## 3 Strength Test
### Fatigue Test Results  
In addition, fatigue tests were carried out on the MTS in the same manner as the strength tests; however, fatigue tests were also carried out under unconfined compressive, flexural tensile, and indirect tensile stress states. Generally, the average speed of vehicles on the road is about 60-80 km/s, at which point the pavements receive a loading frequency nearly equivalent to 10 Hz. Thus, the samples were continuously subjected to sinusoidal wave which was implemented as the loading waveform with a loading frequency of 10 Hz. The fracture of the specimen was utilized as the material fatigue failure criterion. The same specimen size was utilized for the strength test. The curing times were 28 days and 90 days; the cement content was 3-5%, and the selected stress ratios were 0.5, 0.6, 0.7, 0.8, and 0.9. Fatigue tests were carried out with each cement content under different stress ratios and different stress states, and five parallel tests were carried out at each stress ratio. Owing to the variability of the specimen strength and the micro-cracks in the cement-treated aggregate base materials, the cement in some specimens was not completely combined with the aggregate in the specimen, and certain inhomogeneities were noted in the existing specimen-forming process. Owing to these reasons that increased the discreetness of the fatigue test results, some of the large discrete test data were eliminated. The details of the strength and fatigue tests under different stress states are shown in Figure 5. Figures 6-8 show the test results where \(N_{f}\) is fatigue life(times), \(S\) is stress ratio. From the above Figures 6-8 and the Tables 5-7. It can be observed that:  
1. The fatigue life of cement-treated aggregate base materials monotonously increased with the curing time and cement content, monotonously decreased with stress ratio and the fatigue life followed the order of unconfined compressive > indirect tensile > flexural tensile. The result was  
Figure 5: Images of strength and fatigue test procedures: (**a**) indirect tensile specimen, (**b**) flexural tensile specimen, and (**c**). unconfined compressive specimen  
similar to the growth trend of cement-treated aggregate base materials strength. The fatigue life of unconfined compressive at 5% cement content and 90 days was the longest, and that of flexural tensile at 3% cement content and 28 days, the smallest. Test results revealed that the curing time, cement content and stress states considerably affected the fatigue life of cement-treated aggregate base materials. Test results were similar to former studies [3; 7; 24; 38; 39; 40]. 2. The magnitude of the parameters a and b of the fatigue equation varied in a wide range, and the curing time and cement content considerably affected the parameters a and b. Parameter a reflected the slope of the fatigue curve, and the parameter a followed the order of flexural tensile > indirect tensile > unconfined compressive. On the other hand, parameter b reflected the intercept of the fatigue curve, and parameter b was significantly different under different stress states. Parameter b followed the order of unconfined compressive > flexural tensile > indirect tensile. Furthermore, similar to previous researchers [14; 16; 17; 38; 39], the values of parameter a were accessible to change with the types of the test conditions and the stress states. 3. The fitting equation for unconfined compressive fatigue is far from the flexural tensile and indirect tensile strength curves, and the S-N single logarithmic fatigue equations of cement-treated aggregate base materials under different stress states exhibit large differences. The fitting correlation coefficient was too low as shown in Tables 5-7.