Aggregate is a crucial component of concrete. It consists of a broad range of materials like gravel, sand, slag, crushed stone and even recycled concrete. The material used for the aggregate comes in small pieces of various sizes, depending on the project at hand. Most contractors will match the type of aggregate they choose to the needs of a project.
You may be wondering what concrete aggregate size is right for your current needs. It’s wise to get this information now because using the wrong type or size aggregate can be detrimental. Using the right size aggregate for your project will yield the best results possible.
Aggregate Proportions in Concrete
Aggregate comprises a majority of all concrete mixes. While the percentage can differ among products and concrete providers, aggregate in concrete usually comprises 60% and 75% of the mix. The rest of the mix will contain about 10% cement, 15% water and about 5% entrained air. The exact quantities depend on the specific mix you’re using for your job.
With the vast majority of concrete’s mix going to aggregate, you can see why choosing the correct aggregate and amount of aggregate is so essential. The chosen aggregate’s size and quantity will drastically affect your finished product. The right aggregate proportions will ensure that your job is a success and that the final product lasts for years to come.
Concrete Aggregate Types and Qualities
To achieve a good concrete mix, the chosen aggregate must be hard, clean particles free of clay coatings and absorbed chemicals. If these variables are accounted for, then you can trust that you’ll achieve a good concrete mix based on the properties of your chosen aggregate.
The different concrete aggregate types each possess different qualities that cause the concrete mix to behave differently. In fact, the aggregate is what affects the concrete’s elastic and thermal properties as well as its dimensional stability. This means that two concrete pours with similar ratios, but different aggregates can have completely different characteristics during the pour, after the pour and as the concrete sets and cures.
Coarse vs. Fine Aggregate
You can put all the types of concrete aggregate into two categories — coarse and fine. All aggregate types, regardless of their composition, are either coarse or fine. Here’s the difference between coarse and fine aggregate:
- Coarse aggregate: Coarse aggregates generally consist of types of gravel. A cement mix using coarse aggregate may use a majority of coarse aggregate with a fine aggregate like crushed stone filling up the remainder. Coarse aggregate is any material whose particles are anywhere from 3/8 inches and 1.5 inches in width. This is the size of aggregate often used in road construction.
- Fine aggregate: Most fine aggregates consist of crushed stone or natural sand. Most of the present particles must be able to pass through a 3/8-inch sieve.
Because the chosen aggregate so greatly influences the characteristics of the concrete, it’s crucial to consider some of the chosen material’s characteristics, regardless if it is fine or coarse:
- Skid and abrasion resistance
- The surface texture and shape of the particles
- Unit voids and weights
What Aggregate Is Used in Concrete?
You can use various materials, whether they’re coarse or fine, for your concrete needs. Here are some different ways you can categorize aggregates by type with some information on their general qualities:
- Natural aggregates: Natural aggregates are materials existing in their natural state or that have experienced washing, crushing or sizing. Some common examples include crushed stone, manufactured sand, naturally occurring sand and gravel. Natural aggregates can be used in concrete with only minimal processing required.
- Crushed rock aggregates: This type of aggregate includes quarried or excavated stone. The stone is then crushed and screened to achieve a standard size of particles and equal distribution. The crushing process gives this aggregate good compaction properties while increasing its load-bearing capabilities. Crushed rock aggregate is often used in roads, streets and other high-traffic areas.
- Artificial aggregates: Artificial aggregates consist of different types of waste materials. This makes them an economical option as well as an environmentally conscious one. Concrete manufacturers can use artificial aggregate for special work. This can include making special lightweight or high-density concrete, depending on the unique needs of the current project. Artificial aggregate includes artificial cinders, burned clay, expanded shale, foamed slag and steel rivet punching.
- Recycled aggregates: One can use crushed, inert demolition and construction waste to create recycled aggregate. When made from crushed, previously used concrete, it is referred to as recycled concrete aggregate. But it can be made using other materials besides concrete, in which case it is called recycled aggregate. Recycled aggregate is appropriate for many uses, including concrete bases and bituminous concrete.
Aggregate Shape and Size
The shape and size of aggregate will impact the characteristics of the concrete consisting of it. It’s important to note the effect of aggregate size on concrete strength. For instance, when comparing 10mm vs. 20mm aggregate in concrete, the smaller size will yield the strongest concrete.
Here’s a closer look at the different shapes available and how they influence the concrete’s integrity:
- Rounded aggregates: Rounded aggregates get their shape from natural forces and often take the form of seashore gravel. The rounded shape also contributes to high workability. Rounded aggregates are also a great option when you want a low water-to-cement ratio. Note that rounded aggregates have poor interlocking quality resulting in weak bond strength, making them unsuitable for high-strength concrete.
- Irregular aggregates: Gravel and pit sand are two types of irregular aggregates. Their shape is partly nature-made. Due to their irregular shapes, they are a bit less workable than rounded aggregates but provide a bit more strength.
- Angular aggregates: Manufacturers achieve angular aggregates by crushing rocks. This leads to many voids within the mixture, giving angular aggregates low workability. Yet this same characteristic contributes to enhanced interlocking, creating a high-strength concrete.
- Flaky aggregates: An aggregate is flaky if the particles’ thickness is less than their width and length.
- Elongated aggregates: Elongated aggregates have a larger length compared to the thickness and width of each particle.
- Flaky and elongated aggregates: An aggregate can be both flaky and elongated at the same time. This occurs when a particle’s width is larger than its thickness, and its length is larger than its width.
Get Aggregate From Union Quarries
Union Quarries is your destination for aggregate. Since 1961, we have been providing Central Pennsylvania and surrounding counties with high-quality aggregate. Whatever your project, we have the aggregate materials to help you get the job done.
Browse our full list of products and our specialized services to see what we have to offer. Contact us online for more information, or you can request a quote to take the next step. We look forward to supplying your project with high-quality aggregate!