Development of low-CO2 emission cementitious composites using biochar
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Journal Title
Journal ISSN
Volume Title
Kemian tekniikan korkeakoulu |
Master's thesis
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Authors
Date
2024-08-29
Department
Major/Subject
Creative Sustainability
Mcode
CHEM3056
Degree programme
Master's Programme in Creative Sustainability (CS)
Language
en
Pages
78 + 26
Series
Abstract
Cement is a highly CO2 intensive material, with its production accounting for 7-8% of total global anthropogenic CO2 emissions (Andrew, 2019). In Finland, 90% of consumed cement is utilized for soil stabilization ground improvement applications (Kivi, 2021). Because Finnish soft clays are often characterized by low shear strength, soil stabilization is a necessary precursor to urbanization and infrastructure development. The purpose of this study was to explore the possibility of creating a low emission or even a CO2 neutral cementitious composite that still possesses necessary mechanical properties for soil stabilization applications. There were three main objectives for this research. First, the effect of binder type on compressive strength and CO2 absorption capacity of stabilized clay was assessed. Second, the effect of biochar type and binder replacement rate on compressive strength and CO2 absorption of stabilized clay was assessed. Third, the amount of CO2 which can be physio-chemically absorbed in the stabilized clay matrix through accelerated carbonation curing (ACC) treatment was measured. In this research, soft clay soil was combined with standard and low CO2 emission commercial binders to stabilize clay. These binders included KC50, the industry standard; as well as GTC and CEM III/B, which are relatively less carbon intensive. Different types of biochar were introduced as partial replacements for these binders to reduce their CO2 intensity. Half of the samples were carbonated by exposure to pressurized CO2 and the potential of CO2 sequestration was studied through a series of physiochemical tests. The samples were cured for varying lengths of time, either 7 or 28 days. After curing time was complete, unconfined compressive strength (UCS) testing followed by pH measurements and thermo-gravimetric analysis (TGA) were performed. The UCS results helped to determine the mechanical effects of carbonation on the undrained shear strength (Cu). A life cycle analysis (LCA) was completed to assess the life cycle stages with varying binder compositions as applied to an example case study. In this research, it was shown that biochar from beetle infested spruce trunks exhibited both greater strength qualities and sequestration potential than the biochars derived from waste wood or municipal sludge. Tree biochar also performed best with ACC treatment. This is likely due to its chemical composition which is rich in CaO when compared to the other biochars. The strength of samples containing GTC or CEM III/B were most negatively affected by ACC treatment. When these samples were analyzed visually after curing, they exhibited clear cracks in the surface which may have inhibited their internal curing ability. The completed LCA covered the different life cycle phases for an in-situ soil stabilization example. The results highlighted the strong impact of the binder emissions on the total net emissions.Description
Supervisor
Bordoloi, SanandamThesis advisor
Hanafi, MohamadKeywords
biochar, CO2 sequestration, deep mixing method, clay stabilization, carbonation, unconfined compressive strength