Utilization of pulp mill side streams as a part of cementitious binders
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
L5 auditorium (Oulun Puhelin auditorium), Linnanmaa
Topic of the dissertation
Utilization of pulp mill side streams as a part of cementitious binders
Doctoral candidate
Master of Science Juho Rasmus
Faculty and unit
University of Oulu Graduate School, Faculty of Technology, Fibre and particle engineering research unit
Subject of study
Process Engineering
Opponent
associate professor Teemu Kinnarinen, LUT University
Custos
Docent Katja Kilpimaa, University of Oulu
Utilization of pulp mill side streams as a part of cementitious binders
Managing the environmental impact of industrial processes is an important challenge. One the other hand, the consumption of virgin raw materials remains high, while on the other, large volumes of process waste are disposed of in landfills. One of the most used materials is concrete, with cement serving as its primary binder. However, cement production consumes vast amounts of limestone (CaCO₃), releasing carbon dioxide (CO₂) due to the high temperatures required for processing. Additionally, reaching these temperatures (above 1400 °C) requires considerable energy.
To mitigate emissions in the construction industry, various supplementary cementitious materials (SCMs) have been explored. It has also been shown that concrete can be produced without cement through alkali activation. One of the most commonly used SCMs and a key raw material in alkali-activated materials is ground granulated blast furnace slag, a by-product of the steel industry, which has also been used in this dissertation. In addition, the pulp industry generates mineral side streams that, due to their composition, could also be suitable for similar applications, making their potential worth investigating.
This dissertation examines two pulp industry side streams—recovery boiler fly ash and green liquor dregs—and evaluates their suitability for use in cement-based and alkali-activated materials. The results for recovery boiler fly ash were clear: it primarily consists of sodium sulfate and, when used as an alkali activator, exhibits properties similar to those of commercial sodium sulfate.
Green liquor dregs, however, presented more complex results due to their challenging composition. They are removed from the process in a wet, paste-like form. In this study, they were analyzed and used mainly in dried and/or thermally pretreated states, with treatment temperatures kept below 650 °C. It was found that green liquor dregs could act as an activator for blast furnace slag, as their ability to raise pH increased during thermal pretreatment. However, when tested as a cement substitute, the addition of green liquor dregs weakened strength development, suggesting that they do not actively participate in the hydration reaction. Still, the study indicated that magnesium compounds originally present in the dregs reconstructed during the hydration process.
The findings of this dissertation demonstrate that recovery boiler fly ash can function as an alkali activator in applications where high early strength is not required. Additionally, the study provides new insights into the properties of green liquor dregs, a material traditionally considered difficult to utilize. It also offers answers regarding its potential use as a raw material in concrete-like materials.
To mitigate emissions in the construction industry, various supplementary cementitious materials (SCMs) have been explored. It has also been shown that concrete can be produced without cement through alkali activation. One of the most commonly used SCMs and a key raw material in alkali-activated materials is ground granulated blast furnace slag, a by-product of the steel industry, which has also been used in this dissertation. In addition, the pulp industry generates mineral side streams that, due to their composition, could also be suitable for similar applications, making their potential worth investigating.
This dissertation examines two pulp industry side streams—recovery boiler fly ash and green liquor dregs—and evaluates their suitability for use in cement-based and alkali-activated materials. The results for recovery boiler fly ash were clear: it primarily consists of sodium sulfate and, when used as an alkali activator, exhibits properties similar to those of commercial sodium sulfate.
Green liquor dregs, however, presented more complex results due to their challenging composition. They are removed from the process in a wet, paste-like form. In this study, they were analyzed and used mainly in dried and/or thermally pretreated states, with treatment temperatures kept below 650 °C. It was found that green liquor dregs could act as an activator for blast furnace slag, as their ability to raise pH increased during thermal pretreatment. However, when tested as a cement substitute, the addition of green liquor dregs weakened strength development, suggesting that they do not actively participate in the hydration reaction. Still, the study indicated that magnesium compounds originally present in the dregs reconstructed during the hydration process.
The findings of this dissertation demonstrate that recovery boiler fly ash can function as an alkali activator in applications where high early strength is not required. Additionally, the study provides new insights into the properties of green liquor dregs, a material traditionally considered difficult to utilize. It also offers answers regarding its potential use as a raw material in concrete-like materials.
Last updated: 14.2.2025