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What is a Base Material?

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  • Written By: B. Turner
  • Edited By: W. Everett
  • Last Modified Date: 20 November 2016
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A base material is a gravel-based substance used to support a paved surface. Contractors install the base material between the soil and a new roadway, driveway, parking lot, or sidewalk. Base materials not only help paving crews create smoother and more stable roadways, but also act as a layer of insulation to reduce the effects of frost and freezing temperatures. While base material can vary by application, most include some form of aggregate combined with a binding agent, such as asphalt or tar. Many modern blends also include environmentally-friendly components such as recycled concrete, shredded tires, or other sustainable products.

This type of base construction can be found under many different types of paved surfaces. It's used beneath asphalt roads or parking lots as well as concrete patios and walkways. Many homeowners also add a layer of base material beneath a paver-based patio or pool deck. Some very small or temporary paved surfaces may not require a layer of base material.

A well-built roadway base offers a number of advantages over unsupported road surfaces. The base material protects the soil from damage due to construction or heavy traffic. It also minimizes damage on the surface of the roadway by reducing the risk of cracks, spalling, and other signs of deterioration. A paving base also provides structural support to the surface above, and helps spread heavy loads over a larger area. Many material bases can even prevent paving damage caused by small ground shifts and seismic activity.

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The total depth and composition of the material base depends on factors like soil conditions, total loads to be supported, and even the weather. Installers start by excavating the soil to make room for the base, then compacting the soil using a large compacting machine. Next, the base materials are applied to the soil and compacted once again before paving can take place. Some projects also require a moisture or vapor barrier above or below the base to reduce the risk of water damage.

Depending on the application, builders may use loose-fill base material like rocks and gravel to support a paved surface. In other cases, the aggregate must be mixed with a binder to improve stability, strength, and longevity. Most of these binding agents are derived from crude oil, though some experiments have been performed using crude oil sludge and industrial by-products in place of virgin materials. Installers must use care when adding these binding agents as they could contribute to soil and water pollution in some areas.

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titans62
Post 4

I know where I live, there are a lot of problems with putting down roads. I live in the Midwest, and the soils here soak up a lot of water in the spring months and start to expand. Once the summer comes, though, it can get pretty droughty, and the soil loses some of its water and dries out. That, of course, makes it contract. After a few years, the expansion and contraction of the soil really causes a lot of problems for the roads. They can crack pretty easily.

I have a friend who is a civil engineer and has the job of designing roads for the area. A lot of the major roads like interstates and large

state highways get driven on a lot, so they invest the money in buying a good base material and putting down a really heavy duty type of asphalt. Once you get into the county and local roads, though, that's when it turns into a problem.

In the towns, they usually go through and put gravel on them every few years, and that helps a little, but you can still see cracks form in them pretty regularly that need to be patched up.

TreeMan
Post 3

@jcraig - My brother had that exact same problem a couple of years ago. We were at his house for Thanksgiving that year, and he was pretty proud of the new patio they had installed all by themselves. It really did look good at the time, but then I started to ask him about what type of underlayment they had used, and I soon realized that they hadn't used anything like that.

I told him what would start to happen once the summer came and rain started making its way down through the bricks and into the ground. Compound that with the places where people walked the most, and he was going to have a big problem.

Since the

bricks really hadn't been down for too long, they were still easy enough to take back up, so we ended up spending most of Thanksgiving weekend taking the thing up and laying it the right way. It might have been extra work, but I enjoy that kind of thing, and now he won't have to worry about wobbly bricks.
jcraig
Post 2

@Izzy78 - Interesting observation. Now that I think about it, I know I have actually seen gravel used below a sidewalk before. I have also seen sand, though. Maybe it has something to do with the actually mixture of the concrete. Some concrete has a little bit rougher texture, and some of it is really smooth. As far as the concrete mixing with the sand, I think they fix that by tamping it down into a solid layer.

The thing I see a lot of times is when people put down paving blocks or some other type of footpath and don't take base materials into consideration. I guess for someone who doesn't do a lot of DIY work, it might

not be obvious that a base material is needed, but it makes a world of difference.

I don't know how many times I have been to a house and saw bricks that had started turning sideways and sinking into the ground just because someone didn't take the time to lay down a good base. It is definitely something that pays for itself in the long run.

Izzy78
Post 1

I guess I never really thought much about base materials, but I know that a lot of times when I see people laying concrete for a sidewalk or whatever, there is usually a layer of sand that they put down beforehand. I assume it is sand, at least. That is what it looks like.

It seems like sand would cause a problem with concrete, though. Once you started to pour the stuff, wouldn't it start to mix with the sand below it, and not have the intended effect of keeping the concrete level and whatnot?

Also, why choose something like sand over other materials like pea gravel or just plain dirt or something? Are there certain criteria that they take into account depending on the location? For all I know, sand is only used where I live.

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