Recycling engineering sediment waste as sustainable subgrade material using ground granulated blast-furnace slag, electrolytic manganese residue and cement

With the rapid utilization of underground space, a large amount of engineering sediment waste (ESW) is generated, causing serious environmental burden to cities. This study develops a ternary binder named GEC containing ground granulated blast-furnace slag (GGBS), electrolytic manganese residue (EMR), and ordinary Portland cement (OPC) to stabilize ESW as sustainable subgrade materials. Based on unconfined compressive strength (UCS) tests, the optimum mix ratio of GEC was achieved. The durability and leaching toxicity of GEC-stabilized ESW (GESW) and OPC-stabilized ESW (CESW) was evaluated by conducting water immersion, sulfate attack and leaching tests. Furthermore, the micro-mechanisms affecting macro performance of GESW were clarified based on X-ray diffraction, scanning electron microscopy, and thermogravimetric tests. The results show that the optimum mix ratio of GGBS: EMR: OPC inside GEC was 5:3:2, and 7- and 28-day UCS of GESW containing 10 % GEC exceeded 6 and 8 MPa, respectively. Under same stabilization strength level, using 5 % GEC can fully replace OPC, thus reducing binder and OPC dosages by 37.5 % and 87.5 %, respectively. GESW had better water and sulfate attack resistance than CESW, and it can be directly recycled into subgrade without environmental concerns. The C-S-H, C-A-H, and ettringite were mainly responsible for the strength and durability improvement of GESW and CESW. The interactions between GGBS, EMR, and OPC were analyzed and clarified. Replacing OPC with GEC for ESW stabilization can respectively reduce CO2 emission and cost by 84.5 % and 67 %. The key findings provide a low-carbon approach of recycling ESW as sustainable subgrade materials.