Influence of Curing Regimes on Engineering and Microstructural Properties of Geopolymer-Based Materials from Water Treatment Residue and Fly Ash

Geopolymerization is a new method for treating water treatment residue (WTR) from water purification plants to reduce the amount of stored land in urban areas. Polymeric bond formation depends on the curing conditions. In this study, the curing conditions suitable for subsequent treatment to save energy consumption and production costs in the future application were investigated. The WTR had a high aluminosilicate content with low alkaline activity, so fly ash (FA) was added to FA and WTR mixtures in the ratio of 40 and 60 weight percent (% in wt), respectively. The moisture content of the mixtures ranged in 12-15%, suitable for semi-dry pressing to form pellets. After this formation, the geopolymer samples were cured under different conditions (room temperature, microwave oven, in dryer at 110 degrees C, and in autoclave with hydrothermal condition). The experimental results showed that the hydrothermal samples had better properties, such as pH<9, high stability of mechanical strength over 3.5 MPa, and soft coefficient over 0.75. The microstructural properties were investigated using modern analytical tools, such as XRD, SEM, FTIR, and NMR, to detect the chemical functional groups of the aluminosilicate networks in the geopolymer matrix and the close relationship among the properties and its microstructure.