Coir geotextile mats, shredded waste plastic, nano-coated hydrophilic fibres, industrial slag, fly ash, and marble slurry dust are some of the new materials finding a place in road construction. In Kerala, the Public Works Department is testing the use of coir geotextiles in road construction on a 3-km stretch on the Ambalappuzha-Thiruvalla road. Coir geotextile mats improve the properties and strength of the subgrade material, typically soil, thus reducing the thickness of the required aggregate layer and translating into cheaper roads, even after taking into consideration the cost of geotextiles – roughly Rs 50 to Rs 65 per sq m in manufacturing units in and around Alleppey and Kochi.
Use of coir geotextile is based on the California Bearing Ratio, using 900 gsm mats with laterite soil would reduce the granular sub base quantity by about 27 per cent and the binder coarse quantity by 16 per cent, cutting the cost by about 23 per cent. By preventing the aggregate from mixing with the soil, and thereby, averting the loss of the effective thickness of the aggregate layer, coir geotextile mats also improve the performance of the road and cut maintenance costs. In fact, laboratory strength tests of the wheel track, the California Bearing Ratio test and the bearing capacity show that coir geotextile mats strengthen the pavement and result in fewer rut formations.
While coir geotextile mats are useful for both rural roads and highways, albeit so far more field trials have been done for rural roads, introducing relevant standards for the use of the material and approving it in governmental schedules would help boost adoption.
Cost-effective, sustainable, long-lasting self-repairing roads, is a long felt need, dependent on combined research in materials science and structural engineering. India’s ostensibly first self-repairing road is a 650-m stretch connecting village Thondebavi in south east Karnataka’s district Chikkaballapura to the nearest highway has self-crack healing properties from being composed of nano-coated, hydrophilic (water attracting) fibres in additional to conventional materials.
A crack always has unhydrated cement, i.e., cement that has not reacted with water yet, and has the ability to form chemical products that can heal the crack. By keeping the cracks narrow using fibre reinforcement and then by attracting water via hydrophilic fibres, further bond enhancing silicates can be created that in time close or heal the crack. The key is to keeping cracks narrow and then provide mechanisms that repair the crack.
Another standout feature is that the road—built in 2015 as a sample and successfully tested through the 2016 monsoon—is very high strength, and is made of 60 per cent less cement than a conventional road. Instead it uses fly ash for a final road thickness of 100 mm instead of the typical 250 mm. Despite using an imported ingredient – the nano-coated hydrophilic fibres, the road costs 30 per cent less to make than a conventional road for being thinner and therefore needing less material.
Highways can also be built using the self-healing technology and the reduction in thickness is expected to be nearly 50 per cent. The exact savings in cost will depend on the soil conditions, traffic volume and environmental conditions.