PSI - Issue 64

Paula Folino et al. / Procedia Structural Integrity 64 (2024) 1452–1459 Folino et al. / Structural Integrity Procedia 00 (2019) 000 – 000

1454

3

strength of 500 MPa, a Young’s Modulus of 210000 MPa and an ultimate strain equal to 12%.

(a)

(b)

(c)

(d)

Figure 1. (a) Unjacketed beams; (b) SCHSC 60mm jacketed beams; (c) SCFRHSC 30mm jacketed beams; (d) SCFRHSC 60mm jacketed beams.

After three months, the NSC reference beams were strengthened by U-shaped jackets, enveloping the lateral and bottom faces of the beams. Two Self-Compacting High Strength Concrete types were considered: (i) without fibers (SCHSC) and (ii) Fiber Reinforced (SCFRHSC). High-strength CP-50 cement, comparable to ASTM Type III, was utilized for the mixtures in combination with blast furnace slag as a mineral additive. Crushed granitic stone with a fineness modulus FM = 5.69 was used as coarse aggregate. A combination of siliceous river sand and crushed granitic sand was used as fine aggregates, with FM = 1.77 and FM = 3.52, respectively. For the dosage of SCFRHSC, the same mixture as for SCHSC was used with the addition of 0.75% in volume of 33 mm nominal length steel Wirand FS3N macrofibers, and 0.10 % of 12 mm polypropylene Fibro-Mac microfibers. The addition of polypropylene fibers was decided considering that it can mitigate concrete spalling caused by the action of high temperatures, improving therefore fire performance (Kodur and Phan, 2007). Although the action of high temperatures is not included in this paper, it is expected to analyze the performance of jacketed beams under that action in a future experimental program, considering the same geometries and materials than those reported in this work. Fiber properties and mix proportions are detailed in Table 1 and 2, respectively. A modified polycarboxylate-based high-range water-reducing (HRWR) admixture (Sika Viscocrete 9100) was used as a chemical additive. In the case of SCFRHSC, the dosage was increased to compensate for the loss of fluidity due to the addition of fibers, and to ensure proper filling of the jackets. Preparation of the pastes was carried out by first mixing the aggregates with 50% of the water, then adding the cement and slag along with 20% of the water, and finally adding the remaining water with the HRWR admixture. For SCFRHSC preparation, after mixing all other components, steel and polypropylene fibers were introduced through a sieve to improve dispersion.

Table 1. Fiber properties.

Table 2. Concrete mixtures.

SCHSC

SCFRHSC

Steel macro fibers

Polypropylene micro-fibers

[kg/m [kg/m [kg/m [kg/m [kg/m [kg/m

3 ] 3 ] 3 ] 3 ] 3 ] 3 ]

Cement CP50

426 182 214 280 500 780

426 182 214 280 500 780

Length (L)

[mm] [mm] [MPa] [MPa]

33.0

12.0

Blast furnace slag

Diameter (D)

0.750 1100

0.032

Water

Tensile Strength Young's Modulus Specific Weight Aspect Ratio λ=L/D

400

Siliceous river sand Granitic crushed sand Granitic crushed stone HRWR admixture Steel macro-fibers Polypropylene fibers Water/binder ratio

200000

3500

[KN/m3] 78.5

9.1

44

375

[kg/m 3 ] [kg/m 3 ] [kg/m 3 ]

3.2

3.6

— —

60

0.8

[-]

0.35

0.35