Stabilize a racing surface 1

[robbia]

Problem: Bentonite (black) clay surface used for off-road remote control racing in S. Texas. The surface swells 15-18x when wet. As it dries, it cracks and tears itself apart creating "marbles" and dust making the surface un-usable (no traction, large chunks of clay upset vehicles).

Looking for a low-cost additive to stabilize or add some elasticity to the surface without making it too hard (it's dirt racing). I've tried gypsum, portland cement, and cooking oil patches and all erode after heavy rain.

Heard that silt might work, but unable to locate in San Antonio area. Others have suggested thin layer of top soil.

 

[dirtguy4]

robbia,

Without really knowing your site, I don't think that there is a cheap or quick fix solution to your prolem. How thick is your bentonite strata? What lies below the bentonite strata? A possible excavate and replace with a low plastic or granular material may be one possible option, but sounds like it would be far too costly.

Think of your race track as sitting on bags of highly expansive bentonite. As long as the bags are sealed, no moisture in - no moisture out, nothing happens and everything functions fine. As soon as you open the bags, water can get in swelling the soil or vice versa, exposure to the sun draws the moisture out of the soil. This is your flux boundary. Control your flux boundary and you've solved your problem.

 

[layfieldman]

You can place a drainage composite such as delta drain 6" below the surface of the top soil, something not clay, and it will drain the water away from your base. I'm guessing that your racing area is not that large but am not sure what kind of budget you have to import soil and place this product down.

 

[Focht3]

Treat the surface with potassium chloride (KCl). It will alter the sodium montmorillonite - changing it to the potassium variety, which is much less active. Use a water solution with KCl - and apply when the clay is 'bone dry'. (Definitely not right now!)

Where is the track?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[robbia]

The dimensions are 100 x 125 and the clay varies in thickness I'd say from 4 to 24 inches. Beneath it a sand/clay mix commonly used on baseball diamonds - not sure what it's called but has the typical orange appearance. I have not seen the clay dry much more than 1 inch below the surface, but as Focht3 mentioned we've had a surplus of rain.

Dirtguy, I thought about covering the track when not in use, but that presents a problem for racers and kids that drop by at odd hours for practice. I agree that if there were a way to encapsulate the benotonite we'd be on the right path. The challenge lies in the race vehicles. They are powerful little buggers and the tires displace (move) loose compounds quickly.

Focht3, I am definitely interested in any help we can get.

 

[dangnm]

Before I read the whole thread, I was already thinking of baseball diamonds. They make it through a lot of weather conditions with quite a bit of wear. The surfacing is usually a by-product of brick-making called Grog. Grog is usually just bricks gone bad in the kiln recycled by crushing and screening. It seems like bentonite would be the worst surface I could think of. I've also seen people mix in a little cement where they were getting a lot of wear, like in the batter's box, to make the surfacing a little tougher to erode. Hope that helps.

 

[Ron]

Add clean sand. This will mitigate the volume change and help reduce the drying shrinkage as well. Create mix of 50-50 sand/clay then add about 5 percent portland cement by weight, mix well in the upper 6 inches or so, and compact it..... and you'll have a nice, stable soil-cement surface. Some cracks can be expected, but alligatoring is unlikely.

 

[Focht3]

As promised - a typical application rate for a potassium chloride/sodium hydroxide solution:

The treatment should result in an applied chemical concentration within the treated soil volume, expressed as the weight of chemical per weight of dry soil, of at least 0.85% potassium chloride, 0.6% sodium hydroxide and 0.5% ammonium lignosulfonate. This is roughly equivalent to the following weight of chemical per gallon of water: 1.09 pounds of potassium chloride, 0.77 pounds of sodium hydroxide and 0.63 pounds of ammonium lignosulfonate. (The ammonium lignosulfonate acts as a wetting agent, and does not directly modify the clays. This chemical does not provide any direct beneficial reduction in soil swell.) At least ¾ gallon of this solution should be applied per cubic foot of treated volume of soil, with the concentrated chemical solution applied in at least two overlapping passes.

The chemical treatment should result in a post-treatment swell of no more than 1 percent in the treated zone, with a desired swell of no more than 0.5 percent swell in the treated zone. The soil should be re-treated in areas where retrieved samples exhibit an average swell of more than one percent, or any swell test exceeds two percent.

Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"