PSI - Issue 72

Ivelina Ivanova et al. / Procedia Structural Integrity 72 (2025) 338–344

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environmental issues. Natural fibers, also known as plant fibers, are fibers made from plant materials. These fibers are used in different sectors, such as textiles, paper production, and packaging. They are environmentally friendly and biodegradable, making them an attractive option over synthetic fibers. One of the objectives of the current research project is the investigation of the influence of added hemp fiber fabrics to the concrete at different layers and positions on the reduction of the stress intensity at the crack tip and therefore an increase in the remaining lifetime of concrete structures. Natural hemp fibers have high environmental benefits: renewable resources, excellent for environmental protection, and have a high carbon impact, all the time of their development, they absorb a large amount of carbon dioxide, hemp cultivation does not require fertilizers or pesticides, naturally degraded recycling potential, which contributes to a minimal impact on the environment. According to various literature research, the addition natural short fibers like jute, sisal, hemp, flax, cotton, and coconut fibers into concrete can improve the mechanical properties, provide resistance to corrosion, strength, and durability of concrete (Awwad et al. (2012), Çomak et al. (2018), Nayak et al. (2022), More and Subramanian (2022), Özodabaş (2023)). Natural fibers can also lead to an improvement in the thermal and acoustic characteristics of the resulting concrete (Ben Hammed et al. (2021)). Our research with the use of natural fiber fabrics in the strengthening of reinforced concrete structures is recent development research since 2019, in a team of Civil Engineering of laboratory ITheMM UR 7548 at the University of Reims Champagne Ardenne. The technique of external bonding of natural compost materials was used to extend the life and durability of concrete structures (Ivanova et al. (2020), Assih and Ivanova (2021), Ivanova et al. (2021), Bou Abdallah et al. (2022)). However, since natural short fibers have been incorporated into concrete, there are still very few studies on incorporating the fiber fabric reinforcement in concrete. Further research is therefore necessary, particularly to assess the level of adhesion of these fabrics with concrete and their long-term durability. This experimental research focuses on the effect of adding hemp fiber fabrics to mortar to investigate its mechanical properties. This project presents the different reinforcement positions studied as well as the tensile and bending tests used to characterize the mechanical behavior of the reinforced mortar. The results of the bending tests are then analyzed to highlight the effects of reinforcement on the load-displacement curves and the ultimate strength. 2. Experimental part Four series of prismatic specimens of mortars were studied. Figure 1 illustrates the geometry of the pull-out specimen in the different series.

a)

b)

F0

C

d)

c)

F2

F1

1 cm

Fig. 1. Position of hemp fibers fabric reinforcement in mortars – (a) Control specimen without reinforcement; (b) Reinforced specimen with one layer of hemp fabrics positioned 0 cm; (c) Reinforced specimen with one layer of hemp fabrics positioned 1 cm from the bottom of the specimen; (d) Reinforced specimen with two layers of hemp fabrics positioned at 0cm and 1 cm from the bottom of the specimen; The prismatic test specimen, measuring 160 mm long, 40 mm wide, and 40 mm high, is reinforced by one or two layers of hemp fiber fabric placed at different positions, as shown in Fig. 1. There are at least 3 specimens in each series in total 12 specimens. The first series was the reference specimens without reinforcement, designated as C, like the Control specimen (see Fig. 1a). The second series was the reinforced specimen with one layer of hemp fabrics