LUFKIN, TX (KTRE) - A state official speculates a combination of factors was likely the cause of the tar incident on the Lufkin loop on Aug. 31 which debilitated hundreds of vehicles.
Jerry Peterson Jr. is listed on TxDOT documents as the asphalt, chemical and calibration branch manager. Stephen Stovall, who works for the Nacogdoches Area Office Laboratory for TxDOT emailed Peterson on Aug. 31 to get his opinion on what caused the east loop asphalt to stick to vehicles.
KTRE has obtained hundreds of pages of correspondence regarding the incident through the Public Information Act. TxDOT complied with the request without appeal.
TxDOT was forced to close the east side of Loop 287 on Aug. 31 after melted tar began sticking to drivers' tires. According to TxDOT spokeswoman Rhonda Oaks, rain from Tropical Storm Harvey kept the sealing of the road from drying properly. On that Thursday, the seal melted when the sun came up and began sticking to the tires.
TxDOT shut down the road, but not before hundreds of drivers had found their vehicles nearly undriveable. About 600 people have filed damage claims with TxDOT.
Stovall states in his initial email that inspectors said there did seem to be an unusual amount of dust during seal operations.
"But, even if the rock was 'dirty,' why would the asphalt be so soft, gooey, drippy?" Stovall says.
Peterson responds a day later.
"Wow that looks like a huge mess," he says.
Peterson speculates the material could have been contaminated. He also says it may have been possible the material on the wet road was cooled enough by the water to be stable, "but once the pavement was dry, the traffic heated it up."
"Then it would stay soft on the tires until the tires themselves cooled off," Peterson says. "Usually it's hard to get a meaningful sample of seal off the road, but since it appears to be very soft, if you could scrape up a specimen of what came off some tires, we should be able to test it to see if the material really is unusually soft, or if there is anything else goofy about it."
Stovall responds 15 minutes later and confirms they are sending a sample for testing.
"It looks pretty clean; however, the quantity is minimal," he says. "…I do know that y'all stay very busy, but if there is any way of expediting the testing, we certainly would appreciate it because yes, it is a huge mess."
There appears to be no response from Peterson and Shannon Ramos, the Nacogdoches area engineer joins the conversation five days later.
Ramos asks if it is possible that a chemical reaction caused the melting.
"Could there be some sort of cationic/anionic issue with the precoat emulsion and the AC-20-5TR?" she asks. "Or could there be an issue with the rock and emulsion combination? I am definitely not a chemist, but could the hard rock have a high, let's say Calcium content that is reacting with the positive/negative charge from the precoat? Just a thought, since we historically have some minor issue with every one of our hard rock roads (and historically we use the same source). That is we normally loose [sic] some or have to go back and patch. I was thinking maybe the combination of the three components, the natural chemical properties of the hard rock, the emulsion used in the precoat process, and the asphalt used in the seal coat application could be causing a less than desirable outcome."
Ramos also wonders what role the rain may have had.
"Could the H2O have caused a similar robbing of positive or negative charges which caused the rock to let loose?" she says. "From what I have seen I am just not convinced that there was an issue with the asphalt itself. Like a contamination issue or just bad asphalt. It seems like this was literally the perfect storm that caused all the rock loss then inevitably the exposed asphalt could not perform in a way it was not designed to perform and failed. I have seen a carnage of asphalt patties in parking lots, and they are hard/cured. Not like the pictures during the initial failure. I think the rain and overcast 6 days kept the asphalt from curing properly. Maybe that is what ultimately what caused the rock to let loose too, but I wanted to try to explore other ideas that may help to safeguard our sealcoats in the future."
Ramos says in the email that the same asphalt was used in another location and did not cause the same problem.
"They literally finished the SL224/US 59 reference in Lufkin Thursday (8/24/17) afternoon and moved North a few miles from Lufkin and sealed Thursday afternoon and Friday morning," she says. "They used the same equipment, personnel, asphalt, traffic, environment, weather, etc., but not the same aggregate to seal and that seal is fine. That is what really makes me think it is something with the rock."
Peterson responds with a long email a few hours later. He does not think there was a chemical reaction.
"The AC-20-5TR (and most other hot asphalt) is going to be pretty inert in terms of pH, so should be very unreactive with the emulsion," he says. "And that's if there is actually emulsion present. But the water from that emulsion should have long since separated and the asphalt penetrated into the pores of the rock, so there really is no appreciable amount of emulsions left; it's just asphalt at that point."
Peterson then addresses the water theory. He says the asphalt has to be absorbed into the pores of the aggregate so the water cannot get in.
"But if you get rain in there too soon, you have the dual effect of cooling the surface so the asphalt diffuses more slowly, plus giving water a shot at that surface area before the asphalt has had a chance to penetrate really well," Peterson says.
Peterson then says the addition of dust compounds the problem.
"The dust is just like flour in your baking pan," he says. "It has so much surface area that the asphalt coats the dust and has less contact with the main aggregate particle. This creates even more opportunity for water intrusion, and coupled with the early water could potentially give you a lot of aggregate loss."
Peterson then agrees with the "perfect storm" theory.
"It may be a combination of factors that individually might not cause a failure, but all together are a disaster," he says.