Crack Free Concrete Made with Nanofiber Reinforcement

A final report submitted to the Infrastructure Technology Institute DISCLAIMER: The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the information presented herein. This Document is disseminated under the sponsorship of the Synopsis: There have been numerous studies that have aimed at improving the low tensile strength, stiffness, and toughness of cementitious materials. This study aims to show that all of these characteristics can be greatly improved by the addition of ladder scale reinforcement at the nano and micro scale. Carbon nanofibers (CNFs) as well as polyvinyl alcohol (PVA) microfibers were used as reinforcement. The mechanical properties of the nanocomposites were investigated by fracture mechanics three-point bending test. The microstructure and the morphology of nanocomposite samples were studied using an ultra high resolution scanning electron microscope (SEM). The results clearly illustrate that the incorporation of nanofibers and microfibers greatly improves the flexural strength, Young's modulus, and toughness of the cement matrix. Her research interests include investigations into the relationships between microstructure and performance of advanced cement-based materials, high-performance structural materials, concrete composites, and nanocomposites. INTRODUCTION Failure in cement based materials is a gradual multi-scale process. When loaded, initially short and discontinuous microcracks are created in a distributed manner. These microcracks coalesce to form large macroscopic cracks, known as macrocracks. Fibers bridge cracks and transfer the load, delaying the coalescence of cracks. Due to the multi-scale nature of fracture, the influence of fibers in reinforcing cement based materials, mainly depends on the scale of reinforcement. Macrofibers (typically defined as fibers with diameters greater than 500 μm [0.02 in]) can improve post-peak toughness by bridging macrocracks. Fine microfibers (typically defined as fibers with diameter less than 50 μm [0.002 in]) on the other hand, bridge the microcracks which delay the process by which the microcracks coalesce to form macrocracks. However, cracks in cement based materials initiate from the nanoscale where micro-fibers are not effective. The development of fibers at the nanoscale has opened a new field of research within concrete. Previous research by the authors of this work on reinforcing cementitious materials using nanofibers, such us multi wall carbon nanotubes (MWCNTs), has shown that the flexural strength and stiffness of cementitious matrices can be significantly increased by adding very low concentrations of homogenously dispersed carbon nanotubes (as little as 0.025% by weight of cement) 1. Nanoimaging of the fracture surfaces of …