Recently, there has been increasing interest in exploring nano-materials used as an additive to existing concrete materials. With respect to fiber-shaped nanomaterials such as carbon nanofibers (CNF), many studies have shown that mechanical strength properties of cementitious materials can be improved significantly. In this dissertation, the research has focused on the development of nanomodified cementitious materials with CNF. With relatively low CNT dosages (0.05% to 0.1% to cement weight) and a unique dispersion approach, uniform incorporation of CNT into a cementitious matrix is possible. The beneficial increase in properties such as flexural strength, fracture roughness, modulus of elasticity, autogenous shrinkage, shrinkage cracking resistance, and electrical conductivity are all of particular note. For the case of flexural strength and modulus of elasticity, the percentage improvement in properties with CNT is larger with mortar and concrete than it is with cement paste– this unexpected result implies that nano- and micro-structural changes are occurring in the presence of CNT at interfacial transitional zone between bulk paste and aggregates. To approve above statement, nano-scale metrology techniques have been adopted to investigate mechanical and chemical properties of ITZ in CNF reinforced cement concrete. The samples of cement mortar and cement concrete with and without CNFs are prepared. The quantitative nano-mechanical mapping (based on atomic force microscopy, AFM) technique is adopted to measure the Young’s modulus of ITZ. The elemental and phase investigation of the SEM samples are carried out by Energy-dispersive X-ray (EDX). Based on the fundamental chemical composition in ITZ, the Ca to Si ratio is calculated, which proves a potential modification of nanostructure in C-S-H gel. Furthermore, a new numerical modelling considering real interfacial condition is established, and ITZ effect is discussed based on numerical simulation. In addition, transport properties have been investigated which proves that CNF is able to reduce the water absorption rate and chloride penetration depth indicating a refinement of microstructure of cement matrix. The investigation of hydration rate using FTIR and calorimetry test doesn’t find an accelerate or delay effect of the nanomaterials, and other possible mechanisms on property improvement are needed for future work. Each of these topics represents one of the few barriers remaining to commercialization of CNT/CNF as a beneficial admixture for concrete production, demonstrating the large potential impact of this fundamental characterization research.

Last modified

• 10/28/2019

Creator

• Yuan Gao

DOI

• https://doi.org/10.21985/n2-qsk1-kk30

Subject

• Civil and Environmental Engineering

Keyword

• Young's modulus
• shrinkage cracking
• flexural strength
• autogenous shrinkage
• carbon nanotube
• concrete

Date created

• 2018-01-01

Resource type

• Dissertation

Rights statement

• In Copyright