Combustion of low calorific fuel-oil shale-in industrial-scale pulverized firing and circulating fluidized bed combustion boilers produces large amounts of ash. Estonian oil shale ash is characterized by a high content of free CaO as compared to those listed in the European Standard EN 450. The main alternatives to oil shale ash utilization include its use as a lime replacement in mineral binders or as a constituent of Portland cement. The pulverized firing ash formed at 1400 °C has been effectively used as a second main constituent of Portland cement during the last fifty years. Further utilization of the low-temperature circulating fluidized bed ash (formed at 800 °C) depends on its composition and properties. Dust collecting systems of both boiler types consist of bottom dusters, cyclones and electrostatic precipitators. The corresponding ash types differ in specific surface area, grain size and mineral composition. The structure and composition of the dry ash and ash based stone were studied using chemical, XRD and SEM analysis. The results indicated that hydration type, as well as the setting and hardening course of the selected ash type are determined by the firing temperature of oil shale.

To estimate the environmental properties of oil shale ash-based mortars the leaching of harmful components was studied. The leachates were highly alkaline. The predominant ions were Ca 2+ , K + , Na + , SO 4 2-. The leachable content of soluble components in PF ash mortars was higher in comparison with that in CFB ash mortars. Results indicated that over curing time the fraction of readily soluble inorganic components decreased and the mobility of potentially hazardous Cd and Zn did not increase. Addition of bypass dust could affect the content of leachable ions. Results give new knowledge about the environmental properties of oil shale ash-based materials, including backfilling composites for underground mining technology.

Combustion temperature of oil shale in pulverized fuel boilers and in fluidized bed combustion equipment is different. High temperature burnt oil shale from pulverized combustion boilers and low temperature burnt oil shale from a CFB (Circulating Fluidized Bed) boiler differ in their mineral composition and surface properties of ash particles. Variations in the properties of ashes affect hydraulic properties of burnt oil shale as a binder or as the main constituent of Portland cement. Differences in the frost resistance of concretes made with various second main constituents show how significant is the type of hydration of the second main constituent in terms of the durability. Alternate immersiondrying tests were carried out to analyze the frost resistance of concretes compared to the other main constituents.The objective of this work was to investigate the influence of various burnt oil shales as the main constituent of Portland cement on the durability of concrete compared to the main constituent such as pulverized limestone.

The composition and properties of ash in the context of the modernisation of oil shale industry Mai Uibu (a)* , Kadriann Tamm (a) , Regiina Viires (a) , Janek Reinik (b) , Peeter Somelar (c) , Lembi Raado (d) , Tiina Hain (d) , Rein Kuusik (a) , Andres Trikkel (a)

Use of alkyl sulfonate fractions (with overall hydrocarbon chain-length range of Cg-C,) as admixtures to improve the freezing resistance of Portland cement/sand mortars was studied.Alkyl sulfonates were synthesised from hydrocarbon mixtures obtained by polyethylene waste pyrolysis. They act as air-entraining agents but do not show plasticising effect. All of the three different fractions improve freezing resistance but higher than 9% air contents are detrimental to the strength values. The best compromise is the fraction Cg-C,y in 0.02% amount that raises the freezing resistance by 22-28% as estimated from the values of the dynamic modulus of elasticity measured after 200 freezing/thawing cycles. Under these conditions, the bending and compression strength retain not less than 90% of the values measured for the reference mortar after a six-month hardening period.