WARM MIX ASPHALT PATENTS

I am writing this to provide information with respect to some patents that are now being litigated at the present time by A.L.M holding company against those involved in warm mixed asphalt paving. They cover about all methods of warm mix construction except those using foam technologies, all based upon testing that was done at high shear on a modified Dynamic Shear Rheometer (DSR). The litigation can be followed by looking up “H.L.M Holding litigation” . The plaintiffs are A.L.M holdings, Ergon and Meadwestvaco. The patent numbers for six of their patents are 7,815,725;, 7,981,466; 8,138,242; 7,981,952; 7.984.166; and 7,968,627. The prime inventors are Gerald H. Reinke, La Crosse, WI (US);Gaylon L. Baumgardner, Jackson, MS; Steven L. Engber’ Onalaska’ W1 (US). The patents are assigned to A.L.M. Holding Company, Onalaska.

The patent is based upon testing asphalt with and without additives in shear at very high shear rates to the point at which the viscosity decreases and a normal stress is observed. Following is a description from patent 7,815,725:

While not intending to be bound by theory, the present invention is based, in part, on the observations that the lubricating agents and additives disclosed in this application provide a warm mix having desired visco-lubricity characteristics or properties. As used in this application the term “visco-lubricity” means a characteristic of a material that it exhibits under high rotational velocity as the gap thickness of the material being tested approaches zero. As the gap thickness is reduced and as rotational velocity is increased, the material’s viscosity begins to decrease but the normal force between the plates begins to increase. A material that has good visco-lubricity characteristics will exhibit less normal force increase than one which has poor visco-lubricity. Stated another way, the ability of the material being tested to enable the plates to easily rotate relative to each other becomes more important than the viscosity of the material being tested. An example illustrating the meaning of the term “visco-lubricity” is the observed reduced requirements for the mixing and compaction temperatures of polymer modified asphalt binders compared to conventional asphalt binders. Based on purely viscosity data, polymer modified binders should require mixing and compaction temperatures that are 20-50.degree. F. higher than those which common practice have found to be adequate. Many studies have been conducted to explain this apparent contradiction however none have proven wholly satisfactory. It is now believed that these polymer systems are creating a lubricated asphalt binder having visco-lubricity properties that provide adequate mixing to coat aggregate particles and further provide mix compaction at temperatures substantially below those predicted based on viscosity alone.

The word lubricity means slipperiness. The patent implies that the lubricity, or slipperiness, is defined by the test result obtained in their DSR. There is a problem. The normal stresses are an intrinsic property of viscoelastic materials (in the constitutive equation) and would be observable at all shear rates. (It can be observed as material climbing up the shaft of a mixer during mixing of viscoelastic material). In 1967 Puzinauskas published asphalt viscosity data (Proc. Asphalt Paving Technologist, 1967). From his data, with the equipment he was using, the highest shear stress he could reach was about 1 mPa suggesting shear failure at high shear rates. He had noticed some delamination. I mentioned to him at that time that I had observed cavitation in testing with a sliding plate viscometer with high shear stresses. The data shown in the graphs in the patent could be interpreted that the observe drop in viscosity with increased shear rate is shear failure or delamination and the creation of the normal stresses were not intrinsic to the binder but rather cause by the behavior of pieces of failed binder. If this were to be the case, the patent is not valid.

I would suggest that those interested should review the patents. One will find that there is not much in this world that the inventors don’t claim to be covered by their patents.
Robert L. Dunning 509-220-1360
chemistdunning@gmail.com

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