Asphalt and concrete pavements are traditionally divided into two general categories – flexible and rigid. While both rely on aggregate for structural strength, concrete has a stronger structure and distributes the load more widely and evenly. Paving involves a six-step process that includes demolition and removal of the old surface, grading and sloping that helps water drain away from the pavement, preparing the sub-base layer, adding the asphalt binder layer, and finally, the surface layer. Check out Paving Companies Summerville SC for more information.
In a world where we live in a throw-away culture, it’s nice to know that something as durable and useful as asphalt can last forever. It takes a little work to keep it that way, but the results are well worth it. A road designed with perpetual pavements can go decades without the need for major rehabilitation, which saves agencies and drivers time, money, materials, and energy.
The concept behind perpetual pavements is that, if the deep structural distresses that plague most pavement structures can be avoided by keeping tensile strains at the bottom and compressive strains on top of the subgrade below specific thresholds, then the life of a roadway can be extended to indefinitely with only periodic, routine maintenance. Such a system will not only extend the lifespan of the roadway, but also improve its ride quality and reduce fuel consumption for vehicles traversing its surface.
Perpetual pavements are constructed with multiple layers of durable asphalt, including a strong, flexible bottom layer that resists traffic-induced tensile strains and stops cracks from forming from the ground up. A strong intermediate layer adds additional structural protection and a final layer of rut-resistant HMA completes the structure, providing a safe, smooth, long-lasting, low-maintenance roadway for years to come.
HMA is a very versatile material, and it’s the primary ingredient in asphalt pavements, whether used on its own or mixed with recycled concrete aggregate (RCA) to create a reclaimed aggregate base for a new road. Perpetual pavements utilize a mix that incorporates a high percentage of reclaimed material, which helps preserve our natural resources by diverting materials from the landfill. In addition, the use of reclaimed material is environmentally responsible and cost-effective since it’s an economical and sustainable alternative to using brand-new raw materials.
The durability of asphalt is proven by the fact that it’s still in use on many major roads across the country, even after decades of heavy usage. And while some people may be under the impression that asphalt has a shorter lifespan than other types of roadways, they would be surprised to learn that low- and medium-volume truck traffic highways often last 30 or more years before needing rehabilitation, and high-volume truck traffic roads can go even longer.
Compaction
Asphalt paving is a multi-step process that requires constant monitoring and adjustment. Whether it’s the size of the paver, the type of material or the temperature of the asphalt mixture, even small changes can affect the overall outcome. Moreover, the various layers that make up an asphalt surface need to be compacted firmly to prevent rutting and fatigue. This is where a professional asphalt contractor’s expertise comes in handy.
The first step of laying asphalt is grading the site. This involves sloping the surface toward grassy areas so that water is channeled away from the new pavement and does not pool on it. Then a layer of sub-base is put down. This is a load-bearing, supporting layer made from aggregate materials such as crushed rock, sand or gravel. A binder is used to bind these aggregates together. Most commonly, bitumen is used as a binder but today there are a number of bio-based binders that are also being used in asphalt mixtures.
After the base is laid, any soft spots are identified and repaired. Then the asphalt itself is placed on top. This is the final layer of the roadway and it needs to be extremely tough in order to withstand heavy vehicle traffic and the harsh winter weather (depending on the location).
Before starting the paving process, it’s important for contractors to call the plant for updates on material delivery and laydown times. This information is critical as it allows them to determine the right amount of hot mix asphalt (HMA) to bring to the jobsite. It also helps them determine the number of trucks that will be required to transport it.
Once the HMA is delivered to the jobsite, it’s important for contractors to keep up with the paver in order to achieve target density. This requires a thorough understanding of how to operate the paver and the proper asphalt rolling patterns.
It’s also crucial to remember that compaction must be done as soon as possible after the asphalt is poured. Otherwise, the heat from the paved area will evaporate too quickly and cause the mixture to lose its strength. In addition, if the temperature of the mixture is too low, it can’t be compacted effectively.
Edge Work
Asphalt is a combination of aggregates, binder and filler used to construct and maintain roads, parking areas, railway tracks, airport runways, bicycle lanes and sidewalks. Aggregates are hard, inert material such as crushed stone, sand or gravel, that is mixed with the binding agent (bitumen) to form a cohesive mixture. Generally, the asphalt mixture is bound by bitumen, but some projects are using alternative petroleum-based binders in order to minimize environmental impact.
The most important factor in determining an asphalt pavement’s longevity is the condition of the ground it rests upon. Proper site preparation is the key to achieving this. This may include clearing, excavation, proper base materials and compaction. Without these factors the life of an asphalt pavement will be limited.
Asphalt pavements age quickly due to a number of influences that damage the physical bonding between the asphalt binder and the aggregate. These influences include oxygen, water and solar radiation that continually bathe the pavement surface. These forces cause the binder to deteriorate and eventually reduce the pavement to a layer of loose aggregates.
Many State highway agencies have discovered a new and clandestine use of recycled engine oil bottoms in their asphalt mixes. These reclaimed oil products are called REOB and are generally used to lower the cost of road construction and maintenance. However, the composition of REOB varies between producers and even between samples from the same producer on different days. REOB composition analysis is complex, but at TFHRC, researchers are planning to develop a simple test that could help verify the presence of REOB in asphalt mixes.
Skid resistance is the ability of a pavement to offer resistance to sliding or skidding of vehicles. This is usually measured by testing the surface of a paved section with a modified vane plate tester. The results provide a curve that illustrates the pavement’s ability to resist skidding. The curve is then compared to the minimum federal standard. A curve that falls below the minimum standard indicates poor skid resistance. This is an indication that the asphalt mix, paving process or subgrade is deficient.
Steel Trowel
The steel trowel is a key tool in asphalt paving. It is a flat blade that’s curved to a slightly upward angle, with beveled edges and an ergonomic handle. Its shape is designed to make it less likely to gouge the surface. The best trowels are also tempered evenly to normalize the metal and create uniform hardness. They can be made from stainless or carbon steel, though the latter is stronger and more flexible. Carbon steel is often used in plaster and concrete work. The trowel’s handle comes in several shapes and sizes, with camel-back handles allowing for more knuckle clearance. Some trowels are available with a textured grip, while others have a more resilient comfort-grip handle.
Quality control is essential in asphalt paving to ensure longevity and performance. In addition to ensuring all aggregate materials meet specific requirements, contractors must test each batch of asphalt before it is mixed. This allows them to detect contaminants that can impact the integrity of the pavement. The tests are conducted with a dynamic shear rheometer (DSR). The rheometer measures the stiffness of asphalt at different rates, enabling the researchers to identify contaminants and determine whether they are affecting the mix’s viscoelastic properties.
Asphalt consists of a mixture of binders, fillers, and aggregates. The fillers include sand and additives, while the binders are bitumen or liquid asphalt that holds the aggregates together. A high-quality asphalt mix contains 90 to 95% aggregates and sand, with 5 to 10% bitumen or asphalt. The mix is then heated to a temperature that melts the binder, so it’s ready to be placed.
After the sub-base layer is put down, workers lay the new asphalt surface. Then it’s rolled and compacted. It’s important to wait at least 24 hours before driving on the pavement, so it has time to cool and set. A proof roll is also put down to check for soft areas that aren’t strong enough to support vehicles.
Pavement surfaces can be damaged by many factors, from excessive wear and tear to poor drainage. In some cases, the problem can be solved by crack sealing. In other instances, the pavement may require full replacement. Keeping an eye out for signs of damage can prevent costly repairs and maintenance.
