Soil cement is a soil stabilization technology that seeks to increase shear strength and stiffness in soil.
The process consists of injection or mixing a chemical binder into the soil to strengthen it, making it capable of supporting heavy loads such as roadways & concrete driveways without subsidence over time.
In this manner, the soil’s surface layer(s) are bonded together to form a mechanically strong layer. The concept of soil-cement is really attractive, but it has some disadvantages. In this article, we’ll discuss the advantages and disadvantages of soil cement.
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What is soil cement?
Soil-cement is a mixture of gravel or crushed rock, sand, water and portland cement used to fill in the space between the stones before they are covered with topsoil. It was invented in Manitoba by farmer Edwin F. Dalpunas in 1974, who patented the process and later started his own company, DALPUNAS CEMENT. The mixture is typically 70% rock, 20% gravel and 10% sand, with between 5-10% portland cement (depending on application).
The mixture itself is “bentonite enhanced,” which means bentonite – a clay-like compound – is added to the mixture during mixing at a rate of roughly 4 pounds per cubic yard (2 to 3 percent by weight), giving it additional strength and reducing its permeability. The final product is the same as conventional soil-cement but with less portland cement (which can be two to three times more expensive than rock) and uses only 20 percent sand.
How to use soil cement:
Mix enough water with sand and portland cement for a mixture that is the consistency of pancake batter and then add gravel or crushed rock, mixing it in to create a pasty substance. The soil-cement must be vibrated to remove air pockets and settle prior to landscaping overtop of it.
How soil-cement works:
As a building material, soil-cement is a mixture of aggregate (typically any type of crushed rock), portland cement and water that can be vibrated to eliminate air pockets and reduce settling. The aggregate used in soil-cement is typically 20 percent gravel or crushed rock and 10 percent sand, with 5-10 percent portland cement.
Soil Cement Construction:
In soil-cement construction, you mix aggregate (crushed gravel or rock), sand and portland cement together in the proper proportions to form a thick slurry that is then vibrated to eliminate air pockets and settle it into position. Once the material has set, it is covered by topsoil and then landscaping.
What is soil cemet used for?
Soil cement is typically used to build a wide range of structures, including houses and sidewalks. It also can be used as an option for driveways when combined with crushed rock, stone or angular gravel.
Advantages of soil cement under driveways
Cheap and sturdy alternative for driveways
Compared to asphalt, soil cement under a driveway is much cheaper and sturdier. The strength of a poured-in place concrete driveway is directly related to the quality of the base it’s laid on. For a standard residential one-car driveway, an eight inch thick pour will suffice, but that requires a thick layer of asphalt fill. And since that fill is being relying on for support, that means it’s subject to damage from anything that happens on the surface above it that could compromise the integrity of the base.
Asphalt driveways are at high risk when they’re in cold climates because freeze-thaw cycles can cause depressions when the water in the asphalt freezes and causes the ground underneath to heave. And a driveway is even more exposed to damage from vehicles because they’re typically flat at the surface, whereas a gravel or stone driveway is crowned slightly with a raised edge that deflects some of the weight of an ATV’s tires away from the surface below.
In comparison, a properly-poured soil cement driveway is much sturdier because the ground beneath it never heaves. And since there’s never any need for an asphalt base, there are no freeze-thaw cycles to contend with either. All this means that a soil cement driveway will always remain flat, even through harsh winters.
Soil cement under a driveway is also advantageous because it can be done without any specialized equipment. A DIY job that would require a concrete pump and steam roller with an asphalt driveway can be done just as easily by hand with soil cement, and the results will be just as good.
Eco-friendly alternative to asphalt
Compared to asphalt, soil cement is an eco-friendly choice as well as cheaper and sturdier. Some people have been tricked into thinking that they’re doing the right thing for the environment by opting for a poured concrete driveway because it’s made from cement just like the foundation of a house, but that’s actually not the case concerning this matter.
Cements are manufactured through heating calcium carbonate (limestone) to between 1450 and 1500 degrees Fahrenheit in large kilns, which emits several environmentally-hazardous gases into the air during the process.
The other common ingredient for concrete is aggregate, which comes from rocks quarried by the ton from the earth. Asphalt is more eco-friendly because its base can be natural, such as decomposed granite or sand, and since it’s mixed with petroleum instead of limestone, there’s no emissions produced during its production process.
Drives last longer than asphalt
A soil cement driveway is considerably more durable in comparison to an asphalt driveway that’s constantly pounded by vehicles traveling along it. Asphalt is only suitable for areas where the ground doesn’t freeze, whereas soil cement can be used in any climate because there’s no need for an asphalt base. That means there are no depressions caused by freeze-thaw cycles to deal with, and since there are no cracks to fill, a soil cement driveway is virtually maintenance-free.
Disadvantages of Soil Cement Under Driveways
Soil cement has the disadvantage of injuring the soil. When cement is added to soil, microorganisms are destroyed, and organic matter is converted into non-organic collagen. As a result, soil structure changes, and air capacity decreases due to the expulsion of water after mixing with cement proteins.
The physical properties of soils change because of chemical and physical interactions. The penetration, dispersion, and stickiness of the soil improve considerably. When subjected to heavy traffic, the stability of soil-cement decreases rapidly, which is a serious drawback for this technology.
Reduction in Permeability
The pore spaces increase when chemical binding enters into porous soils. Water movement is reduced, and capillary suction increases. Soil bulk density increases, decreasing porosity with time because most biological activity ceases after mixing with soil cement.
According to this driveway company a wide range of factors influences permeability reduction, including process variables such as injection pressure, formulation conditions, viscosity, the water content of binder solutions, etc. Still, these are beyond the control of classical driveway engineering principles.
Elimination of Soil Organisms
Mixing soil cement with the soil microorganisms and their enzymes entails a certain death rate. It is found that the organisms most sensitive to soil-cement are bacteria, actinomycetes, and fungi; protozoans and algae show little sensitivity to the mixture with the chemical components in the soil.
Many species become inactive after mixing, affecting decomposition and making the release of nutrients from organic matter slow down considerably. The formation of humic acids is also eliminated when bonding occurs, which is an essential factor for nutrient absorption by plant roots.
Loss in Organic Matter
Soil organic matter consists of living (bacteria, fungi, nematodes, earthworms, and arthropods) and dead (humified) matter. Live organic matter is responsible for releasing nutrients by the mineralization of soil organic compounds.
This is important for plant growth and contributes to the formation of new nitrogen in ammonium ions (NH), which is one of the most accessible forms of nitrogen nutrient that promotes plant growth. The loss or decrease in the availability of these beneficial components inhibits microorganism activity and causes a reduction in available nutrients.
Reduction in Nutrient Availability
Soil cement binds with nutrients such as phosphorus, calcium, sulfur, and silicon, making them less available to plants over time. Phosphorus becomes less soluble because binding occurs with aluminum hydroxide particles.
Calcium is immobilized by forming new compounds such as calcium silicate and calcium aluminate. This reduces nutrient availability which promotes soil compaction over time.
Soil cementing is associated with a thermal effect of about 5–7 for a period not exceeding 30 days. The temperature increase occurs during the first 10 minutes after mixing due to water evaporation from pores, which causes an intense heat adsorption process (120 calories per gram).
After 30 days, this figure decreases to 0.5–1 because the surface hardening process has been completed, and porosity decreases quickly in soils with high loading rates (>500 kPa) or temperatures above 20 .
Loss of Bearing Capacity
The initially high bearing capacity of soils may be reduced by forming a hard crust on the surface during the initial stages, especially in clayey and loamy soils.
This phenomenon is called “soil welding,” which occurs when cement particles bond together to form a continuous watertight layer at the soil-cement interface.
The impermeability of this layer creates problems for plants developing roots or plants that need water under their roots (grasses, maize), as well as constructing roads and other structures on top of soils cemented with chemical binders.
As time passes, strength gain decreases, plasticity diminishes, rutting increases, drainage decreases, and soil cracking appears.
This is because cement particles gradually re-dissolve as they react with water (drainage process) and some fine particles remain almost unchanged over time (plasticity reduction/diminishing shear strength).
Loss of Soil Structure
The chemical reactions between soil components and cement also negatively affect soil structure, forming new compounds called “soil cement.”
The loss of soil porosity and increased soil stiffness due to the formation of these compounds leads to a decrease in permeability and an increase in bulk density which can cause severe problems for plants that grow below them since they will not receive enough air or water. As a result, their growth may be inhibited.
Loss of Nutrients
Cement does not allow water through its surface, preventing the absorption of nutrients by plants around it.
Reduction in Water Storage Capacity
The cementation process reduces the amount of water stored in soils because it decreases available pore space where water could be stored (up to 40%). This phenomenon is also related to losses in soil organic matter, fine particles, organic compounds, and water-soluble nutrients.
Reduction in Soil Microorganisms
Soil cementation decreases the availability of nutrients for soil microorganisms involved in biological processes such as nitrification, denitrification, mineralization, and immobilization which affects the activity of these organisms within the soil profile.
The soil cementation process also reduces root colonizing fungi, especially arbuscular mycorrhizal fungi (AMF), which are essential for reaching phosphorus at deeper soil layers where other types of fungi cannot reach due to competition from chemicals present in cement. This may be why phosphate fertilizer efficiency is low after cementing soils since AMF contributes to about 80% of nutrient uptake by plants.
Reducing Water Infiltration and Drainage
As a result of soil compaction and damage to the natural structure due to cementation, water infiltration rates in soils decrease drastically from 10–30% for unsaturated soils to less than 1%. In addition, water drainage decreases from 5–10 litres/hour/m² before cementation to 0.001 litres/hour/m² after cementing.
This is because chemical cement has low permeability compared with aggregates making up the original soil structure. Decreased porosity leads to a reduction in available pore space where water can be stored or pass through so that infiltration rates decrease, resulting in higher runoff and erosion of the surface layer of the soil once it rains.
Lower Cation Exchange Capacity (CEC)
The cation exchange capacity is reduced by cementing soils, translated into an ability to uptake fewer nutrients such as calcium and magnesium. This loss in nutrient uptake efficiency can cause deficiencies of these nutrients in plants grown on these soil types since they cannot access the available nutrients due to the low CEC.
Reduction in Soil Water and Salt Holding Capacity
Soil compaction reduces porosity and water storage capacity, while chemical cement formed from cementing compounds reduces infiltration rates and increases surface soils’ runoff and erosion once it starts raining, thus increasing water losses through deep percolation and surface runoff. These phenomena result in the water holding capacity concerning water and salt reduction in the soil.
Soil cement vs concrete for driveways:
There are many advantages to using soil cement for your driveway. The main advantage is the cost, as soil-cement typically costs half as much as concrete. Another benefit of soil-cement is that it requires less labor than concrete, making it a fast and easy option.
Using gravel or crushed rock under the mixture allows the driveway to be built in one day and allows soil-cement driveways to last longer than concrete due to their ability to absorb water better.
What is the cost of soil cement?
The cost of a soil-cement driveway can range from $1.50 per square foot with gravel or crushed rock under it, up to about $2.75 per square foot with angular gravel and $5 per square foot with crushed limestone.
What is the lifespan of a soil cement driveway?
The life expectancy of a soil-cement driveway varies based on climate and initial application, but in general is around 20 years for residential driveways and up to 50 years for commercial applications.
How strong is soil cement?
Soil-cement is much stronger than conventional soil due to the portland cement that it contains, yet it can still easily be tilled or dug into. Soil-cement also reduces water infiltration compared with conventional soil, making gravel base a good option.
How thick should a cement driveway be?
Typically, a soil-cement driveway is 4 inches thick – much thicker than a concrete driveway. However, it should not be applied deeper than the bottom of your gravel and should also be used as a base for any other materials (such as brick, stone or flagstone) that go on top of the soil-cement.
The process of soil cementation is common in arid and semi-arid regions, but it can have serious effects on soil physical properties that benefit plant growth. Although the benefits arising from reducing wind erosion may be significant for many farmers, they must consider all risks and indirect effects associated with this practice before deciding whether or not to cement their soils. This article helps you to understand the disadvantages of soil cement.