Evaluation of flow and in-place strength characteristics of fly ash composite materials

Abstract

Of the seven hundred and fifty millions of metric tons of fly ash that are produced annually worldwide, only a small portion e.g., 20% to 50% of the fly ash is used for productive purposes, such as an additive or stabilizer in cement, bricks, embankments, etc. The remaining amount of fly ash produced annually must either be disposed off in controlled landfills/ mine fills or waste containment facilities, or stockpiled for future use or disposal. As a result of the cost associated with disposing these vast quantities of fly ash, a significant economical incentive exists for developing new and innovative, yet environmentally safe applications for the utilization of fly ash. The main aim of the present investigation was designed to develop an engineered backfill material to be placed in mine voids using fly ash as the major component. Experimental set up was designed and fly ash samples from seven numbers of thermal power plants situated at different parts of the country were collected. Investigation into detail physical, chemical, morphological, and mineralogical characterizations have been carried out to choose the most favorable fly ash source for slurry transportation.Flow parameters such as viscosity, shear stress, shear rate (25s-1 to 1000s-1), temperature (200C to 400C), and solid concentration (20% to 60%), etc. were determined. Flow behavior was influenced with addition of additives as cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and a counter-ion sodium salicylate (NaSal). As the fly ash concentration in the slurry increased an increase in viscosity was observed. Addition of surfactants (0.1% to 0.5%) modified the flowing attributes from shear thickening to shear thinning/Newtonian pattern and eliminated yield stress completely/partially compared to that of untreated fly ash slurry. Temperature of the slurry environment was also observed to influence the flowing behavior.