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Title:	Synthesis and characterisation of ultra-high-performance cementitious composite incorporating carbon nanofibres
Authors:	Jacob Lim Lok Guan (P72664 )
Supervisor:	Sudharshan N. Raman, Assoc. Prof. Dr.
Keywords:	Universiti Kebangsaan Malaysia -- Dissertations
Issue Date:	16-Feb-2021
Description:	Ultra-High-Performance Concrete (UHPC) is a type of concrete that exhibits superior mechanical characteristics and enhanced durability in comparison to conventional normal- and high-strength concrete. However, conventional UHPC has its drawbacks in terms complexity in material selection, lower tensile strength ratio and brittleness, and a requirement for special curing regime. Newly designated Ultra-High-Performance Cementitious Composite (UHPCC) mixes were synthesized in this study by optimizing on its packing density with fewer constituent materials, and by incorporating with carbon nanofibres (CNF). CNF which is known for its superior mechanical properties, act as nano-reinforcement in the composite mix, to create a denser and more ductile composite matrix. The dispersion of CNF in cement-based materials is a challenge due to their high aspect ratio and its agglomerating behaviour. The overall systematic investigation consists of two parts, which includes the mix design, and mechanical and microstructure characterisation of the composite, and, experimental and analytical analysis of the stress-strain characteristics and flexural capacity of the composite under various loading rate. Two sources of CNF with different dispersion techniques and methods were investigated. CNF with various concentrations (0.02%, 0.04%, 0.06%, 0.08%) were dispersed into the UHPCC mixes. The mix design of the UHPCC were optimised by using the particle packing approach and their fresh and engineering properties (including flow expansion, rate of hydration, autogeneous shrinkage, compressive strength, and flexural strength) were analysed. The contribution of CNF was further investigated through a hybrid fibred system by incorporating micro steel fibres. In the subsequent stage, experimental and analytical studies were undertaken to analyse the stress-strain and flexural characteristics of the developed composite under increasing strain rates (0.006, 0.015, 0.03, 0.06) s-1. The overall findings of the research assert that CNF of 0.06% by the weight of cement was able to enhance microstructure of the UHPCC matrix. At 28 days, a 160 MPa compressive strength was recorded and the flexural tensile strength was enhanced by 40% at quasi-static condition. Further, at higher strain rate condition (0.06 s-1), the tensile strength of UHPCC-CNF were enhanced by up to 30% compared to the quasi-static state, and the hybrid fibred model indicated better ductility. Subsequently, empirical constitutive model to correlate the compressive strength, flexural strength, modulus of elasticity and the stress-strain response were developed and validated at both quasi-static and enhanced strain rates. It can be concluded that the stable CNF dispersion contributed in improving the density of the matrix and provides positive effect to the overall characteristics of the UHPCC. The outcome of the study will lead to a more scientifically reliable and robust approach to analyse and design structures subjected to dynamic effects.,Ph.D.
Pages:	196
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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