Cracks, bumps, and potholes are on every roads and highways that our tires ride over every day. But, have you ever noticed that some cracks and potholes form more often on certain roads? That’s because there are two types of pavements; asphalt and concrete pavement and they are made up of different materials and dominate differently.
Roads and highways are used constantly for access and mobility. The Encyclopedia Americana stated back in historical time of the early Christian era, trails were used as routes from Rome to China by caravans to freight animals. Even though trails were used then, it wasn’t till 1990 when automobile was invented and was considered the beginning of modern highway (“Roads” para 4).
Here in Utah we see a lot of asphalt paving, which goes for the United States as well. About 80 percent of that use is for highways, airports, school playgrounds, and other paving. The first use of asphalt street paving began in the 1800’s for Pitch Lake in Trinidad and the Bermudez deposit in Venezuela (Dresser, para 6). That had an influence for the United States to use asphalt for street paving. In the early 1870’s United States laid pavement in front of the city hall in Newark, New Jersey. Before asphalt was used for street paving, its main purpose made reservoirs, canals, and bathing pools watertight. Also, as early as 3800 B.C. it was used as mortar for building stones and paving blocks (Dresser, para 1).
Asphalt is black and dark brown solid or semisolid cementitious materials that gradually liquefy when heated. The main constituents are bitumens that occur in nature are obtained by refining petroleum (Dresser, para 8). With this paving material, asphalt actually paves about 90 percent of the United States city roads and almost all secondary roads (Dresser, para 14). Asphalt is widely used in the United States due to its durability, the smooth sailing ride, and the fast past of construction and maintenance it provides.
Before laying down any type of pavement, there has to be consideration for volume of traffic, speed, and capacity. For highway capacity, the maximum number of vehicles that can be expected to pass a given point over a given period of time is usually expressed as vehicle per hour. Under ideal conditions, one freeway lane can accommodate about 2,000 passenger cars per hour. A two-lane road can carry up to 1,000 passenger cars per hour in each direction. So, there is a relationship between vehicle speed and highway capacity. As the volume of traffic approaches capacity, average speed is reduced. With speeds in the 30-40 miles per hour range, a highway typically has reached it capacity (“Roads” para 6). With the design of freeways there are on and off ramps, keeping traffic off the freeways. The same concept is used for city roads, having intersections with traffic lights controls the road capacity.
Just like a casserole dish or a pie, the structure for roads and highways have layers; three layers. First, is the sub grade, which is the earth beneath the road. For this process it needs to be graded, compacted, and stabilized. The second layer usually holds most of the traffic weight, which is the base course. The base course is laid over the sub grade and should be several inches thick for binding the material. The final layer is what we see and drive on, the pavement or the wearing course. For this layer, asphalt or concrete pavement may be use, sometimes there isn’t a final layer.
With the structure of layers in mind, the actual asphalt paving is done with a machine that spreads the asphalt down evenly and with vibration it slightly compact the material down. But, the actual compaction is down with huge rollers. The final thickness of the asphalt with compaction rages anywhere from 2 to 12 inches depending on how of the road is used (“Roads” para 21). The thickness of the asphalt pavement is a tough and flexible finish that supports the weight of traffic.
Only 12 inches deep, asphalt roads is occupied by hundreds and thousands of motorist ever day commuting to work, school, and many other traveling reasons. With the traffic weight on these roads it is bound to have road damage. The most common damages the roads posses are cracks and potholes. Like most material and products, wear and tear causes deterioration. Weather plays a crucial part in road damages as well. Once a crack is formed by traffic volume or fractures on the side of the road, water can then get under the pavement and starts eroding away the material causing it to sink down and break. Majority of the cracks and potholes are formed during the winter and spring seasons. During the winter time, the water under the pavement can freeze and expand then it thaws and contracts. The thawing and freezing cycle causes the pavement to break faster under the weight of traffic, which loosens the pavement making it crumble and pop out forming potholes (“Transportation” para 23).
From the observations I made in my neighborhood, the asphalt roads consist of several potholes. Over a short period of time, I have noticed motorist driving over these holes as if they don’t exist and watching these potholes grow in dimension with no repairs. According to the Highway Department, the general criterion for repairing a pothole is that a hole in the pavement has to be 2 inches or more in depth and over 8 inches in diameter. Also, where the pothole is located at and the condition it is in will determine the consideration for the repair. Potholes are temporary repairs, especially during the cold and wet weather. Since, cold asphalt mix is being used; the material doesn’t stick as well compared with hot asphalt mix that is used during the war seasons. Even with the temporary fixes, the usage of the road will eventually break again. In certain counties, road repair is classified by priorities. First, are high volume and high speed routes that connect major sections. Second, are those providing access to schools and businesses. The third priority roads are low volume routes. Sometimes potholes can’t be filled due to the responsibility of the property owner, underground utilities, and near railroad tracks (“Potholes” para 6). Since asphalt pavement is widely used, the life expectancy is only 7 to 10 years (Brock, para 3) and the cost of tax payers repairing potholes over and over again can be very costly. When asphalt road is ruin the best solution for prolonging the life is to reconstruct the road.
On a personal opinion, driving over potholes is very irritating and it leaves me pondering if my vehicle will ever function the same again. Potholes are inevitable and my cause serious damage to an automobile. When potholes are formed, loose gravel is scattered all over the road then it waits for a vehicle to kick it up to create a rock chip in another vehicle’s windshield and that could lead to a broken windshield. Other problems that could occur when driving over a pothole is realignment, shocks, struts or even engine mounts that needs to be fixed. If you’re lucky enough to hit a crater, you can be paying big bucks to get a new stabilizer links, axles, or new wheels and rims (Baca, para 11). Regardless of the damages that potholes can cause towards a vehicle, it’s an expensive fix due to parts and labor that needs to be done.
Although asphalt is prone to potholes it’s not the only type of pavement that’s being used on the streets today; concrete roads is becoming more popular for street paving these days. Concrete pavement is mostly common in states with high traffic volume such as California. Nationwide, traffic congestion is growing worse and the Federal Highway Administration had recommended increasing highway capacity along with widening local arterial roads with concrete pavement (Brock, para 1). Even here in the state of Utah we are beginning to see changes on I-15 and 2-15 as they expand in lanes and reconstructing the freeway with concrete pavement. Concrete pavement is being used all over the country because of its durability, long life, and low maintenance.
Unlike asphalt, concrete key ingredient is a binding medium of small pieces of rock or other materials that are embedded. Most concrete pavement is from Portland cement which has elements of the earth’s crust; silica and calcium (Cordon, para 1). Damages are done by the weather as well, when freezing and thawing occurs. Concrete also shrinks and expand when moisture hits. The design and process of laying concrete pavement have been strategically planned out for those reasons. For strength in concrete pavement, reinforcement is used to release these stresses. The combination with concrete is steel, they work well together in reinforcing concrete because they have similar coefficients of thermal expansion (Cordon, para 72).
Concrete roads are paved into sections of slabs. Within these slabs, concrete is poured over steel rods, dowel bars, or metal bars that distribute the weight load of heavy traffic which increase the roads life and reduces noise (Brock, para 9). The slabs are placed inches apart from each other and are filled with a tar like substance to help with the shrinkage and expansions that occurs within the concrete. Also, cutting notches into the concrete at intervals helps prevent cracking, reducing the amount of damages and potholes. With the durability of the material, reinforcement, and surfacing of the pavement; concrete roads life expectancy is 30 to 40 years, some have last almost 100 years old (Brock, para 7) compared with asphalt road it last 23 years or longer without continuing repairs.
Concrete roads have been used in the United States since Michigan laid the first mile of its material in 1909. But, the use of concrete itself was been known by human kind for the past 5,000 years (Cordon, para 5). In the United States cement became widely used in the 1820’s, the most important structure was built during this time was the Erie Canal (Cordon, para 8). Most of the credit goes to the Romans structures, the Pantheon and the Coliseum, which are still standing today. These structures show pure durability and high quality that concrete provides.
With these long standing structures and building it proves that paving roads with concrete will provide strength, high quality, durability, and longevity. Added reinforcement bars, notches, and surface filling will help prevent cracking and potholes. With limited potholes from these technical designs and techniques, motorist will have less windshield repair, auto repairs, and less car accidents on the road from dodging potholes. Concrete is relatively at its lowest cost which lead to the wide use of concrete. So, why doesn’t the United States take in consideration of reconstructing all primary and secondary roads with concrete to help the economy in the future?
Works Cited
Elena Baca, Maria. "Where the rubber meets the (hole in the) road: Potholes in pavement are feasting on our cars, turning tires and suspensions into heaps of automotive trash." Star Tribune (Minneapolis, MN) 05 Apr. 2010: Newspaper Source. EBSCO. Web. 7 Apr. 2010.
Brock,Ed."Science paves the roads of the future."American City & County121.8 (2006): 20- 22. Academic Search Premier. EBSCO. Web. 7 Apr. 2010.
Cordon, William A. "Concrete." Encyclopedia Americana. 2010. Grolier Online. 30 Mar. 2010 .
Dresser, Richard C. "Asphalt." Encyclopedia Americana. 2010. Grolier Online. 1 Apr. 2010 .
"Roads and Highways." Encyclopedia Americana. 2010. Grolier Online. 31 Mar. 2010 .
Potholes. Clermontengineer.org. Clermont County. n.d. Web. 04 Apr. 2010.
Potholes and Potholes Ranger. Seattle.gov. Department of Transportation, Dec. 2009. Web. 04 Apr. 2010.
