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Abstract

Fiber reinforced cement is widely used in non-structural building applications due to its improved toughness, strength, and durability. However, continued reliance on ordinary Portland cement and synthetic chemical additives raises concerns regarding environmental impact and long-term sustainability. This thesis addresses these challenges through two strategies: first, replacing petrochemical or silica-based additives with nano- to micro-scale cellulosic biomaterials, and second, reducing ordinary Portland cement use by partially substituting it with processed waste biomass and by developing a cement-free hybrid geopolymer binder. In the first approach, nano- and micro-scale cellulosic additives were investigated in fiber cement reinforced with softwood kraft pulp. Among the nanocellulosic materials, cellulose nanocrystals at optimal concentrations (2–4 wt.%) produced notable improvements in workability, early hydration, and flexural strength compared to systems containing conventional chemical additives. These improvements were attributed to the high surface area and network-forming morphology of cellulose nanocrystals, which enhanced water transport, supported early hydration reactions, and promoted matrix densification. Micro-scale cellulosic additives also provided distinct benefits: alpha cellulose improved post-cracking toughness and workability by reducing yield stress, while microcrystalline cellulose enhanced peak flexural strength. Despite differences in absolute strength, the strength-to-weight ratios of systems modified with alpha cellulose and microcrystalline cellulose were comparable, suggesting that low-cost alpha cellulose can deliver similar performance benefits. In the second approach, biochar derived from woody biomass was used to partially replace Portland cement. At an optimal dosage of 8 wt.%, biochar improved rheology, time-dependent thixotropy, and mechanical strength while reducing global warming potential by 18 % relative to a pure cementitious system. These effects were linked to its porous morphology and reactive surface, which enhanced water retention and hydration. Furthermore, a cement-free geopolymer binder composed of metakaolin and biochar was developed through mechanochemical processing and reinforced with pulp fibers, achieving flexural strengths of 13–15 MPa with substantially lower embodied carbon, demonstrating a viable route toward sustainable, high-performance fiber cement.