A guide to preventive asphalt maintenance
The following information is provided to help you understand asphalt, its’ capabilities and how to maintain it.
Hot mix asphalt is a mixture of liquid asphalt cement, rock and sand. When the three ingredients are combined they will form a flexible, yet durable wear surface.
From the ground up:
Because the sub-base is generally a clay-based soil, which expands and contracts tremendously, the asphalt surface is at a disadvantage from the start.
In order to achieve the best results for a new asphalt surface, it is recommended that a sub-base of limestone base rock of at least four to eight inches in depth should be installed and thoroughly compacted prior to the asphalt installation. This sub-base will not flex as much as the soil and will allow water to drain through it on a consistent basis. The base rock will also provide the stable structural support for the asphalt surface.
Why asphalt fails:
There are three main factors as to why an asphalt surface will fail:
Water: Because asphalt is a porous material, it allows water to pass through it quite easily. This is from rain and more commonly from the irrigation systems used for the landscaping. Once the water starts to penetrate the asphalt, it will seep to the sub-base causing the sub-base to “soften” and become even more flexible. The asphalt surface can only flex so much and in time, it will crack. The greatest water problem is due to the freeze thaw cycles that take place each winter and spring. When water is frozen it will create 3200 P.S.I. This type of pressure will cause the asphalt to flex and break. Even worse is that this scenario occurs over and over each season.
Oxidation: When a new asphalt surface is installed it is very black in color. This is due to the high amount of liquid asphalt binder. In time however, asphalt will start to “gray out”. This is simply due to the sunlight and oxygen depleting the binder. It is very similar to a piece of metal that is unpainted. In time, it will rust and break down due to its lack of protection from the air.
Petro-chemicals: Fluids such as gas, oil and antifreeze will also break down the integrity of an asphalt surface. Because the asphalt is porous, these chemicals will also filtrate through the surface breaking down the liquid asphalt binder causing the failure of the surface.
Another important factor that will cause asphalt to fail on a commercial surface is weight. Trash trucks and Semi-trailers on a commercial parking lot are too heavy for the designed load of the asphalt. In most cases, the four to six inches of asphalt is designed solely for vehicle traffic. That is why you will see failure in front of trash dumpsters or along the curb where trucks will deliver their goods.
In summation, it is easy to see why asphalt is at a disadvantage from the start.
How long will it last?
According to the Asphalt Institute, a commercial parking lots life expectancy is thirteen to fifteen years before major renovation or replacement is needed. This scenario is based on proper base rock sub-grade being used.
Knowing what elements effect asphalt and how long it is intended to last and what can be done to get the most out of an asphalt surface.
The basic solutions for asphalt maintenance are: hot rubberized joint sealing (crack sealing), asphalt removal and replacement, asphalt seal coating, striping and fabric installation and overlay.
Water infiltration into the asphalt is the number one reason for its failure. As the asphalt surface flexes due to the freeze thaw, it cracks. A crack left unattended will eventually expand and branch out due to the continuation of the pavement failure. Once this scenario occurs you are faced with a condition commonly referred to as an “alligatored” area. The asphalt will look like a jigsaw puzzle with broken pieces.
The solution to limiting this condition is to crack seal when the crack is only a crack and not an alligatored area.
The best crack sealing material to use is a hot rubberized crack sealant meeting Federal Specifications ASTM-D-3405 or ASTM D-1190. The material is essentially a block of rubber that is heated to 360 degrees Fahrenheit and applied directly into the crack in a liquid state. Once in the crack, it will solidify into its original form. This material is used because it provides great flexibility (usually with flexibility to twenty degrees below zero) and will not track in the summer heat.
Applying the material requires a specific piece of equipment called a double jacketed boiler. This piece of equipment uses hot oil to circulate around a tank holding the material. The oil circulation avoids direct heat to the material in the tank thus providing a consistent temperature and product.
What can be crack sealed and what cannot? In order to achieve successful results in crack sealing, it is recommended that the crack be at least one quarter inch or wider to accept the crack sealing material.
Cracks less than one quarter inch (commonly referred to as “hair line” cracks) do not have enough width and depth to support the crack sealing material causing them to open in a short period of time.
Crack sealing because of our freeze thaw cycles should be performed on at least a two year basis.
ALLIGATORED AREAS ARE NOT MEANT TO BE CRACK SEALED. The hot rubberized material is not meant to be used as a “topical” repair. It is specifically designed to be used in individual cracks not associated with alligatored areas.
Asphalt failure and repair:
An alligatored area is an indication that the asphalt has failed due to one of the many factors previously discussed.
Most people will conclude a pothole is asphalt failure when in truth; an alligatored area is the beginning of a pothole.
Because this type of area cannot be successfully crack sealed, it is recommended that the area be removed and replaced with new hot mix asphalt.
Remember that the failure cannot only be attributed to water and the freeze thaw cycles, it can also be attributed to base failure and weight.
To correct the problem it needs to be determined if the base under the asphalt needs to be replaced or if the asphalt was too thin to support the traffic.
If the base has failed you will usually see a clayish soil pumping up through the alligatored area. If no clayish soil is pumping through the surface chances are the asphalt has just been placed in too thin a lift and needs to be replaced with a greater depth of asphalt.
To repair a failed area it is recommended to saw cut the asphalt approximately eight inches past the point of failure. If the base has failed, you will need to dig out the area removing the bad base and replace it with either base rock or a thicker amount of asphalt. The new base rock should be at least six inches thick and thoroughly compacted with a vibratory roller. The ideal area to be patched should be squares and rectangles as much as possible. Odd cuts and angles will only promote premature failure.
All asphalt repairs should have a depth of at least four to six inches depending on the weight expectations of the parking lot. If larger vehicles such as Semi-trailers are to be on the asphalt, eight to ten inches of asphalt is recommended in order to support the weight of the trucks.
The asphalt should be installed in lifts in order to obtain proper compaction. Each lift should be thoroughly compacted prior to placing the next lift. If all the asphalt is placed in the hole at once, proper compaction cannot take place and the asphalt will settle and fail prematurely.
It is recommended that failed asphalt in front of trash dumpsters be replaced with concrete in order to support the weight of the front wheels of the trash truck. The concrete should be reinforced with fiber mesh or rebar and should be a minimum depth of seven inches.
Once crack sealing and asphalt repair have taken place what needs to be done next?
Modified Coal Tar or Asphalt Emulsion sealing:
“Seal coating is just a paint job” NOT TRUE!
At the beginning of this report, we stated asphalt fails because of three factors; water, oxidation and chemicals. If you can protect the asphalt from these three elements does it not make sense that it will last longer? The answer is a resounding yes!
The application of a modified sealer will protect the asphalt from water, oxidation and chemicals.
A properly applied modified sealer will seal the pores of the asphalt thus eliminating water intrusion. If water intrusion is reduced, the sub-base stays drier and produces less flexing. Less flexing reduces cracks which in turn reduces costly asphalt repairs.
A properly applied sealer will protect the asphalt from the three elements that cause failure while providing an attractive, easy to maintain surface.
When should seal coating take place? Seal coating should take place within the first two years life of the asphalt surface in order to provide the greatest benefits.
How often should seal coating take place? This depends on the amount of traffic on the parking lot. The only way a properly applied seal coat will diminish is based on the amount of traffic on the material. A McDonalds for example will probably need to be sealed every two years due to the higher traffic volume where as an office building parking lot may need to be sealed every four to five years.
When you say “modified” and “properly applied” what do you mean? A modified sealant is a sealant that is enhanced with a latex additive to provide greater fuel resistance, darker color and more product flexibility. The sealant is also modified by the addition of sand. Sand is used to provide a longer lasting surface life as well as a more skid resistant surface.
By properly applied we are stating that the material needs to be applied according to and exceeding manufacturer’s specifications. No corners are to be cut in the application process.
All commercial seal coating projects should receive two individual coats of sealer with a third coat on the main drive lanes and entranceways to assure a longer product life against the higher traffic volume.
What are the cost advantages of applying a modified sealer? You will spend approximately one third of the money to seal coat and maintain a lot versus an asphalt overlay while at the same time extending the surface life of the asphalt by as much as sixty percent! (NOTE: Please see cost comparisons of seal coat versus overlay at the end.)
It is obvious that seal coating is an effective and valuable tool when it comes to getting the most out of an asphalt surface.
Asphalt fabric and overlay:
When an asphalt parking lot has not been maintained, it reaches the point where pavement maintenance is no longer a viable option. When that time occurs you are forced to consider completely replacing the asphalt or overlaying the surface with new asphalt.
Another factor to keep in mind prior to an overlay is the concrete curb and gutter surrounding the parking lot. In most cases, you cannot overlay over the curbs because you will create a water drainage problem. So the curbs need to be edge milled. This is a process where a milling machine will remove two inches of existing asphalt away from the curb so the new asphalt will taper and tie into the existing curbs allowing proper water flow.
Once the repairs and milling have taken place, it is strongly recommended the entire lot be covered in non-woven fabric prior to the overlay.
This fabric is placed on a layer of liquid asphalt and is used to provide a water proof membrane between the new and existing asphalt. Keeping the water out of the sub-base will provide for a longer overlay life and will reduce the reflective cracking that can take place after the overlay. If you simply overlay on top of the alligatored asphalt you will eventually have all the alligatored cracks reflect back through the new asphalt and will be in the same position as when you started. Fabrics will add to the cost of the overlay but they are worth every penny towards the final results.
All overlays should be a minimum of two inches of compacted asphalt. Less than two inches will not provide the structural integrity you are seeking.
Re-striping a parking lot is the least expensive, most effective way to upgrade a lot. It is recommended that a parking lot be re-striped at least every two years.
Most re-striping takes place in spring when the effects of salt and sand are finished for the winter and the lot will have an attractive appearance for months to come.
The best machine to use for striping is an airless striper. This piece of equipment does not mix air with the paint, providing a quality line with little or no overspray. The pump literally applies paint only which in turn leaves more paint on the ground and a longer life expectancy.
Maintenance through crack sealing, seal coating and striping versus milling, fabric and overlay:
Parking lot example is an office building lot based on 8918 square yards using 2017 prices:
Crack seal, Seal coat and Striping:
Year- 2017: Crack, Seal and Stripe: $6,596.70
Year- 2021: Crack, Seal and Stripe: $6,596.70
Year- 2025: Crack, Seal and Stripe: $7,242.60
Year- 2029: Crack, Seal and Stripe: $7,850.00
Total for four applications over 12 years: $28,286.00
Edge mill, fabric and overlay based on fourteen year life expectancy using 2017 prices. (Prices will obviously be higher in 2029 when work takes place.)
Edge mill: $3,000.00 (based on one day of milling)
Installation of fabric: $20,065.00
Two inch overlay: $84,275.00
Total for milling, fabric, overlay and striping: $108,267.00
The important factor when looking at the totals is not only the difference in cost but realizing the fact that by seal coating, the life expectancy of the parking lot can be doubled just in proper maintenance!
Also, keep in mind that you will be providing a very attractive, welcoming lot that will be easily maintained for many years to come.
Putting it all together:
Any asphalt parking lot is a large investment. As a Property Owner or Manager, it is our hope that this information will allow you to understand just what is involved in your investment. Even if you own or manage a parking lot for a short period of time, you cannot afford not to maintain it. By performing proper maintenance, you will protect your investment, making for an attractive parking lot that will help in the resale value of that property. You will save money even in the short term by performing pavement maintenance such as crack sealing and re-striping.
It is our goal at Springfield Striping & Sealing to help you obtain the most out of your asphalt investment.