A Look at the Differences between These Two Aggregates and Why Gravel Suppliers Sell These Separately
Did you know that crushed stone and gravel are not the same? Although both come from the same material and the same local stone quarries, these two stone products are produced differently and have different uses in construction and landscaping projects.
Crushed stone and gravel suppliers keep these two aggregates in separate categories because of their differing production methods, sizes, and uses. When deciding on which type to use for your construction project needs, consider these differences when speaking with your local gravel supplier.
Crushed stone is a product of rocks being broken down using a crushing machine. Crushed stone is sourced—also known as quarried—from a parent rock. The most common parent rocks used for crushed stone are:
Limestone is the most common rock type used to make crushed stone in North America due to its wide availability and versatility. It is also easy to crush because it is soft. And it causes less wear on equipment compared to harder rocks.
Ranging in particle size from largest to smallest, limestone is available as coarse aggregate, crushed limestone, mine run limestone, and limestone fines. Limestone is a key ingredient in concrete and is also used to make cement.
Also known as dolostone, dolomite is similar to limestone, and these rocks are often mined together at a quarry. However, dolomite is harder than limestone, making it more durable to abrasion.
Granite refers to various light-coloured igneous rocks used in construction. In the construction industry, the following are some of the rocks that are often referred to as granite:
After limestone, granite is the second most popular rock used for crushed stone. It is durable and resistant to acidic water and soil. Crushed granite is also a suitable and durable substitute for limestone in concrete.
Like granite, trap rock is a name for a variety of igneous rocks used in construction. However trap rock refers to dark-coloured igneous rock.
Here are some of the dark igneous rocks often referred to as trap rock:
Traprock is another common rock used for producing crushed stone. Like granite, trap rock is also very durable to abrasion and acidity, and makes for a suitable concrete aggregate.
Scoria is a vesicular rock, meaning it has voids in it that formed from gas bubbles that were trapped in the rock as it solidified from a melt. These voids make scoria and other vesicular rocks weaker, unable to withstand heavy loads. The voids also make these rocks less durable during freeze-thaw cycles.
But these voids also make scoria more lightweight. And its rough surfaces help it bind well as a concrete aggregate. Scoria is an ideal crushed stone for lightweight aggregates, lightweight concrete, and even roofing granules.
Scoria and other lightweight vesicular rocks, like volcanic cinder, are easy to handle and are also ideal for use in landscaping, garden planters, saunas, grills, filter stone, and traction on snow-covered roads.
Composed mostly of quartz, sandstone is a durable material. However, it does have its drawbacks. Sandstone naturally forms from sand grains that have been cemented together by clay, calcite, or silicate minerals. But since this natural cement doesn’t fill all the voids between the sand grains, sandstone is porous.
The porous spaces in sandstone allow this rock to absorb water easily. As a result, water absorbed in sandstone will expand every time it freezes. Over time, the freeze-thaw cycle will take its toll on sandstone, causing the sand grains to dislodge and the rock to break. As such, sandstone is not ideal for use in cold climates that experience extreme freeze-thaw cycles.
When heated, the sand particles in sandstone weld together. This heated sandstone is known as quartzite. Quartzite is extremely durable, even during freeze-thaw cycles. But this hard rock is more difficult to mine, handle, and transport, making it unpopular for construction use.
Most people rarely use the term “crushed stone” and instead refer to both gravel and crushed stone as “gravel.” But there are key differences between crushed stone and gravel, including their:
While crushed stone is a commercial product created with the use of machines to mine and crush rock, gravel is a product created from natural weathering.
Gravel is fragmented rock sourced from deposits of weathered rock found in rivers, streams, and gravel pits. Although gravel is a natural product of erosion and weathering, gravel suppliers can mine gravel in quarries using the same crushing equipment for crushed stone.
Due to the crushing process, crushed stone typically has more angular surfaces. Gravel tends to have a rounder shape due to the natural weathering process, and is usually much smaller than crushed stone. However, gravel that is crushed will have a more angular shape.
Crushed stone ranges in size from fine stone dust (screenings) to larger and heavier stones. Gravel comes in various sizes that are larger than 2 mm in diameter, starting from about a ¼ inch, and going up to 2 inches or more.
Uses for Aggregates
The most common use for crushed stone is as an aggregate for construction projects. The angular surface of crushed stone makes it easy to tamp, roll, and vibrate into place, locking and forming a stable surface.
Other common uses for crushed stone include:
- As a base for pavers, roads, and driveways,
- As sub-base for pavers, roads, and driveways,
- Construction fill,
- Shoreline riprap—to prevent shoreline erosion,
- Railroad track ballast beds—to provide traction,
- Concrete and asphalt mix,
- Concrete blocks,
- Drainage systems, and
- Retaining walls.
Gravel is more often used for aesthetic purposes due to its smooth, round surface and various natural colours like hues of yellow, red, blue, beige, and grey. Gravel is ideal for:
- Decorative landscaping,
- Garden beds,
- Patios and patio bases,
- Around stepping stones in walkways,
- Driveways and driveway bases, and
- Drainage in flower pots and flower beds.
Making the Most of Both Products
Oftentimes, both crushed stone and gravel are used together in both small and large construction projects to make the most of their qualities. Crushed stone, sand and gravel are commonly used as key ingredients for mixing concrete. These aggregates are also used as:
Crushed stone, sand, and gravel can all be used as drainage aggregates. Drainage aggregates are either natural or processed, and coarse or fine.
Coarse aggregate is typically larger than 5 mm in diameter, while fine aggregates are less than 5 mm.
Road and patio base layers can benefit from using both crushed stone and gravel. Road base layers, such as what you’d find on a gravel road or driveway, often use a top layer of ¾-inch aggregates.
Sub-base layers, immediately below the road, driveway, or patio top layer, are usually 1 ½ to 3 inches.
Both the base and sub-base layers can be a mixture of large (3/4 inch), medium (3/8 inch), and small (less than 1/8 inch) aggregates. The medium-sized particles fill the void of the large aggregates, and the small particles fill the voids of the medium aggregates, making for a dense and sturdy layer.
When compacted, these mixed base layers become impervious to water, securing the roadway (driveway, or patio) from degradation, wash boarding, and potholes.
If you originally considered these two aggregates to be the same, you are not alone. They are often confused for one another since both gravel and crushed stone come from rocks and are aggregates used for construction projects.
But these two aggregates serve different uses. Ultimately, if you want an aggregate for construction, such as building, paving, and any hardscaping, go with crushed stone. If you are looking for decorative stones for your landscape, garden, walkway, and driveway, go for gravel.
For more information on these two aggregates and to figure out which is the best option for your construction project needs, contact your local crushed stone and gravel suppliers.