Trinity officials close section

[L Roebuck]

Trinity officials close section of Old Alabama 24

TRINITY — Trinity officials Thursday shut down a strip of Old Alabama 24 until further notice because of sinkholes, according to Mayor Pro Tem Bruce Sparkman.

Sparkman said to protect motorists, officials closed the road from North and South Greenway Drive at the caution light at the foot of the mountain, to Tower Street and Old 24 at West Morgan Elementary School.

He said drivers going east toward Decatur should either turn right at the caution light onto South Greenway to Alabama 24 (Gordon Terry Parkway) or turn left onto North Greenway, go to Tower Street and turn right and travel Tower until it intersects Old Alabama 24 at the school.

Travelers headed west should turn right at Tower Street, travel to North Greenway Drive, turn left, go to the caution light and turn right back onto Old Alabama 24.

"We've been adding more cold mix as advised in an effort to correct the (sinkhole) problem, but every time it rains, the road settles a little more and we add more cold mix," Sparkman said. "We feel we're getting it stopped, but it's going to take a little while due to the rain and settling."

www.decaturdaily.com/decaturdaily/news/051209/24.shtml

[L Roebuck]

Can someone describe "cold mix "?

[chac]

Lynn,

Cold mix, aka cold patch, is a "cold" asphalt that's often used to patch potholes in asphalt roads. Sometimes it is heated to form a more stable patch, but it's not exactly something for large holes or slumps in the road. You gotta wonder where all the oil goes from the patch that sits on top of this sinkhole!

Jim

[L Roebuck]

Thanks Jim. It seems I have little working knowledge of how they address "fixing" sinkholes in roads. Are their other methods or is this "cold mix" standard practice?

If a patch on a sinkhole contains oil wouldn't it be logical to think the oil is seeping into the groundwater?

[chac]

"If a patch on a sinkhole contains oil wouldn't it be logical to think the oil is seeping into the groundwater?"

Yes, no doubt that oil from this patch is moving toward the water table. Cold mix is a very rough oil/limestone mix. It is limited in both storage and repair life, as it becomes unstable after time. As I recall this is due to the amount of oil/bonding chemicals in the mix?

"Are their other methods [to fix the road] or is this "cold mix" standard practice?"

Cold mix is pretty much a standard band aid remedy for minor road repairs during cold or rainy months (when you can't apply "hot mix" asphalt). It wears out in short order though, so it needs to be replaced later on in the year. Filling the Trinity hole with crushed rock or concrete is not an option. I'm certainly not a highway engineer, but it seems that this (sink)hole on Old Alabama 24 needs a bit more thoughtful attention rather than just patching in the long run.

[L Roebuck]

chac said:

"If a patch on a sinkhole contains oil wouldn't it be logical to think the oil is seeping into the groundwater?"

Yes, no doubt that oil from this patch is moving toward the water table. Cold mix is a very rough oil/limestone mix. It is limited in both storage and repair life, as it becomes unstable after time. As I recall this is due to the amount of oil/bonding chemicals in the mix?

"Are their other methods [to fix the road] or is this "cold mix" standard practice?"

Cold mix is pretty much a standard band aid remedy for minor road repairs during cold or rainy months (when you can't apply "hot mix" asphalt). It wears out in short order though, so it needs to be replaced later on in the year. Filling the Trinity hole with crushed rock or concrete is not an option. I'm certainly not a highway engineer, but it seems that this (sink)hole on Old Alabama 24 needs a bit more thoughtful attention rather than just patching in the long run.

Thanks for the additional information Jim. I never gave thought to the possibility that these sinkhole patches
might add to groundwater pollution.

[chac]

Lynn - Asphalt does have its problems. It's really neat to see a lot of cave restoration projects (both past and present) removing old asphalt walkways and replacing them
with a more neutral design (such as crushed limestone). Part of the oil in the mix can leach out (usually helped by water and gravity) to the soil, while many of the "lighter" hydrocarbons in the oil will escape and evaporate into the air. Obviously neither are good in a cave environment.

By its very nature asphalt "wants" to break down and crack. Believe it or not the mechanized rollers they use to compact and smooth new asphalt actually creates minute fractures - which allows water to penetrate the top skim. With sun, freeze and thaw cycles, and heavy use the cracks get bigger. So more water gets into asphalt and carries more hydrocarbons deeper into the road base and finally the underlaying soil (and - you also get pot holes).

With all the rain mentioned in the Decatur Daily news clip (your first post), it sounds like both a drainage and sinkhole problem. I've seen highway crews in Mexico battle the same problems in Yucatan, Quintana Roo, Campeche, Chiapas and Tabasco. One solution is to dig the section of road up as deep as possible, fill it with compacted crushed rock, and pave it with a thick layer of asphalt. That lasts less than a year in the best of conditions.

Unfortunately for the taxpayer, the more expensive fix initially (but lasts longer and is more environmentally friendly) is bridging over the problem. If you can restore the natural drainage area (including ground cover) as it "was", a span over the depression will solve a lot of problems.

[L Roebuck]

Hummm, this is interesting. Now perhaps I have a better understanding of why some nearby roads (road widening projects) are being raised 2-3 feet higher than the former roadway and filled with crushed rock before the asphalt layer. Also I recently read one article that mentioned a sealant is part of the process.

I would be interested to learn more about this process, the chemicals involved as well as what percentage might leach into the caves and karst groundwater. Can you happen to advise where I could find such data?

[chac]

Here's a couple of links to browse. There's a lot of information on the web, although one needs to be careful in how they digest the information (asphalt _is_ big business!). I tried to include links that address a general spectrum of views.

I don't know if a (recent) specific study has been devoted to the affects of asphalt within a cave environment, perhaps one might exist in the NPS archives. I would certainly be interested to know if one exists! Perhaps Ronal might know of such a study.

The first is a nice overview on asphalt paving:
www.hawaiiasphalt.com/HAPI/

This is a Wikipedia entry:
en.wikipedia.org/wiki/Pavement_%28roads%29

An interesting alternative to asphalt (a resin pavement):
www.buildinggreen.com/auth/article.cfm?fileName=081108a.xml

And this is an older but informative NPS compilation on asphalt, its chemical nature, and reported hazards of the material.
www.nature.nps.gov/hazardssafety/toxic/asphalt.pdf

[L Roebuck]

Thanks Jim! Looks like I have quite a bit of reading to do. ;D I did a click through of the links you posted and also found this site which has even more information.

USGS - NATIONAL HIGHWAY RUNOFF WATER-QUALITY DATA AND METHODOLOGY SYNTHESIS
ma.water.usgs.gov/fhwa/ndamsp1.htm

[chac]

Thanks for the link to USGS resources Lynn. Looks like there are some interesting papers there!

[L Roebuck]

Your Welcome and Thank you for all the help!