Preparation of draining bearing layers from mining in Sweden

Abstract Bearing layers are commonly produced using coarse aggregates, gravel, and filler, where excessive filler content can reduce drainage performance. This study investigates an alternative production method for converting a standard 0/32 bearing layer into a draining bearing layer through the controlled removal of fines at two NCC rock quarries (Släsh and Hammarby, Sweden), where the current product typically contains approximately 4–5% filler. Freshly crushed 0/32 material (with a moisture content of 1–2%) was processed using a vibration-free harp screen that was designed and built. The standard product was run through the harp under full-scale quarry conditions (5 t per test and a 45° inclination) using four different grid and board-cover configurations. The produced material was analyzed in the laboratory to determine the resulting filler content. Digiroad finite element simulations were performed to compare harp layouts and the expected generation of residual material. The results showed that harp sieving reduced the measured filler (< 0.063 mm) from 3.7% to between 1.8 and 2.6%. The 25% grid and 75% board configuration provided the best performance, achieving 2.6% filler, with the lowest observed amount of residual material and a grading most closely matching AMA DCB.33/1. Similarly, the simulations indicated the lowest residual-material mass for the 25% grid layout (71.30 kg). The developed harp screen offers a practical solution for improving drainage performance, thereby contributing to more sustainable and safer infrastructure.