## 3 Results and Discussion
### Samples Characterization
#### 3.1.3 Three Point Bending Test  
Flexural strength and modulus of elasticity were obtained through a three-point bending test. Figure 4 reports a stress-strain curves obtained at different content (50% and 70%) of calcium carbonate and stabilized sample (ash) in comparison with neat polymer. Flexural modulus, evaluated from the slope of the stress versus strain deflection curve determines how much a sample will bend when a given load is applied, while flexural strength is calculated as the maximum bending stress.  
In Figure 4, it is possible to notice first that the neat epoxy shows an elongation at break much higher than that both stabilized sample-epoxy and calcium carbonate-epoxy composites. Moreover, the neat epoxy did not break brittle but it yields above the peak. The presence of 50% by weight of  
Figure 4: Stress-strain curves obtained from flexural tests for different composites.  
filler significantly reduces the elongation at break of the composites and a major amount of filler up to 70% by weight further decreases it. The influence of stabilized FA as filler in epoxy resin matrix on the elongation at break is similar to that of calcium carbonate. As expected, increasing the filler amount in the epoxy matrix the elongation and the straight at break decrease, while the flexural modulus increases [45; 46; 47]. In general, the same content [% wt] of ash and calcium carbonate affects the composite flexural behavior similarly. The flexural modulus and flexural strength of CaCO\({}_{3}\)/epoxy and stabilized sample/epoxy composites with different filler amount are shown in Figures 5 and 6, respectively.  
Figure 5 shows the trend of flexural modulus of stabilized sample-epoxy and calcium carbonate-epoxy composites at different filler content (from 10% up to 70% by weight). It should be noted that the flexural modulus of stabilized sample (ash) and calcium carbonate composites is similar for each filler content and the curves almost overlap. The flexural modulus remains approximately constant up to a filler amount of 30% wt, then it slightly increases to a filler amount of 50% and it strongly increases for filler amount of 70%wt. In general, the flexural modulus raises increasing the filler content by more than 30% by weight of filler content independently of whether the filler is stabilized sample or calcium carbonate.  
Figure 6 shows the trend of flexural strength for of stabilized sample-epoxy and calcium carbonate-epoxy composites at different filler content (from 10% up to 70% by weight). Flexural strength and elongation at brake reduction of composites decreased with increasing of filler loading mainly due to agglomeration process acting as defects in the polymer matrix. It is worthwhile to note that the flexural strength decreases increasing the filler content up to 30% by weight for both ash and calcium carbonate. The composite stabilized sample-epoxy shows a constant decrease in the flexural strength up to a filler content of 50% wt and then it shows a slight increase up to 70% wt. Due to this trend and its standard deviation, it is possible to consider the flexural strength constant for stabilized  
Figure 5: Flexural modulus as a function of filler content.  
Figure 6: Flexural strength as a function of filler content.  
sample content above 30% wt as well as for calcium carbonate composite. The experimental data show a change in tendency of flexural modulus and strength for stabilized FA and calcium carbonate content greater than 30% by weight.