Microstructural investigation on engineered cementitious composites (ECC)

• Main Author: Too, Wee Jet
• Other Authors: Yang En-Hua
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Civil engineering
• Online Access: http://hdl.handle.net/10356/62037
• Institution: Nanyang Technological University

Engineered Cementitious Composites (ECC) is not only a kind of cementitious material with high performance, but also an engineered material that embodies a micromechanics-based design concept. To get ECC in reality, mix design is the very starting point. There is a missing link between factors of mix design and micromechanical parameters embedded in the micromechanical model of ECC. In this study, quite a number of experiments including single fiber pullout tests and matrix toughness tests were performed to fill the gap based on the theoretical analysis of micromechanical design guideline. Single fiber pullout tests were conducted in this research to measure the bond properties of PVA fibers with different matrix mixes. The fiber/matrix interfacial bond properties that are characterized by chemical bond and initial interfacial frictional bond strength. For some of the matrix mixes whereby the fibers can rupture during the pullout tests despite of the small embedment length of less than 1mm. However, rupture of fiber will not affect the determination of bond properties. Most of the time, fibers ruptured during the fiber pullout stage whereby a strong slip-hardening effect was taken place, characterized by the slip-hardening coefficient. On the other hand, wedge splitting tests were also carried out to obtain the common fracture mechanical parameters for example critical crack mouth opening displacement (CMODc), the critical load Pc, critical crack length ac at the peak load and fracture toughness of matrix with various mixes. These parameters obtained experimentally are used to ultimately evaluate the matrix crack tip toughness, Jtip which is an important parameter to dictate the strain hardening effect of the mix of ECC. The Young’s modulus value of each matrix mix was also obtained experimentally through compression tests with strain gauges attached on specimens. There will be two sets of samples to be tested experimentally to obtain all of the abovementioned parameters. The first set of sample contains five mixes with varying water to cement (w/c) ratio. The second set of sample also includes five mixes with varying sand to cement (s/c) ratio. In this research, the author will only focus on the energy criterion of achieving ECC behavior. In the end of the experiment, while all the data are collected experimentally, it will be able to compare the results with the design guidelines derived based on theoretical analysis via the micromechanics model. Therefore, the most suitable design mix or a range of design mixes which fulfill the design guidelines can be identified which then the design mix/mixes will be most probably to achieve highest toughness ratio (Jb’/Jtip) and this can directly relate to the performance of ECC.