Thursday, September 23, 2010

The World of Cracks

Our pavements have never been in a worse state of disrepair than they are today. The reason for this are many. It is estimated that 650 potholes open up every minute in North American streets and highways or 341,640,000 per year. The cost of repairing these would require $51,264,000,000 per year. It is also estimated that there are 88, 070,400,000 feet of cracks in North American streets and highways that need to be repaired annually at a cost of$28,182,528,000. To repair the potholes and cracks requires $79,428,528,000. This is an enormous sum which towns, cities, counties, state and provincial governments have to come up with annually. No matter what, these potholes and cracks will be there every year. In addition, the North American motorist incurs substantial annual costs associated with poor roads above normal routine costs of operating a motor vehicle. A fairly recent report stated that in Los Angeles, the additional cost of operating a motor vehicle is $778. The additional annual cost of operating a motor vehicle in other North American cities is somewhat less, but still significant. Poor road conditions contribute substantially to the number of fatalities annually.
Pavements showing various distresses such as cracks, potholes and ruts also contribute significantly to an increase in fuel consumption. A 1985 road information survey concluded that the additional fuel consumption due to failed pavements amounted to $21.3 billion US dollars annually. The average price of gasoline at the time across the United States was $1.15 per gallon. That means the amount of fuel wasted was 18.52 billion gallons. We can safely say that the amount of gasoline wasted today due to failed pavements is significantly higher. Today, we not only have more failed pavements than ever before, we also have many more cars on the road.
Towns, cities, counties, state and provincial governments have a number programs in place in the hope that it will keep their street and highway pavements in a state of good repair. Their programs consist of preventive maintenance which means filling cracks and potholes, overlaying their failed pavements with a lift or two of conventional asphalt concrete, or reconstruction of a failed pavement. To follow these programs requires an enormous amount of money. This amount of money is difficult to come by, especially during this financial crisis. Cities, towns and counties are near bankruptcy. Even formally wealthy states like, California, are forced to terminate 20,000 government jobs and slashing the pay of 200,000 other employees(during fiscal 2009). The credit crunch of(2008) may last for many more years before enough private capital is available to fuel the economy. Most of the capital available today has come from the stimulus packages passed by Congress. What does all this mean? It means most of our pavements will remain in disrepair for the foreseeable future. If funding is restored to pre2008, it will still be insufficient to cope with all our failed pavements.
Our present approach to deal with all the failed pavements requires new thinking by all of us. The first thing we must do is to think out of the box. So let us look at how we are trying to maintain our extensive network of streets and highways. One term that we constantly bandy about is "Preventive Maintenance". What exactly are we trying to prevent? When we fill potholes or cracks, do we really believe that they are repaired permanently? When we overlay an old failed pavement with one or two lifts of new asphalt concrete, do we really believe that cracks and potholes will not reflect through the new overlay? If we do, then we need a drastic re-evaluation of our experience, training and education. Our so called preventive maintenance involves conventional asphalt concrete either dense-graded or gap-graded. Use of conventional asphalt concrete mixes will do nothing to prevent the old failures from recurring in a very short time. Sometimes it may be only a few months or a few years but they will recur. Paving streets, roads and highways requires huge quantities of crushed aggregate which is readily available. When this aggregate is mixed with the proper amount of asphalt cement as determined in the laboratory, the resultant asphalt concrete mix is classified as conventional asphalt concrete. Conventional asphalt concrete is relatively economical compared to other construction materials. This is one reason why it is used so extensively in road construction. The pavement failures we observe is the direct result of using conventional asphalt concrete mixes. We can change the gradation of the aggregate all we want without improving the performance of the pavement significantly. Thus, we can have dense-graded mixes or gap-graded ones and in the long run find very little improvement. It may take a little longer for a gape-graded pavement to crack compared to a dense-grade asphalt concrete mix. However, the resultant cracks will be wider and grow faster because of the predominantly larger particle sizes. There are many products on the market that claim to mitigate reflective cracking. Some work better than others while some do not work at all.
When we mitigate or even eliminate cracking of a new pavement or reflective in overlays, we will at the same time eliminate the formation of most potholes. As a result, we would drastically reduce the annual cost of $79,428,528,000 to fill all the cracks and potholes that appear every year in North American streets, roads and highways. From the foregoing, we can conclude that, it will continue to require enormous funds to just maintain our highway infrastructure.
To crack a demo for all...............
The various state and provincial governments own, on average, less than 15% of the roads and highways. The towns, cities and counties own the rest. It is these jurisdictions which carry most of the burden of pavement maintenance. As a result, it is they that have to come up with the money. Clearly, this is just too much of a financial burden to cope with. The first casualty of any budget are the funds allocated for street and road maintenance which are drastically reduced. Is it any wonder that our streets and roads are in such disrepair.

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