PSI - Issue 42

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Martina Drdlova/ Structural Integrity Procedia 00 (2022) 000 – 000

Martina Drdlová et al. / Procedia Structural Integrity 42 (2022) 1382–1390 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

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Peer-review under responsibility of 23 European Conference on Fracture - ECF23 Keywords: UHPFRC; concrete; polyurea; vehicle restraint systems; impact toughness

1. Introduction Cementitious composites (concretes) are characterized with good workability, durability, mechanical parameters and relatively low cost. Generally, concrete exhibits high compressive strength, while the tensile strength is about 10 times lower (depending on the composition). Several methods can be used to increase the tensile strength and impact resistance of cementitious composites. Nomenclature FRP Fibre Reinforced polymer HPFRC High Performance Fibre Reinforced Concrete UHPFRC Ultra High Performance Fibre Reinforced Concrete impact toughness E i energy required for breaking the test sample (J) H thickness of the test sample (mm) b width of the test sample (mm) The most common way is incorporation of steel reinforcing bars. Another possibility is the inclusion of FRP (fibre reinforced polymer) reinforcing bars based on glass or carbon. FRP-based bars have certain advantages over steel bars, e.g. higher corrosion resistance, low weight and cost-effectiveness (Al-Khafaji et al. 2021), but their modulus of elasticity is lower which can affect the overal load bearing capacity. The tensile strength and impact toughness of cementitious composites can also be enhanced by addition of steel, polymer, mineral or natural fibres (Popovic et al. 2018, Alyousef et al. 2020, Drdlova et al. 2018). The fibres limit the damage during the impact and keep damaged concrete more intact than plain concrete. The choice of the type of fibre used is a key factor for achieving a high level of concrete impact resistance (Buchar, J. et al. 2015). A combination of rebar (steel or FRP) and fibre reinforcement can also be used to further increase the tensile strength, ductility and impact resistance and reduce the spalling. E.g. in structural concrete beams, the addition of PP macro-fibers contributed to an increase in about 10% the stiffness and up to 40% the concrete ultimate strains (de Sá et al. 2020). Textile reinforced concrete (TRC) is one of the other options for contributing to the enhancement of the tensile strength, flexural strength, ductility index and energy absorption of the cementitious composites. (Kalaimathi and Shanmugam, 2022). Several coatings and retrofitting can also improve the impact resistance and minimize the damage of cement-based composites and structures. The effectivity varies depending on the material used and also is influenced by connection and interaction of the additional layer with the concrete element. A relatively new material for retrofitting the structures is polyurea. Polyurea is an elastic polymer formed by the chemical reaction of amine and isocyanate component, which has high impact resistance, large elongation, and great corrosion resistance. (Grujicic et al, 2011, Kalaimathi and Shanmugam, 2022). Polyurea is strain rate dependent, which could be beneficial for application at higher strain rates. It possesses good adhesion to concrete, very good tensile strength, ductility, which predisposes it to the hardening of elements for impact and high-speed loading. E.g., Raman (2012) and Wu (2022) used polyurea successfully to retrofit reinforced concrete structures against the explosive load. Szafran (2020) reported a positive impact of polyurea coating on the crushing strength of concrete rings (20.3% improvement has been reported). The presented study evaluates and compares the effectiveness of different reinforcement options in increasing the impact toughness of cement-based elements.