## 1 Introduction  
The durability life of a cement structure refers to the whole process from the construction of a cement structure to the destruction of a cement structure [1, 2, 3, 4]. Cement is a kind of heterogeneous material which contains particles with different sizes and types of pores [5, 6, 7, 8]. As a result, seawater containing chloride ions and other harmful substances can invade the cement, accelerate steel corrosion and cause durability change to the structure of the cement. The transmission process of chloride ions in cement is mainly through the connected pores of the cement [9, 10, 11, 12, 13]. This process is not only restricted by the changes of the cement's own composition, structure and performance, but it is also affected by the external service environment of the cement, which makes the transmission mechanism of chloride ions in cement extremely complex [13, 14, 15, 16]. The external service environment of cement is complex and changeable, in which a variety of soluble salts interact to form a multi-salt concentration field, which has been proven to be able to change or even significantly change the diffusion coefficient of chloride ions and is in the seabedstructure [17; 18; 19; 20; 21; 22]. The cement of buildings is affected by the hydrostatic pressure field at the same time, thus forming a multi-field coupling environment, which makes the chloride ion transport mechanism in this environment worthy of further discussion [23; 24; 25; 26; 27].  
Many scholars have conducted systematic research on the influence of cement on chloride ion transport which is worthy of reference. For example, [PERSON] et al. [28] conducted a chloride corrosion test on a marine concrete structure for 22 years, and the results showed that the degree of water saturation had a great influence on the diffusion of chloride ions in concrete. [PERSON] and [PERSON] [29] conducted a 560-day exposure experiment on concrete blocks in a tidal zone. The test results showed that the chloride diffusion coefficient of the concrete in a tidal zone had good correlation with the chloride diffusion mechanism established earlier, and the diffusion coefficient changed obviously with the w/c ratio of the concrete. [PERSON] and [PERSON] [30] studied the effect of chloride entry into HPC under dry-wet cycles. Their test results showed that longer drying times led to higher chloride diffusion coefficients in cement-based materials. Field tests of cement structures in a marine environment showed that the structures exposed to tides and experiencing dry-wet cycles were more vulnerable to chloride corrosion damage than other parts in the immersion zone and atmospheric zone. [PERSON] [31] measured the distribution of chloride ions in 0.6 w/c ratio concrete under the action of the water head pressure and concentration gradient, but the experiment only measured the depth of the chloride ions in the concrete under different pressure heads and action times with the AgNO\({}_{3}\) spraying method, and the distribution of chloride ion concentrations in the concrete along the direction of chloride ion invasion was not given.  
This paper studied the chloride diffusion performance of concrete with different w/c ratios and different aggregate contents under different hydrostatic pressures based on COMSOL finite element software and compared the simulation results with the experimental results to verify the effectiveness of the simulation method. Specifically, this paper is mainly divided into four parts. The first part introduces the research status of the chloride model for cement. The second part introduces the basic conditions and experimental methods of the raw materials which were used in the experiment. The third part introduces the chloride ion transport model and its solution. The fourth part discusses the influence of different hydrostatic pressures, coarse aggregate contents and w/c ratios on chloride ion transport. The main content and conclusions of this paper will be elaborated upon in the fifth part.