# Mechanical Properties of Cement-Treated Soil Mixed with Cellulose Nanofibre
## 6 Conclusions  
This study investigated methods of mixing CNF, the increase in strength and the reduction of variability by adding CNF, and the change in permeability. The results can be summarised as follows:  
1. The method of mixing either the soil or the additive (cement, CNF) in a dry state was attempted to reduce the amount of water in the treated soil. Both methods could be used, but for on-site mixing, it was considered more practical to mix cement and CNF in dry powder or highly concentrated gel form.
2. During the mixing of cement and soil, the water absorption and thickening properties of the CNF reduced the flowability, but as a result, it was possible to mix the cement evenly, which was probably because of the other effects at work. In addition, when the mixing time was extremely short, unevenness was observed between the solidified portions and those that did not solidify in the specimen without CNF, whereas the treated soil was produced uniformly in the specimen with CNF.
3. In regard to the strength development characteristics over time, it was found that the mixture of CNF increased the strength at the initial age, but it reduced the strength development in the long term. Increasing the initial strength and reducing the long-term strength can be advantageous for cement treatment. Observation of the sheared surface showed that a fibrous material, which was considered to be CNF, was widely mixed in the specimens to which CNF with a relatively low degree of friability was added.
4. The effect of shortening the mixing time on the variation in the strength of CNF was investigated. It was observed that the cement tended to mix more evenly in the treated soil with CNF, and the average strength ratio at 28 days of age was 5.1 (strength with CNF/strength without CNF). The coefficients of variation of the strength and failure strain were also smaller when CNF was added. Reducing the variation in the strength of the treated soil has the advantage that the amount of cement added can be reduced, and unwanted high-strength treated soil is not produced.
5. The addition of CNFs increased the flexural strength. This could be attributed to the increased tensile strength. Fibrous material appeared on the tensile fracture surface of the specimen to which CNF with low fibrillation was added. The low flexural and tensile strength is one of the drawbacks of cement-treated soil, and this problem could be solved.
6. The addition of CNF caused a slight change in permeability, although the number of tests in this study was not sufficient to determine a clear effect. It would suggest that the addition of CNF does not significantly change the permeability. The pore water conditions were estimated from the effluent, and it was found that the alkaline atmosphere was the same regardless of the presence or absence of CNF.  
Thus, the addition of CNF to cement treatment had beneficial effects, depending on how it was used. This result is a quantum leap forward in encouraging the use of CNF in cement-treated soil. However, at present, the production volume of CNFs is limited, and their unit price is high. When CNFs are used in large quantities for civil engineering, the production volume will increase, and the price will decrease significantly. In practice, the price must be reduced before CNFs can be utilised. In addition, it is important to conduct trial mixing tests before the actual addition of CNF in the field, as the degree of effectiveness and properties may vary depending on the type of soil and the type of CNF. Moreover, if the chemical mechanism, although complex, can be clarified, it will be possible to add CNF more reliably to achieve the required effect. More detailed investigations of properties other than strength and permeability will be conducted in the future.