PSI - Issue 78

Paolino Cassese et al. / Procedia Structural Integrity 78 (2026) 607–614

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2. Experimental program 2.1. Materials and specimens

Two SSCC specimens were fabricated by incorporating high-purity COOH-functionalized MWCNTs (by Cheap Tubes Inc., United States) into cement paste to enhance the electrical conductivity of the cementitious matrix. The main specific features of the COOH-functionalized MWCNTs are summarized in Table 1. Portland-limestone cement type CEM II/A-LL 42.5 R (EN 197-1, 2011) was used as a binder, with no aggregates. Mapei Mapecure SRA additive was included in the mix to control the shrinkage phenomenon during the curing phase in the amount of 0.5% by weight of cement, following the manufacturer’s recommendations (Cieri et al., 2023). The w/c ratio was considered the experimental variable in this study. Accordingly, two mixing proportions were designed, each one associated with a specimen, characterized by different w/c ratios of 0.50 and 0.42, respectively. Deionized water was used. A unique concentration of functionalized MWCNTs by weight of cement equal to 0.75% was considered. Such a value was selected based on the results of similar research studies available in the literature (Rao and Sasmal, 2020). Table 2 summarizes the mixes and specimens’ nomenclature.

Table 1. Main specific features of the COOH-functionalized MWCNTs.

Appearence Black powder

Outer diameter (nm)

Inner diameter (nm)

Length ( μ m)

Purity (%)

8-18

5-10

10-35

> 96

Table 2. Specimen mix designs and nomenclature.

Specimen C075W050 C075W042

Cement (g)

Water (g)

MWCNTs (g)

Additive (g)

500 500

250 210

3.75 3.75

2.5 2.5

The so-called first admixing method was used to fabricate the SSCC specimens. Accordingly, deionized water was mixed with COOH-functionalized MWCNTs by stirring for two minutes. In addition to the chemical treatment of MWCNT, i.e., COOH functionalization, and to the initial stirring, to improve the dispersion of MWCNTS, the water-MWCNTs solution was sonicated by using an ultrasonic homogenizer type Bandelin Sonopuls 4200 at 20% nominal power for 10 minutes. The sonicated liquid was transferred into the bowl of a Testing standard mortar mixer (EN 196-1, 2016), and cementitious powder was added afterwards. A specific mechanical mixing procedure of 540 s total duration was performed, and then the mixture was poured into a standard 40 × 40 × 160 mm 3 steel mold for mortar specimens (EN 196-1, 2016; EN 1015-11, 2019), previously oiled. The pouring of the paste into the mold was completed in two steps; at the end of each step, the poured paste amount was beaten through a cement mortar shaking table machine compliant with the standard EN 196-1 (2016). Fig. 1 shows the main steps of the preparation procedure.

a

b

c

d

e

Fig. 1. Fabrication procedure of SSCC specimens: (a) addition of MWCNTs to deionized water; (b) sonication of water-MWCNTs solution; (c) mechanical mixing of the mixture; (d) final aspect of the mixture; (e) pouring of the paste into oiled molds.