A method for quantifying the packing function of particles in packed aggregate blend

This paper proposes a method to quantify the packing function of particles in packed aggregate blend. Three indicators are defined to capture the composition of aggregate blend and the packing function of particles in packed aggregate blend, which are the percentage of contribution to the packing volume (PCPV), the percentage of contribution to the bulk volume (PCBV), and the relative change between the contribution of particles to the packing volume and that to the bulk volume (RCsiP-B). Packing strategies to quantify PCPV and RCsiP-B are developed based on the loose filling test, the dry-rodded test and the Superpave gyratory compactor (SGC) test. Two typical aggregates, one with good angularity (denoted as crushed stone) and the other with poor angularity (denoted as gravel), are selected for investigating the proposed method with 3 stone matrix asphalt (SMA) gradations and 3 asphalt concrete (AC) gradations. The test results show that the PCPV provides a new way to understand the composition of aggregate blend. The RCsiP-B can be employed to quantitatively investigate the packing functions of the particles in packed aggregate blend. The zero of RCsiP-B represents the balance point between air voids filling function and skeleton building function. A positive RCsiP-B means more skeleton building function. And the bigger RCsiP-B the stronger the skeleton building function. A negative RCsiP-B means major air voids filling function. And the smaller RCsiP-B the more significant the air voids filling function. The balance size for the SMA gradation with the nominal maximum particle size (NMPS) of 16 mm is 2.36 mm, which is also considered as the balance size for the reference upper limit and a designed gradations of AC with the NMPS of 26.5. The balance size for the reference gradation lower limit gradation of AC is bigger than 2.36 mm but smaller than 4.75 mm. The compact energy of the filling test and the particle morphology have no impacts on the PCPV and RCsiP-B but significant effects on the air void content. The SGC test is recommended to quantify the indicators.