Demystifying the Environmental Impact and Sustainability of Asphalt Plants
Understanding what happens behind the gates at an asphalt plant can dispel many misconceptions. This article explores the inner workings of asphalt plants, looking at their environmental and community impacts, and the regulations governing their operations across the globe.
Global Regulation and Oversight
Asphalt plants, more accurately termed asphalt pavement mixing facilities, are industrial sites where liquid asphalt binder (also known as asphalt cement or bitumen) is mixed with crushed rock, gravel, and sand (collectively called aggregates) to create pavement. Asphalt binder, a product of the oil refining process, acts as the glue binding the aggregates. Occasionally, additives such as performance-enhancing chemicals or natural fibres are included to strengthen specific mixes.
Around the world, asphalt pavement mixing facilities are regulated by various national and regional environmental agencies. These facilities employ multiple emission control systems, and the small amount of emissions they produce is closely monitored to ensure they remain well below the permitted levels. This stringent oversight guarantees that emissions do not pose health or environmental risks to nearby communities.
Emissions — Very Low and Getting Lower
Most emissions at asphalt mixing facilities arise from the combustion of fuel, such as natural gas, used to dry and heat the aggregate and maintain the asphalt’s temperature. Potential emissions, such as dust generated during aggregate drying, are captured by baghouse filters or similar controls, preventing their release into the environment.
Occasionally, visible emissions from an asphalt plant’s stack may simply be steam — water vapour from the drying aggregate. While odours from heated materials can emanate from an asphalt plant, they are harmless and pose no danger to plant personnel or surrounding communities. A noticeable odour doesn’t indicate a health hazard; many natural and man-made odours are perceptible but not harmful.
Studies across various countries have highlighted that the low annual emissions from an asphalt plant are comparable to, or below, those from common community and industrial sources.
Over the past few decades, the asphalt pavement industry has documented significant reductions in total stack emissions while increasing pavement production. Technological advances have further reduced energy requirements and expanded the use of recycled materials in asphalt pavements, significantly lowering their carbon footprint.
The Carbon Footprint of Asphalt Pavements
Asphalt pavements have a notably small carbon footprint compared to other pavement materials. Globally, the industry’s commitment to sustainability and innovation has led to significant environmental benefits.
Many countries recognise asphalt as a top material for sequestering carbon.
Not All Asphalt Is the Same
It’s essential to differentiate between various asphalt products. Asphalt or Bitumen can refer to multiple products with different components and uses. Asphalt pavement material (or asphalt concrete) differs significantly from roofing asphalt and is unrelated to coal tar. These materials’ varied components, properties, and usage temperatures result in different emission potentials.
The asphalt pavement industry has invested decades in advancing technology to reduce production temperatures, thereby minimising emissions.
100% Recyclable and Inert
Asphalt pavement is the most recycled material globally. It can be reused in new asphalt pavement mixes, with recycled or reclaimed asphalt pavement (RAP) containing old asphalt binder and aggregates that replace virgin materials. The old asphalt binder reactivates, reducing the need for new binder, and the old aggregate becomes part of the new pavement.
Each year, millions of tons of asphalt pavement is reclaimed, with the majority being reused or recycled. Asphalt’s inert nature means no materials leach from the pavement itself, as it’s waterproof. Drinking water reservoirs and fish hatcheries often use asphalt for lining due to its inert properties. While vehicle emissions like grease and oil may deposit on roadways, emissions and leachate from RAP stockpiles are practically non-existent.
Many countries acknowledge that RAP piles are unlikely to cause fugitive dust problems and can help reduce dust from unpaved roads. Numerous studies have confirmed that leachate or runoff from RAP storage is not an issue, and RAP is commonly used as clean fill material in highway construction.
Besides reclaimed asphalt pavements, materials from other industries, such as rubber from used tyres, glass, asphalt roofing shingles, and blast furnace slag, are routinely recycled into asphalt pavements. This recycling conserves millions of barrels of liquid asphalt binder annually.
Busy Places and Controlled Traffic
Although asphalt plants occupy a relatively small amount of real estate, they are bustling hubs of activity. From the street, one might see large silos for storing finished pavement material, substantial environmental-control equipment for filtering stack emissions, and stockpiles of raw materials like sand, rocks, reclaimed asphalt pavement, and other recycled materials.
Asphalt plants also house tanks storing both fuel and liquid asphalt. Environmental agencies across the globe closely regulate these tanks to prevent rupture and ensure robust protection systems and safeguards are in place to prevent any discharge in the unlikely event of a leak.
Key pieces of equipment include the aggregate dryer drum, which warms and removes moisture from the aggregate before mixing it in a large mill. The finished pavement material is then stored in on-site silos before being loaded into trucks for transport to job sites.
During peak construction seasons, particularly in summer, truck traffic to and from asphalt plants can be heavy. To ensure the asphalt mix reaches paving sites at the correct temperature, plants and paving companies carefully manage truck traffic to minimise delays. Proximity to roadway work sites also influences the location of new or temporary plants.
Asphalt Plants Benefit the Community
Asphalt plants are often integral parts of their communities, providing local employment opportunities and frequently contributing to community events through volunteer work and financial donations.
Many asphalt plants are family-owned and -operated, having been key community members for decades.
Essential to Global Infrastructure
Asphalt pavements have been produced since the late 1800s, with naturally occurring asphalt used for waterproofing for thousands of years. Asphalt plants are crucial links in global transportation infrastructure. Today, a significant percentage of the world’s paved streets and highways are surfaced with asphalt due to its smoothness, cost-effectiveness, durability, environmental friendliness, and recyclability.
Asphalt pavements support multiple forms of transportation, including walking trails, cycle tracks, bus rapid transit lanes, and airport runways. Specialty pavement mixes, such as porous asphalt, are vital for stormwater management.
The Facts About Asphalt Plants
The asphalt pavement industry has a long history of collaboration with regulatory authorities and agencies worldwide to develop and promote innovations enhancing the sustainability of asphalt pavements, improving worker safety, protecting the environment, and saving money.
Many thousands of asphalt plants operate globally, supporting a significant number of jobs that cannot be outsourced. With a large percentage of paved roads surfaced with asphalt, this precisely engineered product comprises aggregates (stone, sand, and gravel) and asphalt cement, a petroleum product.
Asphalt plants are rigorously regulated by environmental agencies to ensure they do not pose major pollution threats. Asphalt is 100% reusable, making it one of the most reused and recycled products globally. Innovative control systems and manufacturing technology continue to reduce asphalt plant emissions.
Occasionally, odours may emanate from asphalt plants, but they pose no danger to plant personnel or surrounding communities. Recycling asphalt binder from old pavements and roofing shingles saves millions of barrels of oil annually, benefiting taxpayers and reducing environmental impact.
Understanding Asphalt Cement
Not all asphalt is created equal. Asphalt pavement differs from roofing asphalt and other asphalt products, each with unique components, properties, and usage temperatures, resulting in varied emission potentials. Asphalt cement is unrelated to coal tar.
Inert Nature of Asphalt
Asphalt is inert and doesn’t leach materials. Recycled or reclaimed asphalt pavement (RAP) shares this inert property. Storage silos and fuel tanks at asphalt plants are highly regulated to ensure maintenance and prevent accidental material release.
Asphalt Plants as Good Neighbours
Asphalt plants are good neighbours, and if concerns arise, contacting the plant owner or operator is the first step. These plants are active community members, contributing to local economies and events while ensuring sustainable and regulated operations.
In conclusion, understanding the true environmental impact of asphalt plants, their regulatory compliance, and their contributions to community and infrastructure development is crucial. Through global oversight, technological advancements, and a commitment to sustainability, the asphalt industry continues to play a vital role in modern society while maintaining minimal environmental impact.
