PSI - Issue 25

Zuzana Marcalikova et al. / Procedia Structural Integrity 25 (2020) 27–32 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2008, Kasagani, and Rao, 2016.). The choice of fibers is determined according to the purpose of use of fiber reinforced concrete, e.g. it may be foundation slabs (Labudkova and Cajka, 2017, Sucharda et al. 2017a) beams without shear reinforcement, industrial floors. Fibers are particularly suitable for reducing or eliminating shear failure. Great attention is paid to the determination of mechanical properties (Katzer and Domski, 2012, Sucharda et al. 2017b), their testing and identification of mechanical parameters (Sucharda et al., 2015, Sucharda et al. 2018). The basic tested properties of fiber reinforced concrete include usually determination of compressive strength, tensile strength, splitting tensile strength, bending tensile strength and density determination. Particular attention is paid to the tensile strength testing. The frequently used splitting tensile test is technically simpler compared to the flexural tensile test. However, in the case of simplified designs and analyzes of fiber reinforced concrete, the expression of tensile properties in the form of equivalent tensile strength is most often preferred. On the other hand, in the case of computer simulations, it is preferable to determine the fracture energy and a suitable idealized softening diagram (Kurihara et al., 2000, Koniki and Ravi, 2018). However, the resulting fracture energy values are also influenced by the test configuration (three-point and four point) and sample dimensions. When interpreting the test results, it is also necessary to take into account that the character of tensile properties is expressed for basic types of stress (tension, pressure, shear or torsion) for mathematical models of material. For numerical modeling and analysis, the finite element method and nonlinear analysis are often used. Numerical method is used, where for mathematical model of material is chosen fracture-plastic model and 3D computational models (Cervenka, and Papanikolaou, 2008, Sucharda and Konecny, 2018), which specializes in concrete constructions.

2. Fiber reinforced concrete and laboratory testing

Two test series of samples were used in the research, which differed in the type of fibers (Bekaert, 2019) used. Dramix® 3D 65/60 fibers were used for the first series and Dramix® OL13/20 fibers for the second series. The material characteristics of these fibers are given in Tab. 1. The shape of the fibers is evident from Fig. 1. Both test series were for the dosing of fibers 75 kg/m 3 and the concrete formula given in Tab. 2.

Table 1. Material properties of Dramix® 3D 65/60 BG and Dramix® OL13/20.

Material properties

Dramix® 3D 65/60 BG

Dramix® OL13/20

Fiber shape

Hooked ends

Straight

Bundling

Glued

Loose

Length [mm]

60

13

Diameter [mm]

0.9

0.21

Aspect ratio

67

62

Effect on strength of concrete [kg/m³]

15

60

Tensile Strength [N/mm²]

1160

2750

Modulus of elasticity [GPa]

200

200

Fig. 1. (a) Dramix® 3D 65/60 BG; (b) Dramix® OL13/20.