MEETS SPECIFICATION BUT FAILS TO WORKS AS WELL AS BEFORE

Asphalt Construction Nightmares

You have a project going well when all if the sudden things change. How can this happen? You are buying the asphalt from the same source, it meets specification, but it just doesn’t work well. What could have happened?

There are various factors that can address that problem:

Change of Crude Oil Source. First, every crude produces its own distinct asphalt. York and Halstead characterized a multitude of asphalts in the late 1950s and Rostler and White produced a set of punch cards as “finger prints” of the various asphalt sources. References available by request. I have those cards. I mention this as a refinery may switch crudes. The asphalts would still meet specifications, but may behave entirely different. In addition, many asphalts are being modified with polymers (rubber) in different ways with each system having their own distinct set of properties. Some examples.

Asphalt Susceptible Water. In the middle 1970s a contractor was having a problem with stripping which even 1% antistrip would not help. The mixes when soaked turned brown which indicated that water was being absorbed. It turned out that the crude from which the asphalt was produced had been treated with caustic soda which made the naphthenic acids into soaps. As asphalts from caustic treated crudes made lousy emulsions, they also had non-caustic treated crude in stock. Switching to the non-treated crude solved the problem. Asphalt from the treated asphalt caused other problems so the refiner switched to lime treating of the crude. That greatly improved the asphalt making it resistant to stripping.

Changing Grading System. When I first got involved in asphalt technology (1959), asphalts were graded by penetration at 77°F. (How far a needle would penetrate the asphalt in dmm.) The grade mainly used was 85/100. Later the grading system was changed to viscosity at 140° F after an aging test to mimic the effect of mixing on the asphalt consistency. The contractors were told that the grade AR 4000 would replace the 85/100 grade, implying that that no changes in practice needed to be made. However in Southern California the contractors claimed that the AR 4000 asphalt didn’t work the same. I was at a meeting with the contractors, oil companies and the asphalt institute, the latter two of whom stated flatly that the asphalts were the same. Period. In a broad sense they were telling the truth. Averaging all of the available asphalts, the AR 4000 was the same as an 85/100. However with the asphalts in California, the range of penetrations for AR 4000 from the various crudes varied from 40/50 to 120/150. In Southern California a AR 4000 was actually a 60/70 penetration grade. Once the contractors were finally told that, they were fine with it because they also would have known how to handle the 60/70 asphalt if someone would have told them that was what it was. In the roofing industry some specifications actually specify the crude source. It might be well for a contractor to get a guarantee that the crude source will not be changed.

Product Trading among Oil companies. Oil companies trade products, primarily to reduce shipping costs. One example was one company trading California Coastal crude to another for asphalt emulsion in the northwest. But they can also trade asphalts if there are supply problems at the refinery.

Replacing an Approved Product with Another during Construction. Another thing that can happen is that the supplier submits one material for approval then switches the ingredients to lower the cost. The product may still meet specifications, however will not perform that well in the field.

If retains are kept during construction and there is a costly problem, the asphalts could be analyzed. One method is the Rostler analysis ASTM D 2006, (removed) and the Clay Gell procedure ASTM 2007. (We only do the Rostler procedure because the solvents from this method are easier to handle.) There are other new unpublished procedures that can be used including Fourier transform infrared analysis.

Robert L. Dunning, chemistdunning@gmail.com, www.petroleumsciences.com

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