PSI - Issue 64

Alamgir Khan et al. / Procedia Structural Integrity 64 (2024) 539–548 Alamgir khan / Structural Integrity Procedia 00 (2019) 000–000

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3. Results and discussion

3.1 Electrical resistivity and strength measurement of MWCNT/NCB composite fillers The electrical resistivity and compressive strength at normal and elevated temperatures are shown in Fig. 2 (a) and (b), respectively. The electrical resistivity of CNCB1 was notably higher because of the lower number of MWCNT/NCB path/networks, which led to high electrical resistivity. However, an increase in the MWCNT/NCB concentration increased the number of conductive paths; therefore, CNCB2 showed a lower electrical resistivity. Subsequently, the electrical resistivity was investigated after elevated temperature exposure, where CNCB1 exhibited high electrical resistivity at 200 °C; after further exposure to 400 °C, multiple surface cracks were observed on the surface, resulting in higher electrical resistance. However, CNCB2 showed stable electrical resistivity at both 200 and 400 °C in comparison with a lower concentration of CNCB1. The compressive strengths of CAC and CNCB1-CNCB2 by the load control method at a constant rate of 0.5 kN/s. These findings demonstrate that the addition of different concentrations of MWCNT/NCB composite fillers resulted in a notable improvement in the ultimate compressive strength. The CNCB1 lower MWCNT/NCB concentration contributed insignificantly to the compressive strength and 11% strength decline observed due to high flowability, and air bubbles induced by lower concentrations. However, when the MWCNT/NCB concentration was further increased, CNCB2 exhibited a lower flowability and 2% strength enhancement. Subsequently, at 200 °C, CAC control CNCB1 and CNCB2 exhibited improvements in their compressive strengths and peak strengths of 34%, 2%, and 36%, respectively. The enhancement in the compressive strength of the CAC control and MWCNT/NCB composites at 200 °C was attributed to the hydration of the CAC-unhydrated clinker with silica fume and quartz powder thermal stability, leading to the additional formation of C-A-S-H. Upon further exposure to heat treatment at 400°C, the compressive strength of the CAC control specimens remained stable at 32% compared with that at room temperature (RT). However, the strengths of CNCB1 and CNCB2 decreased by 23% and 9%, respectively, owing to the heat-induced damage of the MWCNT/NCB composite fillers at 400 °C. In summary, the addition of the CAC binder MWCNT/NCB increased the compressive strength of the material up to 200 °C compared to that at room temperature. Multiple minor cracks were observed on the CNCB1 surface, but CNCB2 still showed good compressive strength at 400 °C. In general, the incorporation of MWCNT/NCB into cementitious composites is advantageous in terms of both thermal stability and electrical conductivity.

0 20 40 60 80 100 120 140 160 Electrical resistivity ( W x 10 4 -cm) (a)

80

200 ƒ C

400 ƒ C

RT

60 °C

200 °C

400 °C

(b)

RT

70

60

50

40

30

20

10 Compressvie strength (MPa)

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CNCB1

CNCB2

CAC

CNCB1

CNCB2

MWCNT/NCB contents (%)

MWCNT/NCB contents (wt%)

Fig.2 CAC-based MWCNT/NCB composite fillers (a) electrical resistivity and (b) compressive strength