Recycled aggregate blends for backfilling deep trenches in trafficable areas

Limited supplies of natural aggregates for backfilling pipeline trenches in trafficable areas have led to considering secondary resources. Utilizing blends entirely made of recycled aggregates to backfill excavated trenches in trafficable areas is rare if any, where traditionally, natural crushed rock has been used. In this study, 18 blends of various proportions of recycled glass (RG), plastic (RP), tire (RT), and concrete aggregate (RCA) were proposed and studied as alternatives. First, typical pavement tests such as compaction and CBR were carried out to select 7 suitable mix designs based on available backfill specifications. The shortlisted blends were further investigated through a specialized testing program, in particular, repeated load triaxial to simulate site stress levels. The results showed that CBR and resilient modulus characteristics improved by the increase in RCA content and the reduction in RT content. Three recycled material blends were selected as the optimum mix designs, and were next compared with the surrounding natural clay subgrades of the study area. The resilient modulus response of optimum mix designs exhibited up to 1.6 times greater stiffness compared to the clay subgrades under the same stress levels. The outcomes of this study reduce the demand for natural aggregates and promote the use of sustainable materials for backfilling pipeline trenches located under traffic loadings.