# Mechanical Properties of Cement-Treated Soil Mixed with Cellulose Nanofibre
## 5 Effect of CNF on Permeability
### Test Results  
Figure 16 shows the drainage rate per unit time and the chemically measured values for each day. Note that these values indicate the effluent collected at the time of measurement and not the accumulated effluent. The drainage rate per unit time, which indicates the permeability, showed that the permeability of the specimens with TEMPO-CNF was approximately 35% lower and that of the specimens with ACC-CNF was approximately 25% higher, depending on the type of CNF. It was not simply that the CNF itself clogged the pores and reduced the permeability. Figure 17 shows scanning electron microscopy (SEM) images of the permeable and non-permeable specimens. As shown in the images, the specimen with ACC-CNF-S contained fibrous material that could be considered as CNF, and the fibrous material formed a network. On the other hand, CNF did not appear in the specimen with TEMPO-CNF, because TEMPO-CNF has a high degree of fibrillation and cannot be observed at a magnification of 500 times. In any case, the amount of CNF added was found to be small and insufficient to close the pore space. The pore conditions of the soil particles were similar in all cases, and the reason for the change in permeability could not be determined from the SEM photographs. The reason for the change in permeability is not understood, although CNF may have influenced the cement hydration reaction, changing the amount of hydrate formed, or the hydrophilicity of the CNF itself may also have affected the permeability. Incidentally, a difference of 25-35% is not generally considered to be significant, as the permeability frequently varies by orders of magnitude depending on the pore conditions and the amount of cement added. It is necessary to conduct more tests on more specimens to improve the accuracy of the results. In other words, it could be said that the addition of CNF did not change the permeability significantly, at least on a per-digit basis.  
The pH, calcium ion concentration, and sodium ion concentration of the drainage water were also measured and are shown in Figure 16. The drainage was the result of the pore water in the treated soil being pushed out, which indicates the state of the pore water. The pH values were similar, indicating that the addition of CNF did not change the alkaline atmosphere of pore water, and that the environment in all specimens was conducive to cement solidification. The concentration of calcium ions was higher in the TEMPO-CNF specimens. The low permeability of the specimens may have resulted in a higher supply of calcium from the cement hydrate to pore water, or the calcium bound to the carboxylic groups may have been more easily leached than the cement hydrate. Sodium ions were detected early, but not thereafter. The fact that the base soil was marine clay and that the water content ratio was adjusted with artificial seawater suggested that the treated soil contained sodium. The concentration of sodium ions in the specimens with TEMPO-CNF was higher than that in the specimens without TEMPO-CNF, suggesting that the sodium bound to the carboxylic groups may have leached out. The effect of CNF was not apparent in terms of the chemical properties of the effluent.  
Figure 16: Chemical properties of drained water.  
Figure 17: SEM microphotograph of specimens.