coated chippings applied to a rolled-asphalt surfacing sometimes fail to adhere. one reason for this is "coking" or burning of the bitumen coating to a very hard layer which is no longer tacky, even at temperatures of 100 c and above. laboratory investigations showed that no coking occurs during the mixing process, even at high temperatures, but only during storage. when the storage temperature is kept low (150 degrees c),prolonged storage has no deleterious effect on the binder, but at higher temperatures (e.g. 200degrees c) coking can occur in about four hours. some limited tests showed no differences due to type of binder or of aggregate. coking can occur when chippings which were mixed under the recommended conditions are stockpiled while still hot. full-scale stockpiling experiments have shown that with conical stockpiles the temperature can remain high. or even apparently increase, over a period of many hours, during which time the cohesive properties of the binder are destroyed. chipping trials on two trunk roads have shown that laboratory tests can be used to check the quality of chippings. experience of commercial work where partially coked chippings were used confioms the need for a specification which will exclude chippings of inferior quality. recommendations are made for coating and testing to facilitate production and control of high quality chippings. (a).

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