Strength and permeability properties along with microstructural evolution of hardened slurries composed of fly ash from fluidal bed combustion of brown coal and an addition of OPC/BFSC is assessed in this paper. An increase in the amount of fly ash in slurries influences the development of mechanical strength and a decrease of hydraulic conductivity. SEM, XRD, and porosity analyses confirmed formation of watertight microstructures. The structure of slurries is composed of ettringite, C-S-H phase, AFt, and AFm phases. Ettringite crystallises as relatively short needles forming compact clusters or intermixed with the C-S-H phase. The occurring C-S-H phases are mainly of type I – fibrous and type II – honeycomb
This article presents test results for hydraulic conductivity and porosity structure of hardening slurries prepared of Portland cement, betonite, water and fluidal ashes from the combustion of hard and brown coal. The slurries were exposed to persistent filtering action (180 days) of liquids chemically aggressive to cement binders, i.e. distilled water, 0.5% solution of nitric acid, 1% solution of sodium sulphate, 1% solution of magnesium nitrate and 1% solution of ammonium nitrate. Samples exposed to filtration of tap water constituted the reference base. The research was into relations between hydraulic conductivity and pore structure parameters in slurries, as well as into the influence of the type of aggressive medium on leak tightness of slurries (their porosity and hydraulic conductivity).
The research paper presents the results of hydraulic conductivity, pore structure, phase composition and microstructural tests of hardening slurries prepared using Portland cement, bentonite, water and fluidized-bed ashes coming from hard coal and lignite combustion. The slurries were subjected to long-term (210 days) exposure to the filtering action of an environment strongly aggressive to a cement binder. A sulphate solution 2- with sodium content of SO4 2- = 6700 mg/l was applied, which modelled sulphate aggression. The comparative base were samples subjected to filtration in tap water (neutral environment).
The test covered dependencies between hydraulic conductivity k10 (filtration coefficient) and the parameters characterizing porous structure in the slurry, as well as the impact of an aggressive medium on slurry tightness (its porosity and hydraulic conductivity). Changes in the phase composition and slurry microstructure were analysed in terms of its corrosion resistance to the action of sulphate aggression.
Observations from other researchers have been confirmed that the use of fluidized fly-ash addition has a positive effect on increasing the resistance of cement matrix exposed to sulphate aggressiveness.
The growing number of municipal sewage treatment plants in Poland raises the problem of managing more and more sludge. The thermal treatment of municipal sewage sludge (TTMSS), which significantly reduces the volume of waste, results in an increase in the concentration of heavy metals in the fly ashes – the final products of the process. The search for methods of utilization of fly ash from TTMSS resulted in attempts to use it in hardening slurries widely used in hydro-engineering. Due to the nature of the application of this material in the cut-off walls (exposure to groundwater flow) one of the key issues is the degree of heavy metal immobilization. The paper attempted to determine the degree of leaching of selected heavy metals from the hardened hardening slurry, composed of fly ash from TTMSS. For this purpose, the eluates were prepared from samples, after various periods of curing, using a dynamic short-term method called "Batch test". The liquid used for leaching was: distilled water and 0.1 molar EDTA solution – to determine the amount of potentially mobile heavy metal forms. The results show the possibility of the safe usage of fly ash from TTMSS as an additive for hardening slurries.
Along with the increase in popularity of the sewage sludge thermal treatment methods in Poland
resulting from the implementation of European Union law, a management problem with ash, which is produced
as a result of this process, appeared. The paper analyses the chemical composition and physical properties of fl y
ash from thermal treatment of municipal sewage sludge in terms of its use in concrete technologies in relation to
EN 450-1 Fly ash for concrete. Defi nition, specifi cations and conformity criteria (2012) and EN 197-1 Cement.
Composition, specifi cations and conformity criteria for common cements (2011) standards. The tested material did
not meet the requirements related to use of fl y ash for concrete production (chemical composition, low activity
index, high water demand and fi neness), and as main and minor components for cement production. On the basis
of the carried out research and analyses, it was found that the hardening slurry technology creates the greatest
possibilities related to the management of fl y ash from thermal treatment of municipal sewage sludge.