INDUSTRY INSIGHT: Value engineering for flexible pavements

The well-established science of nano technology provides an economical and highly viable proven alternative for maintaining and building road pavement structures. Martin Murphy, Managing Director, GeoNano Technologies, presents his business case and the company’s engineered solutions.

Operating nationally and internationally, GeoNano Technologies is widely regarded as a pioneer in the development and adoption of proven solutions for road pavement designs and construction. Material evaluation and bitumen emulsion tests are conducted in-house at the company’s materials and product research laboratory in Germiston, Gauteng.

“We are proud to be involved with the highest ranked Faculty of Engineering in Africa, having sponsored several final-year and post-graduate students, enabling us to build the foundation for a sound engineering background to our products,” Murphy explains.

“Through the involvement of these students and academics, we have identified the best available new-age (nano-size) technologies. We’ve improved products and developed optimal design methods based on fundamental scientific principles, making them universally applicable. Our products can be used with confidence to add value and contribute to the cost-effective, much needed service delivery of transportation infrastructure,” he continues.

A considerable reduction in road unit costs can be achieved by using material-compatible and safe modifying agents that chemically modify traditional stabilising agents, such as bitumen emulsions (or equivalent). This modification enables the stabilising agent to chemically attach to the particles of naturally available stone/gravel/soil materials.

The chemical attachment (absent in the normal use of bitumen products, which relies on electrical and mechanical forces through interlocking and absorption to gain strength) considerably improves bond strengths. These high chemical-bond strengths enable the use of naturally available materials in all pavement layers of roads, meeting (usually exceeding by some margin) the engineering requirements in terms of stresses, strains and durability in any pavement layer.

Understanding mineralogy

The key to the successful use of modifying agents is in the science associated with the mineralogy of the materials and the identification of a compatible modifying agent with high inter-element bonds – i.e. a sound scientific chemical basis of design.

The small particle sizes (nano-size) of the modifying agents enable a large coverage area, (1 litre of nano-sized material could exceed the coverage area of 1 000 litres of bitumen). This allows for deep penetration into the material. The small particles also attach to secondary minerals found in naturally available material and render them hydrophobic (water repellent).

Hence, any possible negative influence of these secondary minerals on the future behaviour of a road can effectively be neutralised using a scientifically designed, material-compatible modifying agent in the emulsion.

NME agents

The proven concept of these New-Age modifying agents of emulsions (NME) has been demonstrated with the scientific testing and use of NME stabilisation of in-situ materials (ranging from fine Kalahari sands to the use of G8/G7 materials in base/sub-base layers, etc.) in the design and construction of several roads. Accelerated pavement testing (APT) has also

Accelerated pavement testing (APT) has been completed on some roads by one of South Africa’s provincial roads departments been completed on some roads by one of the provinces.

As expected, (based on the scientific design approach followed through the analysis of the mineralogy of the materials and designing of a material-compatible modifying agent), the results of these tests far exceeded the engineering requirements. This resulted in considerable cost savings (materials as well as time of construction).

The general acceptance of new technologies lies in both the value for money and the ease of use. “Our products lend themselves to be used to maximise labour-enhanced construction,” Murphy states. Applications range from simple road construction, using basic equipment (water cart, grader and compaction equipment) to sophisticated equipment using recyclers and/or central mixing plants.

Due to the small particle sizes, these products are also very effective in penetrating and sealing existing old surfaced roads in combination with an ultraviolet-resistant modified emulsion. As a further plus, there is no pick-up by vehicles and no required repainting of road markings. A ‘clear hydrophobic seal’ is achieved via strong attachment to the materials comprising the old surfacings. The same effect could be achieved with the treatment of gravel road surfacings, preserving gravel coverings.

The use of nano products is nothing new in the built environment. Nano technologies have been used to protect stone buildings for more than a century in Europe.

The success of these treatments is closely associated with the type of stone (primary minerals) and the condition of the stone (weathering resulting in the formation of secondary minerals). In the new era, similar new-age products have been developed to protect concrete structures (commonly used in South Africa to protect bridge structures on roads), develop improved paints for the protection of buildings, etc.

Product and design services

In addition to design expertise, GeoNano Technologies provides a range of solutions to achieve a successful end-product.

GeNANO NME solutions ensure that naturally available materials can be utilised in any pavement layer, meeting engineering requirements in terms of stresses, strains and durability. The shelf-life stability (onsite) will be guaranteed for at least four months. However, stability in excess of 12 months has been proven without any detriment to the product quality.

The NME is mixed with the construction water for ease of distribution in a process exactly simulating the compaction of a granular layer with the same control. No pre-heating of the NME is required.

“GeNANO NME is not a ‘one size fits all’ solution. Adjustments to formulas are made based on the material, mineralogy analyses and the structural engineering requirements to be met,” says Murphy.

GeNANO Prime Coat: This hydrophobised nano emulsion is specifically designed to protect the stabilised NME layer against early damage, should the road be opened prior to surfacing. The GeNANO Prime Coat will also ensure that good bonding is achieved between the base and the surfacing. Drying time will occur within an hour.

This product is also ideally suited for the protection of gravel on gravel roads. This is due to the high penetration achieved by using a grading of small particles for deep penetration, enabling strong material binding as well as protection against water damage.

GeNANO Clear Seal ‘Fog Spray’ is applied by watercart or hand sprayer. This product will achieve a high depth of penetration due to reduced particle sizes and provide prolonged protection against water damage (rendering the existing surface hydrophobic). Further advantages include quick drying, no contamination of vehicles and proven no reduction in skid resistance. The product design lends itself to being applied by hand sprayers (requiring little training) during maintenance activities.

GeNANO Slurry Mix: A cold slurry-mix NME binder for the sealing of low-volume roads, this product can be mixed and distributed by hand or used in the production of a Cape seal.

GeoNano's road and built environment solutions include: • Stone/gravel/soil stabilisation (NME technology) • Advanced anionic NME modified bitumen emulsion resins • Prime coats • Stone seals and pre-coating of stone for seals • Deep penetrative aggregate/gravel road seals • Fog sprays • Dust control • Labour-intensive cold slurry seals • Preventative maintenance solutions • Structural protective solutions • Capitalisation of mine waste material (e.g. coal dust, slags, slime and coal ash)

GeNANO CEMSEAL: This is a graded nanostructured solution that results in high (proven) penetration into any cement-based or concrete structure. This will render these structures hydrophobic and provide long-lasting protection against the detrimental effect of climatic influences and protect against chemical weathering. The ‘permanent’ bond effect of GeNANO CEMSEAL within the treated structure has a life expectancy in excess of 10 years.

Advantages

The contribution of GeNANO to value engineering in the provision of sustainable infrastructure and the provision of basic road infrastructure can be summarised as follows in line with the concept of ‘green’ technologies: • Cost factors: The use of in-situ or naturally available materials saves on procurement and transport costs, without compromising quality, while increasing durability and

resistance to water damage. More can be achieved with available funds. • Environmental factors: the use of naturally available materials will largely eliminate the need for blasting of newly crushed stone, and the crushing, screening and long-haul transportation of materials. • Energy factors: the use of locally available natural materials requires less transportation and considerably less energy to achieve specified density requirements.

Concluding Remarks

“When we first started on this R&D road more than 16 years ago, many engineers were sceptical, made references to ‘snake oils’ and needed proof. They were 100% correct ‘you need scientific proof’. Our laboratory and field tests now provide a wealth of information from which to make informed decisions,” adds Murphy.

“As we progress on our journey, GeoNano Technologies wishes to express its thanks to the engineers and academic mentors that have believed in our vision from inception and have shared our passion for innovation. Their selfless support has proved invaluable. NME technology is proven and the answer for Africa’s cash-strapped roads industry,” Murphy concludes.