PSI - Issue 70

Maheshwari Sonker et al. / Procedia Structural Integrity 70 (2025) 477–484

479

% = √ ∑ ( 1 − 0 ) 2 = 1 ∑ ( = (∑ | 1 − 0 | 0 = 1 )/ 1 − 1 1 0 ∑ ( 1 − 0̅̅̅̅ ). ( 0 − 0̅̅̅̅ ) = 1 0 ) 2 = 1 100

(2)

(3)

(4) Where, 1 = damaged state conductance (GD) at frequency I, 0 = healthy state conductance (GH) at frequency i, and N = no. of data considered. The EMI technique operates primarily in high-frequency ranges (typically 30 – 400 kHz), ensuring sensitivity to local structural changes near the PZT sensor. Key parameters, such as resonant frequency shifts and statistical indices (e.g., RMSD, MAPD, CC), are employed to assess the severity of the damage (using equation (2), (3), (4). 3. Materials and Methods Composite fibre concrete specimens were developed using Ordinary-Portland-Cement (OPC), Class F flyash as a partial cement replacement, and crimped polypropylene fibres to enhance tensile performance shown in Fig. 1. The fibre content was maintained at 0.9% by volume of concrete. Concrete specimens of grades M60 and M65 were prepared using Ordinary Portland Cement, fine aggregates (IS: 383-2016 (Zone-II)), coarse aggregates, fly ash and polypropylene fibers at varying contents. A polycarboxylate-based superplasticizer, SIKAPLAST-HE2002, was incorporated to maintain desired workability at a constant water-binder ratio. The admixture had a solids content of 41%, pH of 5.8, and specific gravity (G) of 1.08 (Table 2).

Fig. 1. Snapshot of polypropylene fibre (a), (b) fly ash. After 28 days of curing under controlled conditions, artificial damage was introduced at different depths. Piezoelectric (PZT) patches were affixed using epoxy adhesive to surface as depicted in Fig. 2, and the Electro-Mechanical Impedance (EMI) technique was used to monitor structural changes. Conductance signatures were recorded within the 30 - 400 kHz frequency range utilizing an LCR meter. Damage quantification was performed by calculating RMSD, CC, MAPD between healthy and damaged states (see Fig. 4).

Table 2. Different proportions of concrete mixture variations. Mix Cement Kg/m 3 Fly ash Kg/m 3 Water Kg/m 3

Polypropy lene Fibre Kg/m 3

Sand Kg/m 3

20mm Kg/m 3

10mm Kg/m 3

Admixtur e Kg/m 3

Lab Target Strength at 28 days (N/mm 2 )

5.2710

68.25

M60 M65

438.30 456.22

116.1 122.6

29.29 30.41

158.14 157.14

716.39 703.88

98.99 98.05

890.89 882.49

5.4740

73.9