# Influence of Five Additives on No Loading Swelling Potential of Red Clay
## 3 Results and Discussion
### No Loading Swelling Ratio Test
When the curing time was 28 days, the swelling ratio of specimens with 3% cement content was lower than that of specimens with 15% cement content and a curing age of 7 days, which indicates that prolonging the curing age is a better choice to improve the cement modification effect than increasing the cement content. If the curing time is not long enough to hydrate the cement clinker and water in the red clay, increasing the cement content will result in a waste of cement clinker. In addition, a portion of the cement does not produce CSH and CAH colloids, and this portion of the cement clinker will absorb water from the outside of the clay and continue to react when the clay meets water, which will result in negative effects on the water stability of the red clay. Under 28 days of curing, the change in the soil swelling ratio is no longer obvious when the cement content reaches 6%. Therefore, under the condition of long-term curing, if the water content of the soil is not sufficient, a large amount of cement is not required to modify red clay. The appropriate amount of cement can fully enable the reaction potential of water content in clay and reduce possible cement waste. Compared with the case in which the swelling ratio of specimens with cement increased under the condition of no curing, the swelling ratio of specimens with steel slag was lower than that of red clay specimens without additives under the condition of no curing. In addition, the swelling ratio of specimens with steel slag in all three curing ages showed an overall trend of decreasing with the increase in steel slag content. There was no situation in which the modification effect of the clay swelling potential was no longer obvious after the content of the additive reached 9% when the cement-modified specimens were cured for 7 and 28 days. Figure 2: _Cont._  
Figure 2: The change in the no loading swelling ratio of specimens with different additives relative to the red clay specimen: (**a**)-cement, (**b**)-steel slag, (**c**)-blast furnace slag, (**d**)-fly ash, (**e**)-zeolite. The value of the change in the no loading swelling ratio of the cement and steel slag-modified specimens compared with the red clay specimen without additives was set as the dependent variable (the swelling ratio decreases to a positive value and increases to a negative value) in the binary linear regression equation between the improvement effect of the two additives, and the curing time and additive contents. The linear regression coefficient was calculated according to the following equations:  
\[a_{1}=-\frac{l_{1y}l_{22}-l_{2y}l_{12}}{l_{11}l_{22}-l_{12}^{2}} \tag{1}\]  
\[a_{2}=-\frac{l_{2y}l_{11}-l_{1y}l_{21}}{l_{11}l_{22}-l_{12}^{2}} \tag{2}\]  
where:  
\[l_{ij}=l_{ji}=\sum{(x_{i}x_{j})}-(\sum{x_{i}}{\sum{x_{j}}})/k\]  
\[l_{iy}=l_{ji}=\sum{(x_{i}y_{i})}-(\sum{x_{i}}{\sum{y_{i}}})/k\]  
and \(k\) is the number of test groups. After calculation using Equations (1) and (2), the values of \(a_{1}\) and \(a_{2}\) of cement-modified specimens were 3.26 and \(-1.05\), respectively. The values of \(a_{1}\) and \(a_{2}\) of steel slag-modified specimens were 0.34 and 3.54, respectively. Through calculation, it was again verified that, when steel slag is used to modify red clay, the influence of the steel slag content is more significant than that of curing time, and for cement, the influence of curing time is more significant than that of the cement content. From the above results, it can be concluded that, when steel slag modifies the swelling potential of red clay, the main modification mechanism is not a hydration reaction like that in cement. Combined with the XRF test results, both cement and steel slag contain a large amount of the Ca element, and the contents of Si and Al in steel slag are lower than those in cement, but there are sufficient quantities of Si and Al in red clay. This shows that the relative lack of Al and Si in steel slag is not the main reason for its weak pozzolanic reaction.