The Top 5 Enemies of Asphalt
via http://blackdiamondpaving.com/2011/02/14/februarys-topic-the-top-5-enemies-of-asphalt/
Heavy Trucks
Problem — Asphalt fails much faster in areas exposed to garbage trucks, delivery trucks, moving trucks, and buses.
Reason — In asphalt engineering terms, heavy vehicles have much higher ESALs (Equivalent Single Axle Loads) than lighter weight cars. There’s actually an exponential, not linear, relationship between a vehicle’s weight and its impact on the asphalt. A typical car is .0006 ESALs (a 4,000 pound car with 2 axles) where a large garbage truck may be 1.4 ESALs. That garbage truck is the equivalent of more than 2,000 cars! The slower the truck is traveling, the more damage it is doing, as well. It may cruise through the roadways but it slows and stops at the collection areas – prolonging the pain, and the damage, to the asphalt.
What to do – Fill cracks in heavy traffic areas. Water intrusion itself is not a problem, but heavy loads combined with the softened, moisture-sensitive soils in much of the Bay Area leave asphalt with a weak foundation upon which it will bend and break.
Minimize heavy truck traffic through your property and re-locate collection areas, if possible.
If you have high turnover (residents/tenants move frequently) consider instituting a move-in/move-out fee to cover damage from moving trucks.
When doing reconstruction work, install much deeper asphalt sections (perhaps 4-6”) along the truck route and at the collection area and thinner asphalt sections (2.5-3”) in parking areas. Don’t install the same thickness of asphalt everywhere unless all areas get the same amount and type of traffic.
Sunlight
Problem — Areas exposed to sun turn gray and age much faster than those in shade or covered by carports or parking garages.
Reason — Extended exposure to sunlight can cause oil to suffer accelerated oxidation, which reduces its ability to hold the rocks together. On a molecular level, asphalt reacts with oxygen faster in the presence of ultraviolet (UV) radiation from the sun.
What to do — Protect the surface of the asphalt with a sealcoat. Apply less sealcoat, perhaps a single coat (or in some cases, none at all) in areas that are rarely, if ever, exposed to UV rays.
Surface Water
Problem — Areas with heavy water flow or puddles erode/ravel much faster than areas with little to no water flow.
Reason — Although the friction of water flow can pull fine aggregates from the surface and cause raveling and erosion over time, water itself does not “dissolve” asphalt. Rain water in the Bay Area is relatively pure, but irrigation water is sometimes reclaimed water and may be very basic/alkaline in nature (higher pH) compared to pure water, which is neutral (pH of 7). Water that is alkaline in nature breaks the large asphalt molecules into smaller pieces that are more liquid-like. Irrigation water may also contain some surfactants (soapy compounds) which also help oil break down in water, just as your dishwashing detergent does with grease.
What to do — Ask your landscaper to install drip lines wherever possible and keep watering to a minimum.
Keep areas sealcoated if they are subject to heavy water flow, particularly from irrigation.
In cases where there is heavy damage from water that may be very alkaline or contain surfactants (such as areas where cars are washed), add 2-4% latex to give the sealcoat and asphalt some additional protection on the molecular level.
Motor Oil
Problem — In areas where vehicles park, asphalt is saturated with oil and at the very least looks unsightly and at worst, starts to fall apart.
Reason — Asphalt has a relatively weak molecular structure. Other, related derivatives of crude oil cause the asphalt to break down. Asphalt is not broken up, in the sense of molecules being cut in two, but they become un-hooked pieces in a mixture of the other oils related to crude. The relatively warm weather in CA speeds up the process. Once the asphalt is chemically compromised, it can’t effectively hold the rocks together anymore.
What to do — A flathead screwdriver test is a great way to see how bad the problem is. If the screwdriver merely scratches the surface, the area can likely be scraped and sealed with a latex-based oil spot treatment. Latex does not easily dissolve because its molecular structure is more complex. And because it’s not crude oil based, it does not have a natural affinity for motor oil. If the screwdriver penetrates more than 1/4” to 1/2” into the surface, more costly repairs to the asphalt may be necessary.
Tree Roots
Problem — We’ve all seen it – tree roots wreaking havoc on the asphalt pavement. Given enough time, the roots always win and the repairs are a costly endeavor.
Reason — Tree roots are tenacious growers. Some trees seek moisture near the surface while others go much deeper.
What to do — Arrange a meeting with both an arborist and a paving contractor at the same time to determine a best-case, lowest-cost solution that will allow the roots to be cut and the asphalt to be fixed without compromising the health of the trees.
If planting new trees, consult an arborist about trees that will not overgrow the planters and do not have surface level roots. Also consider installing a root barrier to “train” the roots to go deep.
If mature trees exist and space allows, consider enlarging planter areas to give roots additional room to grow before affecting asphalt or concrete. In extreme cases, a comprehensive, phased tree replacement program may be necessary (although we always hate to see large, beautiful trees sacrificed for the sake of a parking lot).
Don’t overestimate the capabilities of a simple root barrier. They usually will not prevent that 50 year old pine tree from finding the water it wants. Again, an arborist can give you a reasonable assessment of where the roots may re-grow and how quickly they will return.
