## 1 Introduction  
Mass concrete usually refers to concrete with a geometric dimension of not less than 1m or that which is expected to produce harmful cracks due to temperature changes and shrinkage caused by hydration of cementitious materials [1]. The final setting time of concrete is of great significance to the determination of formwork removal time, the selection of effective deformation monitoring zero point and the cracking control of an early age concrete structure [2]. In practical engineering, the final setting time of a mass concrete structure is often difficult to judge due to the influence of temperature, humidity, wind speed and admixture [3]. Making subsequent construction plans according to the parameters determined by experience or laboratory conditions will produce large errors [4]. [PERSON] [5] proposed the earliest method to determine the initial and final setting time of cement in 1912. The initial setting time is when the needle cannot penetrate the concrete for a certain distance. The final setting time is when needle cannot leave marks on the concrete's surface. In recent years, researchers have proposed different methods for determining the setting time of mass concrete structures in practical engineering. By measuring the change process of the lateral pressure of the new concrete formwork, [PERSON] [6] defines the time when the lateral pressure is zero as the setting time of the concrete. [PERSON] [7] used a non-destructive ultrasonic shear wave reflection technique. [PERSON] [8] studied the development law of free deformation of concrete at an early age and proposed that the newly poured concrete has the deformation characteristics of expansion and contraction. The end point of expansion deformation is defined as the setting time of concrete. [PERSON]'s test results [9] indicate that a judicious combination of the three NDT techniques utilizing wave propagation characteristics of UPV, discrete UGW and continuous AE monitoring give a good indication of the setting mechanism of normal concrete, as well as SF modified concrete. [PERSON] [10] studied the setting behavior of concrete with different mortar compositions using ultrasonic monitoring techniques. [PERSON] [11] characterized the setting process and strength development of concrete by changes in the dielectric constant. [PERSON] [12] analyzed the mechanism of early hydration characteristics, studied the early temperature development characteristics of different structural concrete, and proposed the rapid growth point of temperature as the final setting time of solid structural concrete. [PERSON] [13] used electrical measurements to anticipate the setting time of high-volume fly ash concretes. [PERSON] [14] proposed an SH-wave-based method to identify the abrupt increase in the Vs values at the initial and final setting times. The above studies are summarized in Table 1  
The above selection methods of the final setting time are under laboratory conditions or based on a certain characteristic critical point of the whole concrete structure after pouring. These methods have certain limitations for mass concrete structures with large size and long pouring time. The strain response is one of the key characteristics of the local structure. Combined with multi-position strain response monitoring, the final setting time of the local position of the mass concrete structure can be effectively reflected. Since the concrete structure still has plasticity before the final setting, the deformation is invalid. The deformation has no practical significance for the strain monitoring of this period. Therefore, the strain monitoring of concrete should theoretically start with the final setting time as the reference point, which is the starting point of effective deformation. The selection of the starting point of effective deformation monitoring is very important for strain analysis, but there is still no exact selection principle for the determination of this point.