Shotcrete Application — Design with Kratos Macro Synthetic Fiber

Synthetic macro- and micro-fi bers became available for use in shotcrete in the 1990s. Synthetic macro-fi bers can be viable alternative for a full replacement of conventional steel bars in concrete elements (such as shotcrete) with continuous support. Micro-synthetic fi bers provide minimize plastic and drying shrinkage cracks in concrete, macro-synthetic fi bers increase toughness, load-bearing capacity and durability. Macro- and micro-synthetic fi bers conformity with the EN 14889–2 standard

(Fibers — for use in concrete — Part 2: Polymer fi bers — Defi nitions, specifi cations, and conformity). Fibers with an equivalent diameter> 0.3 mm are referred to as macro-synthetic fi bers, while those with an equivalent diameter ≤0.3 mm are called micro-synthetic fi bers. The use of macro-synthetic fi bers in sprayed concretes are included in the technical specifi cations of Highways and EFNARC (European Specifi cation for Sprayed Concrete) and it is aimed to determine the amount of macro-synthetic fi ber to be used, according to class of rock.

Calculation of Energy Absorption (Toughness) Capacity in Fiber-Reinforced Concrete

Kratos Macro fi bers are used to increase the energy absorption capacity and deformation ability of concrete and to reduce the possibility of cracks. Toughness means the ability of fi ber-reinforced concrete to continue carrying loads after cracks have emerged due to tensile stresses. Toughness is referred to as the sum of the area under load-displacement curves. Its unit is the joule ( Newton*meter or kN*millimeter.

Experimental Study

Figure 1: Kratos Macrosynthetic fiber for concrete. * It is made of Polypropylene

Concrete Mix Design

Table 1: Concrete mix design

Concrete is considered in compressive strength class C35/45 at 28 day.

Figure 2: Aggregate Sieve Analysis

Table 2: Kratos Macro Synthetic Fiber Technical Specifications

Test Description

Figure 3: EN 14488–5 Test

In the test , fiber-reinforced concrete specimens were casted 60*60*10 cm, which were tested according to EN 14488–5 (EN14488 Testing sprayed concrete — Part 5: Determination of energy absorption capacity of fiber reinforced slab specimens). The test was carried out in a closed-loop displacement controlled machine. Displacements were measured by LVDT (Linear variable differential transformer). 4 specimens were tested with 1 mm / min. loading speed.

Figure 4: Test samples (Kratos fibers hold the concrete together thanks to the bridging effect)

Table 3: Test Results

Figure 5: 5 kg/m3 Kratos PP 70 — EN 14488–5 Load — Displacement

Determination of Energy Toughness Class

The energy absorption capacities of the fiber-reinforced samples will be equal to or greater than the values specified in Table 4. (Highway Technical Specifications 2013)

Table 4: Toughness Class

Rock quality structure is important in determining the energy absorption capacity of fiber-reinforced shotcrete. The energy absorption capacity of concrete varies depending on the concrete mixture and fiber dosage (kg /m3). Depending on the rock structure, macrosynthetic fibers can completely replace traditional steel reinforcement. Microsynthetic fibers are used to minimize plastic and drying shrinkage cracks in shotcrete in which the cement dosage is high.

Example of Comparable Moment Capacity Calculation for Wire Mesh & Macro-Synthetic FiberReinforced Concrete According to ACI 544. 4R-18

Figure 6: Shotcrete

Wire mesh — Moment Capacity

Figure 7: Schematics of stress block for a cracked reinforced concrete flexural member without fibers: (a) reinforced concrete beam section; (b) actual distribution of normal stresses; and © simplified distribution of normal stresses.

MnRc = As*fy*(d -a/2) Concrete Height: 20 cm Wire Mesh: Q188/188 (One Layer) Concrete Cover: 10 cm Concrete Class: C25/30

Table 5: Wire mesh — Fiber-Reinforced Concrete — Moment Capacity

Fiber-Reinforced Concrete Moment Capacity

Figure 8:Schematics of stress block for a cracked FRC flexural member. (a) FRC beam section; (b) actual distribution of normal stresses; and © simplified distribution of normal stresses.

MnFRC = fd 150* b*h2 6

f d 150 =1.38 Mpa = Q188/188 wire mesh Moment Capacity

Figure 9: ASTM C 1609 Test

Table 6: ASTM C 1609 Test Results

Kratos PP 54 2 kg/m3 fd 150 = 1.61 > 1.38 MPa. When Kratos macro-fibers are used in concrete to replace steel reinforcement, they can provide enhanced ductility, toughness and durability. Kratos fiber dosage can be engineered to provide a desired level of crack control, post-crack tensile and flexural capacity Similar to steel bars, for which the size and spacing are calculated to provide the required reinforcement ratio, the dosage of fibers are also calculated to satisfy engineering requirements. Kratos PP 54 2 kg/m3 dosage can be used completely as an alternative to Q188/188 traditional steel reinforcement.

REFERENCES

• TS EN 14488–5: Testing sprayed concrete. Determination of energy absorption capacity of fibre-reinforced slab specimens
• • Karayolları Teknik Şartnamesi 2013: Yol Altyapısı, Sanat Yapıları, Köprü ve Tüneller, ÜstYapı ve Çeşitli İşler)
• • EFNARC: European Specification for Sprayed Concrete
• • Grimstad, E. & Barton, N.: “Updating the Q System for NMT,” in Proceedings of International Symposium on Sprayed Concrete. Fagernes, Norway, pp 21, 1993.
• • Technical Report No 65: Guidance on the use of Macro-Synthetic FibreReinforced Concrete
• • Concrete Institute of Australia: Recommended Practice Shotcreting Australia, Second Edition
• • ACI 544.4R-18: Guide to Design with Fiber-Reinforced Concrete
• • ACI 506.1R: Guide to Fiber Reinforced Shotcrete
• • ASTM C 1609 : Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading)

Writting by

BURAK ERDAL

Global Technology Project Leader, Kordsa

UĞUR ALPARSLAN

Technology Manager, Kordsa