Research of Building the Reasonable Mixing Ratio between Waste Rock and Fly Ash as Backfill Material in Mongduong-Cocsau Area, Quang Ninh, Vietnam

Abstract

The coal mining industry in Quang Ninh province is primarily focused on serving thermal power plants which has resulted in a
substantial amount of waste rock and ash. This way has not only narrowed the used land but also had a negative impact on the
environment. However, the economic development plan for the province until 2030 emphasizes the development of a greener economy.
Therefore, balancing between economic growth and environmental protection is one of the significant challenges of this province.
To solve the problem of waste rock and ash dumps, some methods have been proposed. It tends to use waste materials for backfilling
the underground mines, this can help to minimize the bad impact on the environment. Additionally, Another solution is to handle the
waste in abandoned mining areas, or use them as construction materials. These ways are expected to partially reduce the bad effects
of waste rock and ash dumps on the environment.
In the world, there are many studies on filling using waste rock and fly ash, but in Vietnam this issue is quite new. In order to turn
waste rock and fly ash into filling materials, the article researches on a laboratory scale, the ability of transportation in hydraulic
pipelines, level of the water separation and shrinkage of mixtures of rock and fly ash in the Mong Duong – Coc Sau area with the
different proportions. The results of the experiments show that the area has appropriate mixing ratio as 70–73% of waste rock and
30–27% of fly ash, this ratio satisfies the transportation conditions in the pipeline and the shrinkage rate of 8, 8–12.3%. The indicators
in experiments show that it is able to take waste rock into mined underground area to fill, which prevents displacement of strata from
mining, protects the underground water flow, and also reduces negative impact of waste rock on environment.