SELF-CEMENTING PROPERTIES AND ALKALI ACTIVATION OF ENEFIT280 SOLID HEAT CARRIER RETORTING ASH

The composition and cementitious properties upon hydration and alkali activation of the solid heat carrier (SHC) ash produced in a new Enefit280 retort was studied. The Engfit280 waste heat boiler (WHB) ash is different from other SHC solid residues. It does not contain residual organics, but is characterized by a low content of reactive Ca-phases and the soluble amorphous (aluminium)-silicate phase/glass material. Cementation of Eneit280 ash upon hydration with plain water is limited and its uniaxial compressive strength stays < 4 MPa after 28 days of curing. Ash mixtures activated with sodium silicate based mixtures show higher compressive strength values, reaching > 10 MPa after 28 days of curing. The Engfit280 ash, compared to other ash types forming in the Estonian oil shale processing industry, has significantly poorer self-cementing properties. This needs to be taken into account when designing waste depositories, if. other types of ash with better self-cementing properties are not co-deposited with this ash.