How Does Asphalt Milling Work?
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How Does Asphalt Milling Work?
Asphalt milling is a process in which asphalt pavement is broken up into small pieces called “asphalt millings”. This process is used for several reasons including recycling asphalt pavement, preparing an area for new pavement, removing weeds, and making topsoil.
In asphalt milling, an asphalt plant mixes aggregate (usually crushed stone) with hot bitumen (asphalt emulsion), and then applies this mixture to road surfaces using a paving machine. The asphalt milling machine breaks asphalt structures down into smaller particles that can be spread on the surface of the roadway. In some cases, the asphalt milling machines are also equipped with vibrating screens or other devices that remove weeds from the milled material before it is applied to the road.
The Benefit Of Asphalt Milling
Asphalt milling has many benefits. It creates a smooth, durable road surface that lasts longer than traditional materials such as gravel and concrete. Because asphalt is more expensive than gravel or concrete, it makes sense to reuse old asphalt roads rather than replacing them with fresh asphalt every few years.
The following are additional advantages of asphalt milling:
• It reduces noise pollution by reducing traffic sounds.
• It improves air quality because fewer cars will need to use their brakes.
• It is an affordable solution because it reduces fuel consumption by eliminating the need for frequent repairs.
• It eliminates surface irregularities and provides a smoother ride for pedestrians and bicyclists.
• It allows drivers to travel at higher speeds without causing damage to paved surfaces.
• It eliminates potholes and ruts depending on the depth of asphalt layers.
• It prevents erosion and protects against water runoff even during harsh winters.
Asphalt Milling Processes
There are two basic types of asphalt milling processes: cold-mix and hot-mix. Cold-mix asphalt is mixed in a batch mixer and transported to the job site. Hot-mix asphalt is mixed onsite and applied directly to the road. Both methods have pros and cons.
Cold-Mix Asphalt Milling
Cold-mix asphalt is mixed at the asphalt plant and stored in large tanks until it is ready to be transported to the job site where it is applied to the existing road surface. Once the asphalt reaches its destination, the milling machine spreads the material across the road surface.
Pros
• Less equipment needed.
• Allows for quick response times.
Cons
• May require multiple trucks to transport the millings to the job site.
• Requires mixing asphalt at the asphalt plant.
Hot-Mix Asphalt Miling
Hot-mix asphalt is mixed right at the job site. A truck pulls up to the work site carrying all of the necessary ingredients for the asphalt mix. The asphalt specialist opens the tailgate of the truck and dumps the contents onto the ground. He then uses a shovel to mix the asphalt together. After the asphalt is properly mixed, he loads the finished product back into the truck and drives away.
Pros
• No waiting time.
• Minimal disruption to traffic flow.
• Avoids complex asphalt milling process
Cons
• More expensive than cold-mix milled asphalt.
• May require special permits if the project involves construction over wetlands or bodies of water.
Components of an Asphalt Mixture
Asphalt from scratch is made up of three components: aggregate, binder, and additives. Aggregate is the largest component of any asphalt mixture. It consists of stones, sand, rock, etc., which provide strength and durability to the road. Binders are the glue that holds the aggregate together. They include asphalt cement, natural rubber, synthetic rubbers, and petroleum products. Additives improve the properties of the asphalt mixture. These may include fillers, stabilizers, de-icers, anti-skid agents, and sealants.
Recycled Asphalt as Base for Parking Lots
In recent years, recycled asphalt pavement (RAP) has become increasingly popular as a stable base material for parking lots. Recycled material is an attractive alternative to a conventional base slab because it does not contain silica sand, which can cause allergies in some people. In addition, RAP requires less maintenance than a traditional and complete asphalt reconstruction project.
The process begins with the removal and collection of old or excess asphalt from streets and other existing structures, like private roads or surfaces that have obtained damage from accidents. This material is crushed and screened in a recycling facility to remove rocks and other debris. Then, the recycled product is heated to about 200 degrees Fahrenheit. Next, it is combined with recycled tires and other materials to make a new asphalt mixture. Finally, this mixture is laid down by professional contractors on top of a subbase.
The advantages of using RAP include lower costs, improved performance, and reduced environmental impact. However, there are disadvantages associated with the use of RAP. For example, recycled asphalt contains more moisture than conventional asphalt. If the pavement dries out too much during the winter months, cracks will form in the pavement. Also, the higher temperature required to execute the recycling processes makes it harder to apply, especially when temperatures drop below freezing.
Pavement Restorations
A pavement restoration is a repair of the existing pavement. Most often, such asphalt paving services involve replacing damaged sections of pavement. There are two types of pavement restorations: patching and resurfacing. Patching involves repairing small holes and cracks with hot-mixed asphalt. Asphalt resurfacing involves removing the entire surface of the pavement and laying down a fresh layer of asphalt.
Patch Paving
Patch paving is used to repair minor potholes and other defects during the asphalt restoration process. To perform patch paving, the contractor first removes the defective section of pavement. Then he lays down a thin layer of hot-mixed asphalt to cover the hole and surrounding area. Once the patching has been completed, the contractor coats the patched area with a thick coat of cold-mix asphalt to protect the patch from further damage.
Resurfacing
Resurfacing is performed when a large portion of the pavement needs to be replaced. The contractor cuts away the old pavement and then installs a new layer of asphalt over the entire surface. A special machine called a miller is used to grind away the old pavement. After grinding, the miller spreads the ground material evenly across the new pavement.
Asphalt Pavement Alternatives
Concrete
Concrete is a common alternative for paving. A concrete slab is durable and long-lasting. Unfortunately, concrete pavement is expensive to install and maintain. Because concrete is so heavy, it must be reinforced with steel or other metal bars before being installed. These reinforcing bars add weight and cost to the project.
Another disadvantage of concrete pavement is that it cannot absorb heat like asphalt pavement. When it gets very hot, concrete becomes brittle and crackles underfoot.
Cementitious Surfaces
Cementitious surfaces are another type of alternative to asphalt pavement. They can be made from natural stone such as granite or limestone, or they can be manufactured by mixing cement with sand and gravel. Cementitious surfaces are usually lighter than concrete and less costly to make. Like concrete, cementitious surfaces also have their drawbacks. One problem with cementitious surfaces is that they do not last as long as asphalt pavement. Another drawback is that they tend to crack if they get wet.
Other Materials
There are many other materials that can be used instead of asphalt for making pavements. Some examples include wood chips, rubberized asphalt, and crushed stone. Each of these materials has its own set of pros and cons. Wood chip pavements are inexpensive but they are susceptible to rotting. Rubberized asphalt is more durable than wood chips but it is much more expensive to produce. Crushed stone is strong and durable but it is difficult to spread on roads because it tends to clump together.