## 3 Test Results and Analysis
### Changes in Compressive Strength After Freeze-Thaw Cycles  
The change in compressive strength of the specimen after different numbers of freeze-thaw cycles is shown in Figure 6. With the increase in the number of freeze-thaw cycles, the uniaxial compressive strength of the specimen gradually decreases. This is mainly due to the following reasons. On the one hand, the hardness of rubber is significantly smaller than that of concrete material. The addition of rubber replaces part of the concrete material, reducing the strength of the concrete. As an elastic material, rubber has a small support force, which affects the compressive strength of the concrete. On the other hand, as an organic material, the bond between rubber and concrete is poor, and the addition of rubber introduces more pores. All these reasons cause an increase in the internal voids of the concrete. When loading, it is more likely to occur in the gap, reducing the strength of the concrete. At the same time, the density of rubber is relatively small, and it is easy for it to float in the concrete specimen, resulting in an uneven distribution in the concrete specimen [43]. When a large amount of rubber is distributed in a certain place, stress concentration occurs, making the concrete structure unstable and more likely to be damaged. At the same time, as seen in the figure, among the three rubber particle sizes, 30-mesh rubber has the smallest impact on the reduction in concrete strength. After different numbers of freezing and thawing cycles, the trend of declining strength of the concrete group with rubber added is significantly smaller than that of ordinary concrete.  
In order to better obtain the change trend of specimen strength with the increase in freeze-thaw cycles, the strength deterioration value is introduced, and the strength deterioration value is calculated as shown below:  
\[k=\frac{F}{F_{0}}\times 100\% \tag{3}\]  
where \(k\) is the enhanced deterioration value; \(F\) is the strength value of the specimen after a certain number of freeze-thaw cycles, MPa; and \(F_{0}\) is the strength value of the specimen after a certain number of freeze-thaw cycles, MPa.  
The compressive strength deterioration value curve is shown in Figure 7. In the first 50 freeze-thaw cycles, the compressive strength decline is relatively gentle. After 50 freeze-thaw cycles, the decline in compressive strength begins to become obvious. Compared with ordinary concrete, rubber concrete shows less decline in strength. After 100 freeze-thaw cycles, the relative value of ordinary concrete compressive strength is lower than 70%. After 125 freeze-thaw cycles, the relative value of rubber concrete compressive strength is lower than 70%, while the relative value of ordinary concrete compressive strength is 0.55. This indicates that the addition of rubber makes the compressive strength degradation value of concrete in the process of freezing and thawing cycles decrease.  
Figure 6: Compressive strength of specimens after different numbers of freeze–thaw cycles.  
In order to better understand the influence of different rubber particle sizes on concrete specimens, research was carried out on specimens after uniaxial compressive damage after different freeze-thaw cycles.  
Figure 8 shows the damage diagram of the specimens after different numbers of freeze-thaw cycles. With the increase in the number of freeze-thaw cycles, the damage phenomenon of the specimen is more intense, the cracks and the degree of specimen crushing become more obvious, and the amount of specimen surface concrete spalling increases. When comparing the different groups during the test, it was found that ordinary concrete is more intact after crushing compared with rubberized concrete, and the sound of shattering is relatively quieter during specimen destruction, but more cracks are produced during compression.