論文の要旨
Reuse of stone powder in slag or cement-treated clay
（スラグまたはセメント処理土における石粉の再利用）
氏

名Nakayenga Joyce

To achieve Goal 12 of the United Nations Sustainable development goals (SDGs), the constructionindustry emphasizes reducing, reusing, and recycling waste materials. Also, to meet the ParisAgreement on Climate Change and the Goal 13 of the SDGs, the industry needs to find innovative
ways to reduce its carbon emissions. The manufacturing process of cement contributes about 8% toglobal carbon emissions; hence alternative materials should be found to reduce the reliance on cement.
Waste materials (stone powders) produced from crushing rocks such as limestone and granite are often
discarded in an environmentally unfriendly manner. Stone powder accounts for up to 25% of thequantity of crushed rock aggregates produced, but due to their small particle size (<1- 850μm), they
are disposed of; hence innovative ways to reuse waste should be investigated. Steel slag, a by-productof steel manufacturing, is increasingly utilized in constructing infrastructure worldwide. However,steel slag is produced in vast amounts and about 40% is used in China, while 1% of the over forty
million tons produced in Japan is disposed of. This leaves the industry with financial andenvironmental costs associated with steel slags’ abundant production, which necessitates further
enhancement of its reuse.
Stone powder is increasingly being reused to improve the geotechnical properties of soils. However, themechanisms governing the strength development of treated soils using stone powder are unclear. Also,
there are limited studies on the reuse of stone powder mixed with steel slag to improve the propertiesof clays.
This research aimed to promote the reuse of stone powder and steel slag in improving the geotechnicalproperties of clay dredged from the sea. We mixed limestone or granite powder with cement or slag andclay to form cement-treated clay-granite powder, cement-treated clay-limestone, and slag-treatedclay-granite composites. We investigated the mixing characteristics and physical, chemical, thermal,and microstructure properties governing the cement-treated clay composites’ unconfined compressive
strength (UCS) development. Further, the durability of the cement-treated clay-granite powder andslag-treated clay-granite powder composites under seawater exposure was determined.
The physical properties that influenced the UCS included granite powder particle size and specificsurface area, and microstructural images proved the phenomena. Thermal properties were calcium
hydroxide and bound water content of the composites. In contrast, the chemical properties included
granite powder’s pozzolanic reactivity and amorphous silica concentration. The slag/cement-treatedclay-granite powder composites were more durable than their control samples, which did not containstone powder under seawater exposure. This implies that granite powder can be used to constructsustainable infrastructure at sea.
Reusing stone powder at contents of 30%, 50%, and 70% results in a 6.9%, 14.7%, and 28.6% reductionin cement used per cubic meter of cement-treated clay, respectively. This leads the constructionindustry to realize target 5 of goal 12 of the SDGs, which emphasizes the substantial reduction ofwaste generation through prevention, reduction, recycling, and reuse. Goal 13 and Paris agreement on
climate change are impacted by reducing the reliance on cement hence reducing carbon emissions.