A SmartRock-Based Method for Determining the Gyratory Compaction Locking Point of Asphalt Mixture

Compaction is a critical step in the construction of an asphalt mixture. To effectively compact an asphalt mixture, the locking point, which identifies the effective compaction, was introduced based on the change in volumes of the asphalt mixture during gyratory compaction. However, the existing definition of the locking point is solely dependent on the volumetric properties of compacted mixtures and may not be necessarily associated with the skeleton of the mixture. In this paper, the locking point for a compacted asphalt mixture was defined and determined using dynamic responses measured by a particle sensor. Gyratory compaction and field compaction tests were carried out with particle sensors embedded to analyze the evolution of the aggregates' dynamic responses. Then, a novel dynamic response rate of the change index Rs was proposed to represent the evolution process of the asphalt mixture compaction. The Superpave gyratory compactor (SGC) results show that the acceleration and rotation angle of the particle sensors varied during compaction and did not converge in the end. The SGC compaction process can be divided into three stages: the initial compaction stage, transition stage, and plateau stage based on the rate of stress (Rs). Meanwhile, the inflection point between the transition stage and plateau stage in the compaction curve was defined as the locking point. It was found that the locking point determined by the sensors in the middle of the compacted specimens was later than that determined by the gyratory compaction. The contact interlocking initiated at the bottom of a compacted specimen and moved upward. The field compaction test results of the particle sensors showed that the contact stress also had a significant trend of convergence after being compacted by a pneumatic-tired roller, which indicates that the test stress index based on the particle sensors could be used for the evaluation of compaction quality.