# Any road paving experts here? **URL:** \ **Category:** Factual Questions\ **Created:** [October 11, 2007, 4:57am UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322 "2007-10-11T04:57:10Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [October 11, 2007, 4:57am UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/1 "2007-10-11T04:57:10Z")
The race track at which I frequently drive my sports car (Summit Point Raceway, a road course, not an oval) has been repaved this week, and driving schools and races will be held on it on Friday, Saturday, and Sunday. Posters at a couple of the racing boards I frequent are bitching that the track owners should have allowed the surface to “cure” for some period of time (at least one suggested “months”) before allowing cars to race on it. However, no one has provided any evidence that such curing is necessary or even desirable. The claim seems to be that without curing, cars running at high speed will “tear up” the new surface. ISTM that when highways and regular roads are resurfaced, traffic (including trucks many times heavier than the average car) are allowed to drive on them almost immediately after the work is done. So I’m skeptical. Any road construction engineers who can give me the straight dope? Thanks. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [October 11, 2007, 6:59am UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/2 "2007-10-11T06:59:45Z")
IANARPE, but some questions are in order. What is the bituminous wearing course which has been installed at your race track? ID-2 is available in four different grades. ID-3 is sometimes used in extreme applications-it’s called airport mix in PA. The installation was done in what thickness? Was the old wearing surface milled? Was a tack coat applied? What is the undisturbed base dimension? Answer all of this, and I’ll give my Civvie bud a shout. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [October 11, 2007, 2:00pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/3 "2007-10-11T14:00:00Z")
[QUOTE=danceswithcats] IANARPE, but some questions are in order. What is the bituminous wearing course which has been installed at your race track? ID-2 is available in four different grades. ID-3 is sometimes used in extreme applications-it’s called airport mix in PA. The installation was done in what thickness? Was the old wearing surface milled? Was a tack coat applied? What is the undisturbed base dimension? Answer all of this, and I’ll give my Civvie bud a shout. [/QUOTE] I’m afraid I know nothing first hand. The OP in [this forum thread](http://www.dcsportbikes.net/forum/showthread.php?t=34036) says that the track was not milled everywhere, and has posted pictures of the crew at work, although I doubt you can determine which bituminous wearing course they’re installing, or anything else useful from them. (Thickness, maybe?) But that’s all I have right now. I may get more details when I get to the track tomorrow, although I’m unlikely to talk with anyone who’ll know which ID grade was used. At another forum people are claiming that the lateral loads of race cars cornering with sticky tires can ripple an uncured surface, and that other tracks have waited weeks or months before letting race cars run. (My suspicion is that that may not have been to cure the surface, but just a matter scheduling the repaving during a slow season, with no events scheduled in the following weeks.) ---
**Author:** ![Eureka](https://avatars.discourse-cdn.com/v4/letter/e/74df32/32.png) [@Eureka](https://boards.straightdope.com/u/Eureka)\ **Post date:** [October 11, 2007, 3:17pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/4 "2007-10-11T15:17:41Z")
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](http://www.bluegrassairport.com/050206RunwayResurfacing.html) 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. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [October 11, 2007, 4:52pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/5 "2007-10-11T16:52:24Z")
FWIW When Cal Club built the [Buttonwillow Raceway](http://www.buttonwillowraceway.com/) they let the paving cure for several months. ---
**Author:** ![RedSwinglineOne](https://avatars.discourse-cdn.com/v4/letter/r/a9adbd/32.png) [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)\ **Post date:** [October 11, 2007, 8:03pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/6 "2007-10-11T20:03:26Z")
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. ---
**Author:** ![Mycroft\_H](https://avatars.discourse-cdn.com/v4/letter/m/898d66/32.png) [@Mycroft\_H](https://boards.straightdope.com/u/Mycroft_H)\ **Post date:** [October 11, 2007, 9:16pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/7 "2007-10-11T21:16:12Z")
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 **RedSwinglineOne** 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 don’t know why Buttonwillow Raceway would have waited. Is part of the track concrete? ---
**Author:** ![Plynck](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Plynck](https://boards.straightdope.com/u/Plynck)\ **Post date:** [October 11, 2007, 11:10pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/8 "2007-10-11T23:10:40Z")
I am not a roadway expert (I think that **robby** 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. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [October 12, 2007, 3:33am UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/9 "2007-10-12T03:33:46Z")
Thanks, all, for the detailed replies. I think there is no basis in fact for the perception among my fellow racers that curing is required. It may have its origin in new courses (e.g. Buttonwillow cited above), in which **plynck** ’s concern about the proper compaction would be relevant, or with improperly repaired or patched underlying layers. Or it may just be a gut guy reaction. If a little bead of caulk around your tub requires 24 hours to cure, surely a big honking asphalt road surface must take weeks. But so far no one on the other side has offered any authoritative cites for curing, or even posted rational and competent-sounding posts like **plynck** , **Mycroft H.** , **RedSwinglineOne** , and others here have. You guys may be full of shit, but at least, in the finest Doper tradition, you have provided well-written and plausible posts. Over there they’re saying, It’s too soon…they’ll tear it up…These guys don’t know what they’re doing…Other tracks waited weeks before their first event, etc. But nothing substantial to back it up. I think it’s a tempest in a teapot, but I’ll see if I can dig up more facts from track staff tomorrow. Thanks again. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [October 12, 2007, 4:03am UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/10 "2007-10-12T04:03:34Z")
Here’s a thought: the straightaways aren’t likely to suffer from problems, as the cars are just zipping along, but the same can’t be said for curves. Centrifugal force has to be overcome by traction between tires and the road surface, or the car skids into the turn wall. We’ve all encountered intersections where the repetitive application of brakes has caused the bituminous paving to become lumpy and irregular over the last 50 feet. If that condition can be linked to insufficient curing, then perhaps that’s what they want to avoid by delaying use of the track. I’m imagining ridges resulting from the paving being pushed laterally as cornering force is applied. A bumpy surface for ordinary motorists is just something to make you spill coffee on your tie, but could cause Speed Racer to lose control. Thoughts? ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [October 12, 2007, 12:59pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/11 "2007-10-12T12:59:18Z")
what danceswithcats said. I am not expert on anything related to this, but I am a fan of motorsports. Racing creates a lot of lateral forces that normal driving does not. I remember the Dallas F1 GP in 1984. The track basically desintegrated with the heat and the stress from racing. I have driven over hot asphalt right next to the steamroller pressing on the next lane. No damage to the pavement. Racing might be different, though. Also, race drivers are a finicky bunch. Every time a track gets repaved (more so for partial jobs), everybody has an opinion (complaint). ---
**Author:** ![Fir\_na\_tine](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Fir\_na\_tine](https://boards.straightdope.com/u/Fir_na_tine)\ **Post date:** [October 12, 2007, 1:00pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/12 "2007-10-12T13:00:00Z")
[QUOTE=Plynck] I have been designing and specifying paved surfaces for over twenty years, and have been on more paving inspections than I can remember. . [/QUOTE] **Plynck** , lets go slightly off topic for a minute. If you are in fact slightly Nawth of Boston you’re familiar with this phenomena called ice, frost and snow we have during the winter and the joy of mud season. My driveway is 400 feet long and graveled. I’ve had several different pavings contractors stop by - unsolicited - and say they could pave it for x bucks. The figures range anywhere from $2,500. to $15,000. How does the average homeowner find the correct specification for a good driveway so he will know if the material being quoted is worth the money? I mean it’s all black, hot and gooey - how to tell if it’s “the good stuff”. ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [October 12, 2007, 7:49pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/13 "2007-10-12T19:49:53Z")
I asked my friend, the road engineer, who replied: > [@](#): > > think many race tracks are concrete-surfaced, but I called my > car-race-loving brother to ask and he says he’s seen both. I would think > that to maintain smoothness, a concrete-surfaced track would have to either > be continuously reinforced concrete (thus, constructed without transverse > joints), or diamond-ground on some regular basis to remove roughness at > transverse joints. But I really don’t know whether concrete-surfaced tracks > tend to be built as continuously reinforced concrete or regular jointed > concrete. > > Anyway, if it’s a concrete surface, yes, the concrete must be given time to > cure to achieve adequate strength before being open to traffic. Not that > race cars weigh very much so they’re not likely to do much if any early > damage to the concrete; the bigger issue is when construction traffic and > other heavy vehicles are allowed on. For road construction all states have > specifications on the minimum number of days and/or the minimum strength > achieved before a concrete surface can be opened to traffic. > > Note, days, not months. Depending on the time of year, the location, and > the mix design, it could be 28 days, it could be 14 days, it could be 7, it > could be 5, it could be 3. There are high-early-strength concrete mixes > used in “fast-track” paving projects that can be opened to traffic in 24 > hours. Rarely if ever, though, will time only be specified. The primary > criterion for opening to traffic is the strength of the concrete, as judged > from breaking sample beams or cylinders cast at the same time as the > pavement. > > Concrete gains strength due to chemical reactions, asphalt pavements do not. > The strength of an asphalt surface is based on the physical binding of the > stones by the asphalt cement, which in turn depends on the gradation of the > stones, the asphalt content, and the density achieved by compaction. That > said, there is a certain small degree of evaporation of volatile compounds > from fresh asphalt cement in the first day or two after placement, which > does contribute to a little stiffening of the surface. There’s a name for > that early evaporation, which I don’t think is “curing,” because it’s not > true chemical curing in the concrete sense, but it wouldn’t seem odd to me > if someone called it that. In any case, that’s a process of a couple of > days at most, not weeks or months. > > I personally can’t think of any reason why, with the right mix design, > placement, and weather conditions, either an asphalt-surfaced or > concrete-surfaced roadway couldn’t be opened to race car traffic within 7 > days at most. Race car tires are treadless, aren’t they? How would they > “tear up the surface”? Shear at the edges of the tires, around turns? For > an adequately banked and, if asphalt, adequately compacted surface, that > shouldn’t be an issue. And race cars are lightweight, as vehicles go. And > fast-moving dynamic loads do less damage than slow-moving and static loads. > So I don’t see what the problem would be. > > My car-race-loving brother did mention an issue with a recently repaved > asphalt track (in Atlanta?) that didn’t involve any damage to the surface, > but rather some boring races for the first year or so because the surface > was so smooth that no good grooves (ruts, rather) had been worn in it yet, > so the drivers had to go slower than they wanted to. Obviously, that’s not > an argument for keeping cars off, but rather putting them on, especially > allowing them to practice at low and medium speeds. > > Hope that helps. ---
**Author:** ![Mycroft\_H](https://avatars.discourse-cdn.com/v4/letter/m/898d66/32.png) [@Mycroft\_H](https://boards.straightdope.com/u/Mycroft_H)\ **Post date:** [October 12, 2007, 7:52pm UTC](https://boards.straightdope.com/t/any-road-paving-experts-here/422322/14 "2007-10-12T19:52:02Z")
[QUOTE=Plynck] … 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). [/QUOTE] **Plynck** , you are so cynical! 😛 (Which reminds me of a T-shirt I saw once that read “I’m not cynical, just experienced.”) Good post! You know of what you speak. **danceswithcats** , in Minnesota the lumpy pavement at stop conditions due to deceleration and acceleration is called ‘shoving.’ In the old days they would make the section a bit thicker, but that didn’t help much. The hardness of blacktop is controlled by the viscosity of the oil or bitumen, which is sort of related to the melting point among other factors. This was measured by the Penetration value; how deep a pin with a weight on it would sink into the bitumen at 77 deg F. A problem with defining the test at one temperature is that it could produce a large variability of viscosity at high or low temps (e.g. 110°F or -30°F, both easily realized during a year). The defining measurement of asphalt material was changed about 10-15 years ago to Performance Grade. For PG asphalt the defined viscosity is measured at a high and a low temperature and has resulted in better performance although at a higher cost. A typical blacktop mix in our area is PG 58-28 which means that the bitumen binder meets the specified viscosity at 58°C and -28°C. You can also call for PG 64-28 or PG 64-34, but these cost more because of the difficulty of maintaining the specifications in the broader range and that they aren’t made much in Minnesota. With the newer PG grade asphalt there has been less problem with shoving at intersections, although it can still happen. But, I don’t know if this would have anything to do with paving of racetracks. It may be possible that the speed and frequency of vehicles would heat up the pavement enough to cause problems, but that would not be fixed by “curing” but instead by defining a particular grade of asphalt. As others have mentioned, it may take someone specializing in racetrack design. On my roads people don’t go much faster than 65 mph. **Fir na tine** , for driveways (and elsewhere when it comes to that) the supporting base is extremely important. If your muddy drive is caused by water from above (rain, snowmelt), paving should be OK. If it is caused by water from below (springs, high water table) or the side (an adjacent swamp or if it is in a low area), that will likely make a poorly supporting base for the blacktop. The cheap guys would probably just place 1-1/2” of blacktop and call it good. The expensive guys may want to dig out poor areas of clay and replace with better dirt and place a 2” layer of gravel on the drive before paving. If you have poor soils, digging them out is a good idea for long term life of the work. The addition of gravel is a good idea too. Most low traffic roads (and parking lots) don’t fail because of the blacktop. They fail because of bad supporting soils or underlying drainage problems (which leads to poor support). As for what to ask for, or to listen for, you want them to place a top or wearing course (to use **Plynck’s** good phrasing) and see if it is from a State certified plant. If the blacktop is typically used on State, County or City projects, it will be “good stuff.”