PSI - Issue 83

Henry Ssenyonjo et al. / Procedia Structural Integrity 83 (2026) 47–56

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2.1. Properties of different materials used in UHPC for self-sensing.

Tables 2 & 3 presents the properties of some of the steel fibres (SF) and nanomaterials that have been explored in various studies. The high elastic modulus and high tensile strength of the steel fibres promote efficient crack bridging and pull-out energy, while their intrinsic electrical conductivity establishes and stabilizes percolated pathways under load for better self-sensing applications.

Table 2.Mechanical properties of various steel fibres used in SS-UHPC

Fiber type

Tensile strength (MPa)

Elastic modulus (GPa)

Density (Kg/m 3 )

Ref

Hooked SF

1100

190–210

7,800 7,800

(Meng & Khayat, 2018) (Meng & Khayat, 2018) (Ahmed et al., 2021) (Ravichandran et al., 2022)

Micro straight SF 2600

250 200

Corrugated SF

1100 1200

7,800–7,900 7,800–7,900

Twisted SF

190–210

Table 3.Common filler types used for self-sensing and their properties

Material

Density (kg/m 3 )

Tensile Strength (GPa)

Elastic modulus (GPa)

Ref

Carbon nanotubes

1300 - 1700

11

300-1000 1000-2000

(Wen & Chung, 2007) (J. Han et al., 2020) (J. Han et al., 2020) (Sassani et al., 2018)

Nano graphene platelets 1800

5000

Carbon black

1800 - 2100

2000-2400

-

Carbon nano fiber

1000

4900

230

3. Self-sensing mechanisms in SS-UHPC 3.1. Electronic / ionic transport in cementitious composites.

Electrical response in cementitious composites arises from a combination of ionic conduction through pore solution and connected capillaries and electronic conduction through conductive fillers and their contacts (Elseady et al., 2023). The relative contribution depends on moisture state, degree of hydration, filler type, and the connectivity of the conductive network. Impedance spectroscopy has been widely used to separate bulk conduction, interfacial polarization, and electrode effects, which is particularly important when interpreting SS-UHPC data collected under varying saturation conditions (Zhang et al., 2022). At low conductive filler contents, electrical movement can be dominated by tunnelling between neighbouring fillers; beyond the percolation threshold, direct contact networks enable low resistivity pathways and typically improve repeatability. Reviews of CNT cementitious composites emphasize the co-existence of percolation and tunnelling and the strong dependence of measured resistivity on dispersion quality and pore water (L. Li et al., 2023). 3.2. Piezoresistivity (resistance based self-sensing). Piezoresistivity refers to the change in electrical resistance or resistivity with mechanical loading. In SS-UHPC, piezoresistive response is commonly attributed to changes in contact resistance between fibres, evolution of tunnelling gaps in nano-filled systems, and damage induced disruption or reconfiguration of conduction paths when cracks develop in the composite (Elseady et al., 2023). Under cyclic loading in the elastic region, resistance changes are expected to be largely reversible whereas under cracking and progressive damage, irreversible baseline drift is often observed and can be exploited for damage diagnosis and SHM applications (Qiu et al., 2021). Common metrics measured in this mechanism include FCR and GF and can be solved using the Eqns. 1 & 2 below where R