PSI - Issue 64

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

541

a substitute for ordinary Portland cement (OPC). The mixed design of the three distinct CAC controls, CNCB1 and CNCB2, is presented in Table 4. Initially, water and the superplasticizer were gently stirred manually, and then, MWCNT were added to the well-stirred water and superplasticizer. Subsequently, sonication for 1 h to obtain well dispersed MWCNT improved the distribution of the composite fillers in the cement matrix, ultimately enhancing the mechanical properties and electrical conductivities. The raw materials, including CAC, silica fume, silica sand, quartz powder, and NCB, were dry-mixed using a Hobart mixer. Silica fume was used as a 20% CAC binder to enhance the dispersion of the MCNT/NCB composite filler. Subsequently, a pre-dispersed sonicated MWCNT solution was added to the well-mixed raw/dry material and mixed further to achieve a good mixture homogeneity. A homogeneous MWCNT/NCB mixture was placed in 50 × 50 × 50 mm molds and vibrated for 20 s before inserting 47 × 70 mm electrodes. Two stainless steel electrodes were inserted into the fresh mix in molds for piezoresistive investigation, and the arrangement is shown in Fig. 1. Subsequently, the fresh mix molds were subjected to an additional 5 s of vibration to eliminate the air bubbles and pores induced by the electrode, which could negatively affect their mechanical and electrical properties. The samples were covered with plastic sheets and maintained at standard ambient temperature. After 24 h, the samples were removed from the molds and sealed in a plastic sheet before curing at room temperature for another 27 d. Additionally, a mini-slump test was performed to evaluate flowability. The spread diameters of the CAC control, CNCB1, and CNCB2 were 320, 290, and 265 mm, respectively. Fig. 1 shows the test setup and electrode arrangement.

Table 1 Electrical and physical properties of MWCNT. CNTs purity (wt.) Inner diameter (nm) Outer diameter (nm)

Electrical resistivity (Ω.cm)

Specific service area (m 2 /g)

Length (µm)

Loose density (g/cm 3 )

>95%

5-10

10-20

10-30

2.1

10-2

100

Table 2 Electrical and physical properties of NCB.

Electrical resistivity ( Ω.cm )

Particle size (nm)

Surface area (m 2 /g)

Pour density (g/cm 3 )

DBP (ml/100gm)

280-300

0.16

0.18

30-45

125

Table 3 Physical and chemical compositions of the raw materials.

CaO

Al 2 O 3

SO 3

Fe 2 O 3

K 2 O

MgO

Others

Materials

SiO 2

CAC

5.6%

34%

54.2%

0.68%

3.25%

0.7%

0.35%

1.12%

Table 4 Mixing proportions of cementitious composites containing MWCNT/ NCB (wt%)

CAC binder

Silica fume

Silica sand

Quartz powder

Super plasticizer/binder ratio (%)

Water/binder ratio

MWCNT

NCB

Mix-ID

CAC

1

0.20

0.88

0.10

0.40

2.2

0

0

CNCB1

1

0.20

0.88

0.10

0.40

2.2

0.25 wt.%

0.20 wt.%

CNCB2

1

0.20

0.88

0.10

0..40

2.2

0.50 wt.%

0.40 wt.%