Cement recipes next on list for tar ponds

By Tanya Collier Macdonald
Cape Breton Post
Mon., Mar. 12, 2007

SYDNEY - Tenders to solidify and keep toxic tar pond sludge from travelling should be ready in September, says the engineering company hired to manage the project.

Earth Tech will identify three cement recipes that offer the best unconfined compressive strength, says Joe Sullivan, Earth Tech project manager. Those mixes will be tested at the tar ponds in May.

Concurrently, the engineering firm will meet with Nova Scotia Department of Environment and Labour to get proper approvals and permits needed before work begins.

The effort builds on bench-scale testing program completed by Jacques Whitford in May, 2006. At that time, samples were taken from the south pond to identify which mix would be suitable for the overall project.

During that program, engineers tested portland cement, fly ash from Lingan Generating Station and slag from Sysco. The report shows that all mix designs met the minimum unconfined compressive strength requirement. However, the mixture using 15 per cent of portland cement mix was the only one that met the hydraulic conductivity performance criteria, which will work to prevent groundwater from moving through the cement. Sysco slag is also proving to be valuable.