# Mechanical Properties of Cement-Treated Soil Mixed with Cellulose Nanofibre
## 2 Materials and the Mixture Method
### Mixture Procedure of Soil, Cement, and CNF  
#### 2.3.1 Method 1  
An attempt was made to add and mix CNF uniformly into the soil-cement mixture in the laboratory. This was performed to reduce the variation between the specimens and to confirm the effect of CNF in the treated soil mixed with CNF. Figure 1 shows the procedure used to prepare the specimens. Three types of CNFs in gel form (TEMPO-CNF, ACC-CNF-S, and ACC-CNF-B) were prepared and watered. Considering the possibility that the gelatinous material might not be mixed uniformly into the soil, water was added until it was no longer gelatinous to ensure uniform mixing. Cement slurry was also prepared by adding water to ordinary Portland cement. As shown in the mixture procedure (Figure 1), the CNF solution and cement slurry were mixed first and then added to and mixed with dry and powdered Kasaoka clay. The reason for mixing the powdered clay with the CNF solution and cement slurry is that if they were mixed with the wet soil, too much water would be present in the treated soil, and a large quantity of cement would be needed to solidify the soil. As this is not practical, the mixing of CNF and cement into wet clay was attempted using Method 2.  
The soil mixer used for mixing was of 5 L capacity in accordance with JIS R5201 [20], with a mixing time of 5 min. Figure 2 shows the soil treated immediately after mixing. As shown in the figure, it can be observed that the flowability of the mixture without CNF is high, whereas that of the mixture with CNF is low. This was due to the water absorption and thickening properties of the CNFs. However, cement was considered to have been well mixed because of its high fluidity at a high strain rate near the agitator blades, which was induced by the thixotropic nature of CNF. The mixed soil was packed in unconfined compression test moulds (50 mm diameter \(\times\) 100 mm height cylindrical) and cured in a constant-temperature curing room at 20 \(\pm\) 2 \({}^{\circ}\)C and a humidity of more than 95% for a specified period.  
\begin{table}
\begin{tabular}{c c c} \hline  & **Kasaoka Clay** & **Kawasaki Clay** \\ \hline Soil particle density, \(r_{\mathrm{s}}\) (g/cm\({}^{3}\)) & 2.700 & 2.671 \\ Initial water content, \(w_{i}\) (\%) & 6.8 & 61.8 \\ Gravel fraction (2–75 mm) (\%) & 0.0 & 0.0 \\ Gain size & Sand fraction (75 μm–2 mm) (\%) & 1.1 & 13.1 \\ Silt fraction (5–75 μm) (\%) & 40.1 & 46.9 \\ Clay fraction (\(<\)5 μm) (\%) & 58.8 & 40.0 \\ Fine fraction content, \(F_{c}\) (\%) & 98.9 & 86.9 \\ Liquid limit, \(w_{L}\) (\%) & 62.1 & 41.0 \\ Plastic limit, \(w_{P}\) (\%) & 20.6 & 23.1 \\ Plasticity index, \(I_{P}\) & 41.5 & 17.9 \\ \hline \end{tabular}
\end{table}
Table 2: Physical properties of soils.  
Table 3 shows the mixing proportions of cement, CNF, water, and soil for the treated soil prepared by Method 1. When CNF was added, the ratio of the dry weight of CNF to the dry weight of soil was defined as the CNF addition rate, \(\alpha\), which was set to \(\alpha=1.0\%\). The reason for setting \(\alpha=1.0\%\) is that in a previous study, the effect of CNF was not clearly visible unless it was mixed with \(\alpha=1.0\%\). Cement was added in the ratio of approximately 100 kg dry weight per unit volume of soil mixed with all other materials except cement. The dry weight ratio of cement to soil was 13.8%. This was slightly less than the amount added in the deep mixing method, which is one of the most common ground improvement methods used on site. Cement was not added as a powder but as a cement slurry. The water-cement ratio was set to \(w/c=7.0\). Considering the water contained in all soil mixtures, the water content ratio was approximately 85%. The treated soil mixed using Method 1 was subjected to unconfined compression tests, and the test results are discussed in Section 3.  
Figure 1: Mixture procedure for preparing specimens (Method 1).  
Figure 2: Appearance immediately after mixture by Method 1.