PSI - Issue 42

E. Tziviloglou et al. / Procedia Structural Integrity 42 (2022) 1700–1707 Tziviloglou et al. / Structural Integrity Procedia 00 (2022) 000 – 000

1702

3

Michigan. A polycarboxylate-based superplasticizer (ViscoCrete ® Ferro 1000, Sika Hellas) was used to achieve a homogenous dispersion of the GnPs. The nanoparticles and the superplasticizer (SP) were added in water (6 % of the total volume of mixing water), where ultrasonic energy was applied by using a probe ultrasonicator. The amount of SP in the cementitious mixtures was varying according to the GnPs. Yet, a constant SP to GnPs weight ratio of 8.0 was used in all the studied mixtures. After the dispersion of the GnPs in the aqueous solution, extra water was added to succeed a water-to-cement ratio (w/c) of 0.3. The resulting mixture was hand stirred and mixed with the cement using a standard mixer according to ASTM C305. Five different mixtures were prepared with different GnPs contents, i.e., 0.0, 0.05, 0.1, 0.2, and 0.4 wt% per cement. The detailed mixture proportions are presented in Table 1.

Table 1. Components proportions of the studied mixtures.

CEM I (g)

w/c (g)

GnP content (g)

SP (g)

Mixture M-0.00 M-0.05 M-0.10 M-0.20 M-0.40

380 380 380 380 380

114 114 114 114 114

0.0

-

0.19 0.38 0.76 1.52

1.52 3.04 6.08

13.16

Two types of prismatic specimens (20 × 20 × 80 mm) were cast to study the mechanical and electrical behaviour of the prepared mixtures. Notched prismatic specimens were used for the mechanical tests (3-point-bending), and prismatic specimens with embedded steel mesh electrodes for the electrical tests. All specimens were demoulded 24 h after casting and kept completely immersed in saturated Ca (OH) 2 solution (0.82 g/l), to prevent the elution of calcium ions from the specimens, at room temperature (20 ± 2 °C) until the age of 28 days.

2.2. Experimental setup

2.2.1. Three-point bending test Three-point-bending tests were conducted on the notched prismatic specimens in triplicates. The tests were performed on an MTS (MTS Systems Co., USA) testing machine with a capacity of 10 kN. The set-up of the bending test is shown in Fig. 1. The load was applied with a speed of 0.0015 mm/s.

Fig. 1 Three-point-bending test set-up and specimen dimensions for the fracture toughness ( K Ic ) determination.

After the completion of the mechanical testing the fracture toughness ( K Ic ) of each specimen was calculated by using the Eq. 1 and 2 according to ASTM E399, as: = ∙ ∙ 3/2 ∙ f ( ) . (1)