Moisture-resistant roads

Use of nanotechnology is ideal for the long life of roads. Dr Ajay Ranka elaborates on the advantages of using nanotechnology-based additives in road building.

Bitumen consumption in India was 4.5 million tonne in 2011-12 costing Rs 18,000 crore (current value). Nearly 80 per cent valued at Rs 14,400 crore used for resurfacing, is the annual binder loss from the existing roads due to leaching and stripping of the bitumen binder. Nanotechnologies from Zydex can save Rs 7,200 crore annually in bitumen savings alone, by doubling the life of bitumen layers (modifying the bitumen binder at the refinery) at a cost of Rs 540 crore. Bitumen being petroleum product is forex-intensive.

Moisture resistant roads (highways/rural) with globally patented nanotechnologies developed in India: 

• Nanotechnology additives allow moisture proofing of soil layers and reduce moisture permeability by 500-1,000 times. This reduces weakening of soil, minimise expansion and contraction issues, which typically lead to cracking and undulations.
• Nanotechnology also makes bond coats (tack and prime) 100 per cent waterproofed, allows 100 per cent stress transfer and saves bitumen by achieving chemical bonding.
• Chemical bonding of nanotechnology makes aggregates oil loving permanently and eliminates moisture damage of bitumen layers (60-65 per cent cost of the road).
• Nanotechnologies are cost negative at capex and improve durability of the road to reduce life cycle cost by 50 per cent or more. This nanotechnology is expected to be as revolutionary as mobile telephony for urban and rural India.
• In India, the technology has been experimented and validated on trial stretches for four years in PMGSY/NHAI (BOT) projects. Commercially adopted by BRO (Defence), NHAI BOT contractors, and Karnataka for their rural roads.

Use of nanotechnology
Soil stabilisation: Nanotechnology-based stabiliser is water-soluble, easy to apply, reacts permanently with the soil's (silt, sand and clay) surface structure and makes it impervious to water. It controls soil's expansiveness by minimum 90 per cent at an affordable cost. Besides waterproofing, it also eliminates wet and dry cycles and maintains strength of the cement stabilised soil over a design life (typically 20 years) of the road. Waterproofed, quick set, penetrative priming: Cationic bitumen emulsion-based prime coats have poor penetration, take longer time to set and show water permeability. Weak physical bonding of aggregates to bitumen causes loss of bonding between aggregates and binder in presence of moisture.

Aggregates and stone powder/dust are water loving and presence of moisture causes de-bonding and results in poor stress transfer in the pavement section, causing cracking and fatigue failure. Nanotechnology-based prime coat is water soluble, easily mixes into bitumen emulsion in water. Its solution in water is neutral and odourless and penetrates up to 2-8 mm, in the WBM/WMM layer. It reacts with the aggregates, stone dust powder and dust and changes their surface to make them asphalt loving. Chemical bonding of bitumen with stone base layer eliminates the moisture susceptibility of the prime layer. It provides a chemically bonded waterproofed drain layer.

Chemically bonded, waterproofed tack coat: Nanotechnology-based tack coat is water soluble, neutral, odourless and easily mixes with bitumen emulsion in water, ensuring trackless tack coat. It reacts with the aggregates, stone dust powder and dust; and changes their surface to non-polar, to make them asphalt loving. This creates a permanent affinity between the asphalt binder and the aggregate, and reduces the moisture susceptibility of the tack layer.

Chemically bonded bitumen nanotechnology: This coating substantially improves coating of asphalt binder on the aggregates. It ensures consistent and higher compaction and eliminates stripping. Thus, surfaces treated with this coat ensure a more durable asphalt pavement.

Nanotechnology-based additives for road building provide excellent moisture resistant, superior performance of HMA mix, significant higher stability and strength compared to control mix. They have the potential to significantly extend service life of the pavement.