DEVELOPMENT AND APPLICATION OF SMART CARBON-BASED COATINGS FOR MULTIFUNCTIONAL SENSING OF CEMENTITIOUS STRUCTURES

The safety and durability of ageing civil infrastructure demand effective and reliable structural health monitoring (SHM). Hence, this research developed carbon-based coatings as innovative, adaptable and scalable self-sensing piezoresistive solutions. While the electrical conductivity of cement paste is influenced by moisture content, cement type and void ratio, small additions of functional fillers can stabilise conductivity despite challenges in mix workability and mechanical integrity. Thus, carbon black, graphite nanoplates, natural graphite, kish graphite, biochar and carbon nanotubes were systematically evaluated in this study for their electrical, physical and mechanical influence on cement. Carbon black emerged as the most suitable option due to low cost (~£3/kg), significant electrical conductivity enhancement at low dosages (168% at 3 wt%) and minimal disruption to physical and mechanical properties. Cementitious coatings with graphite nanoplates provided localised compressive strain (-1,600 με), achieving gauge factor of 17.3. Carbon black-based sensors were encapsulated in epoxy to stabilise their sensing performance under varying humidity, reaching flexural (700 με) and tensile (150 με) strain sensitivities of 110.9 and 15.8, respectively, despite a 27% adhesion reduction. In bending, coatings remained serviceable up to ~10,000 με, outperforming traditional gauges, with partial electrical recovery post-fracture. Polymeric coatings with 0.5 wt% CNT achieved a 309 gauge factor across a wide strain range (0 - 165 με), while higher dosage increased sensitivity but reduced operational intervals. Nanoscale lattice modelling confirmed that high filler concentrations enhanced electrical network robustness, providing stability under large strains while lower concentrations exhibited greater sensitivity to early-stage damage. Additionally, coatings were able to measure corrosion-driven surface damage in chloride-contaminated environments, up to average crack widths (116 ± 45 μm or 33 ± 3 μm) inversely proportional to the distance from the corroding steel. When monitoring self-healing substrates, autogenous and bacteria-driven processes reduced coating’s resistivity, while polyurethane foam and crystalline admixtures showed limited or opposite performance, ultimately correlated to the healing progress. Applied to large-scale beams, the coatings outperformed displacement sensors in early strain detection and crack propagation monitoring, although limitations remained in sensing bacterial healing for cracks wider than ~0.5 mm. In summary, this research developed multifunctional carbon-based coatings characterised by reliable strain and damage detection, continued serviceability during corrosion and compatibility with automated self-healing processes, presenting practical solutions for diverse SHM applications.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Milone, Gabriele

Advisor dc:contributor.advisor

• Al-Tabbaa, Abir

• Piezoresistive coatings
• self-sensing
• smart cement
• structural health monitoring

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/5b77f6b1-470f-47a3-9a86-41bed2e11a40/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

Author Identifier

0000-0003-1131-5828

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/379806