Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Patent
1996-10-09
1998-08-04
Brunsman, David
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
264 50, 264 53, C09D19500
Patent
active
057887551
DESCRIPTION:
BRIEF SUMMARY
This is a filing under 35 U.S.C. 371 based on PCT/FI95/00070 filed 15 Feb. 1995.
The invention relates to a method for producing foam bitumen or the like by mixing liquid, such as water, and bitumen. The equipment according to the method can be used in mobile stabilizing machines or in fixed mixing plants. The equipment according to the invention comprises a foaming reactor, means for spreading foam bitumen and pipes related thereto, and valves required for adjustment.
The use of foam bitumen in asphalt work is prior art. Even though foam bitumen has been commonly used, the method has quite often caused difficulties and problematic situations in practice. The foaming principle in the earlier methods has been to add the foaming agent, in general water, to the substance to the foamed, generally bitumen, under pressure, whereupon the pressure is higher than the saturation pressure of steam at the temperature of a hot bituminous binder, and to let the mixture swell under a pressure lower than said saturation pressure of steam. Finnish Patent 872,911 discloses this type of method and equipment. The method according to this reference also employs an additional substance to improve the properties of the foam bitumen. Finnish Published Specification 57,807 also discloses a method for producing foam bitumen by using water and bitumen as starting materials. The solutions according to the patent are not, however, very well applicable to practice, and for example the static mixers of water and bitumen disclosed in the patent may clog easily, or they do not produce homogeneous foam bitumen.
The previous methods and equipments have usually ignored the effect of the foaming agent on the reaction temperature. The effect of the flow conduits and the spraying on the durability of the foam of the foamed substance has also been ignored. Therefore, the foamed bitumen and asphalt have not been homogenous, and problems have occurred in the use of the foaming equipments.
Tests and experiments have surprisingly revealed a matter which affects, in a cumulative and constant manner, the entire foaming procedure until the moment of spraying. A so-called reticulate structure is formed in the foaming equipment used in the foaming procedure in the beginning of the reaction. The reticulate structure is formed in such a way that at the foaming temperature of the hot bituminous binder under a high pressure, energy is transferred from the substance to be foamed to the foaming agent only in the surface layer. Naturally, the small amount of the foaming agent and the high pressure also have a negative effect on this, thus accelerating the formation of the reticulate structure. The reticulate structure simply consists of a net of molecules developing on the surface of the substance to be foamed according to natural laws, the molecule net trying to prevent other changes once it has itself become saturated. When the foamed hot bituminous binder bursts out of the equipment under a low pressure, the reticulate structure on the surface of the binder is broken, and if the equipment comprises one or two input lines, the reticulate bitumen which has lost its activity is immediately released in the area of the nozzles near the input line, and this shows in the finished processed material as a dark reticulate area. The dark stripes visible on the surface of the road thus result from a large amount of reticulate foam bitumen and inert bitumen being situated at these nozzle areas, and only inert bituminous binder being situated in the other nozzle areas. What is most problematic is that the faulty work performance cannot be detected by means of measurements of the bearing capacity, but in reality the result of the work is of lower quality than assumed. The material has become liable to reforming, and the bearing capacity of the base course has not improved.
If for example the temperature of the substance to be foamed is over 180.degree. C., and foaming water is used over 10% of the substance to be foamed, or if the foaming agent is warmed to a temperature o
REFERENCES:
patent: 2917395 (1959-12-01), Csanyi
patent: 4592507 (1986-06-01), Benedict
patent: 4692350 (1987-09-01), Clarke
patent: 4832747 (1989-05-01), Marchal
Brunsman David
CMI Corporation
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