Asphalt is composed of the following:
a) mineral aggregate – stone, sand
b) asphalt binder – petroleum derivative
Asphalt pavement is a mixture of stone, sand, and asphaltic binder, with the bituminous material comprising between 4% and 0% of the total. Most asphalts are mixed, heated, and blended in a batch plant. The asphalt is then hauled and spread to a uniform depth and rolled until compacted.
- 6-10 Inches Compacted Base
- 3-4 Inches Rock or Crush n Run
- 2 Inches Binder
- 3 Inches Topping or Finish Coat (Typical Application Conditions Vary)
Failures in the construction of an asphalt pavement may be attributed to:
- insufficient or improperly compacted base
- poor drainage
- over-compaction or under-compaction of asphalt
- asphalt is not at optimum temperature when applied
A good asphalt pavement seldom wears out, it is destroyed by external factors.
- water penetrates asphalt and destroys bases
- sunlight (oxidation)breaks down the liquid asphalt that holds the aggregate together – causes raveling and shrinking cracks invites water
- petroleum spills – gas and oil spots soften the asphalt
Types of Asphalt Deterioration
- alligatored (areas of connecting cracks)
- slippage (typical of improper compaction)
- reflection (older cracks occurring in new overlay) – edge joint
- channels or ruts
- corrugations and shoving – grade depressions
- utility cut depressions
- gas and oil spillage
The process of deterioration begins as soon as the asphalt is put down. In normal conditions, after 3 to 5 years major deterioration is taking place.
- oxidation (sunlight) is causing asphalt to turn gray and brittle, resulting in cracking.
- water is entering cracks, freezing during the freeze/thaw cycle, and causing larger cracks and potholes.
- rain is entering cracks and causing base damage.
Just as you paint the dap-boards on a new house to seal up and protect the structure, sealcoating a sound pavement will cause it to have a much longer life than that of an unsealed pavement. Even on a weak pavement, sealcoating will preserve the elastic and adhesive characteristics of the asphaltic binder and seal out the water and oxidizing effects of the sun, salts, and petroleum spillage. This coating preserves the pavement surface, and the asphaltic and aggregate layers will remain dry and in place.
Benefits of Sealer
- Easy to apply
- Outstanding resistance to detergents used to clean pavements subjected to heavy fuel, oil or grease spillages. Excellent resistance to water.
- Unexcelled flexibility over a wide temperature range.
- Superior weathering ability.
- Non-scuffing under normal conditions.
- Readily mixed with sand where a nonskid surface or increased traction is desired.
- Extends the service life of asphalt pavements.
- Lends ease to cleaning and maintenance of asphalt.
- Adds safety by minimizing loose stone and aggregate “roll” out.
- Can be striped with water based paints after curing. (Ideally after 24 hrs If possible)
Sealer is intended to be used only as a protective coat and not as a repair, leveling material or wearing surface. Sealer is only as good as the bituminous pavement to which it is applied. It will not prevent the cracking of bituminous pavements caused by excessive voids, poor mix stability, poor compaction or low use areas. It should be applied to durable bituminous pavements which are made with an asphalt cement having a penetration grade that meets the climate and usage requirements of the pavement in point and properly constructed over a sound and well drained base. Where the sealer is applied over anything less, any cracks that will occur will be magnified by the sealer’s uniform velvet texture.
NOTE: Although the sealer exhibits excellent protective and wearing qualities, periodic resealing is necessary in heavy traffic areas since the film is a surface treatment and subject to wear.
Unless it is premixed, the sealer you purchase from the manufacturer is not yet ready to be applied to the pavement. Before you apply the material you must first add water. It is strongly recommended that in addition to this water, you add, a silica sand and a latex additive to the mix as well. Using sand in your mix makes good sense. You should ultimately rely on your materials supplier for the proper mix design.
It is obvious that sand makes good sense. You may ask, “If sand is good, why don’t all contractors use it”? Some of the reasons are as follows:
- The pump on their machine will not spray the sand. (They obviously don’t own a NEAL unit.)
- No agitation, or underbuilt agitation system.
- Not aware of the cost benefits.
- Inability to mix sand in barrels manually.
What kind of sand do I need, and where do I buy it?
First of all, you can usually purchase the sand you need where you purchase your sealer. It is important that you use sand that has been screened. The most widely used rating for sand is determined by the U.S. Sieve Sizes. The size you should use is rated 30/60 or 20/40.
As a substitute for sand you may use Black Beauty. Black Beauty is a boiler slag that is also crushed, screened and rated in sieve sizes. The characteristics of Black Beauty are that it is a much harder aggregate, and its black shiny colors add a “sparkle” to the finish of the job.
It is recommended that you purchase bagged sand. This insures that the sand is dry, and it is measured in units that can be used in developing your mix design. A major point favoring the use of sand is the fact that sand lowers the per gallon cost of your materials; however, more important than this is the issue of liability. Sealer without sand is very slippery. When the pavement becomes the slightest bit wet cars and people have a tendency to slip and slide. Over the years we have seen numerous lawsuits against property owners and contractors in cases where people have been injured on lots sealed without sand. This, coupled with the fact that there seems to be a great majority of people looking for any reason to sue anyone, makes the use of a proper sand load a necessity.
- Increases solid content
- Less expensive than sealer
- Provides a more skid resistant surface
- Improved wearability
- Decreased sun glare
- More competitive product
- Improves appearance of minor deformities
It is also recommended that you add a latex additive to your mix. Your sealer supplier will be able to make recommendations based on your specific application.
- Enables you to use greater sand volumes due to suspension in tank and content in final product
- Job will wear longer
- Will dry quicker
- Greater oil and gas resistance
- Darker color
- Enables sealer to bond better to pavement
There are a series of procedures that must be completed before sealer can be applied to the asphalt surface. We must first check the condition of the asphalt. Depending on its condition we may need to fill cracks, replace asphalt due to pot holes and alligatoring, treat oil spots and clean the pavement with a push brush, sweeper, or pressure washer. Remember a good sealcoating job is 95% surface preparation.
Curing of Asphalt Pavements
The asphalt pavement must be cured, firm, and sound, prior to sealing. There are some simple tests which can be used to determine whether the pavement is cured and firm. Pour some clean water on the surface of the asphalt; if an oily film appears in the water, the pavement is not sufficiently cured. For firmness, press a screwdriver onto the asphalt surface; if the screwdriver easily makes a depression, then the surface is not set firm enough.
The length of time for curing of an asphalt pavement will vary according to the mixes used and the compaction of the asphalt. This can vary from 30 to 60 days. It will be necessary for the applicator to learn what types of mixes and meth- ods of compaction were used on new pavements. From this, a proper judgment can be made as to how long to wait before sealing a new pavement. If the size of the stone increases and heavier, compaction is employed, the pavement will be ready for sealing sooner.
This general rule applies to a plant mix type asphalt pavement. A pavement which is made of cold mix, or by shooting and chipping, will take one to two years before it is cured sufficiently to seal with a coal tar emulsion.
Blocking off of pavement should be accomplished with as many bulky items as possible. Then twine should be stretched between the barricades at a height of 28 to 32 inches from the ground. Flags can be tied to the twine to make it more visible. Blocking cones can be used, but are not as effective unless a great number of the large variety are used. People generally know they can drive over them or between them.
Cleaning the Asphalt Pavement
The cleaning and preparation of the pavement is a most important function for getting good applications.
When the repairs are complete, the pavement must be cleaned of all oily substances and all dirt. The oil and grease spots must be cleaned and scraped to remove as much of this material as possible. These spots should be then treated with oil spot primer and brushed into the effected area and allowed to dry. Then the entire area must be clean of all dirt. This can be accomplished by the use of the air broom. The air broom should be operated to blow dirt from the wind; however, try to blow the dirt away from the buildings, traffic, and pedestrians.
On large jobs, start in the area where you plan to seal first and continue in a systematic manner across the pavement. Areas will be encountered where dirt and silt are stuck tight to the surface. These will be around the perimeter of the pavement and in areas where water stands. Use the wire broom to brush away these areas while the air broom blows away the dirt. If the loose material begins to build up, remove this with a scoop shovel and the cleaning will go along more quickly. If any areas appear to have silt embedded in the pavement that cannot be blown and brushed off, these should be cleaned with water pressure. All growth dug loose from the edges of the pavement (dirt and stone) should be hauled away or deposited in the owner’s trash container (with the owners permission of course).
Wet spots can be dried with the help of the air broom, or by brushing the water around with a street broom. By spreading the water around in this manner, it will dry more quickly.
Sealcoat Application Guidelines
Below are general guidelines for applying sealer based on a typical application scenario.
Number of coats: Two, Normally
First coat – 40 square feet per gallon
Second coat – 60 square feet per gallon
Total of 2 coats – average coverage around 50 square feet per gallon (or 5 square yards). Drying time at 70 F. and 50% relative humidity:
Dry to touch: 30 minutes to I hour.
Between coats: The first coat must not only dry, but also cure sufficiently to prevent pickup before the second coat is applied. Shady or sheltered areas may require a longer drying time. Allow at least 2 hours between coats on residential driveways so as to minimize pickup or tracking. All manufacturers recommend 24 hours between coats or before opening to traffic.
Methods of application: Apply sealer with a brush in the trimming areas. For the most efficient sealing job possible use a spray sealing applicator capable of mixing and blending, with an agitator, sealer, and sand.
Directions for application: Mix until the sealer is of uniform consistency. Mechanical mixing is recommended and will lessen time in obtaining uniform consistency. Do not apply when temperature is expected to drop below 50 degrees F., or if rain threatens before the sealer is cured. Application is recommended early in the day or when at least 2 hours of sunlight remain upon completion of the job.
Thick coats will not cure readily and could result in pickup and tracking. After the first coat is cured, apply second coat so that all pores are sealed. To determine whether the first coat is cured sufficiently, use the thumb test. At various locations and while exerting approximately 10 pounds of pressure, twist thumbprint 90 degrees. Lack of pickup on thumb indicates sufficient curing of the first coat, and indicates you should be able to continue with your second coat.
To provide traction on smooth surfaces or grades, we have found that normally 5 pounds of clean dry silica sand with each gallon of sealer will provide you with a uniform mix. The gradations of the sand should meet the following:
Sieve Size 30 — 100% Passing
Sieve Size 60 — 0-15% Passing
The sealer and sand must be mixed in machine while applying sealer to insure an even distribution of sand over the sealed area, Best results are obtained when the sand slurry coat is applied in both coats equally. The sand slurry coats can be applied more efficiently and evenly by a spray application designed and developed by Neal Mfg. Co., Inc.
Typical Application of Sealer: Summary
This is an outline of the steps on the application process and not specific instructions for each procedure. We will deal with that elsewhere. Also note that all crack filling should be done a week prior to sealing when using cold pours. Most manufacturers recommend a minimum of 60 days curing time.
1. Check weather forecast for the day
2. Block off the work area
3. Begin general cleaning of the pavement
- Clean and prime oil spots
- Remove growth and deposits from edge of pavement
- Check oil level and start air broom
- Scratch out and blow out cracks
- Dry up wet spots
- Brush and blow off dirt puddles
- Take air broom to windward side of pavement and start systematically blowing all dirt away
4. Prime all areas needing it
5. Prepare to sealcoat
- Start agitator and run for five minutes
- Start pump and start trimming
6. Begin to sealcoat the pavement
7. Inspect area for spots missed
8. Check placement of barricades, police area for tools, complete information on job work order
9. Next day remove barricades
10. Stripe as soon as possible using water base paint
Factors Which Affect How the Job is Completed
- Size, shape, and grade of the pavement; work so the material will be flowing down hill if there is an appreciable grade
- Coarseness of the pavement
- Prior sealed surface
- Man power
- Serviceability of equipment
- When the job can be done, and length of time it is open to work on
- The amount of repairs to be completed
- Accessibility to water and sand
- Application Tips and Techniques
- Keep relative humidity in mind when determining the amount of water that should be added to the mix. RULE: If humidity is high, add less water.
- Longer passes with the applicator will make a better finished appearance.
- Keep sealer off adjacent concrete surfaces; mask them off if necessary.
- Between coats, put away unnecessary tools and always keep applicators clean.
- Complete work orders promptly and keep account of material application rate.
- Workers should know their job and be able to speak intelligently about what is being done. They should always be neat appearing and alert to perform their task.
- Keep truck on cleaned pavement once you start application. Consider sealing an area where you will end the first coat to set the truck on while you wait to start the second coat.
- Never run the truck over partially dried material.
- Don’t block your equipment in on job completion.
- Fill truck with gas and material at end of day.
Clean Up Procedures
Following good clean up procedures is important from two standpoints: To promote optimum efficiency of tools and equipment and to project a good public image in the eyes of the customers, there are some procedures which will make this as easy as possible for your crew.
The first rule to follow is, whenever possible, wash all tools and equipment used on application with water immediately following their use. If you can rinse these tools before the sealer dries they will wash up cleanly and easily. Ideally a container (a 22 gallon drum is ideal) with water, you can wash the tools and filter, is recommended.