# Mechanical Properties and Flexural Behavior of Sustainable Bamboo Fiber-Reinforced Mortar
## 3 Results and Discussion
### Mechanical Properties
#### 3.1.4 Fracture Properties and Toughness  
The limit of proportionality and the modulus of rupture are shown in Figure 8. It should be noted that one out of the 3 samples of the 300 \(\upmu\)m with 8 V% and 6 V% exhibited a significantly lower bending performance as can be seen in Figure 7. This resulted in a high standard variation shown in Figure 8. Samples with the 500 \(\upmu\)m fiber batch revealed a lower modulus of rupture compared to those containing 300 \(\upmu\)m fibers. These values were around 0.0%, 7.7% and 13.0% lower for the 8/6/4 V% fibers specimens, respectively. These findings were in agreement with ACI 544.1R-96, where a lower MOR was reported with decreasing aspect ratio of the fibers [60]. Longer and thinner fibers exhibit a higher bond within a concrete or mortar matrix resulting in a higher pull-out resistance compared to shorter and thicker fibers as shown which was also found by other researchers in [55; 61].  
Figure 6: Photographs of test samples after bending tests involving 500 \(\upmu\)m fibers. Fiber content: (a) 4 V%, (b) 6 V% and (c) 8 V%.  
Figure 7: Bending test results of mixtures with 4 V%, 6 V% and 8 V% of (a) 300 \(\upmu\)m fibers and (b) 500 \(\upmu\)m fibers.  
The toughness was calculated as the area under the load-deflection curve and expressed as energy in Joules. Accordingly, the resulting cumulative energy up to 2 mm deflection is shown in Figures 9 and 10. As expected, a higher fiber content resulted in higher toughness. Thicker and longer fibers, as found in the 500 \(\upmu\)m batch, showed an overall reduction in toughness when compared to the smaller and shorter fibers in the 300 \(\upmu\)m batch. This is explained due to the higher bridge bearing capacity of the mixtures with a higher amount of fibers and a higher pull-out resistance for fibers with a higher aspect ratio as discussed earlier and shown in [59; 61].  
To characterize the post-cracking behavior of the different mixes, two toughness parameters were evaluated in accordance with RILEM RC 162-TDF [53]. The toughness values at a mid-span deflection of span/150, which corresponded to 1 mm deflection, and the toughness at a mid-span deflection of span/75 (2 mm deflection) were evaluated. The corresponding results, presented in Figure 10 and Table 4, revealed that a higher fiber content enhanced the ductility and toughness of the prepared mixes. The toughness values of the 300 \(\upmu\)m fiber specimens at 1 mm deflection were 40.0% and 73.3% higher for the 6 V% and 8 V% mixes when compared to 4 V% mixes, respectively. Assessing the 500 \(\upmu\)m fiber batch, an increase of 16% and 47% increase in toughness was recorded for the 8 V% and 6 V% mixes when compared to 4 V% mixes, respectively (see Figure 10). Furthermore, the results of the mixes containing 500 \(\upmu\)m fibers showed lower energy up to both 1.0 mm and 2.0 mm deflection when  
Figure 8: Bending test assessment: (**a**) limit of proportionality F\({}_{\text{max}}\); (**b**) modulus of rupture.  
Figure 9: Cumulative toughness of the bamboo fiber reinforced specimens up to 2 mm deflection: (**a**) 300 \(\upmu\)m batch; (**b**) 500 \(\upmu\)m batch evaluated from the four-point bending test according to ASTM C1609 [52].  
compared to the 300 \(\upmu\)m fiber results and showed the influence of the aspect ratio of the fibers on the bond strength of the specimen which is in compliance with findings in [55; 61]. The high standard deviation of the 300 \(\upmu\)m with 8 V% and 6 V% is the result of the lower bending performance of one out of three tested specimens shown in Figure 7.