ASPHALT PARKING LOTS ARE CAPITAL INVESTMENTS
Asphalt parking lots and driveways are capital investments, increasing the value and functionality of a property. Like any infrastructure investment, the asphalt surface must be maintained to keep both value and functionality over time.
WHAT ARE THE MAINTENANCE OPTIONS?
Maintenance options include resurfacing or replacing the asphalt periodically and extending the service life of the asphalt by sealcoating.
WHAT DOES SEALCOATING DO?
Sealcoating extends the useful life of the capital asset – an asphalt parking lot – by protecting the pavement from the natural aging process caused by sunlight, water and debris. Sealcoat also protects pavement from degradation caused by leaking oil and gasoline and other caustic products. An added benefit is that sealcoating adds to the “curb appeal” of a paved surface, giving it a clean, uniform look.
WHAT ARE THE OPTIONS FOR SEALCOATING?
There are two essential options for sealcoating: refined coal tar-based sealers and asphalt-based sealers. Other options are cost-prohibitive for most applications.
WHERE DOES THE BASE MATERIAL FOR SEALERS COME FROM?
Refined coal tar-based sealers are based on a selectively refined fraction of crude coke oven tar, which is a byproduct of the steel making process. Similarly, asphalt-based sealers are based on a selectively refined fraction of crude oil.
HOW ARE PAVEMENT SEALERS MADE?
The majority of pavement sealers are an emulsion, a mixture typically consisting of water, clay, sand, polymers and usually less than 20% of either asphalt or refined coal tar.
HOW LONG HAVE PAVEMENT SEALERS BEEN IN EXISTENCE?
Pavement sealers have been applied for over six decades. Sealing is a tried and true way to protect and beautify a pavement, prolonging its useful life and minimizing the need to replace the asphalt, which consumes a lot of energy (fuel to manufacture, deliver and install) and natural resources.
MOST SEALER MANUFACTURERS SELL BOTH TYPES OF SEALER, SO WHY DO THEY CARE WHICH ONE IS USED?
Most sealer manufacturers make both refined coal tar-based products and asphalt-based products. Even though most sealer manufacturers make both, most recommend refined coal-tar based for most applications because the superior performance of tar-based sealcoat allows the manufacturers to stand behind the performance of their products, enhancing the reputations of their businesses. Research and development projects continue to improve the performance of asphalt-based sealer, but there remains a way to go.
WHY REFINED COAL TAR-BASED SEALER?
Refined coal tar-based sealers (1) protect the underlying asphalt pavement from leaking oil and gas spills, (2) last longer than asphalt-based sealer, (3) are more resistant to natural aging processes caused by exposure to the elements (sun, rain, freeze-thaw, etc.), (4) adhere (that is, “sticks”) to the underling pavement better, and (5) are manufactured to a performance-based specification (ASTM® D490).
WHAT IS THE PERFORMANCE DIFFERENCE BETWEEN TYPES OF SEALERS?
Asphalt-based sealers have many of the same beneficial properties as refined coal tar-based sealers. The tar-based product, however, is superior in strength, resistance to leaks/spills of petroleum products, UV bleaching and road salts.
WHAT IS REFINED COAL TAR?
One of the byproducts of manufacturing steel in coking ovens is coal tar. Out of the coking oven, this material is “crude coal tar” which, like “crude oil,” serves as a raw material that is distilled into many different fractions in coal tar refineries. The different fractions are then used to make many different products.
ARE PAVEMENT SEALERS HAZARDOUS?
Air sampling studies showed refined coal tar based sealers pose no inhalation risk to applicators, manufacturers or the general public. People with skin conditions have been applying coal tar creams and lotions (not pavement sealers, but still, a coal tar-based product) directly to their skins on purpose for a century or more with few reported problems. Research with insurance carriers (both in liability and workers compensation) shows a general paucity of insurance claims over the history of sealer use.
WHAT PRECAUTIONS SHOULD BE TAKEN WHEN APPLYING RTS EMULSIONS?
If RTS emulsions contact skin during application in the presence of sunlight, they can irritate the skin and applicators can experience moderate to severe “sunburn” effects if they do not wear appropriate clothing including long sleeve shirts, long pants and work gloves. Depending on the method of application and weather conditions a hat and face shield may be appropriate. Protective creams are available to minimize skin contact with sealer and to block the sun’s ultraviolet rays that can enhance skin irritation. When proper handling and personal hygiene precautions are observed skin irritation should not be a significant problem.
DO REFINED COAL TAR-BASED SEALERS CAUSE CANCER?
Some activists say that refined tar-based sealers are a health threat, but across the two, three and four generation memories of the many family-owned companies in the business of making or applying sealcoat, there are no reports of adverse chronic health effects – including cancer – that can be attributed to exposure to sealcoat.
DO OTHER PRODUCTS MADE FROM REFINED COAL TAR CAUSE CANCER?
Expanding the search for evidence of cancer to other products made from refined tar, every day millions of people world-wide use coal tar soaps, shampoos and creams approved for use as over-the-counter medicines to treat skin disorders such as eczema, psoriasis and dandruff. Coal tar and coal tar derivatives are listed by the US Food and Drug Administration (FDA) as “generally recognized as safe and effective” active ingredients for use to treat these skin ailments with coal tar concentrations up to 5% in over-the-counter products. Because of its use in medicines, many studies have been performed over nearly a century to see if the patients who intentionally expose themselves to high level doses of coal tar for long periods of time have increased risk of cancer. All the studies have reached the same conclusion – there is no evidence of cancer.
WHAT DO STUDIES OF PEOPLE EXPOSED TO NON-PHARMACEUTICAL COAL TAR SHOW?
Studies of humans exposed to coal tar (other than via medicinal coal tar products) can be summarized as follows:
• There is no evidence that low level or intermittent exposure to coal tar or coal tar pitch has caused cancer in humans. This category describes exposures to refined coal tar-based sealer.
• There is little evidence that high level, repeated exposures has caused cancer in humans. This evidence is largely reports from the past, such as chimney sweeps in London in the 18th century (but not chimney sweeps in other countries at about the same time) and late 19th – early 20th century factories, at a time when industrial hygiene practices were virtually non-existent. The working conditions described in these reports include exposures to many chemicals in addition to coke and coal tar.
• There are some studies conducted in modern factories with high temperature (1000s of degrees Fahrenheit) industrial processes such as aluminum smelting or coke oven gases that show some adverse effects.
I’VE HEARD THAT COAL TAR IS LISTED AS A “KNOWN CARCINOGEN.” WHAT ABOUT THAT?
Because of the observations discussed in the previous paragraph, occupational exposures to coal tar and coal tar pitch in high temperature industrial settings have been listed as carcinogens by the International Agency for Research on Cancer (IARC). The listing is specifically for those very high temperature occupational settings, and is NOT for intermittent, incidental low to moderate temperature exposures such as might be associated with pavement sealer.
Similar to health agencies elsewhere in the world, the US FDA lists coal tar as “generally recognized as safe and effective” for sale as an over-the-counter (no prescription needed) skin medication. The FDA has found no evidence that coal tar causes cancer.
As discussed later on, there is a conflict between regulations based on actual human exposures to coal tar and those based on exposures of laboratory animals to laboratory-made compounds, for example in some states such as Minnesota.
IS COAL TAR REGULATED AS A HAZARDOUS SOLID WASTE IN THE US?
In the US, the Resource Conservation and Recovery Act (RCRA) regulates waste materials “from cradle to grave.” RCRA exempts coke oven byproduct materials that are recycled to the “tar recovery process as a feedstock to produce coal tar, or mixed with coal tar prior to the tar’s sale or refining” from hazardous waste regulation because refined coal tar does not exhibit any of the toxicity characteristics used by RCRA to identify hazardous wastes.
In addition to the coal tar generated as a coke oven byproduct,coal tars were produced during the now-defunct process of manufacturing gas from coal for use as a source of energy in municipalities across the North American continent. Hundreds of former manufactured gas plants (MGP) around the country are listed as “hazardous waste sites,” not because of the coal tar but because of substances mixed in with the coal tar that do have toxicity characteristics. The US EPA and federal courts have issued opinions that, unless a material displays toxicity characteristics because other substances are present, “MGP remediation wastes [that is, coal tar] are unlikely to be RCRA hazardous waste under the federal program, and would not be required to meet RCRA requirements, including Land Disposal Restriction requirements.”
Refined coal tar that is the base material used to make pavement sealer has been tested and does not meet the RCRA hazardous waste criteria. Different brands of pavement sealcoat emulsion tested at different times in different labs have all passed EPA’s toxicity characteristic test, indicating that RTS does not meet the criteria to be a hazardous waste and disposal in non-hazardous waste landfills is appropriate.
WHAT IS THE CONNECTION BETWEEN COAL TAR AND PAHS?
The FDA evaluated safety of coal tar based on exposure of humans to medicinal products that contain coal tar. Controversies about the safety of refined coal tar-based sealer began because one of the components of coal tar-derived materials is a class of chemical compounds called polycyclic aromatic hydrocarbons (PAHs). Cancer classifications of PAHs by environmental agencies typically evaluate how laboratory animals such as rats and mice react when exposed to high doses of individual PAH compounds made in a laboratory. Test results in laboratory animals exposed to laboratory-made compounds are then used by regulatory agencies to make assumptions about how humans might react if exposed to PAH-containing materials.
Thus there is a conflict between regulations based on actual human exposures to real-world substances and regulations or guidance based on exposures of laboratory animals to substances that no one (except maybe laboratory technicians) is actually exposed to.
In the US, the Environmental Protection Agency recognizes that there are thousands of products and foods that contain some mixture of PAHs. Testing each one would be prohibitively expensive. So EPA’s solution has been to develop methods of estimating risks that could be associated with products containing PAHs by extrapolating from laboratory animals to humans based on calculations of PAHs contained in a food or product. How the PAH compounds that are part of the make-up of coal tar and, to greater and lesser extents, of coal tar derivatives, could be calculated to cause effects so different from those seen in people exposed to products containing refined coal tar is a matter for academic study.
WHERE ELSE ARE PAHS FOUND?
PAHs occur naturally; they are all around us and always have been. PAHs are made whenever something organic is heated up or burned. Smoke from forest fires and wood burning fire places contains PAHs. Plants decaying in a swamp or a compost pile are making PAHs. Emissions from planes, trains and automobiles, cooking food, lubricating oils, volcanic eruptions – PAHs are in all those substances as well as in materials derived from coal tar. This means that PAHs are everywhere in our environment. PAHs have been around since the dawn of man. If there was a fire that offered our ancestors warmth or light, or cooked their food, PAHs were present.
WHY IS REFINED COAL TAR-BASED SEALER NOT USED AS MUCH ON THE WEST COAST?
Crude coal tar is a byproduct of making steel. The steel industry is largely located east of the Rocky Mountains. To be close to the source of their raw materials, coal tar refineries that make the base material for refined coal tar-based sealer are located near where steel has historically been made. Transportation costs and the more arid climates make locally produced asphalt-based sealers the cost effective choice on the west coast.
ARE ASPHALT-BASED SEALERS CHEAPER?
All else being equal, asphalt-based sealers are generally cheaper on the west coast, but not in the Midwest or east. The pricing of the asphalt-based product tends to be a little more volatile, as it fluctuates with the price of crude oil. Another cost factor can be that manufacture of refined tar-based emulsion is a one stage process, requiring fewer additives whereas making asphalt-based emulsion requires at least two stages and more additives and chemical fortifiers that enhance performance.
IS THERE A DIFFERENCE BETWEEN “DRYING” AND “CURING” SEALER?
Like latex paints, sealer is applied as a water-based emulsion. All emulsions contain water. Evaporation of the water starts the process of “sticking” the sealcoat particles to each other and to the coated pavement. Sealer that is dry to the touch means that the surface can be open to foot traffic, but not vehicle traffic. Sealcoat can be driven on once the process of curing is well underway, meaning that the sealer particles are sticking to each other and the pavement. Curing takes more time than drying because it takes longer to drive out moisture that remains after the initial drying.
WHY CAN YOU SOMETIMES STILL SMELL THE SEALCOAT EVEN AFTER ITS OPEN TO TRAFFIC?
The odor of refined tar-based sealer is easily identifiable, for good reason: refined tar-based sealer has a very distinct odor, and the human nose is able to detect it at extremely low concentrations. But just because it may smell bad doesn’t mean it is bad!
The smell is primarily the presence of one substance among the many that are part of refined tar-based sealer – naphthalene. The odor threshold for naphthalene is below three parts per billion (ppb), a very low concentration. To put this concentration into perspective, the odor threshold for nail polish remover is 7,000.
According to the American Conference of Governmental Industrial Hygienists, the level of naphthalene that is considered safe for workers is ten thousand parts per billion. So the difference between being able to smell it and worrying about it is huge – four orders of magnitude, to be exact. Even refined tar-based sealer workers don’t experience those levels of exposure.
WHY IS SEALCOATING NOT RECOMMENDED IF THE WEATHER IS COLD OR IT’S GOING TO RAIN?
For the same reason that exterior painting is not recommended in cold or wet weather, sealcoat is not applied in those conditions because the water in the emulsion won’t evaporate. If the water doesn’t evaporate, sealcoat particles can’t begin the curing process of sticking to each other and the coated surface.
Dried sealcoat does not wash off. If any sealcoat – asphalt-based or refined tar-based – washes off before it dries, it can suffocate fish. The fish are NOT poisoned. Autopsies have shown that the fish die because sealcoat particles cover the fish’s gill plates.