Historical Context
The use of asphalt is not a modern invention; it traces back to ancient civilizations. In 625 B.C., the Babylonians first employed asphalt as a waterproofing material for temple baths and water tanks, demonstrating its enduring utility (The Asphalt Institute, 2021). Fast forward to the 1870s, and modern asphalt pavements began to take shape in the United States. The credit for this innovation goes to Edward J. de Smedt, a Belgian chemist at Columbia University, whose work led to the first asphalt-paved road in front of Newark, New Jersey’s City Hall in 1870 (American Society of Civil Engineers, 2015). By 1907, the U.S. was producing 3.4 million tons of asphalt annually, marking the beginning of its widespread adoption (National Asphalt Pavement Association, 2022).
Current Usage and Scale
Asphalt has since become the backbone of modern infrastructure, forming the surface of roads, highways, airports, and parking lots across the United States. The scale of its use is staggering: approximately 400 million tons of asphalt are produced in the U.S. each year (National Asphalt Pavement Association, 2021). To put this in perspective, this amount of asphalt could cover an area that is larger than Long Island, NY and about 640,000 soccer fields, assuming a standard field size of 7,140 square meters and a 5 cm thick layer of asphalt. Moreover, asphalt surfaces approximately 94% of the 2.7 million miles of paved roads in the U.S. today (Federal Highway Administration, 2020).
However, the widespread use of asphalt comes with significant environmental consequences.
Carbon Emissions
The production of 400 million tons of asphalt generates approximately 24 million metric tons of CO2 emissions annually. This is equivalent to the annual emissions from about 5.2 million passenger vehicles or the CO2 emitted by consuming 2.7 billion gallons of gasoline (EPA, 2021).
Maintenance and Additional Emissions
In cities like Los Angeles, the environmental impact is magnified. The city's annual asphalt maintenance alone requires about 3.55 million tons of asphalt, producing around 213,000 metric tons of CO2 annually. This accounts for roughly 1.5% of the city’s transportation-related carbon emissions (California Air Resources Board, 2020).
Urban Heat Island Effect and Energy Consumption
Asphalt also plays a major role in the urban heat island effect, which raises local temperatures by 1 to 7°F compared to surrounding rural areas. In Los Angeles, where asphalt covers approximately 24% of the total land area, this effect is particularly pronounced (Los Angeles Bureau of Street Services, 2019). On a hot summer day, with an estimated 4°F increase due to this effect, energy consumption for cooling can spike by around 28% (U.S. Department of Energy, 2018).
Impermeability and Stormwater Management
The impermeable nature of asphalt surfaces significantly affects stormwater management. For instance, a typical 1-inch rainfall event in Los Angeles generates about 4.8 billion gallons of runoff from these surfaces (Los Angeles Department of Water and Power, 2015). To visualize this, it's equivalent to about 7,273 Olympic-sized swimming pools or roughly one-seventh the volume of Lake Tahoe. This excess runoff overwhelms urban drainage systems, contributing to flooding and water pollution (EPA, 2021).
Options for Sustainable Asphalt
Given these environmental challenges, the construction industry is actively seeking more sustainable alternatives to traditional asphalt.
Warm-Mix Asphalt (WMA): This technology reduces production temperatures, cutting fuel consumption by 20-35% and lowering greenhouse gas emissions by 15-30% (Federal Highway Administration, 2018).
Porous Asphalt: Porous asphalt allows water to infiltrate through the pavement, reducing surface runoff by up to 80% compared to traditional pavements (National Asphalt Pavement Association, 2020).
Rubberized Asphalt: By incorporating recycled rubber from used tires, rubberized asphalt extends the lifespan of road surfaces by up to 50% and reduces road noise by up to 12 decibels (Federal Highway Administration, 2019).
These innovations are crucial as they address the multifaceted environmental challenges posed by traditional asphalt, including carbon emissions, heat absorption, and stormwater management. As urbanization continues and climate concerns intensify, the development and adoption of these sustainable asphalt technologies will play an essential role in building more environmentally friendly infrastructure.
References:
American Society of Civil Engineers, 2015. This Week in Infrastructure History. [online] Available at: https://www.infrastructurereportcard.org/this-week-in-infrastructure-history/ [Accessed 10 September 2023].
California Air Resources Board, 2020. California Greenhouse Gas Emissions for 2000 to 2018. [online] Available at: https://ww2.arb.ca.gov/ghg-inventory-data [Accessed 10 September 2023].
Environmental Protection Agency (EPA), 2021. Greenhouse Gas Equivalencies Calculator. [online] Available at: https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator [Accessed 10 September 2023].
Federal Highway Administration, 2018. Warm Mix Asphalt Technologies. [online] Available at: https://www.fhwa.dot.gov/pavement/asphalt/wma.cfm [Accessed 10 September 2023].
Federal Highway Administration, 2019. User Guidelines for Waste and Byproduct Materials in Pavement Construction. [online] Available at: https://www.fhwa.dot.gov/publications/research/infrastructure/structures/97148/rcy1.cfm [Accessed 10 September 2023].
Federal Highway Administration, 2020. Highway Statistics 2019. [online] Available at: https://www.fhwa.dot.gov/policyinformation/statistics/2019/ [Accessed 10 September 2023].
Los Angeles Bureau of Street Services, 2019. Urban Heat Island Effect Study. [online] Available at: https://streetsla.lacity.org/urban-heat-island-effect [Accessed 10 September 2023].
Los Angeles Department of Water and Power, 2015. Stormwater Capture Master Plan. [online] Available at: https://www.ladwp.com/ladwp/faces/ladwp/aboutus/a-water/a-w-sourcesofsupply/a-w-sos-stormwatercapture [Accessed 10 September 2023].
National Asphalt Pavement Association, 2020. Porous Asphalt Pavements. [online] Available at: https://www.asphaltpavement.org/expertise/sustainability/water-quality/porous-asphalt [Accessed 10 September 2023].
National Asphalt Pavement Association, 2021. Annual Asphalt Pavement Industry Survey. [online] Available at: https://www.asphaltpavement.org/expertise/engineering/annual-asphalt-pavement-industry-survey [Accessed 10 September 2023].
National Asphalt Pavement Association, 2022. History of Asphalt. [online] Available at: https://www.asphaltpavement.org/about/history-of-asphalt [Accessed 10 September 2023].
The Asphalt Institute, 2021. History of Asphalt. [online] Available at: https://www.asphaltinstitute.org/engineering/history-of-asphalt/ [Accessed 10 September 2023].
U.S. Department of Energy, 2018. Impact of Urban Heat Islands on Energy Consumption. [online] Available at: https://www.energy.gov/eere/buildings/articles/impact-urban-heat-islands-energy-consumption [Accessed 10 September 2023].