## 3 Experimental Results
### Compressive Modulus of Elasticity  
Figures 7-9 show the results of the variation of the compressive modulus of elasticity with the number of cycles, for the three mixtures and for both series.  
Figure 7: Variation of the compressive modulus of elasticity by number of cycles. HPC (**a**) L-Series. Raw values. (**b**) H-Series. Raw values. (**c**) L-Series. Maximum, minimum, and average relative values, and tendency lines. (**d**) H-Series. Maximum, minimum, and average relative values, and tendency lines.  
Figure 8: Variation of the compressive modulus of elasticity with the number of cycles. SFHPC (**a**) L-Series. Raw values. (**b**) H-Series. Raw values. (**c**) L-Series. Maximum, minimum, and average relative values, and tendency lines. (**d**) H-Series. Maximum, minimum, and average relative values, and tendency lines.  
Figure 9: Variation of the compressive modulus of elasticity with the number of cycles. PPFHPC (**a**) L-Series. Raw values. (**b**) H-Series. Raw values. (**c**) L-Series. Maximum, minimum, and average relative values, and tendency lines. (**d**) H-Series. Maximum, minimum, and average relative values, and tendency lines.  
In contrast to the results depicted in Figures 4-6, Figures 7-9 show that there was no significant variation in the average compressive modulus of elasticity of concrete with the number of cycles. The L-Series showed a slight increase of the compressive modulus of elasticity, up to 15-20%. On the other hand, the H-Series showed a flat behavior, with a variation below 5%.  
As with compressive strength, the compressive modulus of elasticity was not adversely affected by cyclic loading, and no relevant mechanical consequences were observed.  
In a deeper analysis, it may be observed that the variation of the compressive modulus of elasticity not follow a monotonic tendency. First, an initial slight increase of the compressive modulus of elasticity up to a maximum value was observed, which was located between 20,000 and 200,000 cycles, depending on the mixture and on the series. It then started to decrease.  
In this case, an increase of the scatter of the results was observed, although it is not very relevant.  
As happened with compressive strength, the internal stress released by the cyclic loads during the first cycles resulted in microcracking. In this case, this stress relaxation resulted in an increase of the compressive modulus of elasticity. Under low and moderate stress levels, which are the ones used to measure the compressive modulus of elasticity, the results show that the presence of fibers had no influence, since no different tendency was observed between the mixtures with and without fibers.  
The scatter was also similar in all cases, which denotes that fibers had no relevant influence on the compressive modulus of elasticity, i.e., the evolution of the microcracking and its impact on the compressive modulus of elasticity depends on concrete matrix only. The scatter depends on concrete matrix only, resulting in a similar variation in all cases, regardless of the presence or absence of fibers, and the type of fibers.  
Moreover, all the mixtures and both series showed very similar values for the compressive modulus of elasticity (in the surrounding of 40,000 MPa), implying that this parameter was not sensitive to the presence of fibers.