Asphalt or ConCrete?
Written on Sunday, March 27, 2011 by Jose Sanchez Marquez
There are polarized opinions about what is the best material for highway construction, concrete or pavement. In Colombia, asphalt is the most common way to highway construction. However in the last years concrete highways has been taking place in urban areas.
The most important differences of these two methods are the cost, time of construction, qualified staff, durability and the Island heat effect.
Construction Cost
The first aspect about the cost, it is true that the asphalt has a lower price, due to the structure sub granular base, granular base are not so expensive and they conformed a big important percentage in the thickness structure. In concrete roads is the concrete the one that conformed the majority of the thickness structure, reason why the cost per m3 increase the value of the roadway.
Time of Construction
According with the time of construction in new roadways there are not big differences, every process can consume a similar time of delivering the roadway. However if we are talking about maintenance works with the pavement you can give way to traffic in less time, meanwhile with concrete if it is normal you need to wait at least for 28 days, waiting to reach the final resistance.
Qualified Staff
The qualified staff is very important in pavement process, due to you need to count with people that can operate for instance, a motor grader, a rolling vibratory, drum vibratory rollers a tracked paver or wheeled paver, Pneumatic rollers and trucks that carry the pavement. Also you need to count with a topography team and a specialized people that spread the asphalt and help to give the final look. Concrete process doesn’t require the same number of qualified staff and the maintenance is easier and also don't require specialized machines or people.
As a conclusion we can also said that concrete roadways consume less diesel combustible, according with the American concrete pavement Association, ACPA. An asphalt road requires 4.5 more combustible than a pavement design with concrete for the same number of traffic.
With the durability concrete doesn’t has comparison, the pavement life can be between 7 to 10 years, but with concrete the life expectance is between 20 to 25 years.
Heat Island Effect
However the most important difference is the one that few people stop to analyze, the heat island effect. Due to the cities needs roadways, parking lots and all kind of structures to may our lives easier we are changing the urban sustainability. The zones that were before moist permeable now are waterproof dry and this phenomenon is clearer in warm weather cities.
Image from http://www.acca.it/euleb/en/glossary/index.html
One benefit of use concrete is that it reflects the sunlight helping to reduce the city temperature. In the picture below we can see the differences in temperatures between concrete and asphalt. Concrete has a temperature of 38°C and the asphalt has a temperature of 55°C. Reason that explains why in warm cities is so common the use of air conditioning.
Image from http://www.celsias.com/article/cool-roof-could-offset-carbon-emissions/
We need to remember that when it leaves the asphalt plant has a temperature of (152 –154°C) during the course can it lose (2 - 4°C), when it is spread by the tracked paver, it is necessary to wait until the temperature decrease to (130 – 132°C) and then the drum vibratory rollers and Pneumatic rollers can work on the pavement. Once the process is over the asphalt con reaches easily temperatures of (48–67°C) all year long, transferring excess heat to the air above them and heating storm water as it runs off the pavement into local waterways. Further, concrete temperature when leaves plant is around (30 – 32°C) and during the course can earn (0.5 - 1°C). Once is completely finish in a very hot day can reach a temperature of (36 – 38°C).
As conclusion we can say that Concrete has a higher durability, doesn't need many qualify personnel, doesn't consume the same quantity of combustible and can mitigate in a better way the heat. Asphalt could be not so expensive, doesn’t has the same durability and it is not good in mitigate the heat.
Jose Sanchez Marquez
References.
- Noticreto 104. Enero - Febrero 2011. Edición Especial Edificaciones y Sostenibilidad Ambiental
- United States Environmental Protection Agency http://www.epa.gov/heatisld/mitigation/pavements.htm
Posted in
concrete or asphalt,
construcción de vias,
grader,
heavy machines,
highways,
island heat effect
