# Study on Frost Resistance of the Carbon-Fiber-Reinforced Concrete
## 3 Results and Discussion
### Frost Resistance of CFRC  
In the frost resistance tests, the effects of the fiber content on the mass loss ratio and the compressive strength are shown in Tables 5 and 6 and Figures 5 and 6, respectively. The PC showed a maximum mass loss of 3.79% after 300 cycles. Before 100 cycles, the PC displayed a moderate mass loss. Between 100 and 250 cycles, the PC displayed a slow mass loss. In contrast, after 250 cycles, the PC displayed a significant mass loss. The CF0.25 yielded a moderate mass loss at 1.64% after 300 cycles. As shown in Figure 5 and Table 5, after 300 cycles, the mass losses of CF0.50, CF1.00, CF1.50, and CF2.0 were 0.98%, 0.82%, 0.86%, and 0.93%, respectively. When the carbon fiber content was greater than 0.5 wt.%, the mass loss of the CFRC decreased significantly, but the decreases were less than 1%. However, when the carbon fiber content was greater than 0.5 wt.%, the mass loss of the CFRC did not change significantly with the increase in the fiber amount.  
Figure 6 shows that the compressive strength of PC decreases with the number of freeze-thaw cycles. After 150 cycles, the decline of the PC compressive strength was 36.6%. According to GB/T 50082-2009 [14], the frost-resistance mark of the concrete should be based on the maximum number of freeze-thaw cycles after which the compressive strength loss rate was not greater than 25% or the mass loss rate was not greater than 5%. Therefore, the frost-resistance mark of the PC was 100 freeze-thaw cycles, after which the compressive strength loss was 21.2%. After 100 and 150 cycles, the compressive strength values of the CF0.25 declined by 9.0% and 26.1%, respectively. The frost-resistance mark of the CF0.25 was also 100 freeze-thaw cycles, but the degree of decrease of the compressive strength was significantly less than that of the PC. For the CF0.50, the frost-resistance mark was improved to 150 cycles, and the strength loss was 11.8%. The strength losses of the PC, CF0.25, and CF0.50 showed steep declines after the maximum number of freeze-thaw cycles. The CF1.00, CF1.50, and CF2.00 showed high frost resistance performances with frost-resistance marks of 200, 250, and 250 cycles, respectively. After 200 and 250 cycles, the compressive strengths of the CF1.00 were 85.0% and 73.3%, respectively. After 250 cycles, the strength losses of the CF1.50 and CF2.00 were 20.2% and 22.8%, respectively.  
Generally, the frost-resistance mark of concrete exhibited an increasing trend with the increase in the carbon fiber content before 1.5 wt.%. When the carbon fiber content was greater than 1.5 wt.%, the frost resistance of concrete did not improve further. When the water in pores suffered from frost, its volume swelled by about 9%, which would cause tensile stress and the formation of microcracks [2]. Therefore, the compressive strengths of the concrete showed decreases with the increase in the number of freeze-thaw cycles [2]. The improvement in the frost resistance of the carbon-fiber-reinforced concrete can be explained as the tensile resistance of the fibers that shared the stress of the cement matrix and prevented the formation of cracks. Therefore, the appropriate addition of carbon fibers can improve the frost resistance of concrete. Based on the cost, 1.50 wt.% is an optimal carbon fiber addition.  
Figure 5: Mass losses of the carbon-fiber-reinforced concrete (CFRC) after different numbers of freeze-thaw cycles. CF, carbon fiber; PC, plain concrete.  
Figure 6: Effect of carbon fiber content on the compressive strength. CF, carbon fiber; PC, plain concrete.