## 3 Experimental Results  
### Compression and Tensile Behavior  
The 90-day compressive strength of the composite specimens was about 70 MPa. Figure 3 displays the variation in compressive strength test results. It can be observed that SMA fiber addition led to slight or no increase in compressive strength of the composite. For instance, the compressive strength of the ECC2-0.5, ECC2-1, and ECC2-1.5 mixtures slightly decreased by about 1.1%, 1.9%, and 5.8% compared to that of the ECC mixture produced with 2% PVA fibers alone, respectively. This is ascribed to increased porosity because of fiber clustering. Evidence of this was presented by [PERSON] et al. [6]. Similarly, incorporating SMA fibers in ECC led to a general reduction in the elastic modulus and Poisson's ratio of the composite compared to that of the PVA-ECC control mixture (Figure 4a,b). Also, it was observed that the elastic modulus of the different ECC mixtures was generally lower than that of comparable strength conventional concrete. This is attributed to the absence of coarse aggregates in ECC mixtures. The elastic modulus and Poisson's ratio of ECC incorporating SMA and/or PVA fibers ranged from 18.8 to 19.9 GPa and 0.14 to 0.19, respectively, depending on the fiber type and content. The incorporation of SMA fibers in the ECC mixture led to a general reduction in the elastic modulus and Poisson's ratio of ECC compared to that of the mono-PVA control mixture. For example, 0.5%, 1%, and 1.5% SMA fiber addition led to a reduction in elastic modulus by about 3.9%, 4.5%, and 4.7%, respectively, compared to that of the mono-PVA fiber-reinforced ECC mixture. A similar trend was observed for Poisson's ratio. For example, specimens ECC2-0.5, ECC2-1, and ECC2-1.5 had Poisson's ratio of 1.1%, 8.1%, and 24.3% lower than that of the control ECC2-0 specimens, respectively. The overall reduction in elastic modulus of the ECC mixtures can be ascribed to the reduced compressive strength caused by increased porosity due to fiber addition because of possible fiber clustering, while the reduction in Poisson's ratio imparted by fibers is attributed to the fiber restriction on the lateral strain.  
Figure 2: Impact loading testing machine setup.  
Furthermore, Figure 5 displays typical stress-strain curves from uniaxial tensile tests for the various ECC mixtures. The achieved tensile strength ranged between 6 and 8 MPa with strain capacity by up to 8%, depending on the SMA fiber content. Generally, the tensile properties of the composite were improved owing to SMA fiber addition. For instance, the ultimate tensile strength of ECC2-0.5, ECC2-1, and ECC2-1.5 specimens increased by 29.8%, 74%, and 39.8%, respectively, compared to that of mono-PVA-ECC control specimens. Also, the strain capacity corresponding to peak strength was significantly enhanced by SMA fiber addition. The enhanced tensile behavior of the hybrid ECC specimens is ascribed to enhancing the fiber-matrix interfacial bond area (i.e., chemical and frictional) via fiber addition, thus improving the overall load carrying capacity of the composite.  
Figure 4: (**a**) Elastic modulus and (**b**) Poisson’s ratio of composite specimens.  
Figure 5: Typical stress-strain curves for specimens from different composite mixtures.  
Figure 3: The compressive strength of different composite specimens.