Biomineralised hydroxyapatite as a cement coating

  • Ronald Turner

Student thesis: Doctoral Thesis

Abstract

Ordinary Portland Cement (OPC) is the World’s most widely used building material. Cement is thusvulnerable to degradation through many processes. Bacteria are capable of generating minerals, ina process called biomineralisation. This may lead to the formation of many different minerals. Thereis precedent for applying biomineralisation processes to the repair and preservation of cements andconcretes.In this thesis, we observe and describe for the first time the bacterially-mediated deposition of ahydroxyapatite coating onto OPC, and describe the biochemical mechanisms underlying this process.The biogenic hydroxyapatite deposition takes place in a synergistic process with the cementsubstrate material; utilising a Pseudomonas fluorescens biofilm, phosphates from the growthmedium, and calcium from the cement substrate and pore solution.We additionally investigate the capacity of P. fluorescens to form biofilms under variedenvironmental conditions of temperature and carbon source availability, which is relevant to theapplication of the identified biogenic deposition system in the built environment. The investigationof P. fluorescens biofilms under these conditions is yet to be reported in the literature. We alsoestablish that varied P. fluorescens morphologies may emerge under different environmentalconditions, and carry out a novel structural characterisation and assay the fitness of these variedcolony morphologies.Developing upon these initial investigations, we characterise this biogenic hydroxyapatite in detailusing TEM, SEM-EDS, XRD, synchrotron-SAXS, and Mossbauer spectroscopy. We identify that thisbiogenic hydroxyapatite presents a less crystalline; plate like morphology, and reduced primaryparticle size in comparison to abiotic hydroxyapatite.The functional capacities of this biogenic hydroxyapatite as an OPC coating material are alsoinvestigated. We use focus-variation microscopy to characterise the surface topography of thecoating, nanoindentation to measure the hardness and elastic modulus of the biogenic and abiotichydroxyapatites, in combination with X-CT analysis to establish the completeness of the depositionprocess, and contact-angle measurements to investigate the hydrophobicity of the coating.
Date of Award28 Jan 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorAndrea Hamilton (Supervisor) & Joanna Renshaw (Supervisor)

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