# Effects of Cement Treatment on Mechanical Properties and Microstructure of a Granite Residual Soil
## 3 Results and Analysis  
### UCS and Secant Modulus  
One set of the uniaxial compression curves of the saturated untreated and cement-treated GRSs is shown in Figure 6. For the untreated specimen, the stress-strain relationship is of strain-hardening type (see Figure 6a). In this case, the axial stress at an axial strain of 15% is adopted as the UCS of the specimen. For the treated specimens cured to 1-28 d, the stress-strain relationship is of strain-softening type (see Figure 6b-e). In this case, the UCS of the specimen is identified at the peak state. The relationship between the UCS and the cement content at four curing times is shown in Figure 7a. As the volumetric cement content increased from 0% to 3%, UCS increased linearly from 78 kPa to 413 kPa, 763 kPa, 1306 kPa, and 1277 kPa at curing times of 1 d, 7 d, 14 d, and 28 d, respectively. As the volumetric cement content exceeded 3%, the increase of the UCS with the cement content diminished. The relationship between the UCS and the curing time at five cement contents is shown in Figure 7b. For a given cement content, UCS increased linearly in the first 14 d and the increase of UCS with the curing time was then diminished (most notably in the case of \(C_{\text{vi}}\) = 1-3%). In detail, the UCS of the specimens cured to 1 d, 7 d, and 14 d reached 31-53%, 59-71%, and 79-107%, respectively, of those cured to 28 d, and these ratios decreased as the cement content increased. In the case of \(C_{\text{vi}}\)\(\geq\) 4%, the UCS developed successively within 28 d; in the case of \(C_{\text{vi}}\)\(\leq\) 3%, the development of the UCS ended at an early age of 14 d.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Types** & \(C_{\text{vi}}\) **(\%)** & **t (d)** \\ \hline UCT & 0, 1, 2, 3, 4, 5 & 1, 7, 14, 28 \\ OCT & 0, 1, 2, 3, 4, 5 & 7, 28 \\ XRD, SEM, MIP & 0, 1, 2, 3, 4, 5 & 28 \\ \hline \hline \end{tabular} Note: UCT= uniaxial compression test; OCT = oedometric compression test; \(C_{\text{vi}}\) = volume cement content; and \(t\) = curing time. All the cured specimens were saturated under confined conditions.  
\end{table}
Table 3: Arrangements for mechanical and microscopic tests.  
In all the cases, the uniaxial compression curves are nonlinear before the peak state (see Figure 6). In this study, the secant modulus is determined to describe the stiffness of the specimen. The dependence of the secant modulus on the cement content and curing time is shown in Figure 8. The experimental trends are similar to that of the UCS. As the volumetric cement content increased from 0% to 3%, the secant modulus increased almost linearly from 2.8 MPa to 116 MPa, 240 MPa, 319 MPa, and 292 MPa at a curing time of 1 d, 7 d, 14 d, and 28 d, respectively (see Figure 8a). As the volumetric cement content exceeded 3%, the increase of the secant modulus with the cement content diminished. For  
Figure 6: Stress-strain curves of saturated untreated and cement-treated GRSs at various cement contents and curing times.  
Figure 7: Uniaxial compressive strength (UCS) of saturated untreated and cement-treated GRSs at various cement contents and curing times. (**a**) Changes in UCS with cement content at various curing times; (**b**) Changes in UCS with curing time at various cement contents.  
a given cement content, the secant modulus of the specimens increased rapidly in the first 7-14 days, after which the increase of the secant modulus with the curing time diminished (see Figure 8b). Specifically, the secant modulus of the specimen cured to 1 d, 7 d, and 14 d reached 28-43%, 67-109%, and 84-109%, respectively, of those cured to 28 d. A similar conclusion can be drawn that the secant modulus of the specimens developed successively in 28 d in the case of \(C_{\rm{vi}}\geq 4\%\) and may have ended in 7-14 d in the case of \(C_{\rm{vi}}\leq 3\%\).