Lagoon PFA: Feasibility for use as a binder in concrete

Abstract

A B S T R A C T R I~ S U M I ~This paper describes a study carried out to examine the influence of storing pulverized-fuel ash (PFA) in an excess of water, or lagoon, on the properties of the material itself and its suitability for use as a component of the binder in concrete. The work considered PFA slurried and stored in the laboratory (simulated lagoon PFA), and material recovered from power station lagoons (lagoon PFA). The results indicate that simulated lagoon PFA tends to agglomerate and this appears to relate to chemical changes taking place within the material, as indicated by increasing loss-on-ignition, the formation of gypsum and bassanite, and leaching of solubles from particle surfaces into the simulated lagoon solution. Despite these effects, the use of this material, as part of the binder, has only a minor influence on concrete properties, with small changes in workability, bleeding and compressive strength measured. There was general agreement between the results for laboratory and site lagoon PFA. If the effects noted are accommodated within the concrete mix design, there is potential for using lagoon PFA as a binder component in concrete construction.

Dry-processing of long-term wet-stored fly ash for use as an addition in concrete

“…The LOI of LFA1 was 6.4%, while LFA2 and SFA1 were 10.3% and 15.1%, with both, therefore, exceeding the BS EN 450-1 [17] limit. Earlier work [9,10] suggests increases in LOI of around 0.5 to 1.0% can be obtained after wet-storage (6 months, laboratory) compared to dry material, reflecting decomposition (during the test) of reaction products formed. The particle densities are around what may be expected for the materials, given the above properties, and can also be influenced by wet storage, as noted previously.…”

“…The sum of the main oxides (silica (SiO2) + alumina (Al2O3) + iron oxide (Fe2O3)) was greater than 70%, with calcium oxide (CaO) contents less than 3.0%, alkalis (Na2Oeq) 1.7 to 2.1% and sulfate (SO3) 0.5 to 0.6%. The latter three are at the lower end of the typical range [22] and may relate to the loss of soluble components from particle surfaces during wet storage [9]. Typically potassium oxide (K2O) is higher in fly ash than sodium oxide (Na2O) [23] and the differences with LFA1 may reflect the presence of (sodium) chloride (Cl) in the material (also noted in LFA2).…”

“…Studies on siliceous fly ash (Class F, ASTM C618 [7]) in lagoons and stockpiles suggest material may be variable, with a range of fineness levels and moderate to high carbon contents [8]. Short-term tests on wetstored fly ash (laboratory and site, mainly up to 6 or 18 months) indicate that agglomeration occurs, with minor changes in bulk chemistry, and the presence of sulfate-based products on particle surfaces/reduced free lime contents also noted [9,10]. These were influenced by fly ash properties (e.g.…”

“…free lime content), storage conditions (e.g. moisture level) and holding period [10], with reactivity potential affected [9,11]. Wet storage effects at actual fly ash sites (various exposure conditions/periods) have been noted to range from little change in the material [12,13], to processes including dissolution of components at particle surfaces/formation of secondary phases [13][14][15].…”

Fly ash influences on sulfate-heave in lime-stabilised soils

“…It was noted that the silicium dioxide contents of both fly ashes exceeded 70% (as required by BS EN 450-1 (BSI, 2005)) and their amorphous/others contents (by difference) were similar. CA also had a lower TPS level, probably reflecting differences in storage history (McCarthy et al, 1998b).…”