Circularity and longevity of alkali-activated materials

Alkali-activated materials (AAMs) are being envisaged as a future alternative to cements because AAMs (i) can be made solely from locally available secondary raw materials and (ii) because of their low energy consumption during synthesis. However, products that cannot be reused should never enter the market. Therefore, the circular economy viability of AAMs was studied by reusing (alkali-activated) pulverised rock wool in alkali activation synthesis until the theoretically determined limit leading to the efflorescence would be reached. While 25% of the maximal allowed liquid alkali did not offer significant mechanical performance, 50, 75 and 100% of allowed alkali ended up with 15, 20 and 20 MPa, respectively, which is only 5 MPa lower than AAM made with the same technique (pressing) in a one-step approach. Therefore, if the initial AAM does not reach the efflorescence limit, it could still be used as a precursor before it becomes waste.