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Everything You Need to Know About Aggregate - Thursday, April 28, 2016

Aggregate, a familiar mixture of granular materials that forms one of the three components of concrete, dictates much of what a concrete mix will become. From early on, the aggregate is the heart of the concrete. When mixed with water and Portland cement, the aggregate mixture of sand, gravel, and/or pea gravel takes on the unique properties of its mix to become concrete.

Aggregateís significant role in determining the specs of the final product is often misunderstood and underestimated. Hereís everything you need to know:

What Is Aggregate?

60% to 75% of concrete's volume is aggregate. It is an amalgamation of rocks, ranging from gravel to sand, that forms a durable and economic portion of the final concrete product. Itís essential to the mixture, and the properties of aggregate have a huge impact on the final specs of the concrete.

How Is It Categorized?

Aggregates are divided into two categories, fine and coarse. Fine aggregates are the smallest, and generally consist of particles like sand and minutely crushed stone.

Coarse aggregates tend to range from 3/8-inch to 1.5 inches in diameter, consisting largely of gravel, but also crushed stone and reclaimed concrete.

Pulverized concrete can be recycled into new concrete as aggregate. This is an environmentally friendly approach to sourcing aggregate for concrete. A similar process is used in full depth reclamation, used in conjunction with cement slurry.

Where Does It Come From?

Gravel and sand are frequently sourced from a pit or body of water. Here at Angelle we produce our own aggregate for our concrete. We dredge the material beneath the earthís surface and the material runs through a sieve test in order to determine what type of rock was produced. Our pit is located in Greensburg, LA.

Recycled concrete is taken from older projects, or like with full depth reclamation, is taken from a worksite prior to the consequent construction.

Whatís the Shape and Size?

To create a useful concrete blend, the aggregates need to be clean, hard, and free of absorbed chemicals or clay. Particles covered in clay and other mixed in materials can cause the concrete to deteriorate over the course of its lifespan.

The shape and size are very important. Quality concretes use a mixture of sizes. The details of this grading can impact concrete properties, and will dictate, in part, the amount of cement and water needed for the concrete. It also has a direct effect on the ability of the mixture to be pumped, its workability, and the end productís durability.

A jagged, oddly shaped aggregate blend creates a mixture that requires more water to get into a workable state. Having smooth, compact aggregates can require less water to achieve the desired viscosity.

Abrasion and skid resistance is taken into account as well. Every concrete is used differently, and will have different challenges to endure. A harder aggregate should be used in the most abrasive conditions to help minimize wear on the concrete.

Whatís Next?

Once the aggregate is harvested, it is washed to ensure that it wonít degrade the final product. It is then sorted, or graded. Until the aggregate is ready to be added to the cement and water to make concrete, it is stored to prevent contamination. Once a concrete mixture is started, it typically needs to be poured within 3.5 hours.

While the differences between varieties of aggregates, and how they are handled may seem minor, itís the quality and properties of the aggregate that dictates the quality and properties of the final product. This not only affects the hardened concrete, but also the mix thatís ready to be worked into the job site. If youíre interested in learning more, give Angelle Materials a call today.


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