# Durability Investigation of Fiber-Reinforced Functionally Graded Concretes in Cold Regions
###### Abstract
The anti-freezing performance of the polycarboxylate superplasticizer was better than that of the naphthalene superplasticizer [14]. [PERSON] [15] studied the effect of fly ash content on the freeze-thaw cycles and frost resistance of steel-polypropylene fiber concrete. [PERSON] [16] discussed the hydration heat behavior of limestone powder-slag-fly ash-cement composite cementitious materials. The 7 d hydration heat first increased and then decreased with the increase in the water-cement ratio. Fiber-reinforced concrete has received extensive attention from researchers and engineers, mainly because of its good mechanical and deformation properties. However, the distribution of fibers in concrete has been uniform in the studies on fiber-reinforced concrete thus far [17; 18; 19; 20]. [PERSON] [21] studied the penetration resistance and explosion-proof performance of ultrahigh-performance concrete (UHPC) with a single-layer and functionally graded structure. The results showed that the fiber-reinforced target maintained good integrity in damage distribution. [PERSON] et al. [22] tested and simulated the fracture behavior of different combinations of layered plain concrete and synthetic-fiber concrete. Functional gradient analysis can combine the advantages of different materials according to the design requirements to prepare materials with superior performance. For the high-pressure and water-rich environment faced by the concrete of the Wuhan Yangtze River Tunnel, [PERSON] et al. of the Wuhan University of Science and Technology [23] established a gradient concrete pipe section (FGCS) structural system and carried out a layered design for the shield tunnel lining pipe, with a high-permeability layer (cement-based material without meso-interface transition zone (MIF)), structural layer, and fire-proof and explosion-proof layer. [PERSON] et al. of Zhengzhou University [24] also produced three-layer gradient structure samples. They studied the effects of component gradient distribution in the interface region on the mechanical properties of cement-based material layered structures. The results showed that the gradient distribution can effectively relieve the residual stress at the interface, thereby improving the mechanical properties of the whole structure. The current research mainly focuses on the mechanical properties, impermeability, fire resistance, and corrosion resistance of concrete itself. However, there are few studies on the durability of mass concrete structures. Frost- and crack-resistant bulk concrete needs to have a good service performance, and it also needs good stability and durability. Bridges in cold regions serve for a long time under harsh conditions, and the evolution of the performance of frost- and crack-resistant bulk concrete in this long-term process has an important impact on the standard service of the entire bridge structure. This paper determined the proportions of functional gradient concrete after many optimized proportioning tests. Experimental studies were conducted for the long-term performance of concrete in various parts of the bearing and pier, including shrinkage and cracking resistance, seepage and frost resistance, and carbonation resistance. Furthermore, the feasibility and applicability of the functional gradient concrete design concept for bridge buildings in alpine regions were analyzed and verified by comparing the results of model tests with different concrete ratios. Currently, the research on functionally graded concrete is limited to the theoretical and experimental research stage. However, due to the large amount of concrete applied in general practical engineering, how to adopt advanced preparation technology and interface treatment technology is the key to measuring the performance of gradient concrete and determining the future development directions.