Self-Cementing Properties and Alkali Activation of Enefit280 Solid Heat Carrier Retorting Ash

Abstract

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 Enefit280 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 Enefit280 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 Enefit280 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.

Design of High Volume CFBC Fly Ash Based Calcium Sulphoaluminate Type Binder in Mixtures with Ordinary Portland Cement

“…98% of the ash production) landfilled [ 33 ]. The raw oil shale CFBC ash has weak pozzolanic and self-cementitious properties [ 34 , 35 , 36 ], but the ash has been studied for accelerated carbonation and alkali activation to improve the mechanical properties of the ash aggregates [ 37 , 38 , 39 , 40 , 41 , 42 ].…”

Mechanical Activation of the Ca-Rich Circulating Fluidized Bed Combustion Fly Ash: Development of an Alternative Binder System

“…Fly ash from the earlier pulverized combustion boilers was successfully used as an additive to Portland cement, but the low temperature oil shale CFBC ashes do not meet the required criteria because of weak pozzolanic and self-cementitious properties [27][28][29]. Raw oil shale ashes have been also studied for alkali activated material design in recent years but without significant success [30][31][32][33][34].…”