Repeatability and Reproducibility of Analysis Methods for Asphalt Mixture Gyratory Compaction

The output of the gyratory compactor is frequently used to design and study the asphalt mixture properties, such as compacity and workability. To exploit some characteristics of these curves the use of fitting models is recommended. The sigmoidal model is one of the fitting models with more potential due to the possibility of identifying several particularities of the compacity-gyrations curve, such as, its inflection point and maximum slope, or even the slope for any given number of gyrations. However, the precision, i.e., repeatability and reproducibility, of the model parameters is still unknown. This round-robin on gyratory compaction, involving 22 participants, is a contribution to fill that gap-in-knowledge. The experimental compaction data was used to determine the sigmoidal model parameters and the respective precision values were determined following ISO 5725-2:2019. In addition, the log-linear model from EN 12697-10:2017 was also used, and the obtained precision values were compared with literature. For both models, to quantify the effect of the number of gyrations used to determine the parameters of the models, three cases were considered: 60, 120, and 200 gyrations. It was found that the use of a higher number of gyrations improved the precision values and allowed for a better estimation of the parameters. Regarding the ability of the models to fit the experimental data, the sigmoidal model showed a lower RMSE, approximately six times lower than the log-linear model.