## 3 Properties of Multifunctional Cemertitious Composites
### Electrodes Configurations  
To facilitate some functionalities of electrically conductive cementitious composites, it is essential to incorporate electrodes for recording electrical signals [80]. Generally, two types of electrode configurations are employed in these composites: two-probe and four-probe systems, as illustrated in Figure 3[81]. The two-probe system is relatively straightforward for recording electrical signals. However, its major limitation is the significant polarization resulting from contact resistance between the electrodes and the multifunctional cementitious composites [82]. Therefore, the four-probe electrode configuration is often recommended to reduce polarization caused by contact resistance, thereby enhancing measurement reliability [83]. The electrical current used for piezoresistivity measurement can be either direct current (DC) or alternating current (AC), as shown in Figure 3. In the two-probe system, the same electrodes are used for both applying the current and collecting the voltage during electromechanical experiments, as seen in Figure 3a[84]. Conversely, in the four-probe method, the outer electrodes apply the current, while the inner electrodes record the voltage, as depicted in Figure 3b. The choice of electrode material is another factor influencing the capability of multifunctional cementitious composites. Typically, metallic materials such as copper, characterized by low electrical resistance and considerable durability against corrosion, are widely recommended for electrode fabrication [18]. However, [PERSON] et al. [85] reported the deterioration of copper electrodes after exposure to weathering processes. They discovered that silver paste can inhibit corrosion, enhancing the stability of electrical signals under various weathering conditions. In comparison to copper electrodes, the use of carbon fiber-reinforced polymer (CFRP) electrodes in multifunctional cementitious composites resulted in stable electrical signals [85]. Moreover, the shape of the electrode also influences the capability of multifunctional cementitious composites. In this context, perforated copper electrodes demonstrated superior sensing performance compared to the copper wire mesh configuration [86], underscoring the significance of electrode shape in the performance of multifunctional cementitious composites. The installation of electrodes is another factor with considerable effects on the performance of multifunctional cementitious composites [87]. It has been reported that the electrical resistance of embedded electrodes is lower than that of superficial electrodes, indicating the greater effectiveness of embedded electrodes compared to superficial ones [8]. Figure 4 illustrates the embedded and superficial types of electrodes [18]. Figure 4: Installation of electrodes: (**a**) embedded form; (**b**) surficial form [18], published by Elsevier (2020). Figure 3: Electrode configuration: (**a**) two-probe method; (**b**) four-probe method [81], published by Elsevier (2023). Multifunctional cementitious composites can be employed in various forms, including bulk, bonded, coating, sandwich, and embedded forms, as depicted in Figure 5[88]. In the bulk form, the entire structural element is constructed using electrically conductive cementitious composite, making it particularly advantageous for building transportation layers [11]. However, the cost associated with the bulk form may be higher than that of other types, presenting a barrier to its widespread application. In the coating form, a thin layer or a small piece of electrically conductive cementitious composite is utilized to cover the construction material [89]. In the sandwich form, the conventional construction material is positioned between two layers of electrically conductive cementitious composite. In the bonded form, the electrically conductive cementitious composite in the shape of a sensor is affixed to structural elements using adhesive materials.