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What Exactly is Gravel?

Gravel is a fascinating and versatile material made up of a loose collection of rock fragments that have been shaped and created by the natural process of erosion. This means that over many years, wind, water, and weather have broken down large rocks into these smaller pieces. Along with its cousins, sand and crushed stone, gravel is most famous for its role in construction, but its talents extend far beyond that!

Understanding Gravel Sizes and How They Are Classified

One of the key ways to talk about gravel and other rock fragments is by the size of the individual pieces. Imagine sorting rocks on a beach: you’d naturally put the finest sand in one pile, slightly larger pebbles in another, and so on.

• Sand is made up of the smallest rock fragments, finer than gravel.
• Gravel pieces are larger than sand but smaller than cobbles.
• Cobbles are those handsome, hand-sized stones, which are in turn smaller than massive boulders.

It’s important to know that the exact size classifications for gravel can vary. Experts use different standard scales to make sure everyone is talking about the same thing. Two of the most common are the Udden-Wentworth scale (popular among geologists in the US) and the international standard, known as ISO 14688.

• On the Udden-Wentworth scale, gravel is sorted into granular gravel (2-44 mm) or pebble gravel (4-66 mm).
• The ISO 14688 standard classifies gravel more simply as fine (2.0-6.3 mm), medium (6.3-20 mm), or coarse (20-63 mm).

How Much Gravel Will My Project Need?

Figuring out how much gravel you need is one of the most important steps, and the answer completely depends on what you’re building or creating. A gravel calculator (like the one mentioned in your text) is a fantastic tool for getting a quick estimate based on the dimensions of your project area.

Please remember that the price estimate from such a calculator is only for the gravel itself. It does not include other potential costs like labor for installation or fees for delivering the materials to your site.

To manually determine the amount of gravel you need, you must calculate the volume of space you need to fill. Here’s how you do it:

1. Determine the Area: Calculate the square footage (or meters) of the space you want to cover with gravel.
2. Decide on the Depth: Choose how deep you want the gravel layer to be. While the ideal depth changes based on the project’s purpose (a driveway needs more than a decorative path), a good minimum baseline is 2-4 inches.
3. Calculate the Volume: Multiply the area by the desired depth. This gives you the volume of gravel required (e.g., cubic feet or cubic meters).
4. Convert to Weight: Finally, because gravel is often sold by weight, you use the known density of the specific type of gravel you’ve chosen to convert your volume calculation into the mass (e.g., tons) you need to purchase.

The Many Uses of Gravel: More Than Just Rock

Gravel is an incredibly important commercial product with a huge number of applications, ranging from purely decorative purposes to massive, large-scale construction projects like roads. In fact, billions of tons of gravel and sand are produced for construction worldwide every single year.

Construction Uses

In construction, gravel is an absolute essential. Nearly half of all gravel produced in the United States is used as aggregate for concrete. “Construction aggregate” is a broad term for materials made up of medium to coarse rock fragments, which can include not just gravel and sand, but also crushed stone, slag, and recycled concrete.

But gravel’s job doesn’t stop there! It is also crucial for:

• Building the foundation for roads and mixing with asphalt.
• Acting as stable construction fill.
• Helping to produce construction materials like pipes, bricks, and concrete blocks.
• Creating specific surfaces like roof coverings, walkways, and driveways. A mix of sand and gravel can make shingles; walkways often use a blend of gravel and stone; and a driveway can be built using gravel alone or mixed with asphalt.

Furthermore, gravel is the go-to material for drainage systems in both major professional projects and backyard DIY jobs. Its genius is that it provides a solid, stable foundation while the spaces between the stones allow water and excess moisture to drain through it efficiently.

Landscaping and Decoration

Thanks to its variety of shapes, sizes, and natural colors, gravel is a superstar in landscaping. It serves as a beautiful decoration or accent piece while also providing practical benefits like drainage.

For example, it makes an excellent border for a flower garden, shoring up areas that might be at risk of washing away from soil erosion. It can be used as a stable base for a patio or to elegantly line a walkway or driveway.

In some cases, gravel can even be used as a substitute for organic mulch, like wood chips. Gravel mulch has some great advantages: it is far more durable, requires much less maintenance and replacement, and still protects the soil by retaining heat and preventing water from evaporating. Unlike light mulch, gravel is less likely to be blown or washed away, so it stays exactly where you put it, maintaining your desired landscape design.

Water Treatment and Agricultural Uses

Gravel plays a critical role in keeping water clean. It is used as a key part of the water filtration process to remove suspended solid particles (called precipitates). It’s important to know that a gravel filter alone does not decontaminate water or remove chemicals; it is just one step in the treatment process. It physically strains out solid particles that are too large to pass through the gaps between the stones.

In agriculture, certain types of gravel like limestone or chalk can be ground down into a powder to make agricultural lime. This is a soil additive that farmers use to reduce the acidity of their soil, which helps promote healthier crop growth. Interestingly, ground gravel is also used as a form of mineral feed for poultry like chickens and turkeys. These birds need to eat small rocks and minerals to help their gizzards properly break down the food they eat.

A Guide to the Different Types of Gravel

There is a whole world of different gravel types to discover. Generally, gravel is categorized based on two things: the size of the rock fragments and how the gravel was obtained or created. A key distinction is often made between gravel that was formed by natural erosion and gravel that was mechanically crushed.

• Natural gravel from erosion tends to be smoother and rounder (imagine river stones).
• Crushed stone is mechanically broken down, so it has rougher edges and sharper angles.

Because there are so many ways to categorize gravel, it’s always a good idea to clarify exactly what kind of rock fragments you’re getting, as different types have different advantages and disadvantages depending on your project. Below are some common examples.

Bank Gravel

Also known as “bank run” or “river run,” this gravel is harvested from banks next to rivers and streams. It’s a natural mixture of large and small rock fragments, sand, and clay. Its excellent water draining capacity makes it perfect for preventing soil erosion and allowing plants to take root. It’s typically used for filling holes in landscapes and as a foundation for concrete.

River Stone

Also called river rock, this is one of the largest types of gravel. These are the beautiful, smooth stones you find in rivers, creeks, and on beaches, all shaped by natural water erosion. They are primarily used for decorative purposes due to their attractive, smooth surfaces and wide variety of colors. You’ll often see them used in landscaping or for lining water features, creeks, and ponds because they look natural and have great drainage.

Pea Gravel

This is one of the smaller types of gravel, and it gets its charming name from being roughly the size of a garden pea. It’s also one of the most inexpensive types, which makes it useful for a huge range of applications. It’s a common ingredient in the aggregate used to build roads and driveways and to make concrete.

Pea gravel is also a landscaping favorite because it adds a pop of color and interesting texture, as it’s usually made from a combination of small, chipped, and rounded rock fragments. Its high draining capacity makes it great to use around plants, and it’s even a popular choice for use in aquariums.

Crushed Stone

This is a medium-sized gravel made by—you guessed it—mechanically crushing large rocks. The most common rocks used are limestone, dolomite, or granite. By some definitions, crushed stone isn’t considered “true” gravel because it’s processed rather than naturally occurring. The most obvious difference is its rough, jagged surface and sharp edges, unlike the smooth, rounded stones formed by erosion.

Its primary use is as an aggregate in concrete. It can come in many colors and textures depending on the original stone. Crushed stone is the classic material for surfacing roads and driveways because it locks together firmly. It can be used in landscaping, but its sharper edges are often considered less visually appealing. For this same reason, it’s not the best choice for barefoot walkways or pathways, as it can be uncomfortable and even hazardous to walk on compared to smoother gravel.

Pay Gravel

This type of gravel has a much more exciting name! Also called “pay dirt,” it can be made up of almost any type of rock. Its one distinguishing characteristic is that it contains significant concentrations of precious metals, like gold. For obvious reasons, it is rarely used for standard purposes like construction—it’s much too valuable! Its primary use is in the thrilling activity of gold panning.