Asphalt Milling:
How Does It Work?
You may have heard the term asphalt milling, but do you know what it is and how it works? Whether you have a parking lot that needs repair or you're sick of bottoming out your car when you exit your driveway, asphalt milling plays an important role whether you realize it or not. The information below will help you fill in the cracks, literally.
What Is Asphalt Milling?
Asphalt milling, also referred to as profiling, pavement milling, and cold planning, is the process used to remove all or part of a paved surface like a parking lot, bridge, or road, prior to installing new asphalt. Asphalt milling companies follow a complex process to ensure that pavement is built correctly.
During the preparation for the milling procedure, an asphalt maintenance company will remove the all or part of the pavement surface so it can be leveled and smoothed out. The amount of pavement removed generally depends upon the extent of the damage to the asphalt that is to be repaired.
Since pavement is an extremely hard surface, typically concrete or asphalt, a large piece of construction equipment (called a milling machine or cold planer) is required to bust up the surface. The pavement contractor then uses the machine to collect the broken pavement. Once milling is complete, the surface can be repaved with a new mix.
During the preparation for the milling procedure, an asphalt maintenance company will remove the all or part of the pavement surface so it can be leveled and smoothed out. The amount of pavement removed generally depends upon the extent of the damage to the asphalt that is to be repaired.
Since pavement is an extremely hard surface, typically concrete or asphalt, a large piece of construction equipment (called a milling machine or cold planer) is required to bust up the surface. The pavement contractor then uses the machine to collect the broken pavement. Once milling is complete, the surface can be repaved with a new mix.
Concrete vs. Asphalt Milling
According to the most recent national statistics released by the Federal Highway Administration, around 95% of United States highways are paved with asphalt. The use of asphalt is so popular, the National Pavement Association was created in 1955 to represent the interests of asphalt highway paving companies and asphalt manufacturers on a national level before Congress, national trade and business organizations, and government agencies.
Asphalt is the material of choice because it is less expensive to purchase and pour, asphalt repair and maintenance costs less, and asphalt is quieter to drive on. In addition, asphalt is recyclable, a huge plus as the nation attempts to move towards being more earth-friendly. Concrete can be recycled too, but is not done on such a large scale like asphalt recycling.
Asphalt is the material of choice because it is less expensive to purchase and pour, asphalt repair and maintenance costs less, and asphalt is quieter to drive on. In addition, asphalt is recyclable, a huge plus as the nation attempts to move towards being more earth-friendly. Concrete can be recycled too, but is not done on such a large scale like asphalt recycling.
Pavement Milling Machines | Cold PlaNers
The pavement milling machine has a large drum that rotates so that it grinds and removes the hard surface of the road so that the pavement can be repaired or replaced during road construction. The drum contains scrolls of tool holders that are situated around the drum so the pavement moves toward the center when it is ground. It is then loaded onto the conveyor belt. Since manholes and other extremely hard obstacles are often encountered during the milling process, it’s not unusual for the tool holders to wear out.
Carbide cutters are held into place by the tool holders that are located on the drum. They can be taken off and replaced as they wear out and due to the scope of work they perform, they wear out quickly - anywhere between a few days and a few hours.
A housing, or scrapper, encases a drum that contains the collected material that is then collected and deposited onto a conveyor.
Most of the milling machines used today are typically run with a front-loading conveyor set-up with the drum rotating in the opposite direction of the tracks or drive wheels because they are capable of retrieving any material that falls from the conveyor during the milling process.
The latest cold planers are able to control the profile, slopes, and depth by automatic depth controls that use sting-lines, lasers, and other methods to accurately measure the target height. Water is generally applied to the spinning drum in order to cool it off and to control the dust it creates.
Carbide cutters are held into place by the tool holders that are located on the drum. They can be taken off and replaced as they wear out and due to the scope of work they perform, they wear out quickly - anywhere between a few days and a few hours.
A housing, or scrapper, encases a drum that contains the collected material that is then collected and deposited onto a conveyor.
Most of the milling machines used today are typically run with a front-loading conveyor set-up with the drum rotating in the opposite direction of the tracks or drive wheels because they are capable of retrieving any material that falls from the conveyor during the milling process.
The latest cold planers are able to control the profile, slopes, and depth by automatic depth controls that use sting-lines, lasers, and other methods to accurately measure the target height. Water is generally applied to the spinning drum in order to cool it off and to control the dust it creates.
Cold Planer machine operation
It is imperative to operate a milling machine properly in order to achieve the best results. The process should begin by checking the cold planer machine to make sure it’s in excellent working condition. All machine and drum maintenance should be up to date and the leveling controls should be in proper working order.
Communication with other workers is vital. The entire crew needs to be in sync to ensure the project is completed correctly. A milling machine is a beast. The equipment can be very dangerous if it’s not operated safely.
The speed of the machine plays a key factor in the quality of the work. Above all, it is important to start slowly so the rear tires can walk into the cut so the hydraulic legs can adjust. Starting out too fast is likely to cause a dip. Stopping should be a slow process too, first implemented by slowing down gradually.
Some operators feel like going slow is a waste of money. Actually, it’s to the contrary. High-speed milling renders a poor job because it cuts an overly coarse pattern. It is hard on the machine too.
Communication with other workers is vital. The entire crew needs to be in sync to ensure the project is completed correctly. A milling machine is a beast. The equipment can be very dangerous if it’s not operated safely.
The speed of the machine plays a key factor in the quality of the work. Above all, it is important to start slowly so the rear tires can walk into the cut so the hydraulic legs can adjust. Starting out too fast is likely to cause a dip. Stopping should be a slow process too, first implemented by slowing down gradually.
Some operators feel like going slow is a waste of money. Actually, it’s to the contrary. High-speed milling renders a poor job because it cuts an overly coarse pattern. It is hard on the machine too.
When Is Asphalt Milling Necessary?
Asphalt milling is only possible when the sub base is intact. In the event that the damage is too extensive for milling, the pavement will have to undergo full demolition and then repaving.
There are several reasons that pavement milling is used to break up and remove existing pavement rather than just paving over the existing surface. Uneven slopes, raveling, and cracking are among the main problems that present issues that are too major to simply patch but are not large enough issues to warrant completely demolishing the area.
Distressed roads are a huge hazard. Potholes are a leading cause of accidents. Some of the main issues are due to damage from accidents, bleeding (where the binder comes through the road’s surface, raveling (separation of the aggregate of the asphalt), shoving (the ripples that flow in the direction that traffic runs), and rutting (low spot formations in the pavement). Milling allows an individual section of the road to be repaired in a relatively simple and inexpensive process.
A pavement company can use milling to address a specific problem that is present in a certain location. For instance, asphalt parking lot repair can be completed by milling the individual spot where a chug-hole exists without busting up, shutting off, and repaving the entire parking lot, saving tons of time and money.
Milling is also performed when the height of all or part of a road, bridge, or parking lot needs to be controlled or changed like if a slope becomes necessary for proper drainage or a shoulder is being added. Sometimes an asphalt driveway paving thickness needs to be altered to accommodate a change that has taken place on the property such as a new addition or renovation or for landscaping purposes.
There are several reasons that pavement milling is used to break up and remove existing pavement rather than just paving over the existing surface. Uneven slopes, raveling, and cracking are among the main problems that present issues that are too major to simply patch but are not large enough issues to warrant completely demolishing the area.
Distressed roads are a huge hazard. Potholes are a leading cause of accidents. Some of the main issues are due to damage from accidents, bleeding (where the binder comes through the road’s surface, raveling (separation of the aggregate of the asphalt), shoving (the ripples that flow in the direction that traffic runs), and rutting (low spot formations in the pavement). Milling allows an individual section of the road to be repaired in a relatively simple and inexpensive process.
A pavement company can use milling to address a specific problem that is present in a certain location. For instance, asphalt parking lot repair can be completed by milling the individual spot where a chug-hole exists without busting up, shutting off, and repaving the entire parking lot, saving tons of time and money.
Milling is also performed when the height of all or part of a road, bridge, or parking lot needs to be controlled or changed like if a slope becomes necessary for proper drainage or a shoulder is being added. Sometimes an asphalt driveway paving thickness needs to be altered to accommodate a change that has taken place on the property such as a new addition or renovation or for landscaping purposes.
Micro Milling
Micro milling is when only a small thickness of one inch or less of the existing pavement is removed before a surface treatment is placed on. Micro milling and cold milling are different in that micro milling produces a smoother surface than cold milling does. The technique is usually preformed before a micro-surfacing treatment or slurry seal. The reason micro milling is done is that it removes and oxidizes the old pavement and pavement treatments and provides a surface that is conducive to bonding, much like sanding does for a piece of wood.
Micro milling allows for an ultra-smooth ride. The edges near the gutters are clean and neat. It also provides optimal joining to a newly treated surface so that the transition is free of bumps or any discrepancies in leveling.
Micro milling allows for an ultra-smooth ride. The edges near the gutters are clean and neat. It also provides optimal joining to a newly treated surface so that the transition is free of bumps or any discrepancies in leveling.
Specialty Milling
Specialty milling is used for creating a specific effect, like a rumble strip on the shoulder of a highway. The use of specialty milling allows the product or effect to be added to the surface of the road as soon as it has hardened.
The roto milling head can be added to a milling machine to make slots in concrete that are used in dowel bar retrofitting. The process involves saw cutting and jackhammering the slots for the dowels and then the placement of them. After the slots are placed in, they are backfilled with a non-shrinking concrete mix and the pavement is restored to smoothness by a diamond-ground method. The availability of specialty milling cuts down greatly on labor expense and time.
The roto milling head can be added to a milling machine to make slots in concrete that are used in dowel bar retrofitting. The process involves saw cutting and jackhammering the slots for the dowels and then the placement of them. After the slots are placed in, they are backfilled with a non-shrinking concrete mix and the pavement is restored to smoothness by a diamond-ground method. The availability of specialty milling cuts down greatly on labor expense and time.
Pavement Milling Levels
When it comes to pavement milling, the Asphalt Recycling and Reclaiming Association has established five basic classes. The classes are as follows:
- Class I - milling that is performed in order to remove irregularities on the surface
- Class II - milling that is conducted to achieve uniform depth that is laid out on plans and specifications
- Class III - milling that is conducted to achieve uniform depth and cross scope that is laid out on plans and specifications
- Class IV - milling that is performed to the subgrade or base at the full depth
- Class V - milling that is complete to include different depths that take place at different locations
Asphalt Repair Process
Asphalt repair involves ripping up old asphalt, pulverizing the remaining materials, and stabilizing the surface. A large machine drives down the road and rips up any asphalt that still exists. That asphalt is then pulverized and mixed with tar and other binding and waterproofing agents to bind everything together. The mixture is then hardened for a day or two before it’s ready for us. Whether it’s a road, driveway, parking lot, or other project, it is officially complete with a minimal investment of time or money.
Recycling Asphalt Materials
The National Asphalt Pavement Association recently reported at asphalt is being recycled and reused at an astounding rate of more than 99%. The use of asphalt is trending, up by more than 148% since 2010.
The product that is produced from milling pavement is technically referred to as reclaimed asphalt pavement, or RAP. Recycling reclaimed asphalt pavement involves grinding it up and using it as the aggregate in a new mix of pavement. It is combined with asphalt cement as the binder or a recycling agent and is then ready to pour.
The practice of recycling and reusing asphalt caught on with asphalt repair companies in the 1970s. Petroleum, the chief aggregate of asphalt, reached all-time highs in cost and was not easy to obtain. The recycled asphalt product made projects much more affordable to complete during this time and when the economy fared better, the practice remained popular because companies could make more profit and because it was helpful to the environment.
In order to estimate the amount of recycled material an asphalt maintenance company will accumulate from a job, they often revert to an asphalt milling calculator, or asphalt material calculator that calculates the unit weight of asphalt in cubic feet, cubic yards, and even in tons. The asphalt material calculator can be used to estimate the amount of recycled asphalt that will be needed to complete a job too.
The product that is produced from milling pavement is technically referred to as reclaimed asphalt pavement, or RAP. Recycling reclaimed asphalt pavement involves grinding it up and using it as the aggregate in a new mix of pavement. It is combined with asphalt cement as the binder or a recycling agent and is then ready to pour.
The practice of recycling and reusing asphalt caught on with asphalt repair companies in the 1970s. Petroleum, the chief aggregate of asphalt, reached all-time highs in cost and was not easy to obtain. The recycled asphalt product made projects much more affordable to complete during this time and when the economy fared better, the practice remained popular because companies could make more profit and because it was helpful to the environment.
In order to estimate the amount of recycled material an asphalt maintenance company will accumulate from a job, they often revert to an asphalt milling calculator, or asphalt material calculator that calculates the unit weight of asphalt in cubic feet, cubic yards, and even in tons. The asphalt material calculator can be used to estimate the amount of recycled asphalt that will be needed to complete a job too.
Pavement milling is a necessary part of building, maintaining, and rebuilding roads, parking lots, and many other structures. Whether you are a professional pavement contractor or a homeowner with a potential project, the more you know about pavement milling, the wiser decisions you can make when planning and executing the process.
