Polymer soil stabilizers help contractors and engineers improve compaction, prevent erosion, suppress dust, restore foundations, and more. Even better, some types can last for decades! But, there's been some controversy as to whether polymers are a practical, sustainable option. To clear things up, let's explore how how they work and when (or if) it's a good idea to use them.
In this blog, we'll cover what polymers are and compare natural and synthetic varieties. Then, we'll weigh the pros and cons of three polymer soil stabilizers—geosynthetics, injections, and topical sprays—to help you decide if they're a good solution for your next project.
Poly means many, and mer means part. So, polymers are literally big molecules made of many smaller parts called monomers. They look like long chains with many links:
Soil stabilization is the process of changing soil’s properties to make it behave a certain way. Construction projects stabilize soil so it can support the weight of buildings, roads, bridges, and other structures.
So, putting it all together, polymer soil stabilizers use long, chain-like molecules to change soil’s structure and hold its particles together to prevent erosion, dust, shifting, and other problems.
Polymers form through a chemical process called polymerization (simple enough!). That’s when many monomers bond together to create the long chain. Most polymers contain one type of monomer, but copolymers have two types.
Polymerization can occur naturally, such as when our bodies build muscle or when trees produce cellulose so their trunks can hold up their heavy branches. Or, polymerization can occur when people manufacture synthetic materials like rubber and plastic.
Some people prefer natural polymers because they’re more eco-friendly (more about that later). However, synthetic soil polymers are uniformly made and widely available. They often outlast their natural counterparts; some varieties can last over 100 years! Other polymers aim for the middle ground with treated natural fibers or blended materials, offering strength, eco-friendliness, and stabilization for 20 to 50 years.
The key is to choose a polymer based on your project’s purpose. Whether it’s synthetic or natural, the material that comprises a polymer determines its traits, such as strength, permeability, and eco-friendliness.
For long-term soil stabilization that requires good drainage, you might use a synthetic, water-permeable geotextile that’ll last for decades. For a short-term drainage project, you might choose a biodegradable geotextile made from coconut husks instead. (More on geotextiles next.)
People began using polymers to stabilize soil during World War II to construct roads and runways for transporting troops, equipment, and supplies.1 Since then, the number of available products has skyrocketed. We’ll explore three categories of modern polymers: geosynthetics, injections, and topical sprays.
Geosynthetics are the only polymer stabilization method that starts with solid material. The four main types of geosynthetics are:
Each type of geosynthetic has unique pros and cons. Overall, they each prevent erosion and improve tensile strength and load-bearing capacity. They can also improve drainage. And with so many varieties, you can find the ideal material and lifespan to suit almost any project.
However, geosynthetics can be expensive, and the price rises the more complicated your project is. Permeable materials can clog. Certain geosynthetics—especially geotextiles and geomembranes—are prone to rip, and they’re all hard to repair once they’re underground.
Polymer injections are foams or liquids that people insert directly into unstable soil. Once underground, they expand and compress coarse soil particles tightly together. The polymers then harden so they’ll stay in place. Soil’s load-bearing capacity and compressive strength increase, and it becomes less likely to shift and damage structures.
When some liquid or foam polymers harden, they essentially “glue” the coarse particles together and trap fine particles between the coarse ones, making it harder for expansive clays to shrink and swell due to moisture changes. You may hear people call these polymers binders, because they’re literally binding the soil together.
Injectable polymeric resins are often made of synthetics such as polyurethane and acrylic copolymers, which are common in paints and adhesives. Some help with repairs near soil’s surface, like filling and sealing cracks in pavement or foundations, but most work deeper underground.
To use the underground method, you’ll need to hire a geotechnical engineer to evaluate your soil and choose the injection sites. Then, the contractor inserts a hollow, drill-like tool into the soil and injects the polymer into problem areas. The polymer will seep through soil’s pores and fill gaps. (Curing time varies by product and project. Some polymers harden in minutes; some take days to reach full strength, much like cement.)
Injecting soil polymers lets you stabilize soil under existing infrastructure, like paved roads that have already been built. It allows for in situ stabilization, so you can stabilize the native soil on your jobsite without over excavation or hauling. And if there’s not infrastructure already in place, you can compact soil while the polymers are still wet so it’ll hold that shape once they harden.
Once in the ground, injectable soil polymers can withstand a variety of weather, including freeze-thaw cycles. So, they can help prevent concrete from cracking and surface areas from eroding, reducing overall maintenance. Sometimes, contractors mix them with cement for maximum strength; other times, they choose polymer types that are stronger than gravel or cement-treated bases.
So, what are the downsides? The first is cost. These products are extremely expensive, as are the necessary (and highly specialized) installation equipment and geotechnical testing. Savings on hauling rarely offset these costs, so many people opt for more affordable cement or lime stabilization instead. Another pitfall: one mistake with a polymer injection can ruin the project and cost you tens of thousands of dollars.
Some injectable polymers are ineffective for soils that contain primarily silt and clay, since they work better with larger materials, so picking the correct product for your soil type is a must. Most types only work for spot treatments, not large applications. And they all eventually break down due to moisture. When that happens—whether it’s one year or 50 years later—those fine soils begin to shrink and swell again.
Some polymers come in a liquid form that you spray on soil’s surface. These topical solutions, also called emulsions, mix tiny pieces of polymers with water. Like other options, they can be natural or synthetic.
For example, lignosulfonates are natural, sap-like byproducts of the wood pulp industry. They’re common dust suppressants in the mining industry, since they’re non-toxic and eco-friendly. Synthetic polymers include materials like styrene butadiene or styrene acrylic—types of rubber and plastic, respectively.
People use water trucks to spray polymer emulsions onto soil. The emulsions soak in slightly, drying and hardening into a transparent crust that binds particles on the soil’s surface together. The crust’s thickness and permeability depend on the product you use. Some polymers form a hard, sealant crust; others form lighter crusts that still let water into the soil and let project owners rework the soil. In both cases, the polymer binds or weighs down the soil particles, so they don’t fly away. (That’s why topical sprays are popular for dust suppression.)
Emulsions can also improve compaction. For example, contractors can wet a dirt road with a polymer emulsion and mix in aggregate. The moisture makes the soil particles “float” between the aggregate particles, so the compactor interlocks the soil and rocks tighter together for a more stable surface.
Dust suppressant polymers help companies comply with PM10 and PM2.5 regulations. They also improve visibility and safety on jobsites, reducing the risk of accidents; this is crucial since roughly half of mining fatalities involve surface mobile equipment.2 They also help improve air quality and respiratory health. As a bonus, many topical polymers help prevent erosion.
The pitfalls of polymer soil stabilization sprays are similar to those of injections: cost and susceptibility to moisture. Treating one mile of road with lignosulfonates can cost hundreds of thousands of dollars. And the kicker is, they only last three to 12 months. Synthetic polymers may last slightly longer, but not much because they’re exposed to weather and traffic that breaks them down quickly.
The answer is (drumroll please)... it depends on your project!
If you’re trying to keep toxic waste from leaching out of a landfill, you most likely need a geomembrane. If you’re trying to prevent avalanches on steep mountainsides, geocells are a wise choice. If you need to stabilize soil under an existing foundation, polymer injections could make your project much easier.
So, these products may be essential for some things—but not everything. For instance, we don’t recommend polymer injections or emulsions for things like road stabilization or dust control. Let’s explore why we advise using polymers only when necessary, so you can better determine if the risks are worth the reward for your project.
Polymers break down over time due to moisture, UV light, heat, and oxygen exposure. Some degrade within a few months of the initial application. Plastics like polyethylene, polypropylene, polystyrene, and polyurethane take years—sometimes 50 or more. That may seem like a long time, but it’s still short enough that you, your kids, and grandkids could all be around to see it.
Once polymers degrade, they no longer do their jobs. Soil begins to shift, causing erosion, surface issues, dust, and structural damage. All of those take time and money to fix.
When you’re considering whether to use a polymer, consider the ideal lifespan of your project—and how maintaining a polymer stabilizer will impact the overall cost. Do you really want to pay to reapply a dust suppressant in six months, or would you prefer something that lasts a year? When polymers disintegrate, what will it cost you to restabilize your roads or other structures?
When polymers break down, tiny pieces of material work their way into the surrounding soil, water, plants, and air. How that impacts the environment depends on the material.
The good news is that natural polymers are generally eco-friendly. They tend to be plant- or fiber-based, so they come from renewable resources. They can have some negative effects—such as animals trying to eat non-native plant particles or degraded fibers clogging drainage ditches. But, they’re less harmful than synthetic materials.
Synthetic polymers often bear labels saying “eco-friendly,” but this term can be misleading. The truth is that they’re more eco-friendly to make than traditional soil stabilizers like cement or lime because manufacturing polymers leaves a smaller carbon footprint and emits fewer greenhouse gases. But, synthetic polymers contain harmful chemicals, rubber, and microplastics.
Microplastics that enter soil can cause genotoxicity in plants, microbes, and small organisms, meaning they negatively alter genes to be more susceptible to diseases. They can even keep earthworms from growing to full size.3
Polymers can also adsorb pollutants. That means the polymer holds toxic chemicals or heavy metals on its surface and carries them into soil, water, and plants. As animals consume these resources, the pollutants enter their systems and make them ill. One study found that polymers can cause neurological damage and infertility in fish. And humans are the same: consuming plastic polymers through air, water, and food can cause neurological and cardiovascular conditions, infertility, autoimmune disorders, digestive issues, and respiratory illnesses.4
So, when you’re considering polymer soil stabilization methods, it’s wise to think about what will happen when they begin to dissolve.
There are dozens of other soil stabilizers on the market. So, the chances are that you can find a more affordable, eco-friendly alternative in most cases.
Our favorite is an organic, enzyme soil stabilizer called Perma-Zyme. It can suppress dust for up to two years and stabilize soil for 10+ years with just one application, making it an ideal solution to replace polymer injections and emulsions for projects like road maintenance, dust control, pad construction, and more.
Before settling on a polymer soil stabilizer, see how it looks compared to other products. You may need polymers to handle highly specific soil stabilization needs—or, you may find something even better.
No Comments Yet
Let us know what you think