Soil Cement For Road Construction

Sometimes the ideal types of soils that guarantee stability and durability are not found on the roads or land to be intervened since it is common to find soils with poor mechanical properties. It is necessary to resort to a different technique, called soil stabilization, to improve the physical properties of the soil and increase its bearing capacity, and shear strength, among others. This technique improves the soil’s natural properties by adding chemical products; in this case, we are talking about adding a percentage of cement to the soil. The change in the properties of the soil makes it possible to optimize pavement structures and reduce their thickness without deteriorating their mechanical strength over time.

With the world becoming increasingly environmentally conscious, the need for natural soils for road construction has never been greater. With governments always looking for ways to save money and cut their budgets, using environmentally friendly building materials in pavement structures is a no-brainer. Not only is the cost of shaping pavement structures important, but maintaining the pavement over the years has become imperative to achieve pavement sustainability through innovation in the materials that make up the pavement.

With the increasing demand from customers who prefer “greener works,” as well as the latent need for governments and industries to find solutions in material savings that expand the scope of their budget, the use of soils as raw material to create a durable pavement has become a necessary alternative to create sustainable and economic roads.

Commonly, that clay, silt, and sand do not have the right properties to form a resistant structure; normally, these are considered weak soil. Fortunately, different chemical products on the market can strengthen soils to create a pavement material with high compressive strength for durable roads.

It is important to analyze the type of soil to be stabilized to form the pavement structure and also to determine the best technique or product(s) or component(s) for stabilization among the different types of soil stabilization; this can be achieved with the use of cementitious materials, chemical additives or a combination of both: 

Cement stabilization (soil cement)

Ionic stabilization (polymers)

Acrylic stabilization

Lime stabilization (lime soil)

Emulsion stabilization

Stabilization with soil (with better properties)

What is soil cement?

The different types of soil stabilization make it possible to transform soil with low bearing capacity into the soil with high bearing capacity that meets the technical characteristics required in a given design and/or current regulations. In this case, the soil cement, apart from other parameters, is usually measured by unconfined compressive strength, where for example, AASHTO and PCA require a minimum simple compression of 2.1MPa in the standard design requirement.

The process consists of achieving an economical mix with a given stabilizer, in this case, cement. It is necessary to determine, using resistance tests, an optimum cement content to determine the right proportion of cement, measured as a percentage of the weight of the dry material (on its maximum density), which allows obtaining a soil mixture with certain resistance and durability values subjected to a certain compaction energy and a certain compaction process, according to the applicable test or technical standard. The first step is to perform a soil analysis on the treated materials, or those to be treated, to determine the natural resistance values, plasticity, and granulometry, among others. Typically the standards require a granular material; however, cement has a wide range in terms of the extent of soil types that can be treated, not only a granular material but in no case can organic material or soil with a high content of organic matter can be used. Based on the above, a stabilizer dosage is established; in this case, the mixture with cement to achieve the desired strength based on the estimated hydraulic cement performance and the type of cement used; this process is known as a mix design. It is important to know the cement content so that the percentage of cement by weight of soil (%) is economically viable; typically, 8% is set as the maximum to achieve economic stabilization by cement modification. If the cement mixture requires a dosage higher than 8% on the dry weight of the soil, it is advisable to look for a resistant cement of better conditions or to complement the mixture with another type of stabilizer. It is always essential to analyze the cost of stabilization per m³ of soil cement so it is economically viable work.

There is diverse literature on soil cement technology and its implementation that is worth studying, such as Guide to Pavement Technology by AustRoads, Low Volume Road Engineering by Robert Douglas, Soil Cement Construction Handbook by PCA, Manual de Estabilización de Suelos con Cemento o Cal by IECA, and in general, on soil cement technology, it is possible to find very complete literature in the local regulations of each country, such as the AASHTO standard, which is the base for Cement-modified soil norm and other modification of soils norms such as the INVIAS in Colombia or the DNIT in Brazil. However, it is recommended to focus the cement mixture work be done on a technical goal, not only in the parameters of the standards, as these may be limited in terms of the conditions of the treated material since many documents require a granular material or a granulometry of the material determined that makes the material accepted as a construction material is limited, without considering the workability of the material.

In Pro-Road, we have extensive experience in soil stabilization with cement. We also have a series of stabilizers and additives, allowing us to generate stabilized soils at competitive prices thanks to additives, commonly known as soil stabilizer, that modifies the soil particles and reduce cement consumption. It is not only the price per m³ of soil cement but also the versatility of mixing this technique with other techniques and stabilizing products, in terms of the workability of the material that can be achieved in a wide range of base soil and not only in a granular material or a requirement of certain granulometry of the material.

Soil Cement Optimization

At Pro-Road, we manufacture a series of synthetic polymers and co-polymer based products that can be used in combination with soil cement in order to reduce the cement requirement to achieve the degree of compaction or the Cement-treated base required compressive resistance. This type of soil stabilization method with combined soil stabilization techniques is an optimal approach to achieve the base for roads’ required load bearing capacity in unpaved roads. The Compacted Soil-Cement Mixtures are not just about achieving the resistance required in the road design but it is also about achieving such resistance of the cement-based materials in compliance with the economic requirements of the project, and here is when Pro-Road additives come into play, such as PREA-03 and PREI-16 to optimize the cement consumption. 

Benefits of soil cement

This construction method is more than just rammed earth or compacted earth, it is a revolutionary method, along with other soil stabilization methods, that generates great benefits in the short, medium, and long term. The main benefits of this type of stabilization are, among others, the savings in construction costs, starting with the imminent savings in transportation costs, since we replace the use of bases and granular materials in conventional pavements, which are also necessary to extract and transport, with pavements formed with the natural soil of the roads. With the caveat that, to comply with the above mentioned, it is necessary to expand the range of material accepted for the extended layer, according to the guidelines mentioned above, and that we constantly use in Pr-Road, not only limiting ourselves to granular materials accepted within the materials supplied but to a wider range. It is possible to work with materials outside the granulometric characteristics required by some standards, even omitting a granular material, even for roads with heavy traffic. In addition, recycling with cement tends to be much faster than conventional methods for shaping pavement structures. Finally, it is important to consider the environmental impact, not only of the emissions and environmental impact of the work per se resulting from the time savings during the extension of the material regardless of its general properties but also of the emissions associated with the cement used. Finally, the amount of water added to achieve the optimum compaction moisture content is much less than that required in the entire value chain of conventional pavement construction. Thus, achieving the required stress resistance with a smaller ecological footprint is possible. In summary, the main benefits of soil cement are economic savings and savings in construction time for the pavement structure, and a lower environmental impact.

One note worth mentioning is that the test samples required to control the optimal performance of soil-cement stabilized soil are relatively simple and can be practiced mostly in the field, giving a great advantage in real-time concerning other construction systems.

When is soil cement used?

The characteristics of the soil to be stabilized determine the type of stabilizer to be used, or on the contrary, the optimum combination of stabilizers to achieve a successful soil stabilization process, with a level of resistance that meets the technical performance requirements, even for heavy traffic. It is necessary to make a complete analysis, using test samples, of the general and specific properties of the soil, and the main construction material, such as its Atterberg limits, material moisture, granulometry, and compressive strength. On the other hand, it is necessary to know the conditions of use of the pavement (ESAL), traffic category, and its design period to establish a mechanical strength and modulus for the pavement. Second, it is necessary to determine if the cement content to achieve this required stress resistance is economically viable and if soil cement modification is economically and technically optimal. An important factor to take into account when designing the mix is never to work with the minimum cement content obtained in the formula on the treated material or starting material since it is necessary to foresee a waste and a readjustment of quantities in case of any unforeseen variation in the general or specific properties of the raw or natural soil to be treated. In addition, it is necessary to know the compaction equipment on the finished layer to adjust it to the required compaction conditions. It is also important to determine the thickness of the layer to be stabilized according to the traffic category and the amount of traffic; it should never be designed according to the minimum traffic volume. Finally, the design and execution of the work must be carried out in such a way that the work complies with current standards.

Which soils can be stabilized with cement?

In theory, all soils can be stabilized with cement, except very high plasticity and organic soils. Using hydraulic cement or stabilizing cement mixed with soil should generally increase the bearing capacity of the soil to form the pavement structure. Beyond whether or not natural soil can be stabilized with this method, it is important to analyze the cost of stabilizing soil in this way. Therefore, it is necessary to determine the optimum percentage for the soil mix to achieve the required strength and conditions since a high cement content makes the m3 of stabilized soil fall outside the budget. It is also important to analyze the matrix composition of the soil, as very fine soils sometimes require the mixing of aggregates to achieve a compacted mix with a competent modulus. Cement can also be used with ionic stabilizers (PREI-16) in high or medium-plasticity soils to reduce the cost of the soil mix to achieve the desired compressive strength.

How much does soil cement cost?

Soil cement varies depending on road conditions, climate, soil conditions, available equipment, and the execution of the work itself. On average, the cost per m3 of stabilized soil can be expected to be around 70,000-130,000 Colombian pesos (@2021). The difficulty of compaction can be an important factor in determining the overall cost of the work, which depends directly on the geometric properties of the road section. This, and other factors, are critical when budgeting for this type of work. The area’s weather conditions tend to be the most important factor; therefore, it is important to take these factors into account, as well as the starting date of the work, to take advantage of the maximum dry weather.

How is soil cement prepared?

The preparation of soil cement consists, like most techniques for soil stabilization, of incorporating a product in a low-bearing capacity soil, in this case, portland cement or stabilizer cement, with the existing soil, getting the loose soil, and homogenizing it. Always, as with other stabilization processes, the amount of water considered in the design must be added so that the soil reaches its optimum moisture content, either by added water or by drying it, all depending on the percentages of water established in the design to achieve an optimum soil-cement mixture, it is vital never to concentrate on saving water since a soil with water content below its optimum moisture can have fatal results as far as its structural properties are concerned. After mixing the soil with cement, the road is profiled, ideally with a topographical commission to ensure geometry and optimal drainage, and then the soil is compacted. Finally, after compaction, it is necessary to control the setting of the cement, so it is necessary to carry out a curing process that consists of wetting the surface to reduce its dehydration speed and thus avoid the appearance of pathologies such as cracking and to be able to comply with the delivery conditions fully.

In summary, this type of pavement structure allows optimal compressive strength by mixing soil or natural soil with a stabilizing product, in this case, cement, which is responsible for increasing the compressive strength of the soil. It is possible to convert low-strength soil into soil with ideal structural capacity through the increase in strength thanks to the chemical process described above.

Other methods result in equal bearing capacity for certain soils and can achieve good structural properties; however, the main objective of stabilization, in general, is to achieve materials of optimum strength with the maximum use of natural soils and the lowest cost per m3 possible.

To learn more about the different ways of construction execution with different types of machinery and the Darwinism of construction and which is the best construction process for your project, contact us; in Pro-Road, we provide versatile road solutions.

We cannot leave behind, in a complementary way, the pavement layers formed with lime, which, many times, is an excellent complement for the soil cement, especially in fine soils or of high or medium plasticity.

Lime Stabilization

Soil lime, or soil stabilization with lime, consists of mixing lime, usually quicklime, with soils to improve their performance conditions. Lime blending generates an increase in bearing capacity (compressive strength), and a reduction in the plasticity index.

Which soil can be stabilized with lime?

The ideal soils for stabilization with lime are clayey soils, including silty, of medium and high plasticity; other soils, including organic soils, are not suitable for this type of solution. Beyond whether or not natural soil can be stabilized, it is important to analyze the cost of stabilizing soil in this way. For this, it is necessary to determine the optimal percentage of lime to reach the required strength and conditions since a too-high lime content possibly makes the m3 of stabilized soil out of the budget. In a complementary way, cement can be combined with ionic stabilizers (PREI-16) in soils of high or medium plasticity and with portland cement, thus optimizing the dosages and costs.

Construction methods

The soil-cement consists, like most of the techniques for soil stabilization, of incorporating a product, in this case, lime, with the existing soil, homogenizing it to obtain a homogeneous mixture of soil, adding water typically with a water truck so that the soil reaches its optimum compaction humidity, 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, click on the following link:

At Pro-Road we design, optimize and execute your soil cement works. Contact us.