# Influence of Five Additives on No Loading Swelling Potential of Red Clay
## 4 Conclusions  
In this study, the influences of different additives on the swelling potential of red clay were investigated. The following conclusions can be summarized from this paper:  
1. For cement, zeolite powder, blast furnace slag, steel slag and fly ash were added separately to red clay. Cement and steel slag can significantly reduce the swelling potential of red clay compared with the other three additives. The modification effect of cement can be reflected after a certain period of curing, whereas the modification effect of steel slag depends more on the increase in steel slag content. When cement is added to red clay, the cement clinker reacts with the water in the red clay to form a large number of CSH and CAH colloids. These colloids fill the pores in the red clay and bond the soil particles as a whole, which greatly improves the compactness of the clay, reduces the water absorption capacity of the clay, and improves the resistance to inhibit the swelling of the clay.
2. Adding steel slag can reduce the swelling potential of red clay without curing. The main reason for this is that Fe and Mn ions are adsorbed on the surface of negatively charged clay slices, so as to reduce the number of water molecules adsorbed by hydrogen bonds formed on the surface of the clay slices. Because the adsorption of ions on the surface of clay slices can be considered to occur at the same time when steel slag is added to red clay, the steel slag can immediately modify the swelling properties of red clay. SEM images show that the pozzolanic reaction in steel slag-modified specimens is similar to that in cement-modified specimens. A certain quantity of CSH and CAH colloids are formed, but this quantity is far less than that of cement.
3. According to the position and intensity of diffraction peaks of clay minerals shown in XRD patterns, the diffraction peak relative intensity of kaolinite in steel slag-modified clay and cement-modified clay is higher than that in red clay. Therefore, the addition of steel slag and cement can change the relative content of clay minerals in red clay, reduce the relative content of hydrophilic clay minerals such as montmorillonite and illite, and increase the relative content of kaolinite. The content of nonhydrophilic clay minerals in red clay increases relatively, and the water stability of red clay is also improved. The above phenomenon is more obvious in cement-modified clay than in steel slag-modified clay.
4. When steel slag is added alone, it causes a decrease in the water content in the specimen, and then causes a large loss of cohesion in the short term. After a certain curing period, the cohesion of the steel slag-modified specimen can be restored due  
Figure 5: Cohesive strength and internal friction angle of red clay and cement/steel slag-modified specimens: (**a**) the cohesive strength of specimens; (**b**) internal friction angle of specimens.  
to the bonding effect of CSH and CAH colloids caused by the pozzolanic reaction in the steel slag modified-specimen. The production of CSH and CAH colloids in the cement-modified specimen is much higher than that in the steel slag-modified specimen, so the cohesion of the cement-modified specimen can be greatly improved after a certain period of curing.  
Conceptualization, Z.Q. and B.Y.; methodology, B.Y.; validation, B.Y. and Z.Z.; formal analysis, B.Y.; investigation, B.Y. and Z.Z.; resources, Z.Q.; data curation, B.Y.; writing--original draft preparation, B.Y.; writing--review and editing, B.Y.; visualization, B.Y.; supervision, Z.Q.; project administration, Z.Q.; funding acquisition, Z.Q. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The study did not require ethical approval.  
The study did not involve humans.  
Not applicable.  
The authors declare no conflict of interest.