Mechanically Treated Fly Ash from Fluidized Bed Combustion of Peat, Wood, and Wastes in Concrete

Abstract

Fly ash generation in fluidized bed combustion (FBC) is a critical issue in many countries due to its disposal is becoming increasingly restricted and expensive. Because of this, there is a demand for applications in which these types of fly ashes could be utilized efficiently. One promising use for FBC fly ashes is as a cement replacement material in mortar and concrete. The current concrete regulations do not allow the use FBC fly ash as a supplementary cementitious material, but it can be expected to be included in the standards in the future. The properties of FBC fly ashes typically do not fulfill the values set in the standards as such. This study aimed to establish whether the properties of fly ashes from FBC of peat, wood, and wastes can be modified by mechanical classification and grinding so that they meet the requirements of the standards. The sulfate and chloride content, the sum of the main components (Si, Al, Fe), and the fineness of material were analyzed before and after the classification and grinding processes. In addition, the mortar specimens were prepared by using the processed fly ash as a cement replacement material. It was found that air jet classification is an effective fractionating method for fly ashes that effectively removes sulfate and chloride into fine fraction. Classified and ground fly ashes are potential alternative cement replacement materials. It is possible to achieve 80% of the control sample's compressive strength and 90% of the control sample's flexural strength for mortars containing 20% of classified and ground FBC fly ashes. Graphical AbstractLow utilization potential fly ash Fine fraction: 10 -30% fly ash~ Hazardous components: heavy metals, SO 4 , Cl Coarse fraction: 70 -90% fly ash C hemical composition fulfills EN 450-1 concrete standard Waste disposal stabilization Grinding High value product, e.g. for concrete air air Air jet classificationThis study aimed to establish whether the utilization potential of fly ashes from FBC of peat, wood, and wastes can be improved in concrete by mechanical classification and grinding, which is not done earlier. We found that it is possible to modify these fly ashes to fulfill concrete standards. Usually it is thought that fly ashes from fluidized bed combustion are not suitable for standardized concrete, but this study shows that with treatments it is possible.

Development of a Commercial Screed Mortar with Low OPC Content by Incorporation of Biomass Fly Ash

“…A fact that can foresee a positive contribution of particle size reduction on their reactivity. It is possible that the contribution of BFA to the screed mortars strength The satisfactory results obtained in this work with 17 wt.% OPC substitution by as received BFA, are in agreement with other studies that pointed for 20 wt.% OPC replacement as the maximum recommended level [4,6,19,23,24]. Fořt et al [18] suggested 30 wt.% as maximum OPC replacement level.…”

“…The use of BFA1 and BFA2 (as received or pre-treated) as OPC substitute promote, in general, a deterioration of the mechanical properties. The same result was achieved by other authors [4,6,23,24]. The mechanical resistance of the specimens prepared with the as-received ashes is as lower as higher is the ash amount, as reported in previous works [4,6,18,23].…”

“…sieved BFA (<75 μm) and Ohenoja et al [24] used classified and ground BFA, to achieve such results. Figure 9 shows the effect of OPC content decrease, replaced by BFA, on compressive strength values.…”

“…A fact that can foresee a positive contribution of particle size reduction on their reactivity. It is possible that the contribution of BFA to the screed mortars strength sieved BFA (<75 μm) and Ohenoja et al [24] used classified and ground BFA, to achieve such results. Figure 9 shows the effect of OPC content decrease, replaced by BFA, on compressive strength values.…”

“…Ohenoja et al [24] evaluated the benefits of using pre-treated (air-jet classification and grinding) FA as a substitute of 20 wt.% of OPC in cement-based mortars (CEM I 52.5 R-SR5). Three FA types generated from the combustion in bubbling fluidized bed boilers of different mixtures of fuels (peat, wood and wastes) were evaluated.…”