PSI - Issue 83

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

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Table 6. Factors that affect the sensing performance of UHPC

Factor

Discussion

Ref

Functional filler concentration

Affects conductive network formation. Sensitivity relates to the percolation threshold. Impacts the conductive network and mechanism. Long fibres reduce resistivity; spiky particles enhance sensing due to tunnelling. Causes expansion/contraction, altering filler distance. Resistivity is inversely proportional to temperature; the effect is reversible. High rates limit crack propagation. Higher strain rate often leads to a decrease in resistivity at the same strain level. Sensing response increases significantly above a rate threshold. Dry samples have higher resistivity than saturated samples. Influences electrical conductivity of fillers and the matrix. Conduction shifts between electronic (dry) and ionic (wet). Leads to changes due to polarization and can damage the network.

(Chen et al., 2005) (Chiarello & Zinno, 2005) (Demircilioğlu et al., 2019)

Shape and size of fillers

Temperature

Loading rate

(B. Han et al., 2014)

(Maier, 2020)

Moisture

(H. Li et al., 2008)

Dry-Wet Cycle

7. Challenges, Research Gaps, and Future Directions 7.1. Durability of conductive phases and interfaces.

Corrosion susceptibility of steel fibres and degradation of electrode interfaces can reduce conductivity and distort sensing signals over time. Coated fibres (copper-coated or brass-coated) are used to improve conductivity and potentially reduce oxidation effects, but they introduce cost and long-term compatibility questions (Qiu et al., 2021). 7.2. Scale-up and Variability. Laboratory tests often exhibit controlled fibre distribution and stable boundary conditions that do not hold in full-scale members. Fiber orientation gradients, casting-induced segregation, reinforcement interaction, and construction joints can create spatially varying baseline resistivity. Robust SHM therefore requires either distributed electrode layouts or calibration strategies that can handle heterogeneity and localize damage. 7.3. Standardization of Test protocols and reporting. Cross-study comparison is currently limited by inconsistent reporting of electrode geometry, excitation frequency, saturation conditioning, and signal processing. Existing standards for resistivity testing in concrete specify AC excitation and controlled probe spacing, highlighting the need for analogous consensus practices for SS-UHPC sensing studies. Table 7 further explains the various challenges and some mitigation measures that can be followed to further the study on SS-UHPC.

Table 7. Implementation challenges in SS-UHPC and practical mitigation strategies

Challenge

Primary cause

Typical impact on signal

Mitigation strategies

Corrosion / oxidation

Steel fiber / electrode degradation

Baseline drift hence reduced conductivity Coated fibers; durable embedded electrodes; protective detailing Noise; poor repeatability; weak sensitivity Ultrasonication or surfactants; optimized mixing; hybrid filler

Nanofiller dispersion

Agglomeration, high surface energy

Moisture variability

Ionic conduction + polarization Apparent sensitivity changes; drift

Conditioning protocols; multi frequency impedance; Four-probe layouts; embedded electrodes; AC excitation Distributed electrodes; local calibration; model-based inference

Contact resistance

Electrode interface instability Hysteresis; non-mechanical drift

Scale-up heterogeneity Orientation gradients, casting effects

Spatially varying baseline