Open graded surface for tracks

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Ciro Pabón
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Open graded surface for tracks

Post by Ciro Pabón » Mon Aug 28, 2006 7:32 pm

This comes from an idea by Mikey_s: does anybody knows if F1 racetracks use open graded base?

You know: a porous surface that drains the water and therefore diminish the amount of water a car throws when it is raining?

After watching MC image from Monaco, I can be almost sure they do not use it there. This is really unsafe: it is used routinely in freeways to avoid the blinding mist you encounter when you go at high speed behind another car (at least in Colombia). Besides, it avoid the formation of pools of water (I saw a lot of pools on Hungary's track).

I suppose it would be really difficult to try to design a mix that have enough porosity and, at the same time, enough friction in dry conditions, if I understand correctly the mechanism of adherence of F1 tires. Finally, it would cost an eye, because you need to lift the whole surface, put some drain ducts below it and then resurface.
Ciro

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Post by Mikey_s » Tue Aug 29, 2006 8:52 am

Ciro, thamns for posting this thread... at last something I am actually rather knowledgeable about! (even if the topic seems to be dull as ditchwater for the rest of the world!!)

The specifications for the track in F1 require a dense graded surface and have some rather tight requirements for aggregate skid resistance and surface regularity (although looking at the Istanbul circuit around Turn 8 you might be forgiven for wondering what happened to the specs there!). So no chance for Porous Asphalt in the near future. However, no question about the benefits in a wet race... it'd be brilliant.

I'm not sure that Porous Asphalt would be an appropriate mixture for general use on tracks for a number of reasons. Certainly early life skid resistance is poor, due to the binder covering on the aggregate, but in later life the (dry) skid resistance of the mixture is not too different to other mixtures, the flat profile of the aggregate on the surface presents a good tyre/aggregate contact surface area and, provided the polished Stone Value of the aggregate is adequate, you can get good skid resistance values. However, one of the problems with Porous Asphalt is that it relies very heavily on aggregate-aggregate interlock; if the surface suffers mechanical damage it just 'unzips' and the there would be a relatively rapid failure of the track surface. I'm not sure it would necessarily withstand the cornering/decelleration forces either. Having said that many aircraft runways are surfaced with the material and it doesn't (generally) fail there (although I had a very exciting site visit to Heathrow some years back for a runway inspection... they switched the planes onto the other runway for 15 minutes whilst we did it and it was kind of scary when the tower was calling us every few minutes with a countdown before the next 747 was going to land on us!... but that's another story.)

I'm not sure drainage of the layers would necessarily be a problem either; it is perfectly normal in highway contruction to place the drains at the edge of the pavement and manage water egress via appropriate falls on the surface.

But, I believe the achilles heel of using PA on an F1 circuit arises from the fragility of our beloved cars; imagine what happens first time Honda deposit a crankcase (or gearbox) full of lubricant onto the track; it seeps through the layer and sits on the bottom dissolving all the binder and then the structural integrity of the surface is shot! Nothing left to do but rip it out and re-lay it.

... and I'd still be interested to see how such a surface would stuff up the undertray d/f.... (how about just putting it on the straights! (or if you're feeling wicked, just on the corners!!)
:twisted:
Mike

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Post by NickT » Tue Aug 29, 2006 10:44 am

What happens if you have a damp or wet track and the weather suddenly turns very cold, wouldn't the track break up very quickly as the water expands when frozen?
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Post by Mikey_s » Tue Aug 29, 2006 10:50 am

Nick,

the answer is no; The voids content of the mixture is typically above 20%, there is ample room for expansion. The stuff is routinely used in many countries (unfortunately hardly used in UK, where it was invented!). However, there are some thin surfacings which are porous starting to creep onto the market in UK.

however, you raise a good point, ice prevention is an issue for this type of material in cold climate conditions and salt tends to disappear into the void structure after application!... shouldn't be a prob for F1 though!!
Mike

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Post by Ciro Pabón » Wed Aug 30, 2006 3:10 pm

Mickey_s, thanks for your explanation. Do you know of any public source where I can get the mix specifications for tracks that you mention?

Warning! It follows a long rant containing common information on asphalt for tracks... not suitable for all publics. :oops:

At the Autódromo de Rosario the structural team had to devise their own mixture, based on normal road specifications. Some tests were made with the pilots, actually resurfacing several times the same curve with test mixtures, and measuring the curve average speed attained. The record for the Autódromo was broken as soon as they raced on the new surface. To tell the truth, some curves lacking transitions were corrected.

I also worked on drainage design for El Dorado's second runway. Let me give this long explanation about it:

I suppose you know the work of Harry Cedergren, back in the 70's: in his seminal paper, he measured infiltration of water amounting to 40% (on dense bitumen) to 60% (on concrete) of the rain that pours on the highway. When I read about this for the first time in my life, it seemed counterintuitive. After all, we are taught that dense asphalt is, in principle, impervious to water. We tend to forget the high cracking it develops over time.

We take very seriously this infiltration problem in Colombia, where you have a lot of rain (Bogotá, up to 2.500 mm/year; Chocó, up to 10.750 mm/year :!: ). Besides, most soils in Colombia have a lot of clay: rocks degrade because of humidity into clay, not into sand by temperature cracking, like in non-equatorial countries.

Hailstorm in Bogotá (the white stuff is hail, not snow: no winter here).
Image

Besides, as you surely knows, highway engineers make all possible efforts to compact the granular base, wich creates a layer of very low permeability layer under the asphalt. As Cedergreen pointed out and you also surely know, the water pressure, or lateral hydraulic gradient, in this layer is very low, which makes hard for the water to drain.

The end result is that, when you construct in an equatorial country a percolating runway or highway, maybe 100 meters across, on a cut made on clay, you are creating basically a water pool under the track. I have personally found liquid water on test ditches, under the asphalt, one month after the last rain, in places with low watertable.

We started back in the 80's to use Cedergren system for drain calculations. To make short a long story, we use transversal drains in almost any asphalt or concrete surface we construct, specially on wide roads or runways. If we don't, asphalt life is reduced in half or more.

In a hard tropical rain, like the ones we have in Bogotá, (with drops the size of cherrys... :wink: ) I've seen personally El Dorado's runway drainages spilling water with such pressure that it reaches one meter away from the exit of the pipe, after a fall of maybe one and a half meters. All the time we inspect drainages, airplanes are landing (we do not stand on the runway) but I do not find it scary, but exhilarating. Actually, when I was younger and made aircraft models, I went once in a while to the end of the runway just to see the aircrafts taking off (sort of aircraft-spotting)... :)

Now I have to wonder if the bumps on the entrance of curves the pilots complain so frequently are caused by this lack of transversal drainage under the surface. After all, as you know well, the load of car on a track is negligible for structural purposes, so, in principle, tracks should not present any bumps or irregularities caused by traffic loads. I am not sure about shear stresses by braking, that I suppose are phenomenal.

Anyway, I'd bet my slide rule on the idea that most bumps are caused by temperature stress (freezing of soil or heating of surface) and soil humidity. At the entrance of curves, where the superelevation is higher, the drainage problems and braking stresses are higher...

Finally, did you look at MC photo I mentioned? Take a good look at the quality of the patch to the left... it is really such an ordinary repair job as it seems to me, or it is just that I am not understanding something?
Ciro

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Post by Mikey_s » Wed Aug 30, 2006 5:32 pm

Ciro,

responding to your points one by one;

Inf on the track specs; leave it with me, I'll revert with the information. I have changed jobs (and country!!) since being involved in those contracts, I've asked a colleague to send me some detail.

Your race track mixture tests intrigue me; typically early life skid resistance is not too good as the binder must wear off the aggregate prior to gaining the full friction (tyres/bitumen can be rather slippery, especially in the wet).

Drainage; I am not familiar with Cedergreen (in truth I am not a pavement engineer, but a binder man. Having said that over the past 23 years I have learned a little about mixtures and pavements!! My involvement in the contracts typically relates to binder specifications and then mixture spec and design... the pavement design has already been done by the time I get involved - we just have to meet the specs for thickness and stiffness).

I am not familiar with your paving techniques in Colombia, but clearly minimising water ingress is always an issue. The solutions vary, especially on wide pavements, but placing an appropriate fall on the pavement and minimising crack formation (by building the layer stiff enough, and/or thick enough to avoid cracking) is critical in this respect.

As regards typical aircraft runway construction in EU, it is common practice to place 50mm of Porous Asphalt (OGFC) over a dense graded Marshall Asphalt, with full depth bituminous bound mixture on a granular base. Longitudinal drainage takes care of the run-off water from the pavement. The (distinctly!) non-equatorial climate in Europe requires non-frost susceptible construction to a depth of typically 450mm; therefore it is implied that the subgrade must be kept dry.

I would be surprised if the bumps on the track were caused by poor drainage, but without core samples I guess we will never know - certainly I am continually surprised by how bumpy some of the tracks are when the surface regularity requirements are so tight.

I did take a look at the pic of Monaco - very poor workmanship/mixture design... probably the Monte Carlo highways agency is rather poor as it is not a large principality!!

How about you and I propose some (all expenses paid :lol: ) track inspections to the FIA, perhaps we could become their advisors on construction... to save on travel costs we could met with them on race weekends as they would already be there!!
Mike

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Post by Ciro Pabón » Thu Aug 31, 2006 1:57 am

Mikey_s wrote: I would be surprised if the bumps on the track were caused by poor drainage, but without core samples I guess we will never know - certainly I am continually surprised by how bumpy some of the tracks are when the surface regularity requirements are so tight.
Well, this is exactly Cedergren's point.

About the track surface inspection: what they really need to inspect is the alcohol content of people leaving the parties after the race. I'll take the girls, you take Kimi.
Ciro

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Post by Mikey_s » Fri Sep 01, 2006 9:21 am

Ciro,

bad news I'm afraid... it seems there is no publicly available information on the specs for F1 circuits. I asked a colleague who looks after the racing aspects of the bitumen business andgot the following response;

Rainer Hart has a deal with Hermann Tilke / Charlie Whiting / the FIA as far as I know, and it may well be that Rainer sets the specs himself. I know that he is especially keen on scrutineering the asphalt composition (aggregates are checked on site, in the quarry), asks for test section(s), and controls the finished layers, especially evenness.
However, what was interesting was that Shell is currently looking at developing a binder specifically for racetracks - my colleague was at Monza last year discussing it, but there are some legal/licence issues which need to be sorted out apparently.

some (not too technical) information on the tracks here;


http://www.shell.com/home/Framework?sit ... 60702.html
Mike

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Post by Guest » Fri Sep 01, 2006 10:42 am

I am far from an expert on the subject, but I've read somewhere that in the Netherlands, where they use this kind of surface a lot, there seems to be a problem with it.
On roads which don't see much traffic, like racetracks, dirt fils up the pores, so when it rains, it becomes more slippery even. Can't be good!

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Post by Mikey_s » Fri Sep 01, 2006 11:08 am

abarth,

In the Netherlands Porous Asphalt is mandatory on the trunk road network. As with any surface there are some issues, but anyone who has driven a car on PA will tell you that it is a fantastic surface. It is quiet, much quieter than cement concrete and significantly quieter than most asphalt surfaces, and in the rain there is quite simply nothing to touch it; Strangely the UK highways agency doesn't like the stuff and argued that minimising spray from other vehicles (which it does fantastically well) only made drivers speed up. in their view it was safer when drivers could not see the car in front as they would slow down!! (yeah, right!)

The pores do clog eventually, but the surface can be cleaned (expensive) and in a typical European climate, where it rains relatively frequently, the pumping action of traffic serves to keep the pores from clogging very quickly. Having said all of that, even when clogged it is still quiet to drive on and the spray is still far lower in rainy conditions. Another shortcoming is that it does not last as long as a dense surface, so more frequent resurfacing (e.g. every 7-10 years) is required. Some questions have been raised over the early life skid resistance of the material because the aggregate (stones) are covered with a thick layer of bitumen (black glue) which must wear away before the full skid resistance is achieved.

My personal opinion is that it is a great surfacing and from personal experience I know that when you find a stretch of PA in the wet it is really like someone has turned the rain off...
Mike

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Post by flynfrog » Thu Mar 08, 2007 11:13 pm

I learned in my civil eng class that indy is paved with PA

just to reignite this long lost gem of a thread

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Post by Mikey_s » Mon Mar 12, 2007 11:13 am

FF,

Unless it has been resurfaced quite recently I'm afraid that Indy is not PA. I have a small cube of the track surface sitting on my desk and I know the company that surfaced the F1 part of the track. It is a dense graded material based on blast furnace slag. Furthermore, the problems in 2005 with turn 13 were a result of retexturing of the surface by diamond grinding. This is not a solution that one would apply to PA and is used to re-texture dense mixtures that have become polished.

Whilst PA is a good surface for regular highways, I'm not sure it would withstand the stresses in the acceleration and braking zones that F1, or other racing formulae, impose... but it would be interesting to see it improve the spectacle on a rainy race.
Mike

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Post by flynfrog » Mon Mar 12, 2007 3:26 pm

i thought the same thing the gues speaker insisted i was

To be honest i belive you more than him