## 1 Introduction  
As a complex porous medium containing solid, gas, and liquid phases, concrete is vulnerable to several types of damage, with water content being one of the main influencing factors [1, 2]. Several deleterious substances like chloride can enter cement-based materials through moisture diffusion. [PERSON] studied the permeability of concrete in the 1930s [3]. The Feldman Sereda model suggests that only free water (capillary water), adsorbed water, and structural water (interlayer water) can transport inside cement, whereas crystal water cannot [4]. However, in reality, other than in underwater engineering applications, concrete material rarely reaches a saturated state wherein its internal structure is full of liquid water. Considering the process of capillary flow, permeability cannot be used to suitably describe the transport of water in unsaturated porous materials, and gas phase transportation must be considered [5, 6]. The total transmission effect is represented by [PERSON]'s law, which considers the water saturation degree to be a descriptive variable [5, 7, 8]. Analyzing the moisture content in concrete by conventional methods is difficult. [PERSON] and [PERSON] were the first to evaluate the moisture content in construction materials using neutron and gamma-ray diffraction [9]. Subsequently, accurate and non-destructive experimental methods, such as the hygrometer method [10], wave propagation [11, 12, 13], thermal transmittance testing [14, 15, 16], electrical property testing methods [17, 18], and nuclear magnetic resonance (NMR) [19, 20, 21, 22], have gradually been developed. However, each of these methods has its own disadvantages. The gamma-ray test method requires a dry sample and cannot be used for on-site or in-situ testing. The hygrometer method requiresmany test holes to be prepared on the sample and the accuracy is not high. NMR technology is a fast, accurate, non-destructive, and continuous measurement method. Moreover, samples can be tested without drying or injecting liquids. Consequently, NMR technology can be used for in-situ detection and continuous monitoring. It measures the relaxation behavior of hydrogen protons in water molecules inside the material to obtain information such as the state of water, total moisture content [19; 20], and distribution of water in the pores [21; 22; 23]. [PERSON] et al. analyzed NMR-T\({}_{2}\) relaxation to obtain pore water distribution at different distances from the material interface [24]. [PERSON] et al. found the reconfiguration process of moisture from smaller gel pores to larger interhydrate pores by \({}^{1}\)H-NMR--relaxometry [25]. Studying the moisture transfer process of ordinary concrete is insufficient. In practical engineering applications, various waterproofing agents are added to concrete to prevent capillary action and reduce water absorption or water permeability under hydrostatic pressure and achieve a waterproof state. Based on their function, waterproofing agents are divided into three categories: (i) thin-coating surface forming additives, (ii) concrete pore lining forming additives, and (iii) pore blocking additives, all of which have good water resistance [26; 27; 28; 29; 30]. In addition to waterproofing agents, novel admixtures called nano-materials that have good physical and chemical properties have also been used in cement-based materials. The most common types of nano-materials are nano silica, nano clay, and nano alumina. Nano silica can improve the cement microstructure of the interfacial transition zone and increase the density of micro pores [31; 32; 33]. The resulting cement has higher strength, better durability, and improved mechanical properties [34; 35]. Nano clay can enhance chloride penetration resistance in ultra-high-performance concrete [36]. It also improves thermal behavior and increases the compressive and tensile strength of cement [37; 38; 39].