Hydraulic Conductivity and Porosity of Hardening Slurries with Fluidal Fly Ashes in Chemically Aggressive Environments

The article presents the results of hydraulic conductivity and porosity tests of hardening slurries prepared from Portland cement, betonite, water and fluidal fly ashes from combustion of hard and brown coal. In addition, the ashes were in two states of activation: non-activated and mechanically activated. The slurries were exposed to persistent, 160-day filtration of chemically aggressive liquids: distilled water, 0.5% solution of nitric acid and 1% solution of sodium sulphate. A comparative base was composed of samples exposed to filtration of tap water. The research was into relations between hydraulic conductivity and parameters characterizing the porosity structures in slurries, as well as into the influence of sample maturation periods, the state of activation and type of ashes, and the type of aggressive medium on porosity and conductivity of the material. The observed phenomena were typical of materials based on cement binders, and exposed to chemical aggression, e.g. sealing-up of porosity structures in response to sulphate corrosion and de-sealing in response to leaching corrosion, along with effects specific for slurries, such as a decrease of hydraulic conductivity in response to nitric acid solution. A favourable effect of fluidal fly ashes from brown coal was also noted.