Role of soil stabilization in perpetual pavement

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

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.

Why Adhesion Promoters?

Bitumen is used in road construction industry due to its adhesive property. However, bitumen has low chemical affinity towards aggregates, while aggregates have high affinity to water. Wetting of aggregates is difficult in the presence of dust or water-wet aggregate as it is difficult for the oily bitumen to displace the present water.

Water may also enter into the pavement structure, by way of capillary action from subgrade, rainfall seeping through cracks and shoulders, or by the action pressing and pumping effect of the water caused by the front and back tyres of vehicles. The presence of water compromises the adhesion between the aggregate and the bitumen, resulting in stripping. This causes moisture induced damage thereby resulting in premature failure of the road. Therefore, bitumen additives are used to improve the adhesion between the aggregate and bitumen, which is vital for maintaining a longer pavement service life.

Adhesion Promoters, also known as Antistripping agents, are additives generally added into hot bitumen. Upon addition, they migrate to the aggregate bitumen interface, where they act as binding agents/glue, thereby increasing and reinforcing the adhesion between the aggregate surface and the bitumen, thus preventing the penetration of water into the aggregate surface. The choice of adhesion promoters depend on factors such as the type of the aggregate and bitumen being used.

ZycoTherm is a next generation Antistripping agent that reacts with the residual moisture on the aggregate surface, to provide better wetting and coating of bitumen. It forms a permanent chemical bond with the aggregate and improves the adhesion between the bitumen and aggregate. The permanence of the bond formed ensures that the adhesive property does not deplete over time.

ZycoTherm is compatible with all aggregate and bitumen types, works at significantly lower dosages and is an environment friendly additive that is non-corrosive and odour-free.

Microsurfacing Asphalt Manufacturer

Microsurfacing is a thin layer of finely graded crushed stone, mineral fillers, asphalt emulsion and water blended together in proper proportions, spread on the road surface. It is very similar to slurry seal.

Micro-surfacing helps seal the cracks and protects the existing bituminous layers from surface voids & minor ruts, and provides a protective cover from oxidation and moisture ingress. Micro-surfacing is also provided in order to improve skid resistance of the existing surface thus increasing the service life of the pavement. A small amount of additive may be added at times, to improve the setting properties and adhesion of the micro-surfacing.

Microsurfacing is distinct from slurry seals. It hardens much quicker and can be applied in places where there are zero or minimal chances of placing slurry seals. Micro-surfacing can be ideally used on roads that handle substantial vehicular movement. It preserves the underlying pavement structure, while providing a fresh new surface for driving.

Factors for considering Micro-surfacing application

  1. Micro-surfacing can be applied on roads that have low or moderate damage and narrow width of cracks.
  2. Streets with lot of shade are preferred for micro-surfacing
  3. Roads with heavy amount of traffic are suitable for micro-surfacing
  4. It is typically applied on a project-specific basis

Some of the major advantages of Micro-surfacing include:

Environment-friendly: Micro-surfacing is an environment friendly alternative as it requires relatively low energy, emits no pollutants and is applied at ambient temperatures.

Quicker Construction Times: The surface can be opened within hours of micro-surfacing and it gives the appearance of an all-new surface.

Reduced Delays: Micro-surfacing can be performed on roads with high, medium or low traffic volume, without causing any major delays.

Cost Effective: Micro-surfacing covers more area per tonne of mix, thus making it a cost-effective alternative.

NanoTac offers excellent bond strength & delivers water resistant mixes for micro surfacing. These additives impart rapid setting to the bitumen emulsion, saving the time required for micro surfacing.

For further assistance on Zydex Micro-surfacing products, please contact us!
E-mail: | Phone: +91-265-3312000

Soil Stabilisation Techniques

The role of soil is crucial for the design and construction of any structure, be it roads, runways or railway tracks. This is because it acts as the medium for effective load transfer in to the earth. This implies that a weak soil base will eventually cause settlement of the structure, leading to failure.
Stabilisation is the process of improving the engineering properties of the soil before construction. Stabilisation is done to improve the strength of the soil and shrink/arrest the swelling potential, thus improving the load bearing capacity and the overall performance of the in-situ soils.

There are 3 main methods for soil stabilisation:
1. Mechanical stabilisation

This category consists of physical processes such as compacting or tamping with machineries including rollers or rammers. The mechanical soil stabilisation is also achieved by blending (adding or removing) different soil particles so as to obtain effective distribution of soil particle. These techniques are usually used for sub-base and base courses.

2. Chemical Stabilisation

As the name suggests, stabilisation of soils depends on the chemical reaction between the chemical/stabiliser used and the soil particle composition. These include, Cement, Lime, Magnesium Chloride, Bitumen Emulsion and Fly Ash among others.

Traditionally and widely practiced type of soil stabilisation techniques include:

i. Bitumen Emulsion
Bitumen emulsion is used as a binding agent both cohesive as well as non-cohesive soils. However, in soils with finer grain sizes, this method may no longer be cost effective as the soil particles require a high dosage of bitumen emulsion in order to provide the same/better level of bonding. Bitumen emulsion is not environmentally friendly and becomes brittle when it dries, which affects the stability of the soil.

ii. Cement/Lime
Cement/Lime is widely used as a soil stabilising agent. Addition of cement to soil improves the strength of the soil. It is used for the sub-base and base courses of all types of pavement. However, due to the consequent wet and dry cycles, there occurs a degradation of the bonding between the cement and soil particles. Also, this is a very costly in terms of financial viability. Lime stabilisation improves the strength of the soil by imparting increased bonding between the lime and soil particles. This method is cost effective as compared to cement stabilisation.

iii. Apart from the above mentioned stabilising agents, some other alternatives currently in practice include Fly Ash, Cement Kiln Dust (CKD), Tree Resin and Ionic Stabilizers.

3. Polymer Stabilisation

Polymer soil stabilization refers to the addition of polymers to improve the physical & engineering properties of soils (Polymer Soil Stabilisation, 2019).
Polymers tend to increase the strength of the soil through their interaction with clayey particles present in the soil. Many polymers currently used, tend to increase the water retention capability and the shear strength of the soil.
Polymers used for soil stabilisation can be classified into two main categories viz. Biopolymers and Synthetic Polymers. Biopolymers are eco-friendly as compared to other chemical soil stabilisers.

Bitumen emulsion for soil stabilization

What is stabilization?

Stabilisation is the process of improving the engineering properties of the soil before construction. Stabilisation is done to improve the CBR of the soil to be used for a specific construction purpose. This can be done using various additives including Portland cement, fly ash, lime, bitumen etc. These chemicals impart higher bond strength by providing cohesion between the soil particles.

Bitumen emulsion for Soil Stabilization

Using bitumen emulsion for soil stabilisation refers to the process of adding a specified amount of bitumen emulsion to the soil and mixing it appropriately to create a strong and stable base. The bitumen is dispersed in the water in the form of small droplets which are suspended in water by an electrostatic charge of the emulsifier.

Bitumen Emulsions can be used for stabilising both cohesive as well as non-cohesive soils. However, in soils with finer grain sizes, this method may no longer be cost effective as the soil particles require a high dosage of bitumen emulsion in order to provide the same/better level of bonding. Succinctly, the quantity of the bitumen emulsion will depend on the type of the soil so as to offer the desired strength to the soil base.

Following are some of the benefits attributed to the bitumen emulsion being used for soil stabilisation:

Waterproofing: Using bitumen emulsion for stabilisation is slightly different from cement stabilisation, as the soil particles coated with the emulsion renders it water-resistance.

Load bearing capacity: Soil stabilisation using bitumen emulsions result into a permanent sealing of the soil structure. This increases the load carrying capacity of the soil layers. The load distribution is 2-3 times higher than that of the unbound foundation layers.

Flexibility: The soil layers of the roads should act as supporting layers by absorbing the stresses of the vehicles moving on top of it and not deform under these stresses. In order to facilitate this, the soil layers need to be somewhat flexible, so as to retain the shape and size. In case of a rigid structural layer, the risks of crack formation are much higher thus increasing the risk of failure. This is the situation which calls for the use of bitumen emulsion. They are very thin flowing and can be easily mixed with the soil, which also calls for lesser bituminous binder.

Soil stabilisation with Foamed Bitumen

Additionally, foamed bitumen is also currently being used in the industry for soil stabilisation. Foamed Bitumen is a mixture of air, water and bitumen. Bitumen is heated on site and when small quantity of water is injected in to the hot bitumen, it expands explosively to about fifteen times its original volume and forms a mist or a foam. This results in to the formation of bitumen droplets with increased surface area. It has been proven that by applying foamed bitumen, it is possible to produce a semi-rigid layer of stabilised soil.

How nanotechnology provides great solutions to road construction issues

What affects road construction quality the most?

With greater push on sustainability, road construction is becoming an affair that presents many opportunities for innovation and development. The problems are basically two-fold

  • Construction Quality Affected by moisture and other factors
  • Using resources efficiently and sustainably

Water, which is otherwise a boon, can be extremely harmful to pavements. It forces the asphalt binder to strip from the stone aggregate and leads to distresses such as cracking, potholes, ravelling etc. It also compromises the dimensional stability of the pavement by entering into soil bases and making the soil loose which can cause undulations.

Apart from this, incorrect construction practices and injudicious use of resources not just causes inconvenience to construction workers and commuters both, but also results in pavements that need constant rehabilitation which translates to wasted time, effort and money.

With awareness spreading about ruthless depletion of natural resources and the deteriorating environment around us, the need of the hour is to be innovative and come up with solutions that not just ensure sustainability by way of high quality and everlasting roads, but also ensure a nature friendly means of execution.

With economies growing increasingly aware of the use of sustainable road construction, energy saving and proper resource allocation is turning out to be a challenge.

What’s the solution?

The key is to come up with a solution that ensures conservation of natural resources, monetary resources and energy & power while also promising high quality and everlasting roads.

This is what Zydex offers.

By making use of nanotechnology, Zydex has come up with innovative chemical agents that help induce changes on a nano level, effectively changing the properties of the pavement construction material. This ensures higher strength and durability of pavements.

Zydex Road Solutions provides innovative Bitumen Additives that chemically enhance the bonds between the asphalt binder and the aggregate while also making the mix immune to water and the damages caused by it.

The warm mix asphalt solutions allows the contractor to reduce the temperature of the asphalt mix and work at lower temperatures while giving the same, or even better results than hot mix asphalt. This warm mix asphalt solution by Zydex not just helps in saving energy and fuel but also results in better working conditions.

The cold mix asphalt solutions for surface dressings and bond coats is profoundly dependable. The additives used to make this cold mix, enhances the bonds between the asphalt and the aggregate, thus creating a seamless bonding membrane between the pavement layers. It also reduces the amount of asphalt binder to be used. These additives also reduce wastage by eliminating the possibility of tire pick up.

Zydex also provides innovative soil stabilization and dust control solutions that make the soil bases impermeable to water and reduce the expansivity of the base, thus making it dimensionally stable. The nano acrylic co-polymer creates strong inter-particle bonds which when coupled with the water resistant nature of the base, means an immensely strong and self-strengthening base.

Zydex Road Solutions provides the following features:

  • Anti-Stripping: Reactive anti-stripping agent with world class performance.
  • Warm-Mix Anti-Stripping: Patented warm-mix technology for building green and long-lasting roads.
  • Prime Coat: Penetrative, reactive and waterproofed bond coat.
  • Tack Coat: Improved spray, reduced tire tack and quick-setting tack coat.
  • Soil Stabilization: Solutions for expansivity control and bonding of in-situ soil to replace stone bases and asphalt layers in road design.
  • Micro surfacing: Improved coating and strength.
  • Slurry Seal: Improved coating and better WTAT performance
  • Chip Seal (Surface Dressing): Improved strength and bonding to the base.
  • Waterproofing of soil bases: Water resistance with permeability reduced to 10-7 cm/sec.
  • Dust Control: 90% dust control in 1st spray with relief up to 98% in 2-3 sprays
  • Asphalt Emulsion Additives: Improved emulsification, reduced particle size and stronger bond strength.

These nanotechnology solutions provide a 360 degree mitigation and protection of roads. Sustainable construction and energy efficiency become easy to achieve with innovative tools like these!