Soil Binder Products

Global Road Technology (GRT) provides versatile soil binder solutions suitable on a plethora of soil types. The use of GRT products allows even the poorest soil types to be utilised in various engineering applications.

Soil binding is a process involving the application of a soil stabilizer (commonly cement, lime, and/or a combination of other agents) to exposed soil surfaces with the aim to prevent fugitive dust, wind/water induced erosion or ground instability. A research and development program, EuroSoilStab, administered by a consortium of companies from England, Finland, Ireland, Italy, the Netherlands and Sweden identified that the efficacy of soil binders could be categorized into the following four groups:

• Very good binder in many cases
• Good in many cases
• Good in some cases
• Not suitable

In an attempt to categorize various soil binder mixes, such mixes were used to treat different types of Nordic soils with the relative strength increase recorded in unconfined compression after 28 days of curing.

The research identified that cement possessed good binding characteristics in many cases, particularly in silty soils with organic content of 0-2% and also in peats with 50-100% organic content. On the other hand, the same cement mix yielded only satisfactory binding results (good in some cases) with clays and other organic soils with 2-30% organic content. The efficacy of cement mixes was seen to improve with the addition of other compounds, particularly with the addition of furnace slag.
In instances where lime was tested, satisfactory results were yielded for silt and clay soil types. However, in many cases involving peat (organic content between 50-100%), lime and similar mixes failed to suitably bind the samples.

The benefits of soil binding through soil stabilization include drying up wet soil, improving strength, providing volume stability through reducing swell and controlling shrinkage, reducing soil deformations, improving durability to dynamic or repeated loads and freeze-thaw, permeability control through either reduced permeability for water conveyance or retention structures, moisture consistency and dust control. The improvements in the soil are responsible for improved working platforms and workability of soils, reduced thickness of road layers, slope stabilization, foundation and structural support, excavation support and environmental remediation. 

While cement can be used with a variety of soil types, it is important that it is thoroughly mixed with any fines fraction, hence as a rule of thumb, more plastic materials must be avoided because they pose challenges on mixing with cement. On the other hand, lime will react with soils of medium to high plasticity, thereby reducing their plasticity and rendering them easier to mix, while also minimizing swell potential and increasing strength. For example in clay soils, the calcium in lime exchanges with the adsorbed cations of the clay mineral causing the clay to flocculate, and thus reducing the plasticity of clays rendering them more workable and mixable. 

Chemically, cement and lime have similarities because they are both calcium based chemical reactants. As a matter of fact, cement contains lime but it has its own source of reactants known as pozzolans whereas pure lime is limited in use to where other sources of reactant materials are present. Lime increases the pH value of soil pore water releasing silica from the clay mineral which reacts with the calcium present in lime to produce cement which strengthens the soil with curing of the mix. Alternative forms of fly ash which is rich in silica and alumina may contain significant sources of reactive calcium which makes it a cementing agent and nonreactive fly ash that is not self-cementing can also be a good pozzolan additive blended with lime or cement. 

Global Road Technology (GRT) provides versatile soil binder solutions suitable on a plethora of soil types. The use of GRT products allows even the poorest soil types to be utilised in various engineering applications. As an illustration, natural soils categorized as hard soils usually do not yield a UCS of more than 0.4 MPa. However, with a 0.5% by mass addition of GRT stabilizer, a UCS of 2-5.8MPa can be achieved. GRT7000 has proved to be an effective stabilizer in a wide variety of soil types, effective in both highly coarse to highly plastic soils.

Testing of Type 2 gravel treated with a 1% concentration of GRT7000 showed a UCS result of 8.9 MPa after 5 days curing. By comparison, to achieve similar UCS results in cement stabilised Type 2 gravels, a 5-8% cement concentration to material would be required.

Liquid polymers such as GRT 9000 are facilitate physical bonding of soil grains which extends its applicability to dust control and solidifying surface soils. Liquid polymers are widely used as soil moisture stabilizers to prevent water leakage through formation of a thin film of activity in the soil particle surface and soil particles gaps. Water soluble polymers contain functional groups such as carboxyl, hydroxyl, amide, amine, ether and hydrophilic groups which make the polymer valuable with regards to adhesion, film formation, dispersion and flocculation. Interestingly, active hydrophilic functional groups also participate in reactions which form new functional groups. The criteria for meeting the requirements for polymeric stabilization include ability to adhere to soil particles with assistance of water, internally cohesive, capability to work sufficiently at high humidity and at low ambient temperatures and miscibility with water to produce a low viscosity liquid. 

When it comes to fine-grained highly plastic soils, GRT:PCM is needed in much lower concentrations than lime and cement. Soils with a plasticity index higher than 20 (for which lime considered a very efficient stabilizer), generally require a treatment of either 3-5% of lime or 3-7% of cement. By comparison, only 1% concentration of GRT7000 would be required to stabilize the same material.

Lime or cement treated soils often face cracking under pressure. This problem is exacerbated under wet and cold conditions when water enters existing cracks and freezes. The semi-flexible polymeric characteristics of GRT: PCM overcomes these problems, as treated soils are able to withstand high loads. One of the most popular lime based soil binders used today is quicklime. Quicklime comes in the form of a powder and is highly reactive when mixed with water. For this reason, handling of quicklime is challenging. Conversely, GRT binding agents are user friendly and do not generate dust during application.

The type of soil binder product to be used depends on soil type to be treated, purpose of use, engineering properties desired, specifications of engineering properties, availability of materials, cost and environmental concerns. The selection of the appropriate soil binder product follows general guidelines on soil gradation and plasticity. 

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REFERENCES 

Hall, M.R., Najim, K.B., and Dehdezi, P.K. 2012. Soil stabilization and earth construction: materials, properties and techniques. Book chapter. Woodhead Publishing Limited. 

Huang, H., and Liu, L. 2012. Application of Water-Soluble Polymers in the Soil Quality Improvement. Civil Engineering and Urban Planning. 123-130. 

Nicholson. 2015. Soil Improvement and Ground Modification: Admixture Soil Improvement. Book Chapter. 231-290. 

Patel. A. 2019. Geotechnical Investigations and Improvement of Ground Conditions. Woodhead Publishing Limited.