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Self Healing Asphalt: A New Hope
There is a small crack in a certain busy road. No one is paying attention to it as it is not causing any problem. But the next thing is that the crack soon turns into a pothole- the road has been blocked for restoration- the vehicles are moving along the wrong side- traffic problem is worse than before. In addition, heavy rainfall can add extra layer of bitterness. Imagine if that small crack was never there.
It is a pretty common scenario in Dhaka city. The total span of roadways of Bangladesh (the paved & the unpaved portion) is 21,127.493[1] km. The main transportation system in Bangladesh is the roadways. The deterioration of roads is inevitable as they constantly go through tremendous pressure, load & stress everyday. Roads have a lifetime expectancy of 15-20 years depending on the severity of surroundings and environmental factors they are exposed to. When they begin to lose their functionality they have to repaired or replaced. The time, money & wretchedness it cost is tremendous & not worth all the sufferings. Also, reparation is not a permanent solution. Thereupon, a more easy & cheap way should be sought to elucidate the complication.
Self-Healing Asphalt
The main constituent of roads is asphalt which with the help of bitumen binds the other material together & form the roads. Asphalt is naturally self-healing material. When it is exposed to intense heat (i.e. sun) asphalt absorbs the heat & expands slightly due to thermal expansion and fill the tiniest gaps created by the vehicles. But asphalt is a poor heat conductor because of the mineral aggregates. Hence, to earn the required heat level at the desired asphalt layer, the surface of the roads always must be strongly overheated for a relatively long period of time and it takes strenuous effort. Also, it involves huge amount of energy loss due to constant burning of the bitumen layer. But adding a small amount of highly refined steel fibers in the asphalt mix can iron out all these problems. Erik Schlangen, a professor in civil engineering at Delft University in the Netherlands with his co-workers, has discover this method. Here, conductivity of the steel is the main key. An induction machine is used in the compromised area. Because of rapid changing in magnetic field, the steel fibers become hot. They transfer the heat to the surrounding materials (i.e. the asphalt mix). This cause the asphalt (or mortar) to momentarily melt. From there, cracks & gaps begin to fill & return to the previous state. Technically, the process is not completely ‘self’ as an induction machine from outside is needed to instate the self-healing. It is, however, highly effective and sufficiently cheaper than closing the road for a temporary patch or a new road entirely, a process which takes days to complete.
Implementation in Bangladesh
Last year, according to the officials at the Road Transport and Highways Division and Local Government Engineering Department (LGED), over 2,000 km roads are needed to repair every year because of overloaded vehicles. In Bangladesh, another problem is that if any small hole is created on any road, it is not fixed immediately. The authorities concerned wait for repair until the most parts of the road get damaged. The World Bank presented a list of infrastructure cost, especially in road construction previous year. It shows the cost of per km road construction is $2.5 million to $11.9 million in Bangladesh which is one of the highest in the world. So implementation of “self-healing asphalt” is much more practical solution than reparation in Bangladesh. The cost is 25% more than the conventional asphalt but at the same time it promises double lifespan than the traditional porous asphalt. So even if the initial cost of the self-healing asphalt is higher, comparing with the maintenance cost, repair cost, material cost and other conditions, it is evident that it has more financial benefits. Netherlands and China have already implemented self-healing roads and the trials are going smoothly. The technique has already been tested on twelve different roads in Netherlands and all of them are in pristine condition. However, the viability of the new method will only be confirmed once the roads surpass the 10-year threshold- the time at which conventional roads begin to require repairs.
Reference:
[1] www.rhd.gov.bd/RoadDatabase/
[2] https://interestingengineering.com/self-healing-roads-last-80-years
[3] https://www.self-healingmaterials.com/self-healing-asphalt/
[4] Self Healing Asphalt - Extending the service life by induction heating of asphalt (Gerbert van Bochove)