Chemical Soil Stabilisation is the process of blending and mixing chemical additives to improve the engineering properties of the soil. The efficiency of the stabilisation depends on the reaction between the chemical/stabilizer used and the soil particle composition.

Soil stabilisation using chemical additives is adopted not only to arrest its shrinkage & swelling potential, but also to improve its strength, workability & durability, thus improving their overall performance. The increased performance implies reduced the maintenance costs, significantly improving the overall lifecycle costs of the pavement. It also offers other advantages such as reduced dusting requirements, controlled volume changes to soil and better workability.

The performance of the treated soil depends on the ability of the additives to react with the soil, which places a great emphasis on choosing the stabilizer best suited for a particular type of soil, taking into consideration, not only the improvement of its engineering properties but also considering its economic and environmental impact.

It has been a common practice to use calcium based stabilizers such as cement and lime for stabilisation, due to its notable effect of reduction in plasticity, swelling & shrinkage as well as the increased bearing strength. However, there are certain limitations to using these additives. Stabilisation of soils containing sulphate minerals when treated with lime, causes adverse chemical reactions & formation of an expansive crystalline mineral, causing heaving and other pavement distresses. Exposure of lime treated soils to wetting and drying cycles results in the loss of cohesion between soil and lime particles. Lime & cement applied in the powder form is known to burn unprotected workmen and also causes harmful environmental effects. Moreover, cement manufacturing emits large amounts of CO 2 . Fibers have been considered an effective alternative to help prevent cracks; however, its effectiveness in restricted to certain type of soils.

The use of bitumen emulsion for soil stabilisation is also a notable practice as it imparts water resistance to the soil particles, increases the load bearing capacity & stability of the soil. However, it may not be a cost effective solution as the soil particles require a high dosage of bitumen emulsion in order to provide the same/better level of bonding. Foamed bitumen, i.e. mixture of air, water and bitumen, is also being used for soil stabilisation. It has been proven that by applying foamed bitumen, produces a semi-rigid layer of stabilised soil.

New and emerging technologies such as enzymes and silanes are being preferred over traditional stabilisation methods, to solve the problems of swelling and shrinkage as well as to improve the load bearing capacity and compaction densities of poor soils, with no harmful effects on the environment. Major advantage of using chemical additives for soil stabilisation is that it enables the use of in- situ/locally available soils and aggregates. This decreases the effort and time required for hauling good quality materials from borrow areas, allowing for an efficient use of natural resources. This results in minimized cost of hauling, thereby reducing the cost of construction.

Perpetual Pavements are pavements designed and constructed to last > 50 years, with maintenance restricted to the wearing course alone. In order for the pavement to perform through its design life, it is imperative to provide a strong, flexible bottom layer that resists cracking under heavy traffic loads and cyclic weather variations.

Soil bases are critical layers for any pavement, as it transfers the vehicular load to the ground level, allowing smoother rides. They form the foundation for the long term performance of the pavement. However, factors such as unavailability of good materials, variability in the available soils and greater affinity to water challenge the conventional construction methods as they lead to failures causing undulations and cracks. This presents a compelling case to find solutions that can improve the engineering properties of the in-situ soil. Various methods such as the use of geogrids and geotextiles, grouting, increasing the thickness of the subgrade etc. have been adopted over the years, to construct a strong base. One such method is soil stabilisation.

Soil stabilisation is the process of blending and mixing different materials, to improve the engineering properties of the soil. It not only helps to increase the strength of the soil, but also allows to arrest its swelling potential, allowing for better stress transfer thus preventing premature failures. Stabilizers such as cement, lime and bitumen emulsions have been used traditionally for soil stabilisation. However, each method comes with its own disadvantages, be it the environmental or health hazards, or cost effectiveness. Also, with depleting resources, the focus on sustainable construction practices has been ever increasing. New and improved methods are being preferred as they are cost-effective and allows construction of high performance, durable roads with reduced material consumption. This has paved the way for new and emerging chemical technologies that allows to improve the properties of the soil without any harmful effects, along with a keen eye on easy-to-use solutions that have proven its efficacy on field on field and widely accepted.

Zydex offers Terrasil (organosilane) and Zycobond (acrylic co-polymer), which are easy to apply additives for soil stabilisation, that significantly reduces water permeability, imparts higher strength and enhanced flexibility through nano-bonding. These properties make the soil bases non-deforming and dimensionally stable. As this change in the engineering property is permanent in nature, it enables the construction of all-weather water resistant, durable roads. This significantly improved strength and higher modulus with flexibility of soil bases can be utilized for reducing the overall thickness of the pavement, thus delivering a sustainable and perpetual road at the same cost.

Perpetual Pavements are pavements designed and constructed to last > 50 years, with maintenance restricted to the wearing course alone. Perpetual pavements have high structural strength and offer long term resistance to two most devastating distresses i.e. structural rutting and fatigue cracking, keeping the compressive and tensile strains below the failure limits.

Traditionally, highways are designed for a 20 year design life, whereas perpetual pavements are expected to perform for 50 years or more. These pavements are designed with a strong, flexible bottom layer that resists cracking under heavy traffic loads and cyclic weather variations. Several practices such as soil stabilisation using materials like cement, lime, bitumen emulsion and installation of geogrids & geotextiles are adopted to ensure a strong and dimensionally stable base. These practices help improve the engineering properties of the bottom layers. New and emerging technologies such as organosilanes & polymers, offers further improvement in terms of moisture resistance, higher strength and flexible nano bonding. This increases the durability (lifespan) of the pavement layers significantly. Use of emulsion additives also help in effective bonding of the different layers for uniform load/stress transfer.

The bituminous layers of the pavements offer flexibility and resistance to deformations. However, factors such as material variability and operational inefficiencies causes serious problems which lead to premature failures. For example, improper coating of the bitumen on aggregate surface results in water ingress and delamination of the layers, thereby reducing its ability to withstand heavy loads. Therefore, bitumen additives are used at times, to improve the properties of the bituminous mixes. Bitumen additives such as anti stripping agents improve the cohesion between aggregate & bitumen and ensures a tightly bonded structure, thereby facilitating better stress transfer under heavy loads. This eventually translates to longer pavement life. Innovative practices such as the use of Warm Mix Asphalt provides additional environmental benefits by facilitating reduced odor & emissions, lesser fuel consumption and paving friendliness.

The benefit of restricting distress formation to the top layer, is to ensure that when distresses exceed tolerance limits, the distressed top layer can be removed and resurfaced with an asphalt overlay. Cost effective solutions such as microsurfacing or slurry seal can be adopted to ensure a smooth ride quality, thereby reducing the maintenance costs and time.

Perpetual pavements, therefore, offer a durable, long-lasting road, with cost-effective maintenance that restricts traffic disruption thereby saving time for road users and the maintenance crew. Reduced maintenance also conserve the use of the scarce natural resources such as aggregates and bitumen, to provide significant environmental benefits as well as cost savings.

The future lies in high-strength pavements that are faster to construct using limited natural resources, and when constructed for perpetuity, will never need to be reconstructed.