Influence of seawater on the mechanical and microstructural properties of lime-incineration sewage sludge ash pastes

Traditional disposal methods of dredged marine sediment are expensive and environmentally harmful. Reusing marine sediment as construction materials by stabilisation/solidification (S/S) has been an appealing option. This paper reports on a study on evaluating the potential of using incineration sewage sludge ash (SSA) as the principal binder together with anhydrous lime and hydrated lime for S/S in a seawater environment. This study evaluated the effects of seawater on the mechanical performance and microstructural properties of the binder as compared to the use of freshwater. Generally, seawater accelerated and promoted the strength development of the lime-SSA binder. Friedel's salts (3CaO center dot Al2O3 center dot CaCl2 center dot 10H(2)O) were detected in the seawater pastes by X-ray diffraction (XRD) and thermogravimetric (TG) analysis. It was found that the role of Friedel's salt contributed differently to the strength development of hydrated lime (CH)-SSA and anhydrous lime (lime)-SSA pastes mixed with seawater particularly at the later curing age. The 28-day strength of the lime-SSA paste mixed with seawater wasmore than double that of mixed with freshwater, whereas the CH-SSA paste mixed with seawater only showed a comparable 28-day strength with the freshwater mix. This was primarily due to the initial porous structure of the fresh lime-SSA paste allowing the growth of the Friedel's salts. Therefore, the use of anhydrous lime may mitigate the strength reduction caused by Friedel's salts at the later ages. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Traditional disposal methods for dredged marine sediment are costly and damaging to the environment. Reusing marine sediment for construction materials through the process of stabilisation/solidification (S/S) is a promising alternative. This study evaluated the potential of using incineration sewage sludge ash (SSA) as the main binder with lime for S/S in seawater, and found that seawater can accelerate the strength development of the lime-SSA binder. The presence of Friedel's salts in seawater pastes and their impact on the strength development of different binder mixes was also discussed.