# Durability Investigation of Fiber-Reinforced Functionally Graded Concretes in Cold Regions
## 3 Conclusions  
This research demonstrates the bridge engineering applicability of functional gradient concrete in cold regions. As a result, the following conclusions can be drawn:  
1. The concept of differentiated design was presented between external and internal concrete abutment pairs. The durability of the internal concrete of the bridge with an anti-freezing, shrinkage-reducing polycarboxylic acid water reducing-agent, and of the external concrete of the bridge with imitation steel fiber, was analyzed. It was verified by the shrinkage test, early cracking resistance test, and long-term performance studies of attributes such as anti-freezing, seepage resistance, and carbonation resistance. Furthermore, the durability performance of the formulated anti-freezing and anti-cracking mass concrete was analyzed and verified. 2. A large amount of mineral admixture concrete in the core of the casting body and micro-expansion anti-freezing concrete in the outer ring of the casting body can effectively improve the shrinkage resistance of concrete, enhancing the early cracking resistance and improving the durability of the concrete. All of the above technological methods meet the practical requirements of early strength, anti-freezing and anti-cracking, and internal reduction in the heat of hydration of mass concrete for bridges in cold regions. 3. Ratio #4 with the maximum amount of cement had the most extensive drying shrinkage, which was 321.7 \(\times\) 10\({}^{-6}\) for 28 d and 345.1 \(\times\) 10\({}^{-6}\) for 60 d. Increasing the \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**\#1** & **Average** & **Carbonation Depth (mm)** & \multicolumn{3}{c}{**\#2** & **Average** & **Carbonation Depth (mm)**} & \multicolumn{3}{c}{**\#3** & **Average** & **Carbonation Depth (mm)**} \\ \hline
3 d & 7 d & 14 d & 28 d & 3 d & 7 d & 14 d & 28 d & 3 d & 7 d & 14 d & 28 d \\
3.7 & 4.8 & 6.3 & 6.7 & 2.3 & 3.2 & 4.4 & 4.8 & 2.5 & 3.3 & 3.4 & 3.5 \\ \hline
**\#4** & **Average** & **Carbonation Depth (mm)** & \multicolumn{3}{c}{**\#5** & **Average** & **Carbonation Depth (mm)**} & \multicolumn{3}{c}{**\#6** & **Average** & **Carbonation Depth (mm)**} \\ \hline
3 d & 7 d & 14 d & 28 d & 3 d & 7 d & 14 d & 28 d & 3 d & 7 d & 14 d & 28 d \\
3.4 & 4.2 & 5.2 & 5.7 & 2.2 & 2.5 & 2.7 & 2.8 & 2.2 & 2.3 & 2.5 & 2.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Concrete carbonation performance test results. admixture of fly ash and mineral powder can effectively slow the concrete shrinkage rate and reduce the shrinkage value. The lowest self-drying shrinkage was found for ratio #3 of C35-bearing concrete, with a shrinkage value of 132.1 \(\times\) 10\({}^{-6}\) at 28 d. The self-drying shrinkage value only increased by 8.6% at 60 d, and then stabilized. For C40 abutment concrete, #6 had the lowest self-drying shrinkage rate, with a shrinkage value of 169.4 \(\times\) 10\({}^{-6}\) at 28 d. The drying and autogenous shrinkage rates of anti-freezing and anti-cracking concrete mixed with the anti-freezing and shrinkage-reducing polycarboxylic acid water reducer were significantly reduced. At the same time, the crack resistance grade of #3 and #6 reached grade V, which was significantly higher than that of #2, #4, and #5. The addition of steel fiber can significantly improve the crack resistance of concrete and effectively inhibit the generation and development of dry shrinkage and early cracks. 4. The 28 d chloride ion diffusion coefficient of concrete with mixture ratios #2, #3, #5, and #6 was less than 3.0 \(\times\) 10\({}^{-12}\) m\({}^{2}\)/s, significantly improving the chloride ion penetration resistance ability compared with ordinary concrete of the same grade. The admixture of mineral powder can effectively increase the compactness of concrete, hinder the diffusion of chloride ions, and improve the impermeability of concrete.