###### Abstract
At present, most of the related researches on the hydration absorption characteristics of rocks focus on the microscopic or macroscopic characteristics of rocks, and there is a lack of research on the hydration absorption characteristics of sandstone under pressure-less hydration absorption. Studying the deformation behavior of rock is an important step to understand the properties of rock. At present, the direct contact method is mostly used to study the deformation characteristics of rock. Digital image correlation (DIC) is a non-contact strain analysis technology based on digital image processing, which has become one of the important means to study the mechanical properties and deformation characteristics of materials. In laser speckle measurement, DIC is used to measure the surface displacement component, and an image scanner connected to a computer records the laser speckle pattern of the object and is stored in the memory in a reference and deformation configuration. The subset and reference of the formed image are numerically used as a measure of surface displacement [10,11]. [PERSON] et al. [12] studied the delayed behavior of unsaturated argillaceous rocks using the DIC technique, and discussed the time-dependent behavior observed at different scales. Based on the DIC non-destructive optical technique, [PERSON] et al. [13] measured the full-field displacement of the sandstone surface and determined the crack initiation and crack length evolution. [PERSON] et al. [14, 15, 16] studied the mechanical behavior of mudstone at the composite microstructure scale by using environmental scanning electron microscopy (ESEM) imaging and DIC technology, and found some irreversible phenomena in the drying and wetting process of mudstone at the micron scale. [PERSON] et al. [17] studied the deformation behavior of soft and hard interbedded rock using DIC, and studied the deformation and failure characteristics of horizontal soft and hard interbedded rock samples under uniaxial compression. [PERSON] et al. [18] used the DIC experimental platform of coal rock deformation damage to carry out the surface deformation observation test of coal rock around the borehole during the progressive damage process. [PERSON] et al. [19] studied the multi-dimensional non-uniform deformation and failure characteristics of siltstone through linear differential transformer (LVDT), DIC, computational tomography (CT), acoustic emission (AE), and ultrasonic velocity. [PERSON] et al. [20] analyzed the evolution of the strain field on the surface of the sample through DIC, and initially gave the relationship between the proposed stress-strain curve and the strain field. [PERSON] et al. [21] studied the effect of inclusions on the fracture evolution and mechanical properties of mortar structure, and analyzed the deformation characteristics using DIC technology. Based on the multi-fractal of high-speed digital image correlation (HS-DIC) technology and quality screening method,Jin et al. [22] investigated the evolution trend of surface cracks during crushing and the distribution characteristics of sample fragments after crushing from the perspective of a fractal. [PERSON] et al. [23] analyzed the effect of four different tension levels on the strain/stress of the hole specimen based on the DIC system calibration procedure. [PERSON] et al. [24] carried out uniaxial compression experiments on red sandstone samples, analyzed the slow deformation waves under different loading rates, and combined them with DIC technology for microscopic characterization. However, when measuring rock deformation, there are few methods using non-contact measurement technology, and the research on using the DIC method to analyze the hydration absorption process of rock is not sufficient.