Coal-Modified Tar Binders for Bituminous Concrete Pavements EDMUND O. RHODES, Curtiss-Wright Corporation, Pittsburgh, Pennsylvania In Fall 1958, investigations were started by the Re- search Division of Curtiss-Wright Corp. at Quehanna, Pa., with a view to developing improved methods for using bituminous coals and products derived there- from as highway construction materials. It was decided to explore the possibility of making an improved binder for bituminous pavements of the hot-mix hot-lay type by dispersing coal in distilled coal tars and coal tar oils. Previous investigations had indicated that they might also be used to advantage for the production of improved highway binders. During the first half of 1959 a task force at Que- hanna assembled and constructed suitable laboratory and pilot plant equipment; determined optimum condi- tions for the dispersion of coal m tars and oils; com- pared various coals, tars, and oils as to their suita- bility for the purpose; produced and analyzed experi- mental quantities of coal-modified tar binders; and combined them with various aggregates in hot mixes. The latter were then compared with hot mixes con- taining typical asphalt cements and coal-tar binders. The tests appeared to indicate that it would be possible to make hot mixes with coal-modified tar cements equal or superior to those made with usual asphalt or coal-tar binders. After the results of the Quehanna investigations were reported, a contract was made with the Com- monwealth of Kentucky to build a pilot plant at Frank- fort to produce 150,000 gal of coal-modified tar binder for comparison with asphalt cements normally used in Kentucky in Class I and Class I-modified bitumi- nous pavements. During a period of three months it produced 104 batches of binder, of which 100 batches were of the three-component type (coal, tar, and oil); two were of the two-component type (coal and tar), and two consisted only of tar (RT-12). No major difficulties were encountered m the operation of the pilot plant, and binders made in it were equal in quality to those pro- duced at Quehanna. From the Frankfort plant, the quantities of binder weredeliveredto 14 test sites in various parts of the State. At two sites, three-component binder was used in hot mix laid 2 ^/^ in. thick on a tar-primed soil base (Class I-modified). At all other sites, the binder was used in 1 'A-in. Class I overlays on existing black-top pavements which for the most part had required ex-
Coal-Modified Tar Binders for Bituminous Concrete Pavements
Apr 26, 2023
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