Asphalt is used to construct and maintain roads, parking lots, bike paths, and more. It is also highly versatile, affordable, and durable.
Its dark color contrasts with road markings and reduces glare, making driving safer during inclement weather conditions. Additionally, its color allows it to absorb sunlight and heat – melting snow and ice faster than concrete. For professional help, contact Asphalt Paving Philadelphia now!
Asphalt pavements have different performance characteristics, depending on the volume and types of traffic they serve. For example, the stiffness of an asphalt mixture is critical in determining its ability to support a load. The stiffness of asphalt concrete can be determined by a number of tests. The most common is the Structural Number (SN) test, American Association of State Highway and Transportation Officials (AASHTO) designation T 190/99.
Another important strength factor is the aggregate base, which distributes stress over a large area of the road. The thickness of this layer is dependent on the condition of the soft subgrade. For a typical design, the soil should be analyzed to determine its R-value, which is used in combination with environmental and loading criteria to determine a required structural number for the asphalt layer.
The chemistry of the asphalt binder also affects the resulting strength of the asphalt pavement. The quality of crude oil, its refining process and the resulting additives all affect the binder’s properties. A binder with high heat stability, low permeability and lower viscosity allows for the use of a much thinner pavement layer, while one with very high viscosity requires the use of a thicker layer.
Additives can improve the performance of the asphalt paving material by making it less brittle or increasing its ability to carry loads. For example, adding styrene-butadiene-styrene block copolymer or styrene-butadiene rubber polymers can increase the flexibility of an asphalt mixture. These additives can also help to reduce cracking and rutting.
An additional way to improve the strength of an asphalt paving material is to add fibers to it. These fibers are made from materials such as wood, polypropylene or steel and can be added to HMA to make it more resistant to damage such as rutting and cracking.
An additive that can help to improve the strength of an asphalt paving mixture is a stabilizer such as calcium phenate, which increases the stiffness of the mix and helps to keep it from cracking at low temperatures. In addition, an admixture that increases the viscosity of the asphalt binder can improve its ductility and durability in cold weather conditions.
Durability
The durability of asphalt paving depends on many factors. Careful selection of mineral aggregates is critical, in terms of their gradation, angularity, toughness and soundness. These qualities are essential for resisting permanent deformation failures. Careful construction and proper compaction are also crucial. These practices must be employed to ensure the asphalt can withstand traffic loads and weather extremes.
The chemistry of the asphalt binder is also important for its long-term durability. It can be affected by oxidation, volatility and polymerization. These phenomena are influenced by temperature and are a function of the amount of time that the mixture is exposed to air. The presence of moisture may also cause the asphalt to deteriorate.
Governmental transportation agencies, pavement designers and contractors acted on the growing concern that simply combining ingredients in a prescribed manner was not producing asphalt pavements that met expectations for long-term performance. They developed balanced mix design (BMD) as a more realistic approach to designing asphalt mixtures.
BMD takes the guesswork out of achieving desirable performance by using actual laboratory test data to predict the material’s behavior in specific application conditions. It is a more effective method than traditional prescriptive mix designs that use past experience and specifications to determine the amount of each ingredient that should be used.
In the laboratory, BMD results show that SMA-13, Superpave-20 and ATB-25 are comparable in their ability to resist fatigue distress. However, there are differences in their dynamic stability, resistance to rutting and low-temperature cracking.
The resistance of asphalt to rutting depends on a number of factors, including the type of granular material and the temperature at which it is placed. In general, colder asphalt mixes are more susceptible to rutting than warm-mixes.
Rutting resistance can be improved by reducing the percentage of granular material in the mixture. Another way to improve rutting resistance is by paving the surface layer with an appropriate density. This is especially important for heavy-duty roads.
Proper longitudinal joints can significantly extend the life of an asphalt surface. These joints should be constructed in accordance with the standards specified in Standard Construction Drawing BP-3.1.
Safety
Asphalt is a very flammable material. It should be kept away from flames, sparks and cigarettes. It should be stored in a well-ventilated area, or in a covered container. A fire extinguisher rated B or AB should be on hand. Asphalt fumes are poisonous and can cause lung and breathing problems. They can also irritate the eyes and skin. Long-term exposure can cause bronchitis. Wearing personal protective equipment (PPE) can reduce exposure. Wearing thermally insulated gloves prevents burns and stops solvents from soaking into the skin. Long sleeved shirts and pants protect the body from chemical contact, and safety shoes or boots protect the feet. Wearing a face mask is recommended to prevent breathing in fumes. Enclosing kettles and mixing operations helps to prevent overexposure to fumes.
Asphalt mixes must be stiff enough to resist distortion and strong enough to withstand the impact of heavy vehicles. They must also be able to flex slightly in order to handle the pressures of tires pushing down on the road. Insufficient stiffness and flexibility in an asphalt mix can lead to rutting, fatigue cracking, corrugation or crocodile cracking. The stiffness and resistance to distortion of the asphalt mixture can be achieved by proper aggregate gradation and compaction, as well as appropriate asphalt binder content and temperature.
The flexural strength of the asphalt mixture can be accomplished by adding finer aggregate and/or increasing the binder content or temperature. A low viscosity asphalt binder is preferred to a high viscosity. A tack coat can be added to improve adhesion and reduce surface cracking. In addition to standard test methods such as volumetric properties, advanced viscosity, rheology and aging tests can be used for predictive modeling of asphalt paving mixes.
During the paving operation it is important to watch for signs of trouble such as excessive vibrations, pulsations or slippage of the paver or materials. It is also important to monitor the temperature of the asphalt mix, particularly during cool weather paving. When a mix is too cold to be placed or compacted properly, it should be removed and replaced with hotter asphalt. This can be avoided by maintaining constant monitoring and recording of the asphalt mix temperature throughout the paving operation.
Maintenance
Asphalt is a very durable material, but like any pavement it does require regular maintenance to ensure that the surface lasts as long as possible. Commercial asphalt maintenance requirements are important to the safety and functionality of parking lots, sidewalks and other walkways. If not addressed, cracks and potholes can develop into serious problems that can result in costly repairs or even the need for removal and replacement of the entire asphalt surface.
Asphalt paving requires a 6-step process including demolition and removal of existing surfaces, grading and sloping to allow water to drain from the pavement, adding the binder layer to give the surface strength and durability, installing the new surface, adding the final rolling to smooth out the asphalt. The surface is then sealed to protect the asphalt from weathering and contamination.
Heavy loads, frequent exposure to the sun’s UV rays, poor drainage, and temperature extremes can speed up asphalt deterioration. Regular maintenance can prevent these problems, but once damage starts it is crucial to repair cracks as quickly as possible before they expand into major problems such as potholes.
It is also important to keep your asphalt clean by cleaning oil and other chemicals from the surface of the pavement and removing any dirt buildups. This will help extend the life of your asphalt and also make it look nicer for visitors to your business or property.
Lightly traveled roads and off-street pavements are constantly attacked by various destructive elements, eventually developing minor surface cracks that gradually widen and deepen. When the cracks get too severe, they weaken the base course and reduce load-bearing capacity. This leads to rutting and serious alligatoring that may require the pavement to be removed and replaced.
