Introduction. In Ukraine, the procedure for designing asphalt mixtures includes selecting the ratio of aggregates, determining the optimal bitumen content, testing the asphalt concrete with the selected bitumen content, and refining the mix desgn if necessary. A similar procedure is used in the United States, the European Union, Australia, and other countries. However, the key difference lies in the equipment used to prepare asphalt concrete samples.
Problem Statement. In recent years, the method of asphalt concrete sample preparation in Ukraine using compression compaction has been subject to criticism. The main concerns include the lack of a clearly defined loading rate, potential crushing of mineral aggregate grains during sample preparation, and the fact that the compaction achieved in laboratory conditions is often lower than that in road pavement layers. These factors may lead to suboptimal asphalt mixture design and premature defect formation during operation. This necessitates research to optimize laboratory compaction of asphalt concrete mixtures, particularly through the use of a gyratory compactor.
Objective. To implement a gyratory compactor for laboratory compaction of coarse-grained asphalt mixtures.
Materials and Methods. Literature analysis and laboratory research.
Results. The volumetric properties of asphalt concrete depend on the bitumen content in the ashalt mixture. An increase in bitumen content leads to a decrease in the maximum density of the asphalt mixture, a reduction in air voids and voids in the mineral aggregate, as well as an increase in the bulk density of asphalt concrete and the volume of voids filled with binder. The volumetric properties of asphalt concrete are significantly influenced by compaction effort. With an increasing number of gyrations, bulk density and the volume of binder-filled voids increase, while air voids and the volume of voids in the mineral aggregate decrease. Changes in volumetric properties follow a diminishing trend with an increasing number of gyrations. The required air void content can be achieved over a wide range of bitumen content and compaction effort. The "locking point" principle helped determine the optimal number of gyrations at 80. Comparative studies of asphalt concrete samples compacted at 80 gyrations and under a compression pressure of 30 MPa showed that type A-B asphalt concretes exhibit similar volumetric and mechanical properties, with gyratory compaction being slightly more effective. In the case of type A1 asphalt concretes, a more significant difference in volumetric properties was observed, with gyratory compaction proving to be more effective. The compaction method had minimal impact on the mechanical properties of asphalt concretes.
Conclusions. For asphalt concrete sample preparation during the design of coarse-grained asphalt mixtures and quality control, it is advisable to use a compaction effort of 80 gyrations. This method is more effective than compression under a pressure of 30 MPa, promotes the production of "stiffer" asphalt mixtures, and ensures adequate field compaction that does not exceed laboratory compaction, thereby preventing the formation of asphalt with excessively low air void content. Considering the general trend of reducing compaction effort with decreasing applied traffic loads, a compaction effort of 60 gyrations may be used for designing coarse-grained asphalt mixtures intended for pavement layers subjected to low traffic loads.
