Buried high voltage cables are backfilled with cement-bound or selected sands which have desirable thermal properties, but high carbon and economic costs. Crushed limestone dust is a potential replacement material, yet its longevity and performance in acidic groundwater are unknown.
The limestone dust was characterised for particle size distribution, permeability, particle washout, ICP-OES (chemical analysis) and X-ray diffraction (mineralogy). Then 12 column samples were subjected to 25 day dissolution tests in different water compositions with 4D Xray CT used to track structural changes and ICP-OES to track pollutant release.
Image: An XCT image of 6mm diameter limestone dust column after exposure to pH3 groundwater for 25 days, then dried.
Good assessment on the suitability of limestone backfill for use in acidic environment. The results show that cracks in the backfill form after several heating and cooling cycles, and this appears to be independent of the soil acidity. Next steps should include trial installations to investigate overheating phenomena and strengthen our understanding of its behaviour
Watson Peat, Engineering Technical Services Manager, Scottish Power
This has been incredibly useful research to provide experimental evidence on the behaviour and interaction of limestone dust with groundwater. The results have laid the foundation for understanding the impact of using limestone dust as a cable backfill material in the transmission network.
Mini Nambiar, Innovation Project Manager, SSE