Tackling cracks head on

Filling cracks in the road can be both hazardous and time consuming to the workers involved. How can this be done better?

We have all been there. Driving down the road, minding your own business and then 'thwack!?' You hit a pothole. Depending on where you live and how much the road is used, it might be there for a few hours or a few years. Potholes are caused by cracks forming in the road, into which water seeps and then freezes. As the water expands, this pushes the top layer of tarmac up and creates a hole. The trouble is it usually has to turn into a relatively large problem before anyone fixes it. And when potholes are fixed, it can be a time consuming, and dangerous process, with workers having to work alongside fast-moving vehicles. It is estimated that poor roads cost British motorists £2.8 billion every year in burst tyres and suspension damage, with authorities paying out £50 million every year to the motorist as compensation for poor road maintenance. The Challenge The challenge this month, then, is to come up with a way of quickly and easily repairing road cracks before they spread in to something worse. Your device should be easily operated, with minimal personnel and be able to cover a lot of road per day. Unless you have an inspiring leader and take a leaf out of the film 'Cool Hand Luke', it is unlikely road resurfacing productivity can be increased using people alone. Therefore the solution should be an automated systems mounted or integrated within a vehicle. However, the object of the exercise is also to make this a cost effective process so simplicity, and off-the-shelf components are a must. The key to success is likely to be the speed at which a crack can be detected and then filled, so manually identifying the holes is a far from the ideal solution. While a purpose-built vehicle might be optimal, remember to keep costs down and make any device easy to deploy and at a relatively low cost to councils. The solution is surprisingly elegant and is largely an integration exercise involving an array of sensors and some clever software to allow it to be deployed on the move. When you see the solution, you may consider it obvious. In the meantime, see if you can come up with anything better. -Solution- Solution to August 2012 Coffee Time Challenge The solution to this Coffee Time Challenge, to build a device which identifies and fills cracks in the road whilst on the move, comes from the Georgia Tech Research Institute (GTRI). It developed a prototype automated pavement crack detection and sealing system which in road tests was able to detect cracks smaller than one-eighth-inch wide and efficiently fill them whilst on the move. It utilised a stereo camera, light-emitting diodes (LEDs) of two different colours, and an assembly to provide a continuous supply of sealant to longitudinal and transverse axes. The operation requires only one worker to drive the vehicle pulling the trailer. As the system travels along a road, the LEDs illuminate the road in two directions – parallel and perpendicular to the road – and the stereo camera takes two pictures of the road simultaneously, which are analysed using threshold and filtering algorithms. Within 100ms the onboard computer generates a 'crack map' specifying the location and shape of any cracks shown on the images. A master controller then instructs the sealant applicator valves to fire. To fill longitudinal cracks, a single dispensing nozzle capable of continuous operation is attached to a linear servo axis. The transverse sealant distribution system consists of 12 nozzles. The researchers tested their crack detection algorithm on more than 100,000 images they collected of cracks on roads and found the program correctly identified more than 83% of the cracks. GTRI research engineer, Jonathan Holmes, said: "Our crack detection algorithm was limited because we used a vision-based system, which was confounded by regions of high contrast caused by features other than pavement cracks, including dark stains in the pavement, lane stripes, raised-pavement markers, crack sealant and debris. A full-scale system may require a fusion of multiple imaging sensors, such as a 3-D laser scanning system." www.gtri.gatech.edu