Use of residues as fillers in alkali‐activated binders

The demand for resource saving and recycling of waste materials to achieve a circular economy is increasing. In Europe, nearly all blast furnace slag and fly ash are used as supplementary cementitious material. Furthermore, there is urgent need to reduce the CO₂ emissions of building materials industry. Like in OPC‐based concretes, the reduction in the binder content by the use of fillers can be a way to reduce the CO₂ emissions of alkali‐activated binders even further. Therefore, this study aims at the use of industrial residues as a filler in alkali‐activated materials to reduce the CO₂ emissions of alkali‐activated binders. In this study, three industrial residues including municipal solid waste incineration ash (MSWIA), steel slag (SS) and ash formed by the thermal treatment of tar‐containing asphalt (EcoF) are used as fillers for alkali‐activated binders and are compared with fine quartz powder as an inert reference filler. The binder is ground granulated synthetic slag, which is replaced with the four filler materials at a 32 vol.% replacement level. The samples are reacted with 15 and 25 wt.% NaOH solution. The results show a potential advantage of using SS and EcoF as a filler in concrete as they exhibited a slightly higher compressive strength at all tested ages compared to quartz powder.