Asphalt, also known as bitumen, is a sticky, black, and highly viscous liquid or semi-solid form of petroleum. It is a byproduct of the distillation process of crude oil and is present in many oil deposits. Asphalt has been used for thousands of years and was commonly used by ancient civilizations, including Mesopotamia, Egypt, Greece, and Rome. In modern times, asphalt is primarily used as the glue or binder mixed with aggregate particles to create asphalt concrete. Asphalt concrete is widely used for paving roads, driveways, parking lots, bike paths, and playgrounds.
Composition and Properties of Asphalt
Asphalt is composed of complex organic compounds including 85-95% bitumen combined with aggregate materials such as sand, gravel, or crushed stone. When asphalt is mixed hot with aggregate, it hardens to form a strong, solid surface that is durable, flexible, and waterproof. Its inherent adhesive properties allow it to bind with mineral materials to create a pavement surface resistant to wear and weathering. Because of its elastic nature, asphalt pavement can also flex slightly without cracking, making it suitable for high-traffic areas. Asphalt is highly resistant to acids, alkalis, and most chemicals, giving it longevity despite environmental exposures.
Production and Extraction of Asphalt
Production of Asphalt begins with extraction of crude oil from underground reserves. Crude oil typically contains approximately 5-15% by weight of naturally occurring asphaltic bitumen. The crude oil is then processed in an oil refinery to separate and remove other hydrocarbons like gasoline, kerosene and diesel through distillation. The bottom residual material left over contains around 90% bitumen by weight. This residual bitumen is blended with other oils and refined to create asphalt cement that is then ready for use in road construction. Asphalt cement is typically dark brown to black in color and almost entirely soluble in carbon disulfide or chloroform.
Steps in Asphalt Pavement Construction
The construction of asphalt pavement involves several key steps:
Preparation of the Base – The underlying soil or base material is prepared and compacted to create an even and stable foundation. This may involve grading, adding stone, and using a roller compactor.
Application of Tack Coat – A thinly sprayed application of asphalt cement is applied to the prepared base to help bonding of the new asphalt layer.
Placement of the Hot Mix – Hot asphalt cement mixed with aggregate is brought by truck to the site, spread uniformly by a paving machine, then compacted. The mix needs to be at 300-350°F at time of placement.
Compaction – Heated steel drums or rubber-tired rollers compact the asphalt in layers to maximize density and strength.
Joint Construction – Butt joints between adjacent passes of new asphalt are sharp, straight, and sealed with extra hot mix or sand.
Finishing – The final grade and cross slope are established using rakes and squeegees. Manhole covers and valve boxes are adjusted.
Curing – As the new asphalt solidifies and cools, it gains structural integrity through a curing period of several weeks.
Uses, Maintenance and Lifespan of Asphalt Surfaces
Asphalt is utilized not just for roads but playgrounds, parking lots, airport runways, bike paths and more. Benefits include smooth ride, low installation costs, and ability to be easily repaired. Asphalt surfaces generally last anywhere from 15 to 25 years if properly maintained through crack sealing, pothole patching, and resurfacing as needed. Cold patch mixtures can quickly repair potholes. Slurry seals or chip seals add a new wearing surface and extend the life another 7-10 years. A complete overlay or reconstruction using 2-4 inches or more of new hot mix may be needed if pavement has deteriorated too much. Proper compaction and drainage keeps water from weakening the asphalt foundation.
Environmental Impacts of Asphalt Usage and Production
As with all petroleum and fossil fuel based products, there are some environmental impacts from asphalt usage:
– Emissions from crude oil extraction and refining include greenhouse gases, particulates, and pollutants that impact local air quality.
– Extraction activities like fracking can contaminate groundwater if not properly regulated.
– Spills and leakage at production facilities pose environmental and health risks if not contained.
– Heat from asphalt installation raises urban temperatures, contributing to urban heat island effect.
However, asphalt pavement also offers some advantages over concrete in that it is more flexible and produces less dust particulates during uses and repairs. Recycling of removed or milled asphalt for reuse also reduces demand for virgin materials. Manufacturers continue developing techniques and additives to reduce emissions and production impacts for more sustainable asphalt.
Asphalt concrete is a versatile and cost-effective pavement material that has enabled modern infrastructure development worldwide. With proper maintenance through repairs and overlays, asphalt roads, pathways and surfaces continue serving communities for decades. Advances in additive technologies also work to boost sustainability credentials. Asphalt’s widespread availability and engineering properties confirm its enduring importance for paved transport networks both now and in the future.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it