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

UNRELIABILITY OF PG GRADING SYSTEM

Superiority of the AR Grading System

 

AR Grading. The Asphalt Residue (AR) grading system used in the Western part of the United States for decades grew out of the fact that the asphalts in this area differed greatly. While various grades were in use, the workhorse grade was AR 4000 which meant that the asphalt in the pavement, irrespective of crude source, would have the same consistency. AR 4000 meant that the viscosity at 60° C of the asphalt after the RTFO test would be 3000 (2500 in Washington) to 5000 poises. A viscosity of 4000 poise was selected as it was found that at 4000 poises tenderness in oversanded mixes was easier to handle.  60° C is used as in most cases that is about the highest temperature the pavement reaches although in the deserts it can reach considerably higher temperatures. On the other hand, the viscosity at 60° C from the RTFO of equivalent asphalts graded by the AC grading system (2000 ± 400 poises based on original viscosity at 60° F) or by penetration grading system (85/100 based on penetration at 25° C) can vary greatly. For the 85/100 penetration grade, the range of the 60° C viscosity after the RTFO of those asphalts evaluated during the development of the AR grading system varied from about 1600 to over 7000 poises. For an AC 2000 grade asphalt, the probable viscosity after the RTFO aging would range over about 4000-8000 poises, depending on the crude source. The equivalent PG grade is PG 64-XX.

PG Grading. There is an astounding number of PG grades, 7, and up to 6 subgrades within each grade, based upon low temperature properties. If there was consistency within the grades it might make sense, but we have regressed even back beyond the AC grading system. These grades were set up primarily to control tenderness and rutting even while leaving the gradation specification so open that gradations that would allow grievous rutting are included. The equivalent PG grade is based upon the Dynamic Shear test of G*/sinδ of 1.00 kPa at 64° C with no maximum. For a sinδ of 1.00 (close to that of unmodified asphalt) the viscosity is G*· sinδ or 1000 poises. The G*/sinδ value from the RTFO test would be 2.20 kPa min or 2200 poises with sinδ = 1.00 and again there is no maximum. Sinδ for modified asphalts is less than one thus that drops the specification minimum viscosity below that of non-modified asphalt.` In other words, for the asphalt as placed in the pavement, the AR 4000 specification is 3000-5000 poises at 60° C. For the PG 64-XX , the-in place viscosity at 64° C can vary from somewhat less than 2200 poises to as high as one wishes.

 

 

Philosophical Inconsistency of the PG Grading System. I am only addressing the grading system, not the value of the low temperature specification. I am not suggesting that there is anything wrong with the use of the DSR, as it is a handy tool. I am suggesting that the grading should have been based upon the consistency of the RTFO residue whether viscosity tubes are used or the DSR. The value of the DSR data is that we can get information about the effect of polymer modification from the phase angle, sigma (δ).

We have shown above that the range of the allowed viscosity from the RTFO test of any particular PG grade is greater than that of any previous grading system even though there is are 7 specific grades in order to control rutting. The implication is that controlling rutting requires fine tuning. Yet, at the same time there is a movement to use warm mixes, one of the benefits of which is that the asphalt will have a considerably lower viscosity than the intention of the grade.

Controlling Rutting. The prime control of tenderness and rutting should be with aggregate gradation.  As long as the gradation specification allows badly oversanded mixes, rutting will be a problem.

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