# Mechanical Properties of Desert Sand-Based Fiber Reinforced Concrete (DS-FRC)
## 3 Results and Discussion
### Uniaxial Compression Properties of DS-FRC
#### 3.4.2 The Strength Development and Stress-Strain Curves  
As is shown in Figures 4 and 7 and in Table 4, the mechanical parameters are presented, including compression strengths and compression stress-strain curves of DS-FRC with different mixtures. According to Figure 7, the stress-strain curve under the uniaxial compression test was divided into three stages, referring to the elastic stage, the cracking stage and the strain softening stage. The DS-FRC with different mixture showed similar trend until the branch point at the elastic stage, at which there are no micro-cracks. Then, the cracking stage prevailed with the increase of the load, at which the micro-cracks increasingly developed and the bridging effect of fiber was activated. Finally, the curves show a relatively fast declining trend after ultimate compression stresses. It is worth noting that the slope of the descending branch was relatively steep for DS-FRC, which was different from the typical high ductility cementitious composites. It may be attributed to that the particle size of desert sand was larger than that recommended by high ductility cementitious composites. Figure 6: The failure mode of specimens under uniaxial compression test: (**a–c**) the actual failure mode of DS-FRC; (**d–f**): the schematic of failure mode. It can be revealed in Table 5 that the initial cracking stress first decreased and then increased with the increase of W/B, while it exhibited an opposite trend for the S/B with the maximum about 20 MPa at the S/B of 0.36. It can be observed that the initial cracking strength was reduced with the increase of DSRR, except for in NO.8 which had a slight increase. The similar initial cracking strains ranging from 0.3-0.45% were obtained in all mixtures under the uniaxial compression test, which may be due to the improved matrix toughness of DS-FRC caused by fine undisturbed desert sand. It is clearly illustrated that the ultimate compression stress of DS-FRC decreased with the increase of W/B, as is shown in Figures 4a and 7a. The maximum ultimate compression stress could be up to 46.3 MPa. However, it first increased and then decreased with the change of S/B, according to Figures 4b and 7b. The maximum value was obtained at the S/B of 0.36. In terms of DSRR, as is illustrated in Figures 4c and 7c, ultimate compression stresses which could be up to about 40 MPa slightly reduced, except for the DSRR of 100%, at which the ultimate compression stress was 36.8 MPa. However, it was still relatively high, which reveals the feasibility of desert sand as a substitution for engineering sand. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Mix NO. **} & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** \\ \hline \(\omega_{0}\)/MPa & 20.95 & 20.32 & 13.83 & 15.61 & 18.76 & 16.69 & 15.67 & 16.46 & 15.12 & 19.00 \\ \(\varepsilon_{0}\)/\% & 0.39 & 0.42 & 0.34 & 0.33 & 0.37 & 0.51 & 0.30 & 0.33 & 0.44 & 0.39 \\ \(A_{\text{np}}\)/J/m\({}^{3}\)\(\cdot\)10\({}^{6}\) & \(n\) = 3 & 26.78 & 28.36 & 16.76 & 16.69 & 23.15 & 30.73 & 17.09 & 17.23 & 25.47 & 25.24 \\ \(\mu_{\text{s}}\)/MPa & \(n\) = 5.5 & 50.84 & 43.32 & 37.54 & 35.04 & 37.82 & 43.17 & 33.97 & 41.97 & 41.72 & 39.46 \\ \(f_{\text{s}  
In regard of the corresponding strain, the DS-FRC with different mixtures revealed comparable results of about 1%. As illustrated in Table 4, the DSRR of 100% had no negative effects on the ultimate compression strain of DS-FRC. Although the ultimate compression stress was slightly lower than that of the ordinary concrete, the relatively high corresponding strain about 1.19% could still be obtained. The slightly reduced ultimate compression stress may be due to the relatively high content of mud in desert sand. Additionally, the slight porosity caused by the adding of PVA fiber may be related to the reduced compression strength of DS-FRC. However, good structural applicability can be still assured by using the composites with similar properties, according to previous researches.