What materials are used to produce asphalt pavements?
The components of asphalt can be simplified into two major components; liquid asphalt cement and aggregates. The liquid asphalt cement (often called asphalt “binder”) is material that coats the aggregate particles and acts as the glue that holds the mix together. The aggregates may consist of natural aggregates (river gravel and sands) or processed aggregates (from quarry and blasting operations). The aggregates provide the structure and framework that gives an asphalt mixture its stability and strength. Another vital component to a well-constructed asphalt pavement is the presence of air voids in the mixture. The amount of air voids in the asphalt is controlled through the aggregate gradation and the quantity of liquid asphalt. The proper blend of asphalt and aggregates is determined prior to construction (during the mix design phase) in order for the mixture to have the desired properties.
Are all asphalt mixtures the same?
No, it is a common misconception that asphalt used on the interstate roadways is the same asphalt used in residential driveways. An asphalt mixture that is designed for use on a heavily traveled highway has very different characteristics than those used in low volume residential applications. Those differences may include different aggregate types, sizes and proportions as well as different grades of liquid asphalt. Feel free to contact the PAIKY office or your local PAIKY producer member to assist you in determining which mix is appropriate for your application.
What is this Superpave I keep hearing about?
Superpave is a system of material specifications and laboratory mix design methods based on performance criteria developed under the Strategic Highway Research Program (SHRP). Using the Superpave system, materials and mixes can be designed to reliably perform under any loading or environmental conditions. The Superpave system is undergoing continuing development nationally. The Kentucky Transportation Cabinet fully implemented Superpave on January 1, 2000 for all state projects. In general, Superpave designed asphalt mixtures rely more on stone-to-stone contact, they are generally more durable and last longer.
How does the cost of asphalt pavement compare with other road paving materials that I might use?
Asphalt is the most economical paving material in the world. Pavements can be evaluated on both “initial cost” and “life cycle cost.” In the vast majority of circumstances, asphalt pavement will provide the most economical solution in terms of initial cost and also when evaluated over a 30 to 40 year period. This is one of the reasons 94% of all paved roads in the U.S. are paved with asphalt.
Are there advantages, other than cost, why should I use asphalt pavement?
There really are many reasons to prefer an asphalt pavement including: smoothness, quiet, stage construction, ease of maintenance, speed of construction, least user delay cost, ease of repair of utility cuts, no cure time, recyclability and now, that technology exists to design asphalt mixtures to reliably perform under any conditions of load and environment, there is no reason to consider anything else.
What impact does the production and use of asphalt have on the environment?
In many respects, asphalt is the environmentally friendly paving material. First, asphalt materials are 100% recyclable. Virtually all of the reclaimed Asphalt Pavement (RAP) that is removed from existing streets and highways is recycled into new asphalt mixtures. Improvements in technology have been steadily reducing the airborne emissions from the production and placement of asphalt pavement. Dust from the drying of aggregates is the major emission and is now almost totally captured and recycled. Other emissions are primarily combustion products from the burning of fuel to heat the aggregates and fumes from hot liquid asphalt itself. Fuel burners are now much more efficient, resulting in very complete combustion. Studies to date by the government and industry have shown emissions levels to be very low and have not identified any health hazard associated with exposure to asphalt fumes. The Environmental Protection Cabinet (EPA) has “delisted” asphalt plants because they pose no known risk to the public. Nevertheless, the industry continues to develop improved technology for reducing emissions and minimizing exposure.
Why does Smoothness Matter?
Studies have shown that a smooth ride is the number one concern of road users. Furthermore, another study has shown that initial smoothness improves the performance and lowers the maintenance cost of a pavement over its life cycle. Asphalt pavements start out smoother and stay smoother throughout their lives, making them the best choice for new construction.
How are roads paid for?
Gasoline taxes and other highway user fees are used to pay for road construction and maintenance in Kentucky. The people that use the roads, including the general public, businesses (trucks) and visitors to the state pay these taxes and fees. Currently, Kentucky has one of the lowest gasoline taxes in the United States but additional funds are needed to maintain our existing roadway system and to create new roadways throughout the Commonwealth. Additional funding would allow for structural and safety improvements to roadways throughout the state. Since Kentucky has a disproportionate number of deaths occurring from crashes on narrow, two-lane roadways, the welfare and safety of our citizens is at stake. Kentucky has a billion dollar investment in roads and bridges. This huge investment must be protected and properly maintained.
Where does Liquid Asphalt Comes From… A Barrel of Crude Oil is a Marvelous Thing
During the refining process, crude oil is super-heated and different products are produced at different temperatures. For example, petroleum gases, such as propane, butane and methane, start separating at temperatures of less than 104 degrees. As the temperature of the boiling crude continues to rise, other hydrocarbon-based fuels are recovered, including gasoline, kerosene and diesel, as well as lubricating and heavy oils. At the end of the process, residuals are left, which include liquid asphalt. The liquid asphalt is then used as a binder when mixed with aggregate and that’s the hot mix asphalt we’re all familiar with as a paving medium. Since it is a product of the refining process, asphalt is subject to the volatility of crude oil prices, which can have a significant impact on a project’s bottom line. Although it’s only 5 percent of the material in a standard mix, it represents about half of the cost.
What do I need to know about sealing my parking lot or driveway?
Over time, an asphalt pavement will turn from dark black to light gray through a process called oxidation. Oxidation causes the pavement to become more brittle and small cracks will eventually develop in the surface. These cracks in a pavement will allow moisture to seep in below the surface, saturate the soils below, and accelerate the pavement distress. A sealcoat should be applied and is most effective when the cracks are still small (1/8 inch wide) and is intended to fill those cracks and prevent them from becoming wider. Larger cracks should be cleaned and filled by a professional contractor who will use mechanical tools and blow hot compressed air into the crack to remove any moisture prior to sealing. Sealcoating is not recommended immediately after a parking lot or driveway has been paved. The American Public Works Association recommends waiting at least 90 days but suggests that a driveway be sealed within the first year. Sealing products vary from those available at local home improvement stores to professional grade products that are thicker and have a higher percentage of solids (sand, etc.) for filling cracks. In Kentucky, the general rule of thumb is that sealcoating is performed between May 1st and October 31st – from Derby Day to Halloween. Due to temperature and moisture limitations – sealcoating is not recommended in the winter and early spring months. The pavement must be dry prior to sealcoat application – preferably following several days of warm temperatures without rain.
Maintenance and Sealing
While the Plantmix Asphalt Industry of Kentucky (PAIKY) remains focused on our mission to promote, design, produce, and construct hot mix asphalt pavements – we frequently receive calls and field questions regarding sealing products and maintenance techniques. The information below is intended to provide some very basic information about sealing asphalt pavements. A properly applied sealcoat is designed to protect the surface, fill the small surface voids, and extend the life of the pavement.
All pavements will experience a slow rate of deterioration due to weather conditions – regardless of traffic loads. Over time, an asphalt pavement will turn from dark black to light gray through a process called “oxidation”. Oxidation causes the pavement to become more brittle and small cracks will eventually develop in the surface. These cracks in a pavement will allow moisture to seep in below the surface, saturate the soils below, and accelerate the pavement distress. If not maintained, small cracks will lead to larger cracks and additional deterioration. A sealcoat should be applied while the cracks are still small (1/8 inch wide) and is intended to fill those cracks and prevent them from becoming wider. Larger cracks (exceeding ¼ inch wide) should be cleaned and filled (a process called “crack sealing” or “crack filling”) by a professional contractor. Cracks should be cleaned of all debris using mechanical tools and by blowing hot compressed air into the crack to remove any moisture prior to sealing.
Sealcoating Driveways or Parking Lots
Sealcoating is a method of protecting your asphalt pavement by applying a coating to the pavement surface. The American Public Works Association (APWA) brochure entitled “Caring for your new Asphalt Pavement” suggests that Sealcoating should not be applied immediately after a driveway or parking has been paved. The APWA recommends waiting at least 90 days but suggests that a driveway be sealed within the first year and every 2 or 3 years after that.
Selecting Your Sealer
Many homeowners try to do sealing themselves but hiring a maintenance professional will give you better results. Products found in home improvement stores do not have aggregates and may lack the quality to withstand the weather and traffic when applied to the pavement. Professional contractors are able to heat the materials and have better equipment for applying them uniformly to the pavement surface. Sealers used by professional contractors are typically thicker, have a higher percentage of solids for filling cracks, contain additives to accelerate drying and reduce cracking, and have the proper aggregate content to provide an abrasive surface. The sealing products themselves are usually classified as either an “asphalt emulsion” or a “coal tar” sealer. Both products are widely used and effective. Generally speaking, coal tar sealers will provide a longer life, are more abrasive, resist fuel spills, resists ultraviolet rays from the sun, but they are typically more expensive than asphalt emulsions. Asphalt emulsions are generally not very resistant to fuel spills but some sealing products will modify the blend with special additives to make it more resistant to gasoline and oil spills.
In Kentucky – the general rule of thumb is that sealcoating is performed between May 1st and October 31st – “Derby Day to Halloween”. Due to temperature and moisture limitations – sealcoating is not recommended in the Winter and early Spring months. The pavement must be dry prior to a sealcoat application – preferably following several days of warm temperatures without rain.
How many coats and drying times
Similar to painting a room in your house – one coat is usually not sufficient. Additional, one thick coat is more likely to crack and not as effective as two thin coats. Typically, these products should be applied at a rate of about 0.2 gallons per square yard. Most sealers are applied in two coats and it is essential that the first coat dry before the second coat is placed. Two coats won’t cost much more than a single coat and should last longer and provide a better appearance. Water must evaporate from the material and, if placed too soon, the water from the first coat is trapped and tends to cause the second coating to stay soft – especially during hot, humid days. If the sealcoat is not allowed to dry completely, vehicle traffic will cause tire marking, tracking, premature failure, and may also stick to your shoes. At a minimum, allow the sealcoat to dry overnight (without traffic). Ideally, allow 24 hours of drying time.
Caring for your new Asphalt Pavement – American Public Works Association
Plantmix Asphalt Industry of Kentucky
PO Box 286
119 West Broadway, Depot Place
Frankfort, KY 40602