The absolute density of the fibres was measured using a helium pycnometer [12]. This test was necessary because it allows to determine the volume of fibre to be inserted in the mortar according to the percentage (Figure 2).

This test was carried out using the modified protocol according to Davina [13]. A sample of fibres is dehydrated for 3 hours in an oven at 105˚C. Once the 3 hours have passed, and the mass (M_s) constant, the sample is placed in a room under a controlled atmosphere. Every fifteen minutes, the sample is weighed, until two successive equal weightings are obtained. This last value (M_h) constitutes the wet mass of the sample, from which the recovery rate is calculated, using Equation (1):

R % = M h − M s M s (1)

It should be noted that part of the fibres were washed for approximately three hours in a NaOH solution diluted to 6%, with a normal concentration (1 N), in the proportions of 1 g of the fibres per 10 ml of heated water. Beforehand at 120˚C. The purpose of this treatment was to see if the treated fibres improve the mechanical properties better than the untreated fibres.

Let ρ f be the density of the fibers; V the volume of the test piece and X the volume percentage of the fibers relative to the volume of the test piece. The corresponding mass for each volume fraction is given by the following Equation (2):

M f = ρ f ∗ V ∗ X (2)

In our case, we worked with four different percentages; so X took the values: 0.5%, 1%, 1.5% and 2%. The dimensions of the fibres used in this study are as follows: length 15 mm, average diameter: 0.9 mm.

The mixing protocol established in this study and adapted to the fibres is based on the EN 196-1 [14] standard. This protocol is as follows:

­ Add cement and water to the mixer and mix for thirty seconds at a slow speed;

­ Addition of dry fibres and mixing for thirty seconds at a slow speed;

­ Adding sand, mixing for thirty seconds at a slow speed; then mixing for another thirty seconds at a fast speed.

­ Stopping the mixer and hand kneading for thirty seconds, then resting for one minute; then kneading for one minute at a fast speed.

The density of the fresh mortar was calculated from the weighing of the moulds filled after casting using a balance. The occluded air was calculated using Equation (3) [3].

occludedair ( % ) = 100 ∗ ( 1 − ρ f r ∗ ∑ V i ∑ V i ∗ ρ i ) (3)

With: ρ f r the density of mortars in the fresh state; V i the volume proportion of component « i » in the mixture; ρ i la density of the constituent “i”.

The workability of the mortars was measured with the shaking table in accordance with standard EN 1015-3 [15] (Figure 3).

The bending and compression tests were carried out on the 4 * 4 * 16 cm³ prismatic mortar specimens in accordance with standard EN 196-1 [14] (Figure 4).

The capillary absorption tests were carried out in accordance with standard EN-13057 [16] (Figure 5).

The measurement of the porosity accessible to water and the apparent density was made by hydrostatic weighing in accordance with standard EN P18-459 [17] and according to [18] (Figure 6).

We can deduce the apparent dry density ρ a , and the porosity accessible to water ε a c c , using Equations (4) and (5) respectively:

ρ a = m s e c m a i r − m e a u ∗ ρ e a u (4)

ε a c c = m a i r − m s e c m a i r − m e a u ∗ 100 (5)

­ m e a u the mass of the saturated mortar in the suspension system of the hydrostatic balance after immersion for 48 hours (g);

­ m a i r the mass of the mortar in saturated dry surface conditions (g);

­ m s e c the mass of the dried mortar at (105 ± 5)˚C (g).

The thermal conductivity test was carried out using the hot wire method based on standards ASTM D5334-00 and D5930-97 described after Department of Architecture, Geology, Environment and Construction (ARGENCO) [19] (Figure 7).

The grip measurement by direct traction was determined according to standard EN 1542 [20] (Figure 8).

The results obtained from Table 2 show that the more the amount of fibres increases, the greater the content of occluded air and the lower the density. This is due to the moisture uptake rate of the fibres. Other authors have also pointed out the increase in occluded air and the decrease in density as a function of fibre content. This is mainly due to the low capacity of the fibres to compact [21] [22] [23]. This can also be explained by the increase in the void quantity.

The consistency of mortars gradually decreases as the amount of fibre present in the mortar increases; this is due to a loss of handling. This trend was also observed by [24]. Consistency of mortars is almost zero at 2% fibre; because of their great flexibility, the pseudo banana trunkfibres tend to form pellets during kneading when they are in very large quantities [25] [26]; this is the reason why in the rest of our work we did not work much with mortars containing 2% fibre (Figure 9).

The values of average compressive strengths and flexural strengths of the mortars studied after 28 days of cure are shown in Figure 10. There is a decrease in the compressive strength of the mortar as the percentage of fibres increases. These decreases in resistance have also been pointed out by other authors [3] [27]. In terms of flexural strengths, there has been a “sawtooth” development. This is due to the method of extracting the fibres used which is combing.

We also tried to treat a certain quantity of fibres with NaOH to see if their incorporation in the mortar improves the mechanical characteristics of the mortar. We have observed that for a low percentage of fibres, fibres treated with NaOH improve the compressive strength of the mortar but not the flexural strength; this is illustrated in Figure 11.

Capillary absorption results

The capillary absorption of fibre mortars varies significantly depending on the percentage of fibres in the mortar as can be seen in Figure 12. The value is minimum for the mortar containing 0.5% of fibres 1.2 kg∙m⁻²∙h^−0.5 and maximum 1.52 kg∙m⁻²∙h^−0.5 for mortar containing 2% fibre.

The capillary absorption increases with the fibre content in the mortar this phenomenon is due to the pores created by the fibres in the mortar.

The results obtained show an increase in porosity with the percentage of fibres in the mortar. It should also be noted that an increase in porosity leads to a decrease in the density of the mortar. Other authors have also noted this relationship [3] (Figure 13).

We notice a decrease in thermal conductivity as a function of the increase in fibres in the mortar. The more fibre-reinforced the mortar, the better it is a good thermal insulator. This is due to the porosity of the mortar which increases with the amount of fibre (Figure 14).

We can therefore conclude at this stage that the pseudo banana trunkfibres improve the thermal properties of a cement mortar, making it more insulating.

We note a decrease in adhesion with the percentage of fibres in the mortar. This is due to the weak cohesion of fibre mortars. But these values remain acceptable as shown in Figure 15; which means that this mortar can easily be used as a coating up to 1.5% fibre.

Adhesion greater than or equal to 0.7 MPa is acceptable for a mortar incorporated with fibres which can be used as a rendering.