Class-F fly ash

Fig. 3. Phase diagram of a portion of ihe Sitb-AbO% system, showing regions of phase separation of undercooled melts. The projected composition of Class-F fly ash glasses lies in the range of 10-4051 mol /t AI,Ot. Adapted from Roth et al. (1987).

Qian, J. C., Lachowski, E. E. Glasser, F. P. 1988. Microstructure and chemical variation in Class F fly ash glass. Materials Research Society Symposium Proceedings, 113, 45-53. 

A relationship exists between fineness and SAI. While 34 wt% fineness meets the ASTM C-618 specifications, finer ash samples have been shown to achieve higher compressive strengths. While sizing on a 325 mesh screen (>45 pm) can be indicative of the amount of fine materials present, it does not directly measure the reactive component of the ash, which is in the very finest fractions (e.g., <5 pm). The presence of this ultra-fine material has a profound impact on strength development of the concrete, as the surface area available for pozzo-lanic cementitious reactions is contained in the finest fractions. For example, the surface area of a typical Class F fly ash, with a mean particle size (D50) of 24 pm will have over 90% of the total surface area accounted for in the <5 pm... 

Two road patches were repaired at ANL with Ceramicrete matrix composite containing 50 wt% class F fly ash on a trial basis in March 1999. The potholes are located on a road with heavy traflic from dehvery trucks. The debris from the patches was not cleared, nor were the sides cut into smoother shapes as normally done. The temperature was 40 °F. After a few hours, it rained heavily, and the patches, being in low-lying areas, were under water till the next day. In spite of this weather, the patches set well the next day. They have not only withstood traflic for the last four years, but also the freeze-thaw cycles of the three winters have not affected patch integrity. At present, the intact patches show up well because the original asphalt road surrounding the patches is crumbling. 

DOE ash waste Activated carbon, 5 Vermiculite, 20 Class F fly ash, 40 Coal bottom ash, 33 HgClz added such that Hg level was 0.5... 

Fly ash starts out as impurities in coal, mostly clay, shales, limestone, and dolomite, which ends up as ash, and fuse at high temperature becoming glass. Two U.S. classifications of fly ash are produced. Class C and Class F, according to the type of coal used. Class C fly ash, typically obtained from subbituminous and lignite coals, must have more than 50% total of silica, alumina, and iron oxide. Class F fly ash, typically obtained from bituminous and anthracite coals, has more than 70% of these oxides. 

Figure 9.1 Compressive strength of Portland-fly ash cements made with different additions of class F fly ash. Composition of ash Si02, 52.3% AI2O3,24.2% Fe203,10.0% CaO, 4.4%.

La Rosa, J.L., Kwan, S., and Gratzek, M.W. (1992) Zeolite formation in class F fly ash blended cement pastes. Journal of the American Ceramic Society 75, 1574-1580. 

The precursor(s) may contain also variable, but limited, amounts of other oxides, mainly CaO, such as is the case in class F fly ashes. 

The effectiveness of different fly ashes as additives preventing sulfate-induced expansion can vary greatly. When the mineral composition of the fly ash is such that the formation of ettringite occurs before exposure to sulfate solution, the blended cement performs well. However, if at the time of exposure to sulfates phases vulnerable to sulfate attack (such as monosulfate) are present, the sulfate resistance of the binder is poor (Mehta 1986, 1992). It has also been reported that at lower replacement levels (10% and 20%) class F fly ashes perform better than class C ashes (Soroushian and Alhozaimi, 1992). 

Portland cements extended with class F fly ash from coal burning power plants may be used for filler applications (Reeves, 1991) and for lightweight cement slurries. The fly ash content may reach up to 50 wt%. 

T. Bakharev, Geopolymeric materials prepared using class F Fly Ash and elevated temperature curing, Cem. Concr. Res. 35 (2005) 1224—1232. 

Class F fly ash The burning of harder, older anthracite and bituminous coal typically produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than 20% lime (CaO). Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires a cementing agent, such as Portland cement, quicklime or hydrated lime, with the presence of water in order to react and produce cementitious compounds. Alternatively, the addition of a chemical activator such as sodium silicate (water glass) to a Class F ash leads to the formation of a geopolymer. 

Table 4.4 Chemical composition of fluidized bed combustion fly ashes as compared to that of class F fly ash from conventional combustion installations...

Figure 11.2 X-ray diffractogram of cement, class F fly ash, and CaCOs nanopaiticles (Shaikh and Supit, 2014).

South African Class F fly ash derived Na-X zeolite was used as heterogeneous base catalyst for the transesterification of sunflower oil to produce biodiesel. It was shown that a biodiesel yield of 83.53% was achieved with reaction conditions of oil to methanol ration of 1 6, catalyst amoimt of 3% and at a temperature of 65° C for a period of 8 h [92]. The study showed that the process offers value addition to the large amount of fly ash generated every year. 

Gmtzeckand Siemer [45] have investigated the synthesis of zeolites from a mixture of class-F fly ash and slurry of sodium aluminate prepared in proportion of 3 1 (i.e., Na Al). They have reported that a class-F fly ash reacts with the slurry to synthesize zeolites from a highly alkaline waste stream. The reaction has been studied as a function of mixture (i.e., fly ash slurry) composition (3 2, 1 1, and 1 2), time (1, 3, and 7 days), and temperature (80, 130, and 180 °C). The X-ray diffraction analysis of the products has indicated that the reaction between fly ash and sodium aluminate can result final yield as zeolite A, Na-Pl, and Hydroxy-sodalite at 80, 130 and 180 °C, respectively. It has been clarified that the bulk of the sodium has been incorporated into the zeolitic phases. 

It can be observed from Tables 5.20, 5.21, 5.22, 5.23 and 5.36 that the sum total of major oxides (AI2O3 + SiOa + Fe203) present in the raw fly ash, RFA (i.e., the original hopper ash) is about 95 % and hence it can be characterized as Class-F fly ash (ASTM C618-08) [3]. It can be noted from Fig. 6.3 and Tables 5.20, 5.21, 5.22 and 5.23 that activation of this fly ash with NaOH results in loss of SiOa (in majority) and AI2O3 (in traces) in the residues (the alkali activated fly ash, AAF), which is represented as the second data point, from the origin, on the duration axis, for all the durations. Incidentally, reduction in the value of oxides increases with an... 

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