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Get the Most From Concrete Aggregate

Construction of pavement
On the surface, concrete seems like a simple thing. After all, it only has three main ingredients: water, cement, and aggregate. Yet within this simple framework lies a wealth of complexity. Even seemingly minor aspects of concrete production can have large-scale results on the installation, performance, and strength of the concrete.

A surprising amount of variation exists when it comes to the aggregate used in concrete. If you would like to learn more about how this ingredient can affect the fundamental nature of a concrete surface, read on. This article will outline three aggregate factors that concrete contractors must keep in mind.

1. Cleanliness

Aggregate starts out as large chunks of gravel or rock. Several passes through a crushing machine reduce these chunks to the sizes best suited for adding to a concrete mix. As you can imagine, the crushing process can generate a large amount of dust as the aggregate breaks down into fine particles.

Ideally, the gravel should be washed to remove as much dust as possible. Otherwise, numerous problems may ensue. For one thing, a layer of dust on the outside of the aggregate particles will increase the amount of water necessary to ensure an ideal concrete mixture. A water increase can be difficult to quantify, meaning that mixed concrete often suffers from either too little or too much water.

Dusty aggregate also reduces the strength of the bonds that form between the aggregate and the cement. As a result, concrete made with unclean aggregate tends to accumulate problems such as spalling and cracking at a greater rate. An experienced concrete contractor knows to check with the aggregate manufacturer to ensure that the aggregate they buy has been thoroughly washed.

2. Size Distribution

Many people mistakenly believe that all concrete contains only one size of aggregate particles. Yet a uniform aggregate size — also known as poor graded aggregate —doesn't make sense, thanks to the fact that it leaves larger gaps between aggregate particles. As a result, manufacturers must incorporate more cement to fill out the gaps, thus driving up the cost of the concrete.

Instead, most concrete surfaces contain a variety of different aggregate sizes. Two main types of aggregate mixes exist: well-graded and gap-graded. Well-graded aggregate mixes contain fine, medium, and coarse sized particles. Well-graded mixes exhibit excellent strength while minimizing the amounts of cement and water needed.

Well-graded mixes can be tricky to proportion correctly, however. Too much or too little of certain sizes can make it difficult for the particles to fit together tightly. Well-graded mixes also tend to carry a higher price tag, which reflects the fact that more processing much go into their creation.

As a compromise, many contractors opt to use gap-graded mixes, which omit medium sized particles. Instead, fine particles pack tightly around the coarse particles, making it easier to ensure ideal density while also keeping the price of the aggregate at a more economical level.

3. Site Management

In the case of ready-mix asphalt, manufacturers mix water, cement, and aggregate at a production facility and deliver it to the job site in concrete mixing trucks. Yet many contractors prefer to mix their concrete on-site. This allows them to better control the consistency, hydration, and other aspects of the concrete.

Stockpiled aggregate can create difficulties of its own if not managed correctly. Aggregate stockpiles must be protected against intermixing. Their moisture levels must also be carefully monitored. Aggregate that becomes excessively dry or moist will change the way the concrete behaves once mixed.

An experienced contractor possesses a thorough understanding of aggregate quality, selection, and storage. For more information on what it takes to get the best aggregate for your next concrete project, contact the pros at Black Jack Asphalt and Concrete.

Black Jack Asphalt and Concrete
Serving Saginaw, MI

Bay City/Saginaw: 989-791-4444
Birch Run/Frankenmuth: 989-776-1050
Flint: 810-471-3550
Fax: 989-770-2121

Business Hours: 
Open Seven Days a Week
Monday-Sunday, 7 a.m.-10 p.m.
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