## 1 Introduction
Based on scanning electron microscopy (SEM), the effects of pore size, connectivity, and distribution on permeability were analyzed and the relationship between hydraulic gradient, flow velocity, and pore distribution was established. [PERSON] et al. [25] studied the effect of pore tortuosity on the permeability of PC and proposed relative pore size and pore tortuosity indices. Relative pore size and pore tortuosity were introduced into the Kozeny-Carman model to assess permeability. At the same time, the effect of mortar workability, aggregate size, and aggregate-binder ratio on permeability was tested. The experimental results showed that the workability of cement affected the porosity tortuosity and aggregate size affected the connectivity of pores. The aggregate-binder ratio was directly related to effective porosity. [PERSON] et al. [26] studied the relationship between the split tensile strength and compressive strength of PC. The strength experiment was conducted with specimens molded in the lab and core samples obtained from actual pavement. The results showed that the type of aggregate had a great influence on the strength of PC. Based on the experimental data, a relationship between split tensile strength and compressive strength was proposed. [PERSON] and [PERSON] [27; 28] analyzed the influencing factors of compressive strength with different aggregate sizes and aggregate-binder ratios. The results indicated that strength decreased with increased aggregate size. The aggregate-binder ratio affected strength by affecting porosity. A semi-empirical prediction equation for PC compressive strength was established. The effects of cementitious material strength, total porosity, aggregate size, and average pore size on compressive strength were also studied. [PERSON] et al. [29] produced a high-strength PC that was formed by making a certain number of vertical cylindrical holes 4 mm in diameter on high-strengthconcrete specimens. In the test, porosity was 1.3-2.8%, measured compressive strength was over 70 MPa, tensile strength was 10 MPa, and the water permeability coefficient reached 13-22 mm/s. [PERSON] et al. [30] studied the relationship between microscopic pore structure and macroscopic properties of PC through scanning technology and the finite element method. 20% porosity concrete specimens were made in the lab. The pore size, distribution, and shape were obtained. Based on scanning images, the finite element model of PC was established. Strength and elastic modulus calculated by finite element model were compared with the measured values. The results showed that the accuracy of the established model was satisfied. [PERSON] et al. [31] established PC discrete element constitutive law based on cementation between aggregate and cement paste. The effectiveness of the method was verified by the experiments with different aggregate types, grading curves, and aggregate-to-binder ratios. Based on the mathematical approach and the finite element method, [PERSON] et al. [32] established the prediction model of permeability with the microstructure parameters (pore size, pore distribution) of PC. The predicted values of the model were consistent with the measured values. The existing studies are mainly focused on the design of mixed ratios, mechanical properties, and permeability. The test parameters (such as aggregate size, water-binder ratio, and porosity) adopted are different, which results in a great difference among studies. For example, most researchers use mono-sized coarse aggregate, but some researchers adopt continuous-graded coarse aggregate. However, there are few studies concentrating on the influence of coarse aggregate size, water-binder ratio, and porosity on mechanical strength, permeability, and freeze-thaw durability of PC. It is necessary to carry out systematic and comprehensive research.