Research Journal - 1st Draft part 2

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 for 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 sustain differently.


Roads and highways are used constantly for access and mobility. The Encyclopedia Americana by Grolier stated back in historical time of the early Christian era, trails were used as routes from Rome to China by caravans to freight animals (Grolier, para 4). Even though trails were used then, it wasn’t till 1990 when automobile was invented and was considered the beginning of modern highway.


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 1800s for Pitch Lake in Trinidad and the Bermudez deposit in Venezuela (Grolier, Asphalt para 6). That had an influence for the United States to use asphalt for street paving. In the early 1870s 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 (Grolier, Asphalt para 1).


Asphalt are 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 (Grolier, Asphalt para 8). With this paving material, asphalt actually paves about 90 percent of the United States city roads and almost all secondary roads. 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 (Grolier 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 subgrade, 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 subgrade 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 t his layer, asphalt or concrete pavement may be used, 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.