PSI - Issue 83

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

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To evaluate the electrical behaviour of the composite, two current modes are commonly used namely direct current (DC) and AC. Although DC testing is the simplest method, the current does not travel far within the material and can cause ion migration, leading to electrical polarization in the composite. To address this issue, a DC voltage is often applied to the composite prior to loading, allowing polarization to stabilize before measurements are taken. Alternatively, AC can be used, where polarization still occurs but can be controlled by increasing the frequency and reducing the amplitude of the applied AC voltage (B. Han et al., 2007). Piezoresistive performance can be evaluated using cube or prism specimens subjected to various loading conditions in the elastic range, plastic deformation stage, and failure state. The electrical characteristics of the material play a crucial role in assessing its sensing behaviour. Electrical resistance is determined using Ohm’s law under two general conditions. During loading, the V and I are recorded using an ammeter, and the resistance of the material is then calculated from these measurements (Chiarello & Zinno, 2005; Zhang & Li, 2009.). Sensing behaviour can then be evaluated using various sensitivity parameters, including fractional change in electrical resistivity, force sensitivity coefficient, stress sensitivity coefficient, and strain sensitivity coefficient / gauge factor (Z. Li et al., 2006; Wei & Li, 2005). 5. Self-sensing Performance Benchmarking Performance in SS-UHPC should be interpreted as sensor performance, not only as mechanical properties. For translation to SHM, the following key performance indicators (KPIs) are recommended as a minimum reporting set. These include sensitivity (GF or stress sensitivity), linearity, hysteresis, repeatability, drift, response time, cyclic durability, and damage detectability across elastic, cracking, and post-crack durations. Table 4 summarizes some of the KPIs that should be investigated for SS-UHPC and why they are of great importance for SHM applications.

Table 4. Recommended sensor-performance KPIs for benchmarking SS-UHPC (Kim et al., 2024; Pan & Huang, 2020; Zhang et al., 2022).

KPI

Definition / metric

Why it matters in SHM

Sensitivity

GF or (%ΔR) / ε; stress sensitivity

Determines resolution for strain/stress changes Enables reliable calibration and inverse mapping Avoids false damage indications in cyclic environments Supports trend monitoring and anomaly detection Controls long-term stability and recalibration need. Sets detection threshold for small changes

Linearity

R² or max deviation from fit

Hysteresis

Loading-unloading mismatch

Repeatability

Cycle-to-cycle variation

Drift

Baseline change at constant state

Noise/SNR

Standard deviation of signal in steady state Irreversible ΔR or impedance features vs crack width

Damage detectability

Links signal to structural safety

Table 5 provides a comparative summary of the piezoresistive performance of various SS-UHPC as reported in the literature. It is observed that the initial electrical resistivity (ρ₀) decreases dramatically by several orders of magnitude with increasing CNT content (Song et al., 2023). This signifies the achievement of electrical percolation in mixes with higher CNT content, which is directly linked to the observed shift in piezoresistive behavior and the higher GF values. The compressive strength (CS) of the concrete is also reported to have been positively impacted with the addition of nanomaterials as seen from Table 5.