Material collected from a road base was submitted for testing and evaluation after the overlaying pavement installation showed localized distress. The road base was prepared with processed fluidized bed combustion (FBC)  ash. Road base material, as well as, the initial FBC ash were probed using WDXRF, XRD and TGA methods to establish the chemical signature and identify potential detrimental constituents.

X-ray powder diffraction could show that the processed FBC ash consisted of gypsum, ettringite, anhydrite, portlandite and calcite. Distinguishing compounds of untreated FBC ash are free lime (CaO) and anhydrite (CaSO4) because of the co-combustion of the fuel with limestone.

The TGA graph showed the decomposition events expected from the XRD results, i.e., loss of free and combined water and release of carbon dioxide. The fact that an oxidation event was observed also provides information about the type of fuel used in the FBC boiler.

XRD pattern of a processed FBC ash.

TGA graph of the processed FBC ash .