Determination of the Percentage of Free Hydrogen After the Placement of Cemented Fly Ash Grout.

Grouts composed of a mixture of power station fly ash and general purpose cement are pumped into operating and disused underground coal mines for a variety of purposes. In operating coal mines grout is used for strata support, longwall recovery, ventilation control, and monolithic seals. In disused mines, the grout is used to protect surface infrastructure and promote development of surface infrastructure. These applications provide an avenue for recycling fly ash, a bulk material that is produced in significant quantities by coal fired power stations. An international research paper indicates that a grout consisting of fly ash from incinerated municipal waste and cement caused the evolution of hydrogen gas after placement. Such liberation may present an explosive risk if the hydrogen concentration reaches a critical range. This paper examines the potential for hydrogen liberation from grouts composed of Australian power station fly ash and general purpose cement, for the purpose of reviewing their suitability for mining applications. Experiments were conducted in which grout was placed in sealed containers for placement periods of 1 hour, 4 hours, 24 hours and 7 days, before gas was sampled from each container for determination of any liberated hydrogen and comparison to the known explosive range. [ABSTRACT FROM AUTHOR]