and proportions of this common material. However, as most construction professionals learn early on, not all aggregates are alike.

Aggregates can be composed of sand, gravel, crushed rock, and a variety of other geological materials. These materials can vary significantly in shape, texture, density, and ability to absorb moisture. The different characteristics of aggregate means that it is vitally important to choose carefully in determining which types are to be used in any given construction project.

Aggregates have a very wide range of applications—sidewalks, railway tracks, roads, French drains, etc.—and using the wrong kind for a particular job can have disastrous consequences. For instance, aggregates that are best suited as filling materials may not be acceptable for load-bearing applications.

It is also important to prepare the aggregate properly before deploying it, as it is unlikely to be in usable condition in whatever state it is found. This generally involves crushing it, with help from equipment specially designed for this purpose, into smaller materials that fall within a specific range of sizes and dimensions. But before aggregate can be crushed, there are a few steps that should be taken to ensure best results.

The Basics of Aggregate Preparation

Broadly speaking, preparing aggregate involves two stages: processing and beneficiation.

Processing – This is the process of crushing, washing, and screening aggregates to ensure that they conform to standards of size and cleanliness.

Beneficiation – This is a quality-control process that involves separating aggregate according to density and other characteristics. Additional crushing may be involved.

Here we’ll focus on the first stage: processing.

Fine and Coarse Aggregate

Although aggregate can be made from many types of geological materials, it is common to classify it into two general types: fine and coarse. Because construction applications often require one specific type, or a mixed concrete aggregate that has a precise proportion of both, it is important to be familiar with the distinctions between these types.

Fine aggregate – Aggregate particles of this size will pass through a 4.75 mm (no. 4) sieve but not a 0.075 mm sieve. It commonly derives from sand and crushed stone.

Coarse aggregate – Aggregate particles of this size will not pass through a 4.75 mm (no. 4) sieve. It commonly derives from gravel and crushed stone. Coarse aggregate is often grouped in single-size classifications of 10 mm, 12.5 mm, 16 mm, 20 mm, 40 mm, and 63 mm.

Creating the right kind of aggregate for a specific purpose requires high-quality crushing and processing equipment that can produce particles that fall within an acceptable range of specifications.

General Crushing Procedures

If you plan to crush materials in order to turn them into aggregate, it is important to determine in advance where this procedure is to be carried out. If you are engaged in a demolition project, will you crush the materials onsite or send them off to another location? Transporting materials to and from a site can be expensive as well as time-consuming.

One way to solve this problem is to bring portable crushing equipment onsite for processing stone products and similar materials. This is especially useful for cases where materials torn out of an existing site can serve as filling materials for a new construction project. With portable equipment, there’s no need to go through the wasteful hassle of transporting materials offsite, turning them into aggregate, and bringing it back to the original site.

Prior to crushing materials, it may be a good idea to wash them properly. Unclean geological materials can introduce an excessive amount of dust and dirt into the machine, leading to unnecessary wear and tear of equipment components. In addition, the washing of aggregate is often an important part of the post-crushing sorting process.

This is another area where portable equipment can substantially expand your range of options. Senya Tech’s XS Series Wheel Sand Washer and XL Series Spiral Sand Washer are two world-class products that can wash and purify sand stones prior to their use in construction applications. Bear in mind, however, that repeated wetting and drying cycles can harm certain types of aggregate.

Turning geological or old construction materials into aggregate form involves one or more crushing machines. Often it is necessary to utilize multiple machines, each with the capacity to process materials of a particular dimension. Machines should be designated primary (first), secondary (second), or tertiary (third), according to their position in the processing sequence.

Primary crushing machines—often jaw crushers—handle the initial raw materials; secondary machines—often cone crushers—reduce the size of the particles; and tertiary machines (when necessary) produce the final crushed aggregate product. At every stage, it is a good practice to load the materials into the crusher evenly and continuously; a portable feeder is especially helpful here.

Be careful when putting materials into a crushing machine—it can be damaged by objects that are larger than it is supposed to process. If you are not certain whether materials are suitable for a particular machine, stay on the safe side by breaking them into smaller pieces prior to putting them inside the crusher.

Having the right equipment is key to ensuring that your aggregate crushing project goes smoothly. Senya Tech has a wide range of crushers, washers, feeders, and screens that conform to the highest standards of the industry. Feel free to contact us with your questions or concerns.