中英文资料the relationship between asphalt content and the measurable properties of stability, unit weight, and air voids will be discussed here.

Fig.4 Variations in stability, unit weight, and air-void content with asphalt cement content.

If the gradation and type of aggregate, the degree of compaction, and the type of asphalt cement are controlled, then the strength varies in a predictable manner. The strength will increase up to some optimum asphalt content and then decrease with further additions. The pattern of strength variation will be different when the other mix factors are changed, and so only a typical pattern can be predicted prior to actual testing. Unit weight varies in the same manner as strength when all other variable are controlled. It will reach some peak value at an asphalt content near that determined from the strength curve and then fall off with further additions. As already mentioned, the air-void volume will vary with asphalt content. However, the manner of variation is different in that increased asphalt content will decrease air-void volume to some minimum value which is approached asymptotically. With still greater additions of asphalt material the particles of aggregate are only pushed apart and no change occurs in air-void volume. In summary, certain principles involving aggregate gradation, air-void volume, asphalt content, and compaction mist be understood before proceeding to actual mix design. The proper design based on these principles will result in sound pavements. If these principles are overlooked, the pavement may fail by one or more of the recognized modes of failure: shoving, rutting, corrugating, becoming slick when the max is too ‘rich’; raveling, cracking, having low durability when the mix is too ‘lean’. It should be again emphasized that the strength of flexible is, more accurately, a stability第 6 页 共 12 页