Agitating – Mortar mixer type – Methods
Patent
1983-03-28
1986-04-01
Simone, Timothy F.
Agitating
Mortar mixer type
Methods
366 17, 366 18, 366 23, B28C 704
Patent
active
045794588
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and an apparatus for the batchwise production in a mixing plant of asphalt concrete from a bituminous binder tempered into liquid state and particulate aggregate comprising a filler portion, a fine-grained portion and a coarse-grained portion. In the preferred embodiment of the invention the filler portion has a principal particle size effective in applying the invention of below 0.1 mm, the fine-grained portion has a principal particle size effective in applying the invention of below 2 mm and the coarse-grained portion has a principal particle size effective in applying the invention of over 3 mm.
A paving of asphalt concrete on for instance a road must be not only resistant to wear but also elastic so that it can withstand repeated small deformations of the load-carrying foundation without cracking of the asphalt concrete paving. A great deal of research has therefore been spent on establishing suitable proportions between the constituents of the asphalt concrete, suitable material choices and also suitable mixing methods, for it is important that all particles of the aggregate are coated with the bituminous binder or suspended therein in order that a satisfactory elasticity and cohesion shall be obtained. On the other hand, too high binder contents must be avoided because of the high cost of bitumen, because of the risk for bleeding, i.e. sweating of bitumen out of the asphalt concrete at high temperatures, and because of the risk for tracking in road pavings.
One way of effectively utilizing the binding power of the bituminous binder and thus of reducing the required amount of binder in an asphalt concrete is described in Swedish Pat. No. 7016307-6 (Publication No. 347,989). According to the method described therein one first mixes the coarse-grained portion and the bituminous binder to coat the particles of the coarse-grained portion with a bituminous binder film before the remainder of the aggregate is added. This previously known method has brought considerable cost and binder savings while maintaining and in certain cases also improving the characteristics of the asphalt concrete produced.
It has now proved possible to further improved the characteristics of the asphalt concrete to a still higher extent and utilize the binding power of the bituminous binder even more efficiently if the thickness and viscosity of a bituminous binder film deposited on the particles of the coarse-grained portion are increased by introducing the particles of the filler portion into the bituminous binder film in such a way that the free particles of the fine-grained portion when supplied to the mixing plant meet the coarse-grained portion already coated, on the particles of which the binder film has already taken up the particles of the filler portion.
By this production method it is thus possible first to coat the coarse-grained portion with a relatively small amount of binder which, on the particles of the coarse-grained portion, forms a thin binder film which would per se be insufficient to catch and enclose the particles of the fine-grained portion but which after taking up the particles of the filler portion would have acquired a sufficient thickness and viscosity for this purpose. The invention is thus based on the realization that the particles of the filler fraction can be introduced into the binder film and suspended therein so that the filler portion actually will form an integrating part of the bituminous binder which is thereby given increased volume and viscosity and is thus able to take up and also to coat the particles of the fine-grained portion. Under suitable mixing conditions and temperatures it is thus possible, in applying the invention, to ensure that both the filler portion and the fine-grained portion are suspended in the bituminous binder film already deposited on the particles of the coarse-grained portion, which results in an optimum utilization of the bituminous binder supplied and also results in a very homogeneous consistency of the asphalt concrete produ
REFERENCES:
Derwent's Abstract No. 36238c/20 SU 687161, Official Gazette of Oct. 21, 1930--p. 554.
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