Characterization of wastepaper sludge ash for its valorization as a component of hydraulic binders

This paper deals with the physical, chemical and mineralogical characterization of WSA in order to evaluate the interest of its potential reuse as a component in hydraulic binders. The results show that WSA contains hydraulic minerals such as lime (CaO), mayenite (Ca12Al14O33) and α′-Ca2SiO4 in addition to gehlenite, the main mineral. WSA can also be considered as a hydraulic mineral admixture, which is very encouraging for the potential reuse of this material in hydraulic binders. However, WSA has some characteristics that could be worrying for its reuse. Firstly, SEM observations show that its particles are very porous, and that could lead to problems of workability of cement-based materials containing WSA. Secondly, the presence of both lime and metallic aluminium could be responsible for swelling when WSA is introduced into cement-based materials. No swelling was observed visually during the hydration of WSA-containing paste in this study but this first qualitative test is not sufficient and further investigations of this specific characteristic will be necessary. Finally, the presence of lime in the WSA could be considered as a problem for its use in binder for construction (risk of expansion) but, from another point of view, it would be very interesting for applications in road works, especially for the stabilization of soil, in which lime is regularly employed because it has useful properties (drying and reinforcement of the mechanical strength of the soils).

► WSA contains hydraulic minerals such as CaO, mayenite (Ca12Al14O33) and α′-Ca2SiO4.
► WSA can be considered as a hydraulic mineral admixture.
► The presence of lime in the WSA could be interesting for applications in road works.