# Mechanical Properties of Desert Sand-Based Fiber Reinforced Concrete (DS-FRC)
## 4 Conclusions  
In this study, the uniaxial tensile and compression properties of DS-FRC with the changes of W/B, S/B and DSRR were experimentally investigated, including workability, stress-strain curves, uniaxial compression toughness and microstructures. According to the results, the following conclusions can be drawn:  
1. The close consistency values of approximately 60-70 are observed in most DS-FRC, except for the critical W/B, such as the highest and lowest. The W/B and the content of desert sand are main factors affecting the workability of DS-FRC. At the highest W/B, the phenomenon of clumping (balling) or floating of fibers is observed. The high content of desert sand is bad for the fluidity of DS-FRC. Besides, the densities of DS-FRC maintain a comparable level, approximately 1900 kg/m\({}^{3}\), which are 10% lower than that of ordinary concrete, resulting from the lack of coarse aggregates and the porosity caused by the addition of fibers. 2. The Elastic Modulus of DS-FRC are about 13-20 GPa which are lower than that of the ordinary concrete due to the lack of coarse aggregate and increased porosity caused by the addition of fiber. The high content of desert sand has a negative effect on the Elastic Modulus of DS-FRC. It will decrease with the increase of DSRR. When the DSRR was low, the comparable Elastic Modulus  
Figure 9: The microstructure of composites: (**a**) micro-crack; (**b**) the single fiber pulled from the matrix; (**c**) the debonding between fiber and matrix; (**d**) the debonding trace; (**e**) the compactness of the matrix. are observed with the increase of S/B. The Poisson's ratio of DS-FRC is smaller than that of the ordinary concrete, approximately 0.18-0.25. That is because the lateral deformation of DS-FRC is limited by the bridging effect of fibers. 3. The uniaxial tension and compression properties of DS-FRC are mainly affected by the W/B and S/B. The optimum uniaxial mechanical performances are obtained at the W/B of 0.29 and the S/B of 0.36, respectively. The ultimate tensile stresses and corresponding strains are up to 4-5 MPa and 3%, respectively. However, for the uniaxial compression performance, all specimens maintain a high level more than 40 MPa and 1.0%, respectively. 4. In terms of the DSRR, it is observed that slightly improved ultimate tensile stresses due to improved matrix compactness and reduced corresponding strains are obtained. However, for the uniaxial compression performance, slightly reduced ultimate compression stresses and comparable strains approximately 1% are observed. It has few effects on the mechanical properties of DS-FRC, even for the DSRR of 100%, which reveals the feasibility of desert sand as the replacement of fine aggregates. 5. Compression toughness indexes are calculated to evaluate the compression deformation performance of DS-FRC, such as the initial cracking strain, the cracking strain energy density, the equivalent compression strength and post-peak fiber toughening index. The results show that the ratio of the cracking stress and the ultimate stress is at the range of 0.39-0.49, while the ratio of the equivalent compression strength and the ultimate compression strength is about 0.5 to 0.8. The cracking strain energy density is closely related with the ultimate compression stress. Besides, all specimens have the characteristics of the multiple cracking before the compression destruction. It reveals that DS-FRC can be determined as a ductile material. 6. As far as the microstructural of DS-FRC, the excellent crack controlling performance with micro-crack widths of about 40-60 \(\upmu\)m is observed. The phenomenon of fiber debonding and pulling out is obvious, which promotes the development of tensile strain hardening. Besides, good compactness of the matrix is obtained due to the filling effect of fine undisturbed desert sand. Currently, the structural health monitoring technology has become a research focus [65; 66; 67].