# Effects of Cement Treatment on Mechanical Properties and Microstructure of a Granite Residual Soil
## 4 Discussion
### Effect of Cement Treatment on Pore Structure  
To further quantify the effects of cement treatment on pore structure, a detailed analysis must be performed based on the MIP results. The volumetric constitutions of the as-compacted untreated and cement-treated specimens are illustrated in Figure 21. For a given cement content, various void ratios of the as-compacted specimen are defined as:  
\[e_{\text{Mi0}} =V_{\text{vMi0}}/(V_{\text{si0}}+V_{\text{s0,GRS}}) \tag{8}\] \[e_{\text{mi0}} =V_{\text{vmi0}}/(V_{\text{si0}}+V_{\text{s0,GRS}})\] (9) \[e_{\text{i0}} =e_{\text{Mi0}}+e_{\text{mi0}} \tag{10}\]  
where \(V_{\text{vMi0}}\) and \(V_{\text{vmi0}}\) are the volumes of the macro- and micro-pores in an as-compacted specimen, respectively. \(V_{\text{si0}}\) and \(V_{\text{s0,GRS}}\) are the volumes of the solid particles constituting the cement and GRS components in an as-compacted specimen, respectively. Additionally, the volumetric cement content was previously defined as:  
\[C_{\text{vi}}=V_{\text{si0}}/(V_{\text{si0}}+V_{\text{s0,GRS}}). \tag{11}\]  
For the untreated specimen, the macro- and micro-void ratios that followed confined wetting were determined based on the MIP results (see Figure 15). Given the non-swelling nature of Kaolinite, it is likely that the pore structure of the GRS altered slightly upon confined wetting; this is evidenced by MIP results that the intruded void ratio of the saturated untreated specimen is close to its initial void ratio (see Figure 16). Hence, the macro- and micro-void ratios of the as-compacted untreated specimen are adopted as:  
\[e_{\text{M0,GRS}} =V_{\text{vMi0,GRS}}/V_{\text{s0,GRS}}=0.35 \tag{12}\] \[e_{\text{m0,GRS}} =V_{\text{vm0,GRS}}/V_{\text{s0,GRS}}=0.32 \tag{13}\]  
Figure 21: Illustration of volumetric constitutions of an as-compacted specimen with different cement contents. Figure 20: Compression index of saturated untreated and cement-treated GRSs depending on vertical pressure. (**a**) Curing time = 7 d; (**b**) Curing time = 28 d.  
where \(V_{\rm vM0,GRS}\) and \(V_{\rm vm0,GRS}\) are the volumes of the macro- and micro-pores in an as-compacted untreated specimen, respectively. Moreover, the GRS components in all the as-compacted specimens were scheduled to an identical dry density of 1.58 Mg/m\({}^{3}\) (which gives \(e_{\rm 0,GRS}\) = 0.67); therefore, the following correlations can be established according to Figure 21:  
\[e_{\text{Mi0}} =V_{\text{vMi0}}/(V_{\text{si0}}+V_{\text{s0,GRS}}) \tag{8}\]0  
\[e_{\text{Mi0}} =V_{\text{vMi0}}/(V_{\text{si0}}+V_{\text{s0,GRS}}) \tag{8}\]1  
where \(V_{\rm vMi0,GRS}\) and \(V_{\rm vmi0,GRS}\) are the volumes of the macro- and micro-pores of the GRS component in an as-compacted treated specimen, respectively. The \(V_{\rm si0,GRS}\) is the volume of the solid particles of the GRS component in an as-compacted treated specimen. Finally, the macro- and micro-void ratios of the as-compacted treated specimens are derived as:  
\[e_{\text{Mi0}} =V_{\text{vMi0}}/(V_{\text{si0}}+V_{\text{s0,GRS}}) \tag{8}\]2  
\[e_{\text{Mi0}} =V_{\text{vMi0}}/(V_{\text{si0}}+V_{\text{s0,GRS}}) \tag{8}\]3  
During the curing of a treated specimen, the hydration of its cement component modifies the pore structure in three possible ways: (i) the formation of C-S-H and the micro-pores within the C-S-H; (ii) the intrusion of C-S-H into the macro- and micro-pores between the quasicrystals and clay lamellae (see Figure 13b,c); and (iii) a wrapping of the quasicrystals by the C-S-H to form aggregates and the emergence of the macro-pores (between the aggregates) and micro-pores (within the aggregates) (see Figure 13d-f). The C-S-H was regarded as a porous medium with nano-scale pores of 0.5-2.5 nm [48]. The minimum pore size that the MIP test can detect is 3 nm; hence, the formation of C-S-H produced non-detectable pores (sorted into the micro-pores) within the C-S-H.