Optimizing RAP sieving efficiency of linear vibrating sieve using DEM simulation

Producing recycled hot-mix asphalt mixtures (RHMA) requires an adequate stockpile of reclaimed asphalt pavement (RAP). To improve the content of RAP in RHMA and maintain the quality stability of RHMA, crushing and sieving technology was applied to pretreat RAP, which is mentioned in various technical standards across the world. However, the obstacle that affects the RHMA output during continuous production in any real-life project is the low efficiency of RAP crushing and sieving. A model of a three-dimensional, three-layer linear vibrating sieve was established in the numerical software of the Discrete Element Method (DEM) by considering the sieving combination commonly used in engineering. The Linear Model and Linear Parallel-Bond Model were defined for the contact properties of the RAP particles. Based on DEM simulation, the influence of sieving parameters such as vibration amplitude and frequency as well as inclination and length of the sieve mesh were evaluated by sieving efficiency. Furthermore, the optimal RAP sieving parameters were obtained and verified in the project. The results show that the sieving efficiency first increases and then decreases with an increase in amplitude, frequency, and inclination; however, the length of the sieve mesh has little effect on the sieving efficiency. The order of influence of the different parameters on the RAP sieving efficiency is as follows: amplitude > frequency > inclination > length. The optimal sieving parameters of RAP were 20 Hz, 3 mm, and 10°, respectively, for frequency, amplitude, inclination. The optimum sieve inclination of virgin aggregate was 20° higher than that of RAP. The deviation between the sieving efficiency of the DEM simulation test and the plant sieving test was within 15%, indicating that the DEM simulation had high accuracy. The study could be of interest to sieving plant manufacturers, pavement maintenance sector, and construction contractors.