PSI - Issue 64

Chiara Pepi et al. / Procedia Structural Integrity 64 (2024) 1896–1903 Maria Eleonora Pipistrelli / Structural Integrity Procedia 00 (2019) 000 – 000

1900

5

The trends show the effects on the tensile properties resulting from these treatments, compared to the untreated fibers (illustrated by blue continuous lines in figure). The addition of graphene coating notably increases tensile properties values, particularly concerning tensile stress and modulus of elasticity. These results are of utmost importance for the use of vegetal fibers in natural textile reinforced mortar. In particular, non-coated fibers are characterized by values of initial stiffness (i.e. E IN in Figure 5) lower than the mortar stiffness, resulting in cracking of the matrix before the fibers start their reinforcing effect. Treating the fibers can enhance initial stiffness and tensile strength, improving adhesion to mortar and delaying mortar cracks. Furthermore, coated fibers are characterized by values of tensile strength higher than non-coated fibers, resulting in a stronger reinforcing composite material. Mean values of the registered tensile properties are listed in Tables 1 and 2 for different duration of alkali treatment and graphene coating, respectively. Figure 6 shows the tensile strength (top panels) and Young’s modulus (bottom panels) variation with time duration for each sample of hemp (left panels) and Spanish Broom (right panels) fibers. Square red dots and dashed red line refer to alkali treated fibers samples and their mean values, respectively. Black circles and dashed black line refer to alkali+graphene coated fiber samples and their mean values, respectively. Dashed green and blue lines show the mean values of the untreated fibers and graphene coated only, respectively . It’s worth noting that although the numerical values ranges differ for the two types of vegetal fibers, graphene coating without prior alkali treatment is ineffective for Spanish broom fibers, whereas it is effective for hemp fibers.

Fig. 4. Stress-strain curves for: (a) hemp fibers samples at a selected treatment time (30 min.); (b) Spanish broom fibers samples at a selected treatment time (30 min.).

Fig. 5. Stress-strain curves for idealized trends according to the treatment implied.