Creating Self-Healing Roads
We have all experienced driving on bad roads, whether it be through potholes, road cracks, or a horrendous bumpy ride on the way to your favorite ice cream shop.
In Canada and the United States, 43% of roads and highways show significant deterioration, and 15% are defined as barely serviceable, or in need of urgent replacement. To repair all of them, it would cost a combined total of $545 billion. Not to mention that around the world, potholes cause more than 42,000 deaths per year.
To put this into perspective, we are sending rocket ships to space, but we can’t even maintain our own roads? At Rever, we are creating the solution to fix this extremely costly and destructive problem.
Why Are Current Roads So Bad?
In Canada and the US 90+% of roads are made of asphalt mixtures, which are made of 30–50% water. In winter, the water freezes creating ice. The ice expands the asphalt as it takes more space than the original water. When the warm weather comes, the ice melts creating a gap within the asphalt, allowing the formation of small microcracks when the road is subjected to heavy traffic loads.
While our roads don’t become unusable after a single winter, they experience compounded damage over multiple years. Since damage begins to build up years before it becomes noticeable, the accepted approach of doing maintenance after problems occur is highly ineffective; not to mention extremely costly and time-intensive.
Solution: Self-Healing roads
Self-healing roads have the potential to increase road lifespans from 40 years to 80 years (2x improvement). With our steel fiber asphalt and induction machines, we can save the government around the world up to $1.1 trillion(or $28,125 per mile)per year.
Current asphalt roads already have self-healing properties, but they require long rest times. To accelerate this self-healing process we need a high temperature. To increase our asphalt temperature we will be adding steel fibers and using induction heating.
The reason we are using steel fibers is that they conduct heat 106 times more effectively than asphalt. These steel fibers pass on their heat to asphalt enabling better and faster healing. This specific metal was chosen as it was highly conductive without being a burden on our manufacturing costs (explain in “cost” section).
Induction heating involves the process of using a magnet to rapidly heat up a metal (in our case steel fibers). This happens by using an induction machine to drive over the asphalt. This process involves sending an electric current through a series of coils, resulting in a magnetic field. The magnetic field heats up molecules within a ferromagnetic metal (a substance that is highly susceptible to magnetization)- in this case, the steel fibers.
The reason we are heating steel fibers (a conductive metal) is because they transmit more heat to asphalt than if we asphalt did not have steel fibers. We heat the asphalt due to the research of Qiu et al that demonstrated that asphalt healing was dependant on two variables: time (rest periods) and temperature. The following graph shows his results using 2 different asphalt mixtures in 3 different temperatures.
Through this experiment, we can see that the higher temperature results in faster and more effective heating of asphalt. When heat is applied to asphalt it makes the material more malleable creating a gel state allowing recovery from structural damage which is called the thixotropic effect.
According to the research of Liu et al, the optimal heat to be applied to the steel fiber asphalt is 85°C and if it is anything over 110°C it causes adverse effects on the quality of asphalt and its performance.
According to the research of Mallick et al, high temperatures close surface cracks but dissipate quickly throughout the pavement. This means that cracks 20–30 mm below the pavement surface are not reachable by current induction heating methods. As a result, it does not heal and these deep cracks reappear at lower temperatures or because of heavy traffic loading.
This means that we have to rebuild roads with our steel fiber material (when the lifespan of a normal road is done) to ensure these cracks never happen in the first place. The induction machine to create the induction heating will be used over roads every 2–4 depending on weather conditions as a preventative measure for cracks and potholes.
Results
According to research at the University of Granada in Spain, they found that we can take a fresh crack and heal it within 3 hours.
Without the induction machine, this crack would open up more over time and it would only get fixed when the problem is costly and time-intensive.
The process is technically not entirely “self-healing” because we need an outside force (electromagnetism caused by the induction machine)to initiate the healing process, however, it is highly effective and sufficiently cheaper than closing the road for a temporary patch or a new road entirely, a process which takes days or weeks to complete.
The Gap We are Bridging
It seems pretty clear from the research above, that induction heating with steel fibers in asphalt will create better road conditions by acting as a proactive measure so road deterioration does not happen.
You might be asking “If it is so obvious why is this not on every road?” Even though this technology has been around for at least 10 years, there is NOBODY that is mass-producing or mass-distributing the needed materials. At Rever, our goal is to commercialize these products to make your next ride that much smoother.
Economic Incentive
Erik Schlangen, a materials scientist with over 25 years of experience has conducted research that predicts this self-healing road technology can increase the lifespan of roads up to 2 times.
On average, $2.9 trillion is spent yearly on rebuilding roads based on ($3 million per mile). With self-healing roads lasting 2x longer, we stand to save $1.1 trillion/year on construction efforts from governments. Keep in mind we are not taking into account the extra amount that governments need to pay to fix normal roads. This would create an even larger saving amount (since our roads will not have potholes or cracks).
Cost
You might be wonder about the prices of these products. The induction machine costs about $500,000 and the asphalt costs $120 per tonne. This might sound like a lot but imagine that had 20 miles of our roads for 10 years generating you $28,125/mile/per year in savings (in road longevity). Overall you would get $5,625,000. Now let’s factor in the cost of the steel asphalt mixture.
In the U.S interstate highway (which are much larger than normal roads) have a 3.7m road width with 4.5 inches deep with 20 miles costs. Using this tonnage calculator this highway would need 36,053 tonnes of our asphalt mixture costing $4,326,375 + $500,000 (for the induction machine). Overall it would cost $4,826,375 to maintain the road saving that city’s government $798,625 for 20 miles.
Keep in mind that this also factors in a width of a road that is larger than most urban inter-city roads. This is meant to represent a bad case scenario but governments still came out positive.
So, if you are tired of driving on bad roads, get excited for us to make your next ride that much smoother.