You Bet Your Asphalt

While running errands yesterday on a roundtrip drive of no more than 20 miles (32km) I bypassed three road repair crews: two simply patching potholes and a third stripping the road surface in preparation for repaving. At all three sites the familiar aroma of asphalt was in the air. Getting the work done now is a sensible precaution. There is not much more than a month of more or less reliably favorable weather in this corner of the world. You never know about November; it could be anything from a heat wave to a deep freeze with any variety and quantity of precipitation. Emergency repairs aside, roadwork not done by then had best wait until spring.
 

Last week while working outside my house I was approached by a fellow about the asphalt on my own driveway. You know the pitch. Anyone with a blacktop driveway has heard it: “I see your driveway is in bad shape. We’re redoing your neighbor’s around the corner. Hey, we’re here, we have the equipment. So, we’ll make you a special offer.” I passed on the multi-thousand dollar special offer. I’m a cheap old bachelor. I don’t replace things like windows, countertops, or appliances unless the current ones are actually broken. (Unfashionable doesn’t count as broken.) Also, when repairs are within my skill set I do them myself. The same goes for my driveway. I patch it when it needs patching. It is not in bad shape overall despite the remarks of the pitchman: there were no loose chunks or potholes except for one spot where the driveway meets the road. Snow plows in the winter sometimes catch there and cause damage. It has happened before and will happen again. It is an easy fix. The special offer did at least prompt me (belatedly) to make it.

Some professionals distinguish among bituminous concrete, blacktop, asphalt, and several other terms, but even the experts are inconsistent in their usage. The words are used interchangeably in everyday speech. It’s fair enough to call pretty much any thick hydrocarbon sludge “asphalt” (with or without aggregate and whether mostly dry or mostly liquid) though there are different mixes for different purposes. A more significant distinction is the source. Natural asphalt can be can be found at or near the surface in areas where it has gurgled up from deeper petroleum reservoirs. These natural deposits range in viscosity from hard and crumbly to wet and sticky. So-called “tar pits” such as those at La Brea are asphalt, not tar. Non-natural asphalt is a byproduct of petroleum refining. When you crack crude oil by successively separating out the various fuels and lubricants (kerosene, gasoline, diesel fuel, etc.) you are left at the end with a residue of asphalt. You can’t help it. Fortunately there is a market for that, too. Further, the formulations of asphalt from refineries can be adjusted to suit specific needs. The kind you dig out of the ground is catch-as-catch-can; each deposit has a unique admixture of sand and other substances.
 
Natural asphalt deposits were exploited by the earliest civilizations for waterproofing. From Sumerian times onward asphalt was used to secure cisterns, sewers, and boats against leaks. The Greek word “asphaltos” means “secure.” It supposedly waterproofed the reed basket in which the future King Sargon as a baby was set adrift in the Euphrates in 3800 BCE. Its first recorded use as pavement was 625 BCE in Babylon for a road from King Naboppolassar’s palace to the north gate of the city. His son Nebuchadnezzar paved more roads from the palace. The idea didn’t catch on more broadly in ancient times however. The Romans, inveterate roadbuilders though they were, ignored the stuff as a paving material. They used it to line baths, aqueducts, and drains. They used it to caulk hulls. They didn’t surface roads with it. The reason was that Romans were aware of asphalt’s weaknesses. They intended their roads to last, and last they did. As late as the 18^th century most of the best roads in Europe were still the old Roman ones with their multilayer bases, proper drainage, and fitted paving stones. Asphalt pavement is relatively inexpensive and provides a great surface, but it does suffer from weather and traffic. It requires maintenance. It doesn’t last.
 
Today our calculations are different. The upfront cost of building a four-lane interstate highway to Roman standards would be prohibitive, and it still wouldn’t hold up to pounding by modern heavy vehicles. We expect constantly to maintain and repair our roads, so relatively cheap asphalt makes economic sense, as it has for well over a century. There is some competition from concrete, which, though more expensive than asphalt initially, lasts longer, but eventually concrete must be repaved, too. It is repaved with asphalt. Asphalt is not only affordable straight from the refinery, it also is endlessly recyclable. It can be torn up, heated, and laid right back down again. It is, in fact, the most recycled material – more so than aluminum cans. In the US, the EPA’s position since 2002 is that asphalt by itself is not a significant pollution hazard.
 
As that may be, I patched that pothole in the driveway yesterday. I had a couple of bags in the barn. One was enough. If snow plows damage the driveway again this winter, I’ll patch it again next spring. If only we could repair the potholes in our lives so easily.
 
 

Randy Newman – Potholes