When considering how cars and trucks produce such a large part of the world\'s greenhouse gas pollution, it\'s easy to ignore what\'s underneath them.
But there are roads under all the traffic.
Paving material itself
Asphalt, concrete and rock
How it is placed has an important impact on the atmosphere.
Whether it is made of asphalt, concrete, or even gravel, energy is put into the construction of each road and sidewalk;
Whether it\'s a narrow ribbon that winds through the mountains, an endless flat strip through the grasslands, or a crowded highway.
In addition, the way roads are built and maintained has a great impact on the energy consumed by vehiclesor crawl-on the surface.
When governments consider spending money to restore or expand existing roads in developed countries and build new roads in the developing world, their question is sustainability that has never been considered in the early days of infrastructure construction --out.
The answer is not easy.
S. and European public investment in road, street and bridge construction is about $190 billion per year, and researchers are working to develop a method for decision makers to choose road construction, every step of the road\'s long life cycle takes energy into account.
The asphalt and concrete industry is introducing new technologies and collecting evidence of old technologies, all of which show their commitment to making roads greener.
Of course, road construction is widely regarded as the opposite of sustainable activities, as Song author Joni Mitchell lamented when writing memorable lyrics, \"They paved heaven, \"At the dawn of the modern environmental movement, we built a parking lot.
But a branch of environmental science today is dedicated to paying closer attention to the sidewalk itself.
These scientists believe that as long as society relies on roads to transport goods and personnel, government officials should have data to make design and construction decisions that minimize the impact on land and air. (
They noted that the same problem exists with railways, canals, airports and any other transportation infrastructure. )
When it comes to roads, the fact is hard to figure out because of the two competing industries that make pavement materials --
Manufacturers of asphalt and concrete
As a sustainable choice, everyone has a lot of evidence to prove the value of their respective products.
Asphalt, also known as asphalt, is an oil product, but the industry is quick to point out that it makes fewer greenhouse gases than cement production releases, characteristic adhesive materials for concrete, due to the carbon intensity in the cement kiln manufacturing process. (
Nearly a ton of carbon dioxide (CO2)
Every ton of cement produced in the United States will be discharged. )(
Related: \"new chemistry, less energy can produce more green cement \")
Asphalt is certainly a more visible Road.
Building materials, accounting for more than 90% of the surface.
5 million miles (
Paved roads in the United States and 3.
2 million miles (5.
2 million)in Europe.
But concrete is often in the road structure below, and public transport officials are looking for a long-term
Long lasting surfaces often choose concrete.
Advocates in the industry stress that the durability of concrete in the long run means less energy needed for raw materials and repairs.
But John Harvey, chief researcher at the University of California\'s Pavement Research Center, said \"asphalt and concrete\" is the wrong way to look at environmental problems around the road.
What is often forgotten in debates, he says, is that no matter which glue sticks the pavement together, more than 90% of the pavement is rock.
\"We need to remember that rocks are the main ingredients, so there is tremendous energy going into the mining, crushing and transportation of rocks in the material production phase of the roadway, said Harvey, professor of civil and environmental engineering.
The centers of the University of California, Berkeley and Davis are working to develop a framework and model to help government officials make better decisions about the road, taking into account these long life cycles
Civil engineering projects.
For example, he said such a life cycle assessment (LCA)
Helps highlight the benefits of using recycled materials when rebuilding roads.
\"Like oil, rocks are a limited resource, and many of our best rocks are on the road now,\" Harvey said . \".
Any driver trapped behind the milling machine
sees the road recycling working.
When roads are renovated or re-laid, these milling machines crush, remove and crush existing roads to make the product known as recycled concrete aggregates (RCA)
Or recycled asphalt pavement (RAP).
By using recycled aggregates for pavement, road builders save energy for mining and transporting raw rocks, Harvey said.
In life cycle analysis, the energy consumed in transporting raw rock and recycled materials should be considered so that road builders can consider the maximum energy
This is an efficient choice, Harvey said.
Many of the original rock quarries and some sources of recycled materials are far away from the population center of road construction, so recycling materials from existing roads to the same section eliminates all the energy to transport these heavy objects.
If this on-site recycling is not possible, it has become increasingly popular to import recycled materials and raw materials into aggregates --
Urban areas of low hunger
Energy barges, usually hundreds of miles away.
For a long time, the concrete industry has been promoting its road surface as \"100% recyclable;
\"It says recycling goes back to 1940 in Europe and 1970 in the United States.
The asphalt industry also has a high record in recycling. The U. S.
At present, the industry produces about 0. 4 billion tons of new asphalt paving every year and recycles about 73 million tons in 2010.
In fact, all of this rap music is recycled onto the sidewalk, which industry insiders point out is its highest and best use.
Now, due to an important development of green pavement: \"Warm Mix\", the use of recycled materials in asphalt pavement can be greatly increased.
\"Hot mix asphalt must be heated to 300 degrees F (150° C)
Or more in order to be feasible during mixing, laying and compaction.
However, by introducing water into the asphalt mixture with additives such as foamer or wax, asphalt manufacturers have found that they can reduce the temperature of the mixture by 50 ° to 100 °F (30 to 60°C)
While providing roads
Surface media with the same properties as hot mixing.
Warm-mix asphalt was first introduced in Europe, and then in the United States less than a decade ago, warm-mix asphalt became more and more popular. The U. S.
National Association of asphalt pavement (NAPA)
An industry organization said that the United States is now leading the world in production, from less than 100,000 tons in 2004 to about 47 million tons in 2010.
The industry group expects market share to soon be well above its current 11%.
\"A warm mix can reduce factory emissions, provide construction benefits for workers and provide more comfort.
Howard Mark, director of environmental and regulatory affairs at Napa, said: \"All of this stuff is rolling out the technology together . \".
\"Now, as the cost of fuel increases, contractors will see this as a competitive advantage for them, because it does take less fuel to use a warm mixture.
John Reid, Shell Oil\'s global asphalt technology manager, said lowering the temperature of the asphalt mixture has long been considered an ideal goal for the industry, but the challenge is huge.
Shell engineers believe that the idea of emulsion is promising to cool the hot mixture
Break the asphalt into particles suspended in water with lotion or soap.
The paving industry has long used asphalt emulsion in some applications
A closed road or lane, or a new look.
However, the risk of actually making the asphalt mixture with the emulsion is that when the asphalt is pressed in real time during the paving process, the water is trapped.
The road is too soft to rust.
Researchers at Shell have developed
Called the phase mixing solution of the WAM foam process, during which the hard asphalt component is steamed into a soft asphalt component.
The result is a mid-range mixture that is as effective as a traditional hot asphalt mixture, but the temperature is much lower: about 230 degrees Fahrenheit (110° C)
Reduce by about 70 degrees Fahrenheit (40°C).
Shell said energy consumption and carbon emissions during the mixing and paving process were reduced by about 35%.
But there is also a simpler foaming technique that does not require any modification to the mixing device in addition to adding nozzles to bring water into the mixture.
Admittedly, these can be very professional at times;
The two-barrel green system developed by Astec industrial company in Chattanooga, Tennessee relies on more
Nozzle foaming device controlled by computer, used to adjust the speed and production.
Other manufacturers rely on additives to reduce the temperature.
PQ, a special chemical manufacturer based outside Philadelphia, has a synthetic zeolite on the market-
A mineral containing water.
Water is time-
Release when the asphalt mixture is heated, resulting in a controlled foaming effect.
Sasobit, produced by a Department of South African oil company Sasol, uses paraffin additives to reduce temperature. (It is a by-
Sasol uses coal to produce diesel products in South Africa. )(
Both technologies were used in the iconic application of 20,000 tons of warm mix in Yellowstone National Park in 2007, a project to help build the United StatesS.
Government support for cooler road laying programs. )
There are a total of more than 20 technologies and numerous brands to choose from.
For some, the cost has increased, but for others now the cost is about the same as the traditional hot mix, Napa said. The U. S.
The Federal Highway Administration says fuel consumption is typically reduced by 20% in all technologies, and there is a significant reduction in smoke and multi-ring aromatic hydrocarbons exposed to road workers (PAHs.
It is important that the various properties of the warm mixture
Including it improves the ability of the coating
A higher proportion of recycled asphalt is allowed to be incorporated into the road surface.
This further reduces energy consumption and carbon emissions as there is a decrease in demand for the extraction and transportation of raw rocks.
Germany even conducted on-site testing of warm-mix asphalt 100% M from recycled asphalt pavement.
Shell said the biggest demand for its WAM foam products is in countries that have already taken action on carbon emissions.
The company did not have a WAM foam permit in Switzerland until the state passed penalties for carbon dioxide emissions;
Reid said the company received eight licensees in a few months.
\"When we started in 1995, if we were really honest, it wasn\'t about carbon dioxide,\" Reid said . \".
\"This is to improve the experience of the workers.
But reducing carbon dioxide is a consequence.
At the same time, manufacturers of concrete pavement have also taken measures to reduce the carbon footprint.
Industry insiders pointed out that the United StatesS.
Since 1972, cement manufacturers have increased energy efficiency by 33% and have pledged to reduce carbon dioxide emissions by 10% by 1990 from 2020 levels.
Concrete manufacturers also improve their environmental conditions by using cement substitutes as adhesives, including fly ash and slag generated when burning coal in power plants, remnants of the steel industry.
These waste products can be recycled into concrete, replacing half of the cement content and reducing the demand for carbon.
Reinforced cement manufacturing.
According to the United States, the use of fly ash also increases the ease of the road surface, even while increasing the strength of the road surface and reducing water consumptionS.
Federal Highway Administration
Back to 1974, the United StatesS.
Governments encourage countries to replace cement with fly ash when feasible.
Harvey says the California Department of Transport requires that most of the concrete used for sidewalks contain 25% of fly ash. (
Related article: \"seeking a safer future for volcanic ash waste from electric power \")
But Harvey believes that if road builders take into account the energy impact of the entire life cycle of the road, warm mix fuel savings and a reduction in cement manufacturing and carbon dioxide emissions from concrete mean more on some roads than on others.
For highways that carry a lot of traffic, compared to the oil burned by cars, trucks and buses driving on the road every day, the fuel consumed by road construction is negligible.
The way roads are built has an important impact on the amount of fuel consumed by these vehicles.
\"When your vehicle is rolling, if it goes through roughness, roughness affects shock absorbers and tires, they are basically energy-hungry,\" Harvey explains, \"they actually get hot, eliminate bumps.
\"Due to the impact of the road surface on the fuel economy of the vehicle, the researchers continue to explore other aspects of the road surface, including the concrete industry\'s argument that its harder surface reduces rolling resistance.
But Harvey says the scientific consensus is clear in terms of fluency.
Studies have shown that driving on smooth roads means a 2-5% increase in fuel economy compared to rough roads.
\"These proportions are small, but when we talk to people who manage the greenhouse gas strategy, we find these numbers to be big,\" Harvey said . \".
\"One interesting thing about improving the flatness of the road surface is that it affects every car on the road and it happens immediately.
\"As for the warm asphalt, Harvey believes that the most important thing may not be the energy saving of the asphalt plant, but to help the road stay unblocked for a longer period of time, and the data seems to indicate that it is more efficient to compress the specific heat asphalt mixture.
The concrete pavement industry is keenly aware of carbon
The strength comparison focuses only on the manufacture of the road surface, not on the service life of the road surface, and believes that if the decision maker holds a longer view, its benefits will become more obvious.
Most concrete pavement is designed for 20 years, typically for 25 years or more, with no major repairs or repairs, the industry said.
The asphalt industry said its survey showed that the transportation sector repaired the asphalt surface on average after 15 years, although the underlying structure could be designed to be as long as the concrete pavement. \"[
Traffic community has]
When we talk about sustainability, we focus almost exclusively on the construction and production phases of this infrastructure lifecycle, \"said Leif Wathne, a professional engineer and vice president of Road and federal affairs at the American Association for concrete pavement.
This is natural.
Engineers focus on what they can control.
But our argument is that, as a traffic community, we may inadvertently ignore some of the important opportunities in the use phase of the road life cycle.
But Harvey stressed that neither concrete nor asphalt is the winner of smoothness.
As he said, both types of pavement can be \"naturally rough\" if you do not pay attention to producing a smooth surface during the laying process.
In later life, if the joints between concrete slabs are uneven, the concrete pavement may create bumps.
The old asphalt is easy to create friction over time.
All materials expand and shrink in the cold and are under pressure from heavy trucks, resulting in cracks and kerbs for each driver, potholes.
Ironically, that\'s why Harvey and other road researchers believe that policymakers who are weighing how to reduce carbon emissions should consider road investment --
At the very least, in terms of updating and maintaining the current infrastructure to eliminate bumps that cause cars and trucks to burn more fuel than they need.
Harvey and his researchers will urge smooth processing of existing road networks before building new roads, which requires additional maintenance.
There is no doubt that the sidewalk industry is also urging more investment in roads.
Their request is usually to expand the system, but they, like industry-independent road Sustainability researchers, also advocate the restoration and protection of existing infrastructure.
In fact, the government has neither kept up with the pace of road maintenance nor eased congestion.
Adjusted for inflation, US Highway spending per mile has fallen by 50% since the 1950 s, and estimates the gap between spending and road demand (pdf)
It ranges from $47 billion to $166 billion a year.
Ironically, these costs increase as rehabilitation is delayed and repair work becomes more difficult and expensive.
At the very least, the asphalt and concrete industry agrees that more attention needs to be paid to roads.
\"The cost of doing nothing is far greater than meaningful and sustainable capacity expansion,\" said Wathne of the concrete pavement Association . \".
Mark of the Asphalt Association said, \"We have to make the public aware of how important this is.
That\'s how our economy works.
So far, we can only ship things, so far we can only take the railway.
They have to go on the road.
\"This story is part of a special series to explore energy issues.
For more, please visit the huge energy challenges.
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