Evaluation of Sand–tire Crumb Mixtures as Lightweight Fill Materials

ABSTRACT The reuse of scrap rubber crumbs mixed with sand as lightweight fills is considered as a sustainable application. However, the performance of sand–crumb mixtures and the optimum content of crumbs have not been consistent. The purpose of this study was to investigate the feasibility of using sand–crumb mixtures for applications such as embankment fills, backfilling for subgrades, and retaining walls, and assess the optimum crumb contents in the mix. Mixtures of fill sand and rubber crumbs with sizes of 1–2 mm at crumb contents of 0%, 10%, 20%, and 30% by weight of dry sand were tested in a laboratory for compaction and penetration using the California bearing ratio (CBR) test and for shear strength using direct shear tests. The dry unit weight, CBR, dilation, and friction angle decreased as the crumb content increased, while apparent cohesion was introduced in the mixtures with the addition of crumbs, and it increased with the crumb content. Sand–crumb mixtures were effective as lightweight fill materials over soft soils, but were not suitable as subgrade materials. Furthermore, sand–crumb mixtures with an optimum crumb content of 20% provided the maximum reduction in lateral earth pressure when they were used as backfill materials behind retaining walls.