One of the most versatile, durable and highly viscous substances on the planet, asphalt, aka bitumen, is both a naturally occurring substance and a manufactured material refined from distilled crude oil. Asphalt is typically a black, sticky liquid or petroleum byproduct that must be heated to very high temperatures so it can be used as a binding medium when laying down load supporting surfaces.
With over 1.3 billion cars and trucks on roads worldwide and a combined automobile manufacturing industry valued at over $6 trillion ($9 trillion by 2030) a lot is riding on the quality and safety of roads and highways. Perhaps this has never been truer now that the auto industry is moving toward driverless vehicles.
Ninety percent of paved roads and highways in the United States and 70% worldwide are made using asphalt concrete which is composed of 5% asphalt cement and 95% aggregates such as crushed rock, gravel, stone, sand, slag and rock dust. Driveways, parking lots, airport tarmacs, embankment dams and rooftops also benefit from this durable, waterproof binding substance.
Highway engineers use different layers to accommodate a wide range of loading expectations and local climate conditions. A typical road or highway includes road bases or courses which are the bottom layers, second or binder course layers which are the middle layers and the top or surface layers referred to as the surface courses.
Industrywide specifications have been developed taking into account historical low and high temperatures at construction sites. Binder properties determine how asphalt will act as a constituent in asphalt concrete. Other properties to be considered include coarseness, fineness, angularity, flatness, elongation and clay content.
Potholes the Bane of the Auto Industry
Highway EngineersPotholes are one of the leading causes of car, truck and motorcycle accidents and vehicle damage in cities like New York, Los Angeles and San Francisco and in cities worldwide. Potholes develop when the top layer of the road, asphalt, wears down exposing the concrete base.
Potholes can grow to several feet, and more than 10 inches deep. Rain water, ice and snow accelerate the process creating hazardous obstacles for vehicles. Roads and highways are usually covered with asphalt because it does such a good job repelling water and snow and then, redirecting it to the sides of the roads and into drains and culverts.
Kinds of Asphalt Mixtures
Asphalt is mixed under high heat with aggregates including crushed rock, gravel, stone, sand, slag, and rock dust to create “asphalt concrete.” These aggregates make up 90% to 95% of the weight of asphalt concrete pavement and 75% to 85% of volume. Mixing different types of asphalt requires minimum and maximum mix temperatures. In addition, when laying down new highways or roads the air and pavement temperatures can affect the compacting of the materials and their long term durability.
Asphalt Testing Methods & Quality Control
Manufacturers of asphalt use laboratory ovens for testing and analyzing material characteristics, detecting defects and failure susceptibility. Despatch LBB forced convection ovens, for example, offer heavy-duty, forced air, highly uniform and repeatable testing with extremely tight temperature tolerances for consistent testing. It is in the laboratory that new types or mixes of asphalt can be thoroughly vetted before being used in multi-million dollar projects.
Federal & State Agencies Work to Keep Roads Safe
Given the heavy use of highways and roads and their importance, the US Federal Highway Administration (FHWA) oversees a federal quality assurance program called the “Long Term Pavement Performance Program” (LTPP). LTPP sets standards, monitors pavement performance and spearheads research, design, analysis, materials quality assurance, sustainability, construction technology and pavement management and performance.
Finally, FHWA oversees the Strategic Highway Research Program (SHRP) and the “Superpave” (SUperior PERforming Asphalt PAVEments) system to help highway administrators, engineers and contractors create asphalt pavement that performs well under extreme weather conditions and heavy traffic.
Natural Deposits of Asphalt
Pitch Lake aka Asphalt Lake, located southwest of Trinidad, is the largest natural deposit of asphalt holding more than 10 million tons of asphalt. Another large deposit of natural asphalt is located in the Canadian province of Alberta in the Athabasca oil sands which is an area larger than England.
Top Asphalt Producers & Product Makers in 2020:
- BP Plc
- Exxon Mobil Corporation,
- Petroleos de Venezuela SA
- Royal Dutch Shell plc.
- Akzo Nobel
- Anglo American
- Atlas Roofing Corporation
- Aggregate Industries Limited
- CEMEX UK Operations Limited
- CertainTeed Corporation
Image Credits:
Cover Image by LeFox from Pixabay
La Brea Pitch Lake, Trinidad by Grueslayer from Wikipedia, CC BY-SA 4.0
