The objective of this research is to evaluate the pavement performance degradation of nano-TiO 2 /CaCO 3 and basalt fiber composite modified asphalt mixtures under freeze-thaw cycles. The freeze-thaw resistance of composite modified asphalt mixture was studied by measuring the mesoscopic void volume, stability, indirect tensile stiffness modulus, splitting strength, uniaxial compression static, and dynamic creep rate. The equal-pitch gray prediction model GM (1,3) was also established to predict the pavement performance of the asphalt mixture. It was concluded that the high-and low-temperature performance and water stability of nano-TiO 2 /CaCO 3 and basalt fiber composite modified asphalt mixture were better than those of an ordinary asphalt mixture before and after freeze-thaw cycles. The test results of uniaxial compressive static and dynamic creep after freeze-thaw cycles showed that the high-temperature stability of the nano-TiO 2 /CaCO 3 and basalt fiber composite modified asphalt mixture after freeze-thaw was obviously improved compared with an ordinary asphalt mixture. adhesion between the asphalt binder and sensitive aggregate against moisture damage [4]. Nano-TiO 2 is a commonly used nanomodified material. Shafabakhsh et al. found that nano-TiO 2 could effectively improve the viscosity, anti-rutting, and anti-fatigue properties of asphalt mixture [5]. Sadeghnejad et al. used nanomaterials to modify SMA and the test results showed that nano-TiO 2 could improve the anti-rutting ability and splitting strength ratio and prolong the service life of an asphalt mixture [6]. Nazari et al. evaluated the microstructure and chemical properties of nanocomposite modified asphalt by X-ray and scanning electron microscopy. It was found that the addition of nanomaterials improved the fatigue resistance of asphalt mixture [7].There are many kinds of fiber modifiers used in asphalt mixtures in recent years, such as polyester fiber, lignin fiber, carbon fiber, glass fiber, basalt fiber, etc. Different fiber modifiers have their own advantages and disadvantages. The low-temperature crack resistance of asphalt mixture is the main problem in the frozen region of northeast China. Compared with other fibers, basalt fiber is a mineral fiber that is abundant and easy to obtain in northeast China. Also, it will not cause environmental pollution. Basalt fiber has some advantages in terms of modifying road performance of asphalt mixtures. Zheng studied the pavement performances of basalt fiber, lignin fiber, and polyester fiber modified asphalt mixtures and found that the performance of the basalt fiber modified asphalt mixture was superior to that of the others [8,9]. Morova et al. studied the usability of basalt fibers in order to bear the stresses occurring at the surface layer of pavement and the optimum value of the fiber ratio leading to the optimum stability value was determined [10]. Chen found that basalt fiber, at the optimal fiber content, could improve the water stability and high-temperature stability of the asphalt mi...

Culvert is an important part of roads whose healthy operation is related to the efficiency and safety of road transportation. Therefore, it is very important to evaluate the safety of culvert structure by load test. Four types of prefabricated reinforced concrete box culverts (integral BC, round hinged BC, flat seam BC, and mortise BC) were designed in this paper. By designing a scale model test, the sensor system was used to test the mechanical properties of BC, which included dial indicators, strain gauges, and a pressure sensor. The finite element analysis based on material nonlinearity and contact nonlinearity of round hinged BC and integral BC was carried out. After validating the finite element models, mechanical properties of reinforcement and concrete of BCs were analyzed. The experimental results show that the failure mode of BC was tensile failure of concrete at the bottom of top slab under bending action, and integral BC had the maximum carrying capacity. The contact behaviour of sliding and rotating at hinge joints caused the first principal tensile stress of concrete at the internal surface of the side wall below hinge joints.

The modifiers NTC (nano-TiO2/CaCO3) and BF (basalt fiber) were adopted to modify a base matrix asphalt mixture. The base matrix asphalt mixture and three kinds of modified asphalt mixture under F–T (freeze–thaw) cycles were scanned by computed tomography. The air voids and morphological changes of asphalt mixture were summarized by image processing technology, and the development process of F–T damage to asphalt mixture was explained from a micro-view. The porosity of NTC-modified asphalt mixture changed little, and the void distribution between base matrix asphalt mixture and NTC-BF (nano-TiO2/CaCO3 and basalt fiber) composite modified asphalt mixture was more uniform. The macro-pores in the asphalt mixture under 15 F–T cycles began to connect gradually, and the pore characteristics also changed. The number and shape of the pores changed under 15 F–T cycles. According to the state characteristics, the change amplitude of the pore characteristics of matrix asphalt mixture and NTC-BF composite modified asphalt mixture were the most stable under F–T cycles.

This research optimizes the mix ratio of nano-TiO2/CaCO3 (NTC)-basalt fiber (BF) composite modified asphalt mixture. Based on the Box–Behnken method and the response surface method, a three-factor and three-level test was designed. The input indicators were the asphalt–aggregate ratio, NTC content, and BF content. The output indicators were the density, air voids, Marshall stability, flow value, voids in mineral aggregate (VMA), and voids filled with asphalt (VFA) values of the asphalt mixture. The response surface model was established according to the test response index value. Then, the function was fitted through multiple regression equations and multivariate analysis of variance was performed. Finally, according to the specification requirements and engineering needs, the selected conditions of each response value were determined to optimize the asphalt–aggregate ratio and the contents of NTC and BF, and the predicted values were verified through the measured data. The test results show that the optimal contents of NTC and BF and the optimal asphalt–aggregate ratio were 5.1%, 3.9%, and 5.67%, respectively. By comparing the measured Marshall test index value with the predicted value, the minimum relative error was 0.096% and the maximum error was 6.960%. The results show that response surface methodology can be used to optimize the mix ratio of composite modified asphalt mixtures.

No abstract