Thesis defence in the University of Oulu

Doctoral Candidate

Master of Science (Tech) Jouni Rissanen

Faculty and research unit

University of Oulu Graduate School, Faculty of Technology, Fibre and Particle Engineering Reach Unit
+358 294 48 2394

Field of study

Process Engineering

Date and time of the thesis defence

2.10.2020 13:00

Place of the thesis defence

Linnanmaa, auditorium L10. Remote connection: https://oulu.zoom.us/j/66809929910

Topic of the dissertation

Utilization of peat-wood fly ash from fluidized bed combustion as supplementary cementitious material

Opponent

Professor Nina Štirmer, University of Zagreb

Second opponent

Doctor Anna Kronlöf, (Emerita)

Custos

Professor Mirja Illikainen, University of Oulu

Utilization of peat-wood fly ash from fluidized bed combustion as supplementary cementitious material

Approximately 500 000 tons of non-coal fly ash are produced in Finland annually from energy generation sources, most of which is fluidized bed combustion fly ash (FBCFA) from the burning of peat and wood. This significant industrial side stream is not yet fully utilized, so that some is
still escaping from the material circulation of circular economy. FBCFA is nevertheless a promising novel supplementary cementitious material, as it naturally possesses a fine particle size as well as suitable chemical and mineralogical composition properties. Utilization of this material
would be beneficial for the environment, as it could potentially reduce the carbon footprint of concrete production and the environmental impacts of ash disposal. It would also be beneficial for ash producers, as it would provide a new route for reducing the amount of waste generated.
The aim of this thesis was to study how FBCFAs originating from the co-combustion of peat and wood affect the properties of fresh and hardened mortars when used to replace 10–40% of the cement normally used in them, and also to examine the effect of FBCFAs on freeze-thaw durability.

In general, fluidized bed combustion fly ash slightly reduced the compressive strength of the mortar samples, but it clearly out-performed non-reactive filler materials and achieved roughly similar compressive strengths to those resulting from conventional coal fly ash. FBCFA increased the water requirement of fresh material due to irregular particle shape. However, sufficient dosage of superplasticizer enabled to prepare mortar with good workability even when 40% of the cement was replaced with fly ash. FBCFA worked well also in freeze resistant mortars.

From a technical perspective, approximately 20% of the cement could be replaced with good quality FBCFA without significantly impairing the performance of the hardened material, although at the moment FBCFA does not conform to the European fly ash standard, which hampers its use. The future feasibility of FBCFA as a supplementary cementitious material is highly dependent on the legal incentives laid down and customers' attitudes towards sustainable construction materials.

 

Dissertation

Last updated: 2.10.2020