# Durability Investigation of Fiber-Reinforced Functionally Graded Concretes in Cold Regions
###### Abstract  
Introducing the differential design concept of functional gradient into mass concrete structures is a feasible design concept that can meet the requirement of crack resistance and internal hydration heat reduction for mass concrete in cold regions. This study analyzed functionally graded concrete's long-term performance and durability behavior through experimental tests. Based on various concrete mix proportion designs, six concrete groups were selected to test. The shrinkage performance tests were conducted according to the specifications, and early crack resistance tests were also carried out. In addition, the crack development characteristics of concrete with different mix proportions were compared and analyzed, and the impermeability, frost resistance, and carbonation resistance tests were conducted. The test results show that concrete's long-term performance and durability can be effectively improved by adopting the functional gradient concrete design. The functional gradient concrete adds an anti-freezing polycarboxylate superplasticizer, steel fiber, and polypropylene fiber. Therefore, it can better meet the actual needs of mass concrete structures in cold regions. The drying and autogenous shrinkage rates of mass concrete structures mixed with a composite water reducer were significantly reduced. As a result, this method effectively improved the microporous structure, reduced the loss of dynamic elastic modulus, and improved the anti-freezing performance of concrete of various strength grades. Furthermore, adding steel-like fiber and monofilament polypropylene fiber to the concrete outside the structure can improve the crack resistance of concrete and effectively inhibit the occurrence and development of dry shrinkage and early cracks. Therefore, it can better meet the actual needs of mass concrete structures in cold areas. functional gradient concrete; long-term performance; durability; shrinkage tests +
Footnote †: journal: Applied Sciences  
of mineral admixture and heat-of-hydration reducing agent in the internal temperature control of the concrete. On the other hand, it can give full play to the imitation steel fiber, polypropylene fiber, and expansion agent in the early stress concentration on the upper surface and outside of the concrete to improve the role of the anti-freezing agent in the frost resistance of the concrete [7; 8]. It can also meet the need for early anti-freezing and anti-cracking of external concrete, while effectively reducing the heat of hydration and avoiding excessive temperature stresses leading to cracking of the cast body. [PERSON] et al. [9] evaluated the performance of the functionally graded reinforced-concrete beams exposed to cyclic loading. The reinforced concrete increased the dissipated energy due to the applied cyclic loading. [PERSON] et al. [10] investigated functionally graded concrete using red mud and fly ash. The test results indicated that 10% red mud and fly ash is the optimal value for concrete beams, based on a load-deflection curve. [PERSON] et al. [11] used numerical design methods to develop the gradation layout, and described tests performed on functionally graded beams. Numerical simulations subsequently replicated the test results and calibration based on the principle of topology optimization. [PERSON] et al. [12] introduced stepwise layered and continuously graded concrete systems, and investigated concrete mix combinations. The graded concrete's durability, fracture resistance, strength, ductility, cost-effectiveness, weight reduction, and lower embodied energy improvements were discussed. Finally, [PERSON] et al. [13] investigated the impact resistance of functionally graded reinforced concrete (FGRC) without conventional reinforcement under drop weight and projectile impact. The test results revealed that employing functionally graded reinforced concrete reduces the penetration depth and destroys the front and back areas.