Issue 75

M.-A. Hossam El-Din et alii, Frattura ed Integrità Strutturale, 75 (2026) 200-212; DOI: 10.3221/IGF-ESIS.75.14

In a recent study published online on September 12, 2025, Cai et al. [8] studied the effect of a/w on the K IIC of FRC using DNC TTC specimens, this means, or in other words, to the best of the authors' knowledge, that no research has been found in the literature to date addressing the K IIC of FRC using MC specimens. Therefore, the main object of this study is to introduce the novel experimental approach by employing DNC specimens with MC to accurately measure K IIC , addressing the limitations of previous studies that relied on TTC and failed to capture the realistic fiber bridging effect. Various a/w, which equal 0.3, 0.4, and 0.5, and Vf% equals 1 and 1.5% were investigated. Three series of fiber arrangement, as well as an SCC without fibers, were considered for comparison to illustrate the effect of the presence of intact fibers (fiber bridge) on the pre-notch surfaces on the accuracy of K IIC measurement for FRSCC: First, TTC specimens, second, MC specimens, and third, the fibers were dispersed between the two pre-notch surfaces (fiber bridging existed) while the specimens were completely cast without fibers (MC/C), i.e., SCC specimens without fibers. A major contribution of the current study is the comparison of the K IIC measured from TTC and MC/C specimens, which shows the efficiency of fibers behind the crack tip in resisting crack growth, and those ahead of the crack tip. Materials and mix proportions FRSCC was designed for the experimental program. Type I Portland cement with grade 42.5N was used. Coarse aggregate (dolomite) with NMS 10 mm and specific gravity of 2.7 was used; natural siliceous sand with a specific gravity of 2.55 was used. The physical and mechanical properties of the coarse and fine aggregates are listed in Tab. 1. High water reduced the named Viscocrete-3425 from Sika Company, with 1.5% of the cement weight used to produce SCC, the water-cement (W/C) ratio was 0.4. On the other hand, hooked-end steel fibers of 50 mm in length and 1.0 mm in diameter were used by a Vf% of 1 and 1.5%, the tensile strength and density of the used fibers were 1200 MPa and 7.87 t/m 3 , respectively. The hooked-end steel fibers benefit from their strong bond with the cement matrix and better flexural performance. SCC was designed to achieve 30 MPa in compressive strength; the mix proportions of SCC with Vf% = 1% are listed in Tab. 2. The fresh concrete properties of SCC were measured just after mixing, through the following tests: the slump flow, T50, V-funnel, and L-box tests according to EFNARC [20]. The fresh property results of SCC with Vf% = 1% are listed in Tab. 3. The Table shows that all mixes were within acceptable limits according to EFNARC [20]. S E XPERIMENTAL WORK

Coarse aggregate (dolomite)

Fine aggregate

Property

Measured Value

Property

Measured Value

Specific gravity

2.7

Specific gravity

2.50

Unit weight, (t/m 3 )

1.455

Unit weight, (t/m 3 ) Fine material (75 μ )

1490 1.1 %

Absorption, %

0.86 %

Crushing value, % Impact value, % Los Angeles value, %

23.73 11.92

17.4 Table 1: Coarse and fine aggregates' physical and mechanical properties.

Cement

Water

Sand

Dolomite

Steel Fiber

Admixture (1.5%)

400

160

970

970

79

6.0

Table 2: SCC mix proportions with Vf% = 1% in kg/m 3 .

Slump Flow (mm)

T50 (sec)

V-Funnel time (sec)

L-box (ratio)

Property

Measured value

730

3.0 2-5

7.3

0.96 0.8-1

Acceptance criteria (EFRNARC) [20]

600-800

6-12

Table 3: Fresh Properties of SCC with Vf% = 1%.

202