All About Asphalt
*Information on this page obtained from www.myasphaltpavingproject.com
How can your asphalt paving project fail? There are several culprits. By choosing a reputable contractor and using a little preventive maintenance, you can be sure that your asphalt paving project will last a long, long time.
- The Sun and the Air. In the aging process, the thin layer of mastic on the surface of the asphalt pavement ages (oxidizes) from exposure to air (oxygen) and sun (ultraviolet light). In the oxidation process, the chemistry of the asphalt changes, turning it more brittle, less sticky (adhesive) and less elastic. In cold weather, cracking can begin. The thicker the film of asphalt, the longer you have before there is any damage. Hint: A preventive maintenance light application of new asphalt (a fog or other seal) on the aging surface rejuvenates the surface, slows the aging process and protects the rest of the pavement structure.
- Traffic. Traffic continuously flexes and fatigues the flexible pavement. As the fatigue stresses build up, micro-cracks begin to form, especially when it gets cold. While these micro-cracks self heal as the asphalt binder flows back together in hot weather, after enough time the micro-cracks get bigger and form fatigue cracks. Hint: That preventive seal mentioned above will also seal these micro-cracks and extend the pavement life.
- Water. Remember, water is the enemy. If surface water can’t get away, it works on debonding the asphalt binder from the aggregates. The loose, unbound rocks can then ravel off the road. If water is allowed in the base layers, it can wash away the underlying pavement structure. If moisture is trapped underneath the pavement, the water vapor creates pressure, forcing the asphalt to bleed to the surface, leaving the aggregates unbound and the pavement unstable. Hint: Remember the three most important things in pavement design? Drainage, drainage and drainage.
- Insufficient Design. The pavement structure needs to be able to handle those 18-wheelers, or whatever the loading will be on your asphalt paving project. This begins with the sub-base, the base and everything that’s on top. See the section on pavement design for more information. Hint: As traffic increases, it may be necessary to increase the thickness of the pavement by adding more layers.
- Poor Materials. The liquid asphalt (AC), the aggregate, the sand (fine aggregate) and the job mix formula can all cause problems if they don’t meet industry standards. If the asphalt is too soft, the problem will be rutting in the summer. If it’s too hard, the problem will be cracking in the winter. If the aggregate is not right, it won’t have the needed structural strength. If there is too much asphalt, it will rut and bleed. If there is not enough asphalt, it will crack and ravel. Hint: Make sure the materials used on your asphalt paving project meet standard specifications and quality control requirements. Choosing a reputable, experienced contractor is a big step in the right direction.
- Poor Construction. You can have the best pavement design and the best materials, but if they are not applied properly, there’s a good chance the project will prematurely fail. If the asphalt pavement is not properly compacted, the air voids will be too high, allowing in water. If the air voids are too low because of the wrong temperature and/or too much compaction, the mix will be subject to pushing, shoving and rutting. If the asphalt is not well mixed, the proportions of rock sizes will vary throughout the pavement (segregate), and the mat will not have the correct structural strength. If there are poor joints between passes of the paver, water can enter into the pavement structure. Hint: Reputable contractors know the pitfalls and take measures to prevent them. Confirm that they have taken the necessary measures and use a quality control plan.
- Lack of Maintenance. With a planned preventive maintenance program, your asphalt paving project can last nearly forever (perpetual pavement). Engineers estimate that each $1 spent on preventive maintenance can save $3 – $10 in future rehabilitation costs. Hint: See the sections on preventive and corrective maintenance for information on methods to preserve your asphalt paving project and save money.
Just as you put oil in your car and you paint your house, you should do a little preventive maintenance on your asphalt paving project. Preventive maintenance is defined as those activities that correct minor surface deficiencies of a pavement in good condition and extend the pavement life by protecting the structure. They include:
- Drainage maintenance. Remember, water is the enemy.
- Crack Seals. A highly polymer-modified asphalt is heated and applied to fill and seal cracks. This treatement helps to reduce water intrusion. The SHRP, the multi-million dollar federal study, found that thin asphalt surfacing, chip sealing and crack sealing are the most cost-effective maintenance treatments.
- Fog Seals. A diluted water-based asphalt emulsion is sprayed on the surface of the pavement. The emulsified asphalt allows a very light layer to be evenly spread on the surface. The water evaporates leaving just enough asphalt to fill in any tiny cracks, cover the oxidized surface asphalt and waterproof the surface.
- Chip Seals or seal coats. Liquid asphalt (may be emulsified, hot applied or cutback) is applied to the surface, immediately followed by a layer of aggregates. The asphalt fills any cracks and seals and waterproofs the surface. The aggregate restores skid resistance and adds another layer of protection.
- Slurry Seals. An asphalt emulsion is mixed with fine aggregate and additives and placed in a very thin layer to fill, seal and renew surfaces and protect against moisture and the sun. The seals can also can improve skid resistance.
- Micro Surfacing. This application is a high performance slurry seal using polymer-modified asphalt, high quality fine aggregates and special chemicals that allow quick cure for thicker applications, filling small ruts and fast traffic return.
- Thin and ultrathin asphalt overlays. Layers up to one inch of asphalt surfacing are placed over the existing surface. These renew the surface, restore skid and provide a smooth black riding surface.
The National Center for Pavement Preservation website is a comprehensive library of useful information about preventive and corrective maintenance.
Corrective maintenance activities fix pavement distresses to return the pavement to acceptable condition. These activities include pothole fillers, patching and repairs, surface treatments that fill and seal cracks, slurry seals, micro-surfacing, and thin (<1”) overlays of asphalt surfacing.
Hint: Before doing any corrective maintenance, it’s important to determine the cause of the distress. You can fill a pothole, but if a drainage problem or poor base is the cause and it isn’t fixed, the pothole WILL come back.
Caltrans has developed an excellent guide to pavement maintenance.
Contact us now for a free estimate and quick reliable service. A qualified estimator will meet with you personally to evaluate your asphalt paving needs and promptly provide a free written estimate. Alaniz Construction also excels at developing pavement maintenance plans for your long term needs.
Fremont, CA 94538
(510) 770-5020 FAX