###### Abstract
The parametric modeling method can easily change the internal structure parameters while parameterizing the internal structure information to establish a numerical model, which provides the possibility to solve the above problems. As a typical representative of parametric modeling methods, the concrete random aggregate modeling method (CRAMM) has been widely used because it is clear and convenient in modeling. However, the existing CRAMMs have many shortcomings in the application to the study of the relationship between pore structure parameters and concrete mechanical properties. Most existing concrete random aggregate models (CRAMs) ignore pores [21; 22; 23; 24; 25; 26] and treat concrete as either a two-phase (mortar and aggregates) or three-phase (mortar, aggregates, and ITZ) material. So far, only a few CRAMs contain the pore phase [27; 28; 29; 2] and model the pore phase as a series of randomly distributed single-graded circular or elliptical pores, which is inconsistent with the real pore structure in concrete. Moreover, the above studies mainly focused on the effect of total porosity on the mechanical properties of concrete and ignored other pore structure parameters such as pore gradation, pore size, and pore distribution. For example, [PERSON] [2] and [PERSON] [3] simulated the pore structure as a series of randomly distributed circular or elliptical pores whose diameters were uniformly distributed in the range of 2 to 4 mm. According to the CRAMM, some scholars have also begun to explore the influence of pore structure on the mechanical properties of concrete. For example, [PERSON] [29] used a series of randomly distributed circular or elliptical pores with a certain fixed diameter to simulate the pore structure, established concrete models with different pore sizes and porosity, and studied the effects of porosity, pore size, and pore shape on the mechanical properties of concrete. However, the pore structure he established did not take into account the pore gradation and was too different from the actual pore structure in concrete. [PERSON] [28] preliminarily explored the establishment of a complex pore structure based on fractal theory, and based on this modeling method, they studied the influence of total porosity on the mechanical properties of concrete. However, this pore structure modeling method can only control the total porosity, pore fractal dimension, and the maximum and minimum pore sizes, but cannot control the pore gradation and the sub-porosity and pore size of each gradation segment. Therefore, this method is defective in studying the effects of pore structure parameters on the mechanical properties of concrete. To sum up, there are still many deficiencies in the research on the influence of pore structure on the mechanical properties of concrete, especially in scientific simulation and parameterization of the complex pore structure and the accurate application of the control variable method (CVM). This paper aims to accurately use the CVM to study the influence of the pore structure on the mechanical properties of concrete on the basis of accurately constructing the complex pore structure. Firstly, based on the existing modeling methods, a new CRAMM is proposed, which introduces the concepts of pore gradation and sub-porosity to establish a more reasonable and realistic pore structure and can realize the independent change of pore structure parameters such as total porosity, pore gradation, pore size, and sub-porosity of each grading segment. Based on the CVM, 25 CRAMs with the same aggregate structure and different pore structures are established. Secondly, zero-thickness cohesive interfacial elements (CIEs) governed by nonlinear normal and shear traction-separation laws are inserted within cement mortar and ITZ to simulate complex crack initiation and propagation. Finally, uniaxial tensile experiments are performed on these specimens.