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Asphalt pavements represent a major investment in any real property and their protection, and preservation is naturally a concern for their owners and managers. We have taken the opportunity to present an overview and some pertinent details on sealcoatings for your consideration.
Sealcoatings are specialty coatings which were introduced in the late 50’s, expressly for the protection and preservation of asphalt pavements. Asphalt pavements are composed of asphalt binder (AC), aggregate, and silica and specialty chemicals. Asphalt binder has an outstanding capability to hold the aggregate together in a firm structure (pavements) and keep the water out of the sub-base and base of the pavement. Asphalt, however, breaks down by sun’s ultraviolet rays and is easily attacked by salt, gasoline, oils and other petrochemicals. Sealcoatings act as a barrier coat to stop all the damaging elements to preserve the properties of the asphalt binder.
The value of sealcoatings has been well recognized over the years and it has been established that the life of the pavement can be extended more than three (3) times, by spending only 1/3rd of the cost of the total asphalt replacement. Soon after their inception, sealcoatings were adopted as the standard pavement maintenance methods by the FAA, several governmental agencies, commercial installations and residential properties. The performance properties are well laid out by FAA (Federal Aviation Administration) and ASTM (American Society For Testing and Materials). Sealcoatings, though indigenous to the US, are steadily gaining international acceptance.
With immense pleasure, I invite you to visit our newly designed website which you will find informative and user-friendly. Ever since the inception over 25 years, STAR has strived to serve you to the very best in technical support, product performance and sterling customer service. Over the years, STAR has offered unequaled consistency in performance, while expanding its product lines in sealcoatings and other supporting products. STAR has risen to the challenges in today’s sealcoating industry, with innovation for tomorrow, and a commitment to doing the hard work that moves the industry forward.
Kindly review the following information which you may find helpful in making a decision for the products and services you use. You are always welcome to call us at 800-759-1912 or one of the STAR plants in your region. We will be delighted to assist you.
Asphalt pavements, like other construction materials, have a service life, which can be extended through proper maintenance by protecting them from the damaging elements of weather, salts, chemicals, petrochemicals, etc.
The purpose of this presentation is to demonstrate the cost benefits, in real dollars, of a properly maintained asphalt surface versus an asphalt pavement which has been minimally maintained.
Life-Cycle Cost Analysis (LCCA)
Life-Cycle Cost Analysis (LCCA) is a process for evaluating the economic worth of a pavement segment by analyzing initial costs and discounted future costs such as preventive maintenance, resurfacing, rehabilitation and reconstruction cost, over a defined analysis period. LCCA is only a tool in the decision-making process, it does not dictate the decision.
All alternatives are to be included in the LCCA. For example, complete replacement is generally the most expensive alternative but it should not be disregarded simply because of the expectations of the high cost. The analysis may show replacement as the highest cost but the cost difference between replacement and the other alternatives may be small enough to make the replacement a better choice.
Life Expectancy of Asphalt Pavements
The general consensus of the industry regarding the life expectancy of an asphalt pavement is approx. 7-8 years without any maintenance.
Home driveways may last 10-15 years, without maintenance.
The life of an asphalt pavement depends on the following factors;
- Pavement design i.e. base, sub-base, drainage, asphalt mix, compaction, depth of the asphalt, etc.
- The traffic bearing capacity
- Traffic frequency
- Exposure to damaging elements, e.g. de-icing salts, oil, grease, gasoline, fats, etc.
- Maintenance e.g. sealcoating, crack filling, patching, etc.
For the sake of understanding, the life of an asphalt pavement is the period during which it will preserve its strength to bear the traffic loads for which it is designed. For example a commercial parking lot will need to be repaved after 7-8 years.
LCCA of a commercial parking lot (10,000 Sq. Yards) is tabulated below, both;
a. with a regular preventive maintenance program, using a sealcoating based on refined tar emulsion.
- The sealcoating and other repairs will be done at every 3 years.
- The sealcoating is to be done during the first year of the installation.
- The pavement shall be allowed to cure to rid of the surface oils. The time period is minimum 90 days.
- After the first three years, some minimal repair (crack filling) may be required. Cracks may develop due to pavement distress.
b. Without seal coating, only the damaged areas are repaired as needed. The cost of repairs escalates with each passing year. It has been observed that fine hairline cracks appear during the first year of installation, which widens and multiply with time. Water seeps into the pavement through these cracks and damages the base courses. Generally, a parking lot will require an overlay after seven years.
Sealcoating’s for the Protection & Preservation of Asphalt Pavements
Asphalt is the most extensively used material for paving highways, roads, parking lots, home driveways, etc., due to its outstanding binding (for the aggregates) and waterproofing properties. Asphalt, however, has poor resistance to chemicals, salts, oils and sun’s ultraviolet rays. Pavements with low to medium traffic (parking lots, airport aprons, restaurants, gas stations, schools, etc.) deteriorate under the attack from these damaging elements. If not protected, such pavements become useless and have to be repaired or replaced to keep them functional. Highways and major roads have the benefit of continuous rolling traffic, which keeps the pavement functional through the kneading action of the traffic.
Low to medium traffic pavements can be protected and preserved through the use of sealcoatings, which are specialty water-based coatings, specially designed to resist the destructive elements of weather and chemicals. Sealcoating is a protective measure, designed to keep an asphalt pavement lively and attractive. The very term “sealcoating” means keeping the redeeming properties (like waterproofing, flexibility) of asphalt sealed in to extend the pavement life and preserve its functional properties. After all, the pavement is a sizable investment. In this article we will review;
- The basics of an asphalt pavement, its weaknesses, and strengths.
- The damaging elements: weather, salts, and petrochemicals.
- How to protect: the Sealcoatings types and their use.
- Saving and value to the property owner.
Asphalt Pavements & The Damaging Effects
The major strengths of asphalt are its adhesive (gluing), waterproofing and flexibility properties. Asphalt pavements are not what you see on the surface. It goes much deeper. The asphalt mix, which you see, is only the roof, so to speak, of the entire pavement. It covers a bed of graded stone aggregates of varying depths according to ground conditions as well as the traffic requirements. The base of aggregate is what really carries the load of the traffic. The strength of a pavement is directly related to its design from the ground up. Asphalt mix provides a firm resilient surface over the stone base and keeps the pavement bed dry.
Hot asphalt, mixed with stone aggregate and a mineral filler is most commonly used in paving material. The hot mix contains 4-12% asphaltic binder (AC or asphalt cement) the rest being aggregates and mineral. The mixture is made in a hot mix plant by blending selected aggregates and mineral fillers with hot molten asphalt. The mix is then transported to the paving site, spread in a uniform thickness and compacted with rollers. As the pavement cools it becomes firm and ready to carry traffic loads.
Asphalt has poor resistance to sun’s ultraviolet rays, petrochemicals, salts, etc. due to its chemical makeup. Asphalt is a very complex mixture of thousands of chemicals, which are predominantly open chain (aliphatic) in structure, with a considerable degree of unsaturation within their molecular structure. The open chain and unsaturation make asphalt an easy target for deterioration. The first visual sign of this phenomenon is a progressive change in the color of asphalt pavement: rich black to brown to gray.
Asphalt is a by-product of petroleum distillation so are gasoline, mineral solvents, oils, grease, fat, etc. When it comes in contact with these materials it is easily dissolved by them. The treason is quite logical. Asphalt has a natural affinity, after all, they existed in nature in form of crude petroleum, separated only through the process of petroleum refining. Additionally, asphalt has poor resistance to deicing salts.
How To Protect: Sealcoating Types & Their Use
Major roads and highways, having the advantage of continuously rolling traffic do not need protection. The rolling action of the traffic steadily brings up the lower layers, rich in asphalt, to the surface and kneads the oxidized surface layers back into the pavement. In due course, depending on traffic volume and the climatic conditions, all the asphalt binder is eventually exhausted and the aggregates begin to unravel due to the absence of binding cement (asphalt). The next step is the development of minor cracks, which widen and deepen with time. If the cracks are not repaired at this stage, water seeps into the base courses and damages the load-bearing capacity. It is evidenced by rutting, shifting and serious alligatoring. The roads must then be either overlaid with fresh asphalt mix or the pavement completely removed and reinstalled, depending upon the condition.
The need to protect asphalt pavement generally applies to “off-street pavements” which are defined as those carrying very low traffic e.g. parking lots, minor streets, airport aprons, runways, service stations, home driveways etc. Off-street pavements do not have the advantage from the “kneading action” unlike the major roads. The surface layers under continuous attack by the weather and other destructive elements develop minor surface cracks. Again, aggregates start unraveling producing minor cracks, which widen and deepen with time. The damage will continue if proper protective actions are not taken.
Based on the foregoing facts, it would be logical to conclude that off-street pavements can be preserved if a “protective coating” is applied to the surface. It will form a barrier and shield the pavement from attack by the damaging elements of weather, chemicals, and salts. The sealcoating should be applied as soon as the oils from the surface of the pavement are oxidized and dissipated.
Sealcoating & Types
Sealcoatings are stable dispersions of refined tar or asphalt, ball clays, fillers, emulsifiers and specialty chemicals. The dispersion is obtained either in a high-speed disperser (batch process) or a colloid mill (continuous process). The resulting product is thixotropic with heavy paint consistency. The product in a wet state is chocolate brown in color that dries to black/dark slate. Contractor grade sealcoatings are supplied either in a concentrated which must be diluted with water and sand/aggregate added, for proper application consistency. For retail customers, it is supplied in a ready to use form, packaged in 5-gallon pails.
Sealcoatings based on refined tar (RTS) were introduced in the late 50s and have been used extensively to protect off-street pavements. Refined coal tar is also a very complex mixture of thousands of chemicals but quite different in their molecular structure than asphalt. The molecules have a predominantly “closed ring” (aromatic) structure with a minor degree of unsaturation. Being stable in molecular structure, these chemicals do not allow the destructive elements of weather and chemicals to affect the properties of coal tar. The most commonly used sealcoatings are, therefore, based on refined coal tar.
In recent years, sealcoatings based on asphalt emulsions have been introduced with a considerable degree of success. Such coatings are fortified with rubbers, specialty chemicals, additives etc. to overcome some of the basic deficiencies in asphalt binder.
Sealcoatings have the ease of application and clean up of water-based systems. Prior to application of sealcoatings, pavement must be properly cleaned, oil spots primed and the damaged areas repaired.
Sealcoating is mixed with 25-30 gallons of water and 200-300 lb. of sand/aggregate per 100 gallons of sealer. This yields a good workable consistency. Commonly two (2) coats are applied at the combined coverage rate of approx. 35-40 square feet/ gallon of the mixture. When applied per recommendations and instructions of the manufacturer, the sealcoating will last two to three years, depending on traffic frequency. Both hand or machine applications are used.
Savings & Value To The Property Owners
Sealcoatings applied at the recommended rates to asphalt pavements;
- Protect the Surface against Water, Frost and Snow Damage. Asphalt surfaces are sufficiently porous to allow water to seep into the base courses. The water softens the aggregates and reduces the overall load carrying capacity of the pavement. More severe damage is caused by the expansion of the trapped water in the pavement during winter months. The freeze-thaw cycles create large cracks and the problem is steadily worsened. The sealcoating forms an impervious barrier that does not allow the water to seep into the pavement, thus protecting it.
- Protect against weathering. Asphalt binder in the pavement is shielded from ultraviolet rays.
- Protect against attack by petrochemicals and deicing salts.
- Beautifies the asphalt pavement and adds improves its value.
- Saves money to the owner. Like most good maintenance practices, the regular sealcoating of asphalt is economically sound. An owner can have a quality sealcoating job done at a small expense, and secure as much as 300% greater life on his asphalt surface. Such treatment is far less expensive than repair and resurfacing work. The commercial property owner will enjoy lower snow removal costs on properly sealcoated lots due to a smoother surface.
Sealcoatings have been successfully used for protection and preservation of asphalt pavements over 40 years for all types of commercial and residential applications. They impart beauty and value while protecting one of your major investments, asphalt pavement.
About The Author
Girish C. Dubey is the president of STAR, INC. He has 40 years of professional experience in the coatings industry. He holds master’s degrees in polymer and inorganic chemistry and has authored several papers on coatings and related subjects. He also has lectured at many technical conferences. He was the chair of The Pavement Coatings Technology council in 2000.