Hydration Chemistry of Sewage Sludge Ash Used as a Cement Component

Abstract

The hydration chemistry of sewage sludge ashes (SSAs) used as cement components is examined using X-ray diffraction, thermal analysis, and isothermal conduction calorimetry. The presence of SSA leads to the formation of significant quantities of Al2O3-Fe2O3-mono (AFm) phases. Large quantities of amorphous hydration products are also formed. An additional series of small-scale experiments is used to show that it is highly probable that amorphous or poorly crystalline hydroxyapatite (Ca5(PO4)3OH) is generated in addition to calcium silicate hydrate gel. Thus, the reactions of SSA in combination with portland cement cannot be viewed simply as comparable to the pozzolanic or latent hydraulic reactions of other by-product materials used in similar ways.