If y'all want an expert opinion on this... I asked my older bro. He's VP of a construction company that does bigger projects (major highways, airports, etc, down in GA and FL).

Quote:
So basically, what Summit is doing isn't bad. In fact, it's what most people would do.

Q: Are there any comparisons between highway and racetrack paving?

Forbes: It is not night and day. It is like the difference between assembling a grandfather clock and assembling a wristwatch. All of the processes are similar; they're just much more fine-tuned for a racetrack. They're more critical, and not to put down or understate the importance of highway paving, (but) they're dealing with a whole different set of loading criteria than a racetrack does. The difference is, when a highway asphalt surface fails, it almost never has a life-or-death consequence. When a racetrack pavement fails, it could mean the difference between life or death. There are just tighter controls. Everything is done a little slower.

Not a road construction engineer. But a teller of anecdotes.

When the main runway at the airport in Lexington, KY was resurfaced just over a year ago, they closed the airport for 48 hours, put hot asphalt from 4 different plants on the runway in various locations, planned an elaborate ballet of road construction vehicles, and prayed it didn't rain. (announcement from the airport prior to the resurfacing)

Airplanes--which are a lot heavier than cars-- and which travel pretty damn fast-- were allowed to start landing on the runway 48 hours after they closed the runway. It seems to me that the 48 hour mark was intended to permit some time for curing, as well as just some leeway incase something took longer than anticipated.

I don't know all the specifics, but I did work for a paving company when I was younger. Asphalt is basically aggregate (gravel and sand) and tar. I believe it may have a small amount of cement and some solvents in it also. For the most part, asphalt doesn't 'cure', as much as it cools. When it comes from the plant, it looks basically like (steaming) hot, oily gravel. I believe it is something like 275 degrees F. As it cools it becomes stickier. It is spread out flat and compressed with a roller. Once it is cool, it is basically done. We regularly drove over it the same day.

I have never heard of curing as applied to bituminous pavement. Concrete pavement should not have traffic loads for a while. With a driveway entrance I designed for a Post Office we checked with a testing firm and allowed vehicles back on within 4 days, but that was pushing it. Usually you try to wait at least a week. Concrete will continue to harden for a long time (years?), but for all practical purposes, a month will get you to 98% of absolute hardness.

But, back to blacktop – Blacktop sets up differently than concrete. As [the poster above] indicated, it cools and then sets up. Before it cools it is important to have it compacted by steel drum and rubber tired rollers. (What are still referred to by some as “steam rollers.”) The amount of compaction is defined and measured but once the material cools, it can’t be decently compacted any more. (If you let the bituminous cool without compacting I would imagine it would just crumble if driven on.) Over time I suppose that blacktop might compress a bit more, but not substantially. Also over time it will lose a bit of surface oil due to weathering and not be as black, but again, for the most part this is not substantial. After 10, 20 or 30 years the weathering will take its toll, but I think that is beyond what you are talking about.

For roadways I’ve been project manager on we let traffic get on as soon as it is striped with pavement markings. (First striping never lasts long but that is probably due to the effect of fresh oil.) For smaller patches, this can be the same day after it has cooled down

I am not a roadway expert (I think that [another poster] has more expertise with this), but I have been designing and specifying paved surfaces for over twenty years, and have been on more paving inspections than I can remember. A roadway paving expert may not be able to answer your question; it may be more geared toward a racing expert.

In the Northeast, paving is traditionally done with bituminous concrete pavement, now renamed "hot mix asphalt" or HMA (presumably renamed so that all the manuals can all be reprinted at taxpayer expense to reimburse some pol's nephew). The mix is a specific gradation of aggregate (gravel or crushed stone) with a percentage of bitumen (typically 4-8%, depending on the particular application). Stone size is larger and bitumen percentage is less where more bearing strength is required. This is called the binder or base course, placed on a compacted gravel course. As you might expect, this will leave a coarse looking surface that is also hell on tires. So this structural layer is then topped with a mix that has smaller stones and more bitumen (the top or wearing course). While this does certainly have some bearing strength, it is primarily to provide an acceptable driving surface.

As stated above, the mixes come heated from the batch plants, and are placed while still extremely hot. The bitumen coats the aggregate and causes it to adhere to itself and damn near everything else within 20 feet of the paving job. After placement, the pavement is rolled for as long as is practical, usually an hour or two. This is to make sure that the aggregate is compacted as much as possible, and to fill as many voids as possible. After rolling, cars can drive on the pavement. I've seen cars allowed on pavement in less than an hour when necessary, but most good pavers prefer to leave this for a longer time, if allowed.

The above was for a new paving project, but it isn't all that different for an "overlay" job. Sometimes a new top course is placed directly over the old top course if there is no concern as to the raised height of the roadway. Otherwise, the existing surface is cold-planed or milled down a certain amount (as danceswithcats referenced), and then repaved with new top course.

Over time, bitumen in pavement will slowly "dry out", losing some volatiles. Therefore, standard practice for overlays is to have a truck spray asphalt emulsion over the old surface to provide a "tack coat" prior to placing the overlay. The thought is that the old bituminous pavement will absorb some of the bitumen from the new pavement, thereby robbing it of some of its use in the new pavement. The jury may be out on this practice: I have heard experts argue that it is pointless and a waste of money. However, most engineers feel that it is better to be safe, especially if the existing pavement has some age to it.

It would be interesting to know if the pavement was completely removed and replaced, or whether it was an overlay. If completely replaced, the waiting period might be to discover if inadequate compaction left loose areas that would cause the pavement to deform or sag.

If an overlay, then I am stumped. In normal roadway or highway paving, no "curing" is required. However, it is unusual for them to see the intensity that racing courses see; hence my original reference to asking a racing expert. If this is standard practice in the race industry, I can only surmise that it is to let the bitumen dry out a bit to ensure that the pavement will not deform under intense racing.