Waste paper ash as a hydraulic road binder: Hydration, mechanical and leaching considerations

Waste paper fly ash (WPFA) and bottom ash (WPBA), derived from fluidised bed combustion of a paper recycling plant, exhibit cementitious properties owing to its mineralogical composition, and hence, could be proposed as a hydraulic binder. However, it may also contain some traces of heavy metals. Considering it is necessary to understand the effect of reusing any kind of waste on the environment, this study proposes of reusing WPFA/WPBA as a hydraulic road binder by evaluating its mineralogical composition and leaching activity. Chemical, physical, and mineralogical properties of raw WPFA/WPBA and the microstructural evolution of binders were carried out. Results showed that both ashes undergo hydration reactions while showing some cementitious properties by forming C-S-H gel, Friedel's salt, and calcite. According to the European standard EN 13282-1, both WPFA and WPBA can be categorised as N1 considering they reach 5.3 and 3.6 MPa, respectively, at 56 days. Furthermore, the mechanical performance of various soils was improved by using WPFA and WPBA as a binder. From the environmental point of view, the amount of barium in WPFA and WPBA, which is the main problem, was significantly decreased by using these ashes as a binder.