Influence of cellulose derivatives as an additive in cementitious composites.
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School of Engineering |
Master's thesis
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en
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76
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Abstract
Increasing interest in bio-based admixtures has demonstrated that cellulose materials can enhance mechanical properties by modifying their hydration and contributing to the development of the microstructure of sustainable building materials. This thesis deals with the influence of cellulose derivatives, namely microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC), on fresh and hardened properties of cementitious mortar. The research investigates different types of cellulose at various dosages to study their influence on workability, compressive strength, flexural strength, and hydration kinetics. Tests for flowability demonstrated that all cellulose-modified mortars were workable but with reduced workability compared to the standard of 197 mm. The dosage of cellulose, as well as its fineness, determined the magnitude of reduction 4 % to over 20 %. Mechanical tests demonstrated that the flexural strength continued to improve. Cellulose modified mixes demonstrated 28-day flexural strengths of (5.0-6.7) MPa, representing a 15% to 51% increase over reference samples without any cellulose derivatives. Compressive strength, on the other hand, was reduced by 5 to 22% at early age due to delayed hydration but recovered to values equal to or somewhat better than the reference (45-49 MPa) by 28 days. Isothermal calorimetry indicated that cellulose derivatives delayed the main hydration peak by 0.3 to 3.0 hours and reduced peak power by 6 to 24%. However, the total heat release at 160 hours was the same as the reference at 360 to 382 J/g, indicating that cellulose prolongs hydration without reducing the total degree of hydration. There was a clear influence of particle size on all cellulose types. The smaller the size of cellulose, the higher the impact on flowability, flexural strength, and hydration delay. The incorporation of MCC and CNC in 0.5-1.0% dosages range, improvements were consistent and significant in several mechanical and hydration-related properties. Overall, the results obtained indicate that cellulose derivatives could serve as active, functional additives, which improve the mechanical performance, control the hydration kinetics, and contribute towards developing multifunctional cementitious composites.Description
Supervisor
Bordoloi, SanandamThesis advisor
Al-Neshawy, FahimIravanian, Anoosheh