PSI - Issue 83

Samia M. Mohamed et al. / Procedia Structural Integrity 83 (2026) 63–71

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content approaches the percolation threshold, a connected or nearly connected network forms, so even small changes in particle spacing or fiber contact caused by loading can produce measurable resistance changes. Due to this reason, filler dosage and dispersion quality are critical: poor dispersion causes agglomeration and unstable signals, whereas well-dispersed CNTs or CNFs can reduce resistivity and improve piezoresistive sensitivity. Previous studies have shown that effective ultrasonic dispersion with surfactants is particularly important for CNT-reinforced cement systems, while hybrid filler systems can improve sensing performance by combining conductive pathways across different length scales (Konsta-Gdoutos et al., 2010; Konsta-Gdoutos and Aza, 2014; Lee et al., 2017b). When mechanical loading is applied, the distance between conductive particles changes, causing either formation or disruption of conductive pathways, which results in measurable resistance variation. The sensing response is commonly expressed using fractional change in resistance (FCR), usually written as Δ / ଴ , and gauge factor (GF), which relates normalized resistance change to mechanical strain, as shown in Fig. 1. These metrics are widely used to compare sensitivity across different self-sensing cementitious systems, but their values depend strongly on filler type, percolation state, loading mode, curing age, moisture condition, electrode configuration, and test method. For example, a study used hybrid CF and multi-walled carbon nanotube (MWCNT) reported that composites containing 0.1 vol.% CF + 0.5 vol.% MWCNTs achieved sensing performance comparable to 1.0 vol.% MWCNTs (Lee et al., 2017), with a reported GF of 160.3, showing that hybrid system can improve efficiency while reducing nanotube demand. In more ductile cementitious systems such as Engineered cementitious commposite(ECC), self sensing behavior has also been extended beyond compression toward tensile strain and crack monitoring, which is important because conventional brittle cement-based materials are often limited in tensile sensing studies (Elseady et al., 2023; Huang et al., 2018).

Fig. 1. (a) 3D printing-induced anisotropy and sensing pathways, and (b) Typical FCR-strain response (cyclic loading)

2.2. Materials Development for Self-sensing Cementitious Composites The development of self-sensing cementitious composites (SS-CCs) is fundamentally a multi-objective mix design challenge, the conductive phase must be high enough to create a stable percolated network, but not so high that