## 1 Introduction  
As an abundantly utilized type of material in buildings, the industrial energy consumption of cement production has reached 40% of the total energy consumption of human production, and its carbon dioxide emissions account for 8% of the world's total [1]. The development of high-performance cement\(-\)based material, under the same bearing capacity, can effectively reduce material consumption, which is of great significance in achieving sustainable development [2]. Concrete is mainly composed of gel, aggregate, and the interface transition zone (ITZ). The interface transition zone, which is the link between the gel and the aggregate, has a remarkable effect on the overall performance of cementitious composites [3]. The ITZ has a greater porosity than the substrate, as well as being relatively loose, leading to micro-cracks, which seriously affect the durability of the material [4]. Consequently, a large amount of research has been conducted into this problem.  
The microscopic properties of concrete ITZ have mainly been evaluated using microstructure identification techniques, such as scanning electron microscopy (SEM). For instance, [PERSON] et al. [5] used the SEM images of concrete ITZ to analyze how the interfacial wetness influenced the adhesive performance of the gel and aggregate pull-off. [PERSON] et al. [6] applied backscattered electron (BSE) imaging and nano-indentation techniques to study ITZ change characteristics during the carbonation of concrete. Using atomic force microscopy (AFM), SEM, and nano\(-\)indentation techniques, [PERSON] et al. [7] discussed the subject\(-\)to\(-\)mix ratio, the types of aggregate, and the hydration period for interfacial characteristics of recycled concrete ITZ. [PERSON] et al. [8] adopted X-ray computed tomography (XCT) to reconstruct the micromorphology of concrete, and comprehensively examine the impact of the ITZ, pore, and aggregate upon the chloride ions' diffusivity flux. However, most of the above techniques require relatively specific specimens, and the spatial resolution cannot fully reveal the composition information of the interface microstructure.  
The molecular dynamics (MD) technique is a computational simulation tool using the basis of traditional Newtonian mechanics. It has been extensively used in investigating the microstructure and characteristics of cement composites [9; 10]. [PERSON] et al. [11] utilized molecular dynamics methods to research the atomic interactions, structural changes, and kinetic characteristics at the interface of the C-S-H structures and the graphite structures with various functional groups. They discovered that interfacial interactions are the most predominant role of the electrostatic forces. [PERSON] et al. [12] revealed the weakening mechanism for the adhesive performance at the interface of C-S-H and epoxy resin in a thermal environment from a nanoscale perspective, and found that an increased temperature decreases interfacial interactions. [PERSON] et al. [13] worked with the atomic interaction mechanism of the common aggregate calcite/silica and C-S-H, and discussed the influence of moisture on the interactions. From the above studies, it is clear that most research works have focused on C-S-H/carbon-based nanomaterial interfaces and C-S-H/polymer interfaces, while only a few studies have examined and considered the effects of the interfacial water molecule content on the adhesive properties of C-S-H/aggregate interfaces.  
In this study, the MD technique was employed to evaluate the influence of the interfacial water content on the evolution of the interface structure, the interaction energy, and the mechanical property of the C-S-H/SiO\({}_{2}\) system. The C-S-H/SiO\({}_{2}\) interfacial weakening mechanism in a humid environment was revealed. These results are crucial for understanding nanoscale gel/aggregate interactions, and for developing high-performance cementitious materials.