If properly installed and maintained, asphalt pavement will last for more than a decade. On time maintenance is key to maximizing the pavement’s lifespan and performance. Important maintenance and repairs over time include investing in asphalt milling, an asphalt overlay or eventually full pavement replacement.
Property owners are frequently confused about what each of the three processes entails and when it is time to put them on the schedule. Here is a brief look at each of these asphalt services:
- Asphalt milling – During asphalt milling, the asphalt’s surface is milled down (pulverized) to a specified depth and replaced with a new surface course of hot mix asphalt.
- Asphalt overlay – An asphalt overlay is similar to asphalt milling, except that the existing pavement is not milled down first. Instead, the new surface course is rolled out directly onto the pavement’s surface.
- Full asphalt replacement – Compared to asphalt overlaying or milling, full asphalt replacement is a much more involved form of maintenance. During replacement, all of the asphalt’s layers are extracted and removed from the property. A new base is then installed, followed by several layers of asphalt and then the surface course.
What is Asphalt Milling and When is it Recommended?
During asphalt milling, the pavement team will use a special milling machine to grind down the top inch or two of asphalt. The milling machine is equipped with a steel rotary drum with teeth that breaks up the pavement’s surface and gives the team access to the pavement’s deeper layers. The milling machine can be calibrated to any depth, allowing for precision surface removal, without damaging the pavement’s deeper layers.
Once the asphalt’s surface is removed, the pavement team will assess the base’s condition and correct any issues. This could be deep cracks, subsidence, water intrusion or unstable soil. The goal is to fortify the pavement so that a new surface course of asphalt will not deteriorate early.
Following any base repairs, a layer of tack coat is applied to the pavement. This tack coat promotes better adhesion between the existing pavement and the new surface course. Once the tack coat cures, the new surface course of asphalt is installed and rolled out over the pavement.
Asphalt milling restores the pavement’s surface integrity and therefore extends its lifespan. Paving professionals typically recommended this service when the following signs emerge:
- The asphalt’s surface is worn or damaged, but the underlying pavement is stable – As a surface form of treatment, asphalt milling is intended to restore the pavement’s surface but is not ideal for resolving issues with its base. As long as the asphalt’s base is stable, milling its surface and installing a new top layer of asphalt will restore the pavement’s stability and performance.
- Overlaying would raise the pavement’s height too much – Without milling, an asphalt overlay will increase the asphalt’s height, which can cause drainage issues or interfere with driving performance. If the pavement’s surface needs to be restored, but the asphalt’s grade needs to remain the same, milling and overlaying is recommended.
- When the pavement’s drainage needs to be addressed – During asphalt milling, the pavement team can adjust the asphalt’s grade and fix any drainage issues. If water is pooling on its surface or if the pavement is showing signs of water-related deterioration, milling the asphalt first will be necessary to address any drainage problems caused by improper grading.
What is an Asphalt Overlay and When is it Needed?
An asphalt overlay is similar to asphalt milling and surface replacement, but in this instance, no milling is required. Instead, the new surface course is installed right over the existing surface. If necessary, the pavement team will perform spot repairs to improve the asphalt’s overall stability. This may include pothole patching, leveling out depressions and repairing severe cracks.
During an overlay, tack coat is applied to the existing asphalt surface to improve adhesion between asphalt layers and to reduce the likelihood of delamination. Once the tack coat is sprayed on the surface, a new layer of hot mix asphalt is installed over the top.
Asphalt overlaying is a moderate form of maintenance that can extend the pavement’s life and restore its surface integrity. It is typically recommended when:
- The surface is worn, but the pavement’s structure is otherwise intact – Asphalt overlaying is similar to asphalt milling in that it is only intended to resolve surface level issues like cracking, raveling, aggregate loss or discoloration. If the pavement’s base is still in stable condition, overlaying will improve the surface’s condition without affecting its base.
- The asphalt’s surface performance or ride quality needs to be improved – An overlay will restore the asphalt’s performance and smoothness, improving ride quality for motorists and reducing the risk of damage to vehicles.
- The pavement’s lifespan can be greatly extended in the process – If the pavement’s base is still in good condition, overlaying the asphalt will protect its stability and long-term durability, ensuring property owners get maximum value from their pavement investment.
What is Full Asphalt Replacement and What Does it Include?
Compared to an overlay or asphalt milling, full pavement replacement is an involved form of maintenance that goes beyond the surface. This is a full depth form of repair that replaces the pavement down to its base, and typically includes:
- Pavement removal – First, the existing asphalt pavement must be removed down to the base. This is typically done with milling machines and extractors. The removed asphalt may be reclaimed and used as stock for a new run of pavement.
- Base excavation – Base excavation is not always necessary, but it is if the base is saturated with water. It is also required if the subgrade soil is unstable or otherwise incapable of supporting the pavement and expected traffic. The base is removed using excavators.
- Subgrade stabilization and prep – Following base excavation, the exposed subgrade will likely need work in spots. This process includes regrading the soil, compacting it effectively, and adding lime or cement to improve stabilization. In some cases, geotextile or geogrid reinforcement may be necessary.
- Base installation – Once the subgrade is stabilized and ready to bear weight, a layer of crushed aggregate is installed over the prepared soil. This aggregate is designed to distribute weight from vehicle traffic, which preserves the asphalt’s condition. Most crushed aggregate is derived from limestone, basalt, granite or another type of durable stone.
- New asphalt installation – With the subgrade stabilized and the aggregate base in place, it is time to install the new subsurface and surface layers of asphalt. A layer of tack coat is sprayed down to act like a “glue” for the new asphalt, and the binder layer goes down first. This layer is structural and improves the pavement’s overall stability. The wearing, or surface course is installed over it and is responsible for taking on the abrasive and compressive wear resulting from vehicle traffic.
- Drainage installation and striping – Once the new asphalt is installed it is time to place the drainage structures, which include curb and gutter systems, catch basins, trench drains and culverts. Once drainage is built out, the new asphalt can be striped for use by traffic.
Talk to the Asphalt Experts to Determine Whether Your Asphalt Pavement Needs Milling, an Overlay or Full Replacement
The worst thing property owners can do when their asphalt is worn is ignore the damage. Delaying maintenance will increase the risk of total pavement failure, which will mean more extensive and more expensive repairs.
If your asphalt is noticeably worn, it needs some form of maintenance. However, it is not always obvious to determine which type of maintenance is required. A knowledgeable and trusted Houston pavement contractor can inspect and assess your asphalt’s condition, determine if any wear is structural and recommend the right type of maintenance to restore its condition.
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