Heat Retention of Rubberized (Plexipave) Track surface

[TrackCoach]

Hello all - I'm a long time Track & Field coach in the South that also happens to be a structural engineer. Let me give you a little background before I pose a question:

The school where I coach recently had "field turf" (i.e. - the nice, new artificial turf where about 2 1/2" of rubber pellets are dumped into artificial grass blades) installed in the stadium which is also where the track is located. It's a typical set-up with the football/soccer field inside a Track. As part of the process, the "D" zones where completely asphalted. Of course the current track is also a black, synthetic rubber surface. So now, we have a big heat sink! The before/after field turf heat retention difference is noticably greater.

We now need to resurface the track which leads to my question:

Most high school rubberized tracks are some sort of recycled rubber pellets held together with a binder and ultimately coated with a chemical to provide some UV protection. These surfaces are black. Some manufacturers offer colored surfaces. When I say "colored," I'm referring to a truly colored surface where each epdm rubber module is coated - instead of just painting the surface. The true colored surfaces are significantly more expensive. Will choosing a light color have a significant impact on heat retention? We're hoping to retain less heat.

Thanks in advance!

 

[Zoobie]

As I see it, the material will 'retain' pretty much the same amount of heat as this would be a function of the heat capacity of the material. So if the rubber hasn't changed than the heat capacity will be the same. The color of it (or rather the emissivity) will effect the rate at which (or rather the flux) of radiant heat transfer. The heat flux is what someone above the surface will feel. Having said that, black rubber when being heated by solar radiation will absorb heat at a higher flux than white rubber so on a sunny day black rubber will absorb at higher rates but its capacity for holding that heat will not change...just the rates of radiant transfer to and from. I'm not sure if that makes any sense....and I sure hope I got it right because if I recall correctly, radiation was the part of my heat transfer class that made the least sense.

 

[BillPSU]

Heat retention will be affected by what the coating is made of. Certain materials give off heat by different processes. An example is aluminum and cast iron. solidifying and cooling cast iron gives up a great deal of heat by radiation while aluminum gives up heat primarily by conduction and and convection. Depending on the material which coats the surface its method of heat flow could be different. Your perception about your current track may also be flawed as you may perceive higher heat above the black surface but the rate of cooling may make it appear to be hotter as more heat is being transferred into the air causing you to think the heat is being retained while in fact it has been transferred to the air.

 

[MintJulep]

What was the football field before the field turf was installed?

 

[TrackCoach]

Prior to installation of artificial turf, the field was good old-fashioned bermuda grasss with lots of sandy soil underneath.

When turf is installed, lots of the subgrade is removed because a big crown isn't necessary. Then drains lines are installed then 6-12" of stone is placed, laser screeded, and compacted. The turf then rolls out over the compacted stone and the rubber pellets are "swept" into the turf. It's amazing stuff - much, much better than old style carpet turf.

The track has always been there. It's always been black - asphalt with a low end synthetic surface, also black, on top. But the end zones were paved (black asphalt) as part of this project. The idea is that ultimately virtually no maintenance is required with the field area of the stadium. This is going to become very common for land-locked high schools without many practice fields.

 

[MintJulep]

The change from grass to artificial turf probably has the largest effect on the tempertures you are seeing in the area.

Real grass pumps a lot of moisture into the air via transpiration, using up a bunch of heat raising the latent energy of this water. Turf doesn't.

Back when I ran track the track was made from cinders.

 

[MetalsInc]

There is a turf compnay that has a system that sprays a mist of water on the turf to drop the temperature. They claim a staggering temperature drop. Field hockey turfs are always wet and never have heat issues. Unfortunately football players believe that field turf is less likely to cause injuries and demand it. The heat issue is a big problem with unbearable temperatures frequently reported.

 

[Ron]

TrackCoach...academic discussion aside, yes, if you change the color of the track you will change its thermal characteristics. White would be best, but any of the lighter colors would reduce. Black is not good, silver is not good (but better than black) (while one would think that silver would be reflective, go stick your hand on a piece of chrome car trim in the south in August!)

MintJulep is right about the natural to artificial change....that's the most significant.

If you currently have stripes on your track, check the surface temperature difference between the track and the stripes....you'll get your answer. If you know anyone with an infrared thermographic scanner, that will show it up very readily.

As for changing the color, you can use a white silicone coating, spray applied. DowCorning has good ones. Check compatibility with your crumb composite. Note that a coating will affect your surface drainage, as you currently have some pervious texture that will be lost when coated.