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Large Aggregate in Concrete

12 May 2021, Posted by F.A. in Tips
Large Aggregate in Concrete

When concrete is being mixed, the majority of the volume in the final mixture will be made up of a structural filler called aggregates. These aggregates are what cement paste coats and ultimately binds together, making it an important part of any concrete project. Before concrete formwork ties and other materials come into play, aggregates are one of the most important elements in a project, and their varying properties can have an impact on the final outcome of your work. Larger chunks of aggregate can have a unique effect on your concrete mixture that is critical to understand.

Why Use Aggregates?

Aggregate itself is a broad category and technically refers to any particulate material. This can include gravel, crushed stone, sand, slag, recycled concrete, or geosynthetic materials; they can be natural, manufactured, or recycled. The exact aggregates chosen for a given project will be selected for their durability, strength, workability, and ability to receive finishes. The best aggregates are clean, hard, strong particles that are free of absorbed chemicals or coatings of clay and fine materials, which could cause the deterioration of concrete.

Aggregates, like concrete wall forms, are an ideal material for construction because of their utilitarian properties. It has predictable and uniform composition, allowing for stable foundations, high hydraulic conductivity for drainage applications, strength and durability for composites, and low-cost versatility that can be applied to a variety of projects.

Properties of Aggregates

It is crucial to be able to select the correct aggregate for your specific project each time you plan to create a mixture. These are some of the main items to consider when planning.

Size and Workability: The size of concrete aggregate will determine the ultimate amount of water needed in order to make a mixture workable. Large chunks of concrete aggregate lead to low water requirements because they tend to have a minimal absorption rate. As the size of aggregates goes down, the mixture requires more water to suspend the particles and create a workable solution.

But as liquid composition increases, the strength of the final mixture decreases. Selecting the appropriate size of aggregate means considering the balance of workability and strength.

Strength: Like large aggregate chunks increase strength by requiring less water, the pieces can also reduce voids that may act as weak points in your cured concrete. Although tiny particles may full those voices, they will not be as strong as solid aggregate.

The shape of your aggregate will also impact the strength of finished concrete products. Angular aggregate offers the most strength, with rounded pieces at a close second. This will all play a role in the required spacing and size of concrete formwork ties when creating structures.

Durability: Rock particles selected for ready-mix concrete are typically selected for their high crush strength, impact value, and abrasion resistance. This leads to highly durable aggregate in most cases, allowing for use in a range of structures. To keep durability high, you should avoid flaky or elongated pieces of concrete aggregate, as they generally require more water. These pieces may also segregate, leaving weak spots in your structure once concrete formwork ties are removed.

Absorption: Aggregates will always absorb some amount of moisture, especially if they are saturated with water frequently or for a long period of time. A coarse aggregate mixture will usually stay in the 1% range of absorption, while fine mixtures can soak up to 5% of standing water, even with a perfect mixing ratio during the initial install.

If the concrete will be subject to constant abrasions, such as heavy-duty floors or pavement, additional factors like abrasion and skid resistance may need to be considered. Different minerals used in aggregates wear and polish at different rates. Typically, harder aggregates are selected for highly abrasive conditions to minimize wear.

Making the Right Selection

Based on these properties, you can see how it is critical for the right aggregate to be chosen for each project. The shape and type of aggregate play a role in many of the important characteristics of concrete. The size also is important. Large aggregates are known for requiring less water, leading to more strength and workability in the final product.

Like aggregates, choosing the right concrete formwork ties is crucial to a project. If you need to buy or rent equipment for concrete projects, Forming America can help- contact us today!