When constructing roads, the base layer is crucial. Roads require a strong, resilient base to prevent failures due to soil under the road shifting and settling.
A good base starts with good soil. The trouble is that the soil in many parts of the world contains expansive clays that are difficult to build on. We’ll explore what expansive clays are, the problems with building on clay, and some clay stabilizers you can use to construct better, stronger roads on these soils.
Clay is one of the four main soil types (the others are silt, sand, and gravel). Clay is filled with organic matter from dead plants and animals, making it nutrient-rich. It also has the finest particles of all the soil types.
There are several subtypes of clay soil that are often named for their color, such as blue, red, and yellow clay. There’s also clay loam, which contains some silt, sand, or both. You may see people categorize clay loams based on the percentage of clay, such as 40% clay soil.
Clays are plastic, meaning they’re stretchy and shapeable. They expand and contract due to changing moisture, and when they contain the right amount of water, they’re easy to mold into shapes.
Highly plastic clay soils are called expansive clays because they expand the most when wet. They can become extremely soupy and sticky, hence their nickname gumbo clay. You may also hear people call them fat clay or heavy clay because the particles absorb water and swell up, which makes them weigh more.
Clay’s shapeable nature sounds good for road construction; it should make roads easy to shape, right? No! Unfortunately, all that plasticity makes construction more challenging, whether it be for unpaved roads, paved roads, or any other project. Let’s cover some of the main problems with building on clay soil.
Clay reacts so highly to water that it can change shape during the construction process. The crew may water the soil to its optimum moisture content (the amount of moisture it needs to fully compact). But as the day goes on, air and sunlight begin to dry the clay, causing it to expand and contract unevenly on different parts of the jobsite. That makes it difficult for the construction crew to compact expansive clays uniformly and for the soil to retain a consistent shape when it dries.
Expansive clays are heavy, clumpy, and sticky when wet. If the construction crew oversaturates them, these soils can stick to machinery or clog equipment. That can slow down the project timeline significantly.
Soil under roads will get wet due to groundwater, rain, and other moisture seeping in. When expansive clay soil gets wet, its particles change shape—and some changes could be permanent. When expansive clays dry out, they often contract and change shape again. They can even harden into a concrete-like material that’s extremely difficult to break up.
That’s bad news for road construction. Any soil that shifts under the roadway will cause structural failures and safety issues on the roadway. (Hello, potholes and collapsing asphalt!)
Clay soils drain poorly because they absorb water rather than letting it filter through their particles. That can cause problems. For example, if the soil is waterlogged when the temperature drops, it can freeze and damage the road’s subgrade. Poor drainage also means clay warms up slower in the spring than other soils because water warms slower than minerals.
Think about a time when it didn’t rain for days, and you saw soil that developed large cracks. That soil probably contained clay. When it dries, clay becomes extremely brittle and cracks apart. That makes unpaved clay roads difficult to drive on and opens them up for potholes, ruts, and freeze-thaw damage when it does rain again.
Because clay particles are so fine, they dry quickly, and it only takes a little breeze to send them soaring into the atmosphere as road dust. Road dust poses serious health and safety risks to drivers, nearby communities, and the environment. So, people who build and manage unpaved clay roads find themselves locked in a constant battle against dust.
When you build on expansive clay, you’ll often need a clay stabilizer—a soil stabilizer that’s durable enough to hold clay soils together. Unfortunately, the options for effectively treating unpaved clay roads are limited, but there are a few. You can use the following options for unpaved roads and pad construction for things like drilling pads, storage pads, and parking areas.
A layer of gravel above the clay filters out water, decreasing the amount that goes into the soil and, thus, decreasing its potential expansion. Treating expansive clay roads with gravel helps limit the likelihood of impassable mud or ruts. It’s also an option that’s available to most people. In the U.S., crushed limestone is the most popular aggregate for constructing gravel roads.
The downside is that gravel treatments don’t last forever. Storms can wash away the gravel, and traffic can fling gravel off the road or embed it into the clay so it disappears. Most gravel treatments only last from a few weeks to six months—or up to a year if you’re lucky. The cost of applying gravel to clay roads adds up as time passes, making this clay stabilizer expensive long-term.
Chlorides are road salts that pull moisture from their surroundings and wet the clay particles. This makes them heavier, so they can’t fly up into the air as dust. And since chlorides form a crust over the soil’s surface, they also help stabilize unpaved clay roads to prevent erosion.
However, chlorides have some significant drawbacks. They only last about three to six months, so you’ll have to pay to apply them multiple times a year. They only work in humid climates. They’re corrosive to cars and concrete bridges. And they can build up in water and soil over time, which can sicken or kill plants and animals. Clay soils are more prone to salt retention than other soil types, so they’re at greater risk of chloride contamination.
Paved roads are built in layers. They generally have a soil subgrade on the bottom, an aggregate subbase in the middle, and an asphalt or concrete topcoat. But as we discussed, building on a clay soil subgrade can cause the pavement to crack and fail. It’s crucial to stabilize the clay before adding any more layers to the road, so let’s explore our options for doing that.
During over-excavation, the construction crew removes most or all of the expansive clay from the jobsite. Then, they import more stable materials like sand and Type II aggregate to fill the void. Over-excavation is common because completely removing the expansive clay removes all the problems of building on it.
However, over-excavation is expensive and time-consuming because it requires digging up and hauling out all the old material, then hauling in and compacting the new material. So, you’ll pay the trifecta of large road construction expenses: material, hauling, and labor costs.
Cement and lime are common clay stabilizers. They’re both binders, meaning they hold expansive clay together when you mix them into the soil. This process often increases the soil’s strength and adds a chemical bond that helps decrease the likelihood of the soil expanding or contracting later on.
The largest downside to lime and cement-treated base is the cost, as it usually takes a lot of material to stabilize soil with these options. Additionally, costs and local availability can be unpredictable and fluctuate from region to region.
Perma-Zyme is one of the only soil stabilizers that uses clay soil to achieve optimal results. It’s a unique, enzyme-based formula that doesn’t just counteract clay; it works with expansive clays to stabilize roads.
Perma-Zyme works by chemically reacting with the clay particles to permanently bond them together. It will also bond around any aggregate in the soil, locking the gravel particles in to make the soil up to 13 times stronger. You’ll see a significant reduction in dust. And because the finished surface is hard like concrete, it’s nearly impermeable to water—meaning your clay soil will no longer expand or contract.
Unlike other options for remediating expansive clay soils, Perma-Zyme lasts over 10 years for most unpaved roads and over 30 years for paved roads. It’s highly cost-effective, and you can complete the easy application in as little as one day. Plus, it’s effective in all climates.
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