Soil Stabilization

The ideal types of soils that guarantee the stability and durability of the pavement structure are not always found on unpaved roads or land to be intervened. Therefore, as an alternative to the use of borrowed granular soils and quarry exploitation for unpaved roads upgrading, it is necessary to use different methods of soil stabilization (alternative chemical soil stabilization) to improve the conditions and characteristics of natural soils through soil stabilization technology. The change in soil properties through a chemical modifier allows the optimization of pavement structures, together with the reduction of thicknesses, without affecting the performance of the pavement structure over the years with long-term permanent strength gains.

The growing demand for works with less environmental impact and “green works”, in addition to the latent need of governments to save and extend the scope of their budget, makes using natural soils a highly viable option for improved road conditions and avoiding the gravel road maintenance costs find road construction and preservation projects. 

On-site, clay-based soils, silty soils, and sandy ones can be found that do not meet the strength characteristics to form a structure. It is possible to take advantage of this natural soil and improve it through the implementation of different chemical soil stabilization technology techniques to improve its physical and mechanical conditions, and increase the load bearing capacity, ultimately increasing the soil’s load-bearing capacity and durability. Different methods of soil stabilization in the market achieve different results; it is essential to determine a suitable soil stabilizer that fits the soil properties to achieve a successful soil treatment, among the best forms of soil stabilization and the best soil stabilization technology, such as:

• Cement stabilization (soil cement)
• Ionic stabilization (polymers)
• Acrylic stabilization
• Stabilization with lime (Quick Lime, Hydrated Lime is not widely used)
• Stabilization with emulsion
• Enzymatic soil stabilization
• Mechanical soil stabilization
• Confinement in geogrids

These types of systems must be complemented throughout the construction process with mechanical stabilization techniques for soils. 

What is soil stabilization?

Soil stabilization allows converting weak soil, or one that does not meet the necessary characteristics for the preservation and durability of a pavement structure, into soil that does meet the technical performance characteristics and end properties of soil, such as compressive strength, shear strength, mechanical strength, structural capacity, permeability, durability, wear resistance, among other factors, basically improving the soil’s physical properties through the use of additives using the different methods of soil stabilization.

The process typically consists of a previous analysis of the soil that allows knowing its basic characterization; to know the strengths of the soil and also its deficiencies, it is crucial to know the soil particles in depth, it is necessary to know if they are expansive soils and other relevant conditions of the material properties to determine the best way to stabilize the existing soils. Based on the characteristics found, it is determined which is the best stabilizer(s) to “fix” the deficiencies of the soil and choose from the range of products, the one that has the best performance and also achieves development of resistance so that the stabilized material complies with the current regulations and the required design.

Subsequently, it is necessary to make a mix design with the ideal stabilizer(s) for the soil to be worked, through the analysis of the performance obtained with different dosages, typically three or four points of effort vs. dosage, to find the optimum. It is not always possible to achieve an unconfined compression with a single product; some unstable soils require more than one type of stabilizer in the soil mixture; it is even possible that a single stabilizer can achieve unconfined compression and comply with current regulations; however, it may be possible to achieve the same results of the aforementioned regulations with the stabilized material through the combined use of products.

There is diverse literature on the subject, on design methodologies, execution methodologies, site controls, such as Guide to Pavement Technology by AustRoads, Low Volume Road Engineering by Robert Douglas, Soil Cement Construction Handbook by PCA, Manual of Soil Stabilization with Cement or Lime by IECA. It should be noted that not always the local literature in each country is suitable, many times the texts tend to be pachydermic or outdated, in comparison with literature available in the rest of the world, which is fully advanced and updated, not only that, but in constant progress and updating.

At Pro-Road, one of the fundamental pillars of our value proposition for road construction through the modification of soils and paving, is the stabilization of natural soils, as we have alternative stabilizations with varied soils. The Pro-Road group of companies has state-of-the-art technology and materials that allow us to cover most of the soils found in the world. The work starts with the manufacture and development of stabilizing and cementing products, the design of structures with these products, up to their implementation in road works.

Not all stabilizers provide hydrophobic surfaces, and non of them provide 100% hydrophobic surfaces, making it a mandatory requirement to use a complementary wearing surface (operating surfaces) that allows for the road base to remain unaffected by the effects the ingress of water. Be it a subgrade stabilization or a final road base course, the end result must be paved roads, independent of the arguments placed by dust suppressant, dust control solutions, dust control products, dust control experts, dust suppressing salesman; all manuals recommend the installation of a wearing course for mid to long term road projects. 

What are the types of soil stabilization?

The characteristics of the soil determine the optimum type of stabilizer or, failing that, the optimum combination of stabilizers. It is necessary to analyze the characteristics of the soil, such as its Atterberg limits (plasticity index), granulometry and compressive strength, the latter can be in the form of simple compression, CBR (California Bearing Ratio), DCP (Dynamic Cone Penetrometer), etc. On the other hand, it is necessary to know the structural needs of the paved roads in terms of traffic (TPD and accumulated ESALs) and stresses to which it will be subjected during its design period. Finally, it is necessary to know the budget, because at the end of the day it is the one that makes the track become a reality.

In conjunction with the above factors, one or several stabilizers are determined to meet the performance requirements within the required budget. For example, it is common knowledge that clay-based soils or medium-high plasticity characteristics share well when stabilized with products such as lime, ionic stabilizers (PREI-16) or Portland cement in a complementary way. It is also common to find sandy soils, with low or no plasticity, without any type of coarse grain size, acrylic stabilizers (PREA-03) work well, sometimes in conjunction with cementitious or ionic stabilizers. Granular soils, pavements, ballasts, work well with cement stabilization, or soil cement, it should be noted that it is essential to analyze the plasticity and granulometry to ensure a good matrix, and also an optimum resistance.

Many times it is also more economical to add another soil depending on the clay content of the soil, not only selecting one of the types of soil stabilization methods available; for example, if there is an affirmation nearby, it can be added to the existing soil and it can be more economical than chemical stabilization, achieving the same soil quality in the stabilized layer of soil. It is also possible the combined use of stabilizers, for example in high plasticity soils the ionic stabilizer PREI-16 works very well and sometimes it is possible to optimize the design of the soil layers by adding lime to the soil. It is always essential to classify the soil categories prior to the start of the design. It is also crucial to control the water sensitivity as well as the optimum result found in the proctor water for each soil. The optimum water content must be achieved or approximated in the field, regardless of the stabilizer used, so it is also necessary to know the rainwater and weather trends on site to avoid moving away from the optimum water content and existing soils becoming unstable soils without optimum compaction. Stabilized soils must comply with the water and stabilizer dosages obtained in the laboratory, only in this way can optimum soil compaction be obtained on site. On site, it is also essential to achieve a homogeneous mix; it is not enough to control moisture content and environmental conditions; failure to achieve an optimal soil mix with earthmoving equipment can result in a low quality soil that does not reach the required bearing capacity. It is possible to carry out field controls to check the design density, ideally, several samples per lot or section executed, as well as it is necessary to take several samples to fail in the laboratory, according to the current regulations that govern this type of procedures in each country.

Low plasticity silts tend to be somewhat complex, as it is possible to achieve resistance with various products, however, their physical and chemical characteristics are those that will allow, or not, that certain stabilization solutions work, these fine soils can have a high variability. For example, in some soils, it is possible to achieve strength by stabilization with asphalt emulsions, possibly with the addition of some type of cementitious agent. Additionally, it is possible to achieve resistance conditions with acrylic stabilizers (PREA-03), many times, complemented with ionic stabilizers (PREI-16), depending on the plasticity of the soil, in case of having low or no plasticity, it will be better to complement it simply with portland cement.

Soil Cement

Soil cement, or soil cement stabilization, consists of mixing cement, usually portland cement, with soils to improve their performance conditions. Mixing with cement results in an increase in bearing capacity (compressive strength), and a reduction in the plasticity index.

Which soils can be stabilized with cement?

In theory all soils can be stabilized with cement, except very high plasticity and organic soils. Beyond the question of whether or not a base soil can be stabilized in unpaved roads, it is important to analyze the cost of stabilizing a soil in this way. For this purpose, it is necessary to determine the optimum percentage of cement to reach the required strength and conditions, since a cement content that is too high, possibly makes the m3 of stabilized soil fall outside the budget. In a complementary way, cement can be used in combination with ionic stabilizers (PREI-16) in soils of high or medium plasticity, and thus optimize the dosages and costs.

What is the process of stabilization?

Like most soil stabilization techniques, soil cement consists of incorporating a product, in this case cement, with the existing soil, homogenizing it, adding water so that the soil reaches its optimum compaction moisture content, and thus being able to shape the soil and subsequently compact it. Finally, after compaction, a curing process follows: moisturizing the compacted surface to reduce its dehydration rate and thus prevent the appearance of pathologies such as cracking.

To learn more about the different ways of construction execution, with different types of machinery and to learn about the Darwinism of construction and which is the best construction process for your project, click on the following link: Construction Process.

Ionic Stabilizers (Polymer Soil Stabilization)

Ionic stabilization, or soil stabilization with ionic polymers, consists of mixing a surfactant product (an anglicism, taken from the word surfactant, which in turn is a term that comes from “Surface active agent”), in this case, at PRO-ROAD we use the product PREI-16, which is an acronym for Pro Road Ionic Stabilizer 16, with problematic soils (unstable) and fine soils (in a percentage) to improve their performance conditions. Mixing the PREI-16 ionic product with the soils generates a chemical-ionic reaction with the soil molecules that results in an increase in bearing capacity (compressive strength), and a reduction of the plasticity index, resulting in stabilized soils with high durability. The PREI-16 product also acts as a binder between the particles of existing soils, also taking advantage of its cohesive condition, but with plasticity reduction, it ends up generating ideal conditions to convert a clayey (clay particle) or silty soil, generally cohesive and of low bearing capacity, into a high performance soil and converts a low quality structure into a high quality structure.

Which soil can be stabilized with ionic stabilizers?

In theory, all soils with a minimum of plasticity can be stabilized with PREI-16, except those with no plasticity and organic soils. Beyond whether a natural soil can be stabilized or not, it is important to analyze the cost of stabilizing a soil in this way. For this purpose, it is necessary to determine the optimum percentage or liters per m3 of product to reach the required strength and conditions, since a stabilizer content that is too high will possibly make the m3 of stabilized soil fall outside the budget. Additionally, it is necessary to analyze the complementarity of this type of product with other stabilizers, such as cement or lime, in order to optimize the stabilization mix. In a complementary way, PREI-16 can be used in combination with lime and/or cement in soils of high plasticity, thus optimizing the dosages and costs.

Soil Stabilization Process

The polymer soil consists, as most of the techniques for soil stabilization, of incorporating a product, in this case, PREI-16, with the existing soil, homogenizing it, previously mixed/diluted with water so that the soil reaches its optimum moisture for compaction (also must include the product concentration in water), and thus being able to shape the soil and subsequently compact it. Finally, after compaction, a curing process follows, which consists of moisturizing the compacted surface to reduce its dehydration rate and thus avoid the appearance of pathologies such as cracking.

Acrylic Stabilizers

Acrylic stabilization, or soil stabilization with acrylics, consists of mixing a surfactant and liquid cementitious product (an anglicism, taken from the word surfactant, which in turn is a term that comes from “Surface active agent”), in this case, at PRO-ROAD we use the product PREA-03, which is an acronym for Pro Road Acrylic Stabilizer 03, with soils to improve their performance conditions. Mixing the acrylic product PREA-03 with soils generates a chemical-cementing reaction with the soil molecules that results in an increase in the bearing capacity (compressive strength) by acting as a cementitious agent. The PREA-03 product also acts as a cementitious adhesive between soil particles, binding the particles and hardening them as a monolithic soil matrix, thus creating ideal conditions to convert a low plasticity, generally loose soil and with low bearing capacity, into a high performance soil with high hardness.

Which soil can be stabilized with acrylic stabilizers?

In theory, all soils with low plasticity can be stabilized with PREA-03, except high plasticity and organic soils. Beyond whether a natural soil can be stabilized or not, it is important to analyze the cost of stabilizing a soil in this way. For this purpose, it is necessary to determine the optimum percentage or liters per m3 of product to reach the required strength and conditions, since a stabilizer content that is too high will possibly make the m3 of stabilized soil fall outside the budget. Additionally, it is necessary to analyze the complementarity of this type of product with other stabilizers, such as cement or lime or ionic stabilizers (PREI-16), in order to optimize the stabilization mix. In a complementary way, PREA-03 can be used in combination with lime, cement and/or ionic stabilizer PREI-16 in soils of medium plasticity, thus optimizing the dosages and costs.

Construction methods for Acrylic Stabilizers

The acrylic soil consists, like most of the techniques for soil stabilization, of incorporating a product, in this case, PREA-03, with the existing soil, first loose soil strata, homogenizing it, previously mixed/diluted with water so that the soil reaches its optimum compaction humidity (also must include the product concentration in water), and thus being able to outline the soil and subsequently compact it. Finally, after compaction, a curing process follows, which consists of moisturizing the compacted surface to reduce its dehydration rate and thus avoid the appearance of pathologies such as cracking.

Bitumen Emulsion Stabilization

Emulsion stabilized soil, or emulsion soil stabilization, consists of mixing an emulsion, usually CRL (cationic slow breaking), with soils to improve their performance conditions. Emulsion mixing generates an increase in bearing capacity (compressive strength), and adhesion between particles, generally accompanied with quicklime, cement or other cationic acrylic additives (PREA-03+).

Which soils can be stabilized with bitumen emulsion?

The soils suitable for stabilization with emulsion are those of low plasticity, either of granular characteristics or a silt of low or no plasticity, the rest of soils, of medium or high plasticity, including organic soils, are not suitable for this type of solution. Beyond whether or not a natural soil can be stabilized, it is important to analyze the cost of stabilizing a soil in this way. For this, it is necessary to determine the optimum percentage of emulsion, as well as the asphalt content of the emulsion, in order to reach the required strength and conditions, since too high an emulsion content may cause the m3 of stabilized soil to be outside the budget. In addition, the emulsion can be used in combination with acrylic stabilizers, cement and/or lime to optimize dosages and costs.

Construction methods

Emulsion-stabilized soil consists, like most soil stabilization techniques, of incorporating a product, in this case asphalt emulsion, with the existing soil, homogenizing it, adding water with water trucks (possibly) so that the soil reaches its optimum compaction humidity, and thus being able to profile the soil and subsequently compact it. Finally, after compaction, a curing process follows, which consists of allowing the compacted surface to aerate to allow the evaporation of solvents and excess water, and thus avoid the appearance of pathologies such as cracking or bleeding over time. In the event of bleeding, it is possible to add a crushing bed to prevent the asphalt emulsion from coming into contact with vehicle tires.

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