Long-term performance monitoring was conducted on a demonstration project in which road base materials were constructed from reclaimed hydrated fly ash (HFA) and atmospheric fluidized-bed combustion (AFBC) and cement-kiln dust (CKD) by-products were used as calcium activators. Reclaimed HFA is a form of artificial aggregate produced from compacted, hydrated Class C fly ash at pulverized-coal combustion facilities. Strength testing and chemical analysis indicate that AFBC and CKD activators increase cementitious and pozzolanic reactions in the HFA material. Laboratory analysis determined the preferable range of activator to HFA artificial aggregate ratios for AFBC- and CKD-activated mixtures based on strength development, freeze-thaw durability analysis, compaction characteristics, and optimum moisture content ranges. Results of long-term strength gain from core samples show significant strength increase in the CKD-stabilized HFA base mixture, while the AFBC-stabilized HFA mixture shows signs of freeze-thaw durability problems compared with satisfactory performance experienced in the laboratory with the standard for fly ash for use with lime (ASTM C593). It appears that the AFBC section is still performing well but is probably functioning as a flexible aggregate base rather than a stabilized and cemented semirigid base. Long-term testing indicates that the high-volume application of these by-products is an economical and suitable alternative when used with an appropriate calcium activator.
Fly ashes from the Lansing and Ottumwa power plants in Iowa were agglomerated by means of a continuous pan agglomerator, a continuous auger and a batch turbine agglomerator. In order to compare agglomeration mechanisms the following parameters were determined: (a) particle size distributions of the untreated fly ashes; (b) particle size distributions of the agglomerated fly ashes; (c) pore size distribution of agglomerates; (d) crystalline hydration products by X-ray diffraction; and (e) morphological characterization by scanning electron microscopy.In the batch system coalescence mechanisms were favoured. The agglomerates were fairly irregular in shape and had a rough surface texture. As residence time in the system increased breakage of agglomerates occurred, reducing the average agglomerate size. In the continuous systems layering of the fine feed particles onto established agglomerates was the predominant growth mechanism. The agglomerates were smooth and spherical. The layer structure was observed by scanning electron microscopy. Agglomerates of widely varying size, strength, and pore matrix can be produced in both systems. It is envisaged that while agglomerates could be produced with characteristics essential for their proposed end use by either method, continuous pan agglomeration would be the most versatile system to utilize.
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