# Influence of Five Additives on No Loading Swelling Potential of Red Clay
## 3 Results and Discussion  
### No Loading Swelling Ratio Test  
The variation in the swelling potential (the relative change in the no loading swelling ratio of specimens containing different additives compared with red clay specimens, taking a positive value when increasing and a negative value when decreasing) is shown in Figure 2.  
Under three different curing conditions, the no loading swelling potential of steel slag-modified clay generally showed a more obvious decrease with the increase in steel slag content. Compared with the red clay without additives, the swelling potential of the fly ash-modified specimens and zeolite powder-modified specimens did not achieve the effect of reducing the swelling potential because of the lack of lime in the clay. The XRF test showed that the main components of zeolite and fly ash are SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\). This indicates that their functions in pozzolanic reactions are similar. When zeolite powder and fly ash are used as additives, due to the lack of calcium ions, the pozzolanic reaction is not sufficient to produce CSH and CAH colloids, so it cannot effectively reduce the swelling potential of red clay. Because of the hygroscopicity of Al\({}_{2}\)O\({}_{3}\), the soil expansion potential increased slightly after the addition of zeolite powder and fly ash. The no loading swelling potential of the blast furnace slag-modified specimen did not show a significant decline. Combined with the XRF test results, the blast furnace slag used in this test was alkaline slag with high CaO content, and its composition is similar to that of cement, but they have different effects on the swelling potential of red clay. This shows that the pozzolanic activity of blast furnace slag is far lower than that of cement. If blast furnace slag is used to improve the swelling potential of red clay, some methods need to be used to stimulate its reaction potential. It can be observed from the above figure that the cement can significantly inhibit the swelling potential of red clay under the curing times of 7 and 28 days, but cement-modified clay specimens without curing resulted in swelling potential that exceeded that of the no-additive clay specimens. Adding steel slag can greatly reduce the no loading swelling potential of specimens without curing. However, with the increase in curing age, the swelling potential of specimens to which steel slag was added did not decrease further. This shows that the mechanisms of cement and steel slag used as additives to reduce the swelling potential of red clay are different. The cement-modified specimens having a curing age of 28 days showed a further decrease in the swelling potential compared to the specimens with the same cement content with 7 days' curing. In other words, when cement  
Figure 1: The specimen in the stainless steel ring (**left**) and schematic of the test setup used for the no loading swelling ratio test (**right**). is used as an additive, it needs a certain curing time to show the effect of reducing the swelling potential of red clay, and the longer the curing time, the better the effect. Without curing, or when the curing time is insufficient, a large number of unhydrated cement clinkers will no longer hydrate with the water distribution in the soil after immersion, but will directly absorb the outside water to form CSH and CAH colloids, which will promote the expansion of the clay. After curing the cement-modified specimens for a long enough period, sufficient parts of the clinker can react with the water in the clay. The hydration products are generated to fill the pores of the red clay, bond the red clay particles, reduce the water absorption of the red clay, and increase the resistance of the red clay expansion. When the cement content exceeded 9%, the swelling rate of specimens rose slightly, which indicates that the hydration reaction of cement is limited due to the limited water content in the soil.