Beneficial Use of Recycled Materials in Controlled Low Strength Materials

This study investigated the engineering characteristics of recycled materials in a controlled low strength material (CLSM). Controlled low-strength material (CLSM) is a self-compacting, flowable, low strength, cementitious material used primarily as backfill and void fill. CLSM is primarily used as a replacement of compacted soil in cases where the application of the later is difficult or impossible. Strength requirements are low in comparison to typical structural concrete. This enables the use of low cost, abundant, industrial by-products for the production of CLSM. The flowability and compressive strength of CLSM mixtures created using industrial by-products is the focus of this paper. The flowability of CLSM must allow efficient placement without segregation, while the compressive strength must provide structural support but allow for easy excavation. Consequently, there are minimum and maximum performance criteria for both consistency and strength. This research investigated the effects of using recycled materials in CLSM on the fresh and hardened CLSM properties. A total of six materials were used to create 18 mixtures that were batched and tested. The cementitious materials investigated were Class C fly ash and spray dryer ash; and the aggregates tested were bottom ash, crushed glass, recycled concrete fines, and crumb rubber. The results showed that CLSM with acceptable strength and flowability properties is attainable using these recycled materials.