Air-Void Characteristics and Permeability of Fibre Reinforced Repair Mortar for Conservation

• Author / Creator

  Islam, Md T

• Masonry is among the oldest and widespread construction materials, used to build structures traditionally, both in North America, and worldwide as well. Most of the historical buildings have been built with pre-Portland cement mortar. A large number of existing masonry buildings in Canada have been constructed in the last 200 years and most of them were built with lime mortar. These mortars exhibit good workability and high water retentivity in the plastic state and develop strength slowly over time. Over the years, the integrity of these old masonry buildings has constantly declined. One of the main reasons for this deterioration is the mortar’s inherent permeability. The addition of polypropylene micro-fibres in cement-based systems was found to be effective in improving permeability properties. However, the effect of polymeric fibre on the permeability of Hydraulic Lime Mortar (HLM) is unknown. In addition, it is hypothesized that applying nano-lime onto HLM shall suitably modify its water permeability. Therefore, a part of this thesis focuses on determining the permeability of the HLM, Type N mortar, and Type O mortar, along with the effects of micro-fibre and nano-lime.In this study, the permeability test setup was used to monitor the onset of the steady state condition in fluid flow. The permeability apparatus consisted of five major sections: a cylindrical concrete specimen with a hollow core; a permeability cell that houses the concrete specimen; a pressurized water supply unit; an outflow measurement device (with an accuracy of 0.01g); and a Materials Testing System (MTS). In addition, this permeability cell was further instrumented with a computer and programmed to measure and record the mass of water flow in real time, thereby enabling detection of the onset of equilibrium in flow. Hollow cylindrical specimens were prepared with HLM, Type N mortar, and Type O mortar. Specimens were cast and tested to investigate the influence of fibres and nano-lime upon permeability. The results show that the addition of fibres lowers the permeability coefficient significantly across all binder types, without unduly altering the mortar strength. On the other hand, applying nano-lime was most beneficial in limiting water permeability in the natural Hydraulic Lime Mortars. The microstructure of cementitious materials has great influence on their engineering properties such as permeability, strength, and durability. The pore structure is important for understanding and modeling the transport phenomena through this material, which in turn decide the material’s durability. In order to understand the physics of fluid flow and transport processes through porous media such as cement-lime mortar and HLM, one must have a detailed knowledge about the pore space geometry and their arrangement in three-dimensional space. Transport properties such as permeability depend on the porosity. In addition, the size, shape, and connectivity of the porous path strongly influence the transport properties. It is well known that the microstructure within cement and lime-based systems is very complex in nature. Fluid passes through this porous medium taking a path that is often very tortuous. X-ray micro computed tomography is a powerful tool to investigate the 3D microstructure of cementitious materials. It is an image-based non-destructive 3D radiographic technique. In this method, a high-energy X-ray source is used to acquire 2D radiographic projections of each specimen by rotating it at certain angular intervals. Then a 3D computed reconstruction of the sample is performed from those 2D images by applying suitable algorithms of mathematical tomography. In this study, the microstructure and water permeability of the mortars, with various dosage of fibre reinforcement, were evaluated using X-ray micro CT. Besides, the effect of polypropylene micro-fibre on water permeability and other microstructural properties was also examined. Here, the permeability values as predicted by analysis of images captured by X-ray microcomputed tomography are compared with experimental results. A Mathematica® based program was used to calculate microstructural parameters including the porosity, pore connectivity, tortuosity, formation factor, and the specific surface area. Thereafter, the water permeability was predicted by using the well-known Kozeny-Carman equation. The results show that the predicted permeability coefficients of both plain and fibre reinforced mortars are in agreement with the experimental values. In addition, there is an optimum fibre dosage, found to be 0.15% by volume, to achieve a favourable microstructure and the minimum water permeability.

• Subjects / Keywords

  • Permeability
  • Fibre
  • X-ray micro CT
  • Reapirmortar

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-akka-dd69

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.