The Potential of High Flow Concrete Mixtures Utilizing Recycled Coal Bottom Ash as Underground Cable Trench Backfill Material

Abstract

In this study, the potential recycling Coal Bottom Ash (CBA) through replacing sand in flowable fill for cable trench backfill is determined. The new material is targeted to replace the soil backfill of narrow trenches to mitigate problems related to compacting soil backfill.. Targets were set for the workability, flowability, compressive strength and thermal resistivity, which corresponds to suitable properties for cable trench backfill. Three (3) concrete mixes were made as preliminary trial mixes for preliminary testing. Mix No.1 is a control mix made with cement and sand. Mix No.2 was prepared through substituting 50% of the natural sand content of Mix No.1 with CBA. In Mix No.3, CBA is fully used as the aggregate. In the Slump test, only that Mix No.3 fulfils the workability and flowability targets. All three mixes exceeded the limits for compressive strength. It is found that only Mix No.1 and Mix No.2 fulfils the requirement for thermal resistivity. In conclusion, recycled CBA can potentially be utilized in flowable fill for underground cable trench backfill, however more studies must be conducted to further improve the mix design to fulfil the requirements.