# Flexural Strength and Acoustic Damage Characteristics of Steel Bar Reactive Powder Concrete
###### Abstract  
In this paper, the steel bar was used to prepare steel bar reactive powder concrete (SBRPC). The three-point bending test was adopted to investigate the effect of the number of steel bars on the flexural strength of SBRPC. The acoustic emission (AE) was used to monitor the fracture process of SBRPC in real time. In addition, the parameter RA and AF ratio (RF) was defined to analyze the distribution of shear cracks and tensile cracks during the fracture process. The experimental results showed that with the increases in the number of the steel bar, the flexural strength of SBRPC gradually increased. The fracture stage of SBRPC can be accurately divided according to the curve slope change in hits and cumulative counts. Moreover, the early warning of SBRPC damage can be realized by observing the amplitude of the AE amplitude value. The dynamic changes in the rising angle (RA) and average frequency (AF) values can be used to determine the cracks mode and fracture mode. Based on the results of RF analysis, adding steel bars will improve the proportion for tensile cracks during its fracture process.  
steel bar; reactive powder concrete; flexural strength; acoustic emission; fracture behavior +
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the effect of the embedded depth of the steel bar on the bond intensity between the steel bar and RPC, and the peak bond intensity of specimens decreased with the increase in the embedded depth. [PERSON] et al. (2018) researched the bond stress between conventional steel bars and RPC. The experiment result showed that as the compressive strength of RPC increased, the bond stress gradually enhanced, but the corresponding increase rate gradually decreased. Nevertheless, relatively little research has been carried out for the fracture process of RPC reinforced with steel bars.  
Acoustic emission (AE) technology, as a non-destructive method ([PERSON] et al., 2018; [PERSON] et al., 2019), is adopted to detect the real failure condition of structures, as well as material damage behavior ([PERSON] et al., 2019). It has the characteristics of high sensitivity, accurate location of damage sources, and real-time monitoring ([PERSON] et al., 2019; [PERSON] et al., 2020). The internal damage of the concrete releases a certain intensity of elastic waves and propagates to the surface of the concrete ([PERSON] et al., 2019; [PERSON] et al., 2020), which are collected and processed by AE sensors into electrical signals and used for the fracture analysis for concrete ([PERSON] et al., 2020). At present, some scholars have studied the characteristics of concrete during the fracture damage process through AE technology. [PERSON] et al. (2018) researched the fracture behavior of concretes reinforced with synthetic fiber, steel fiber, as well as mixed fiber through AE technology, and divided the cracks as shear and tensile modes. [PERSON] et al. (2018) introduced AE technology into the study of uniaxial dynamic tension. The result showed that the increase rate of the AE parameters of concrete under dynamic load gradually decreased with the increase in the initial quasi-static load, and the more the initial loading period, the less the AE signal generated in the dynamic loading period. [PERSON] et al. (2018) adopted AE technology to study the fracture characteristics of concrete containing hybrid fiber, and they found that the identification of crack positions through AE analysis is pretty close to real fracture damage development.  
In this paper, steel bar reactive powder concrete (SBRPC) was prepared with steel bars, and the influences of the steel bar number on flexural intensity and fracture behavior for SBRPC were investigated. The failure process of SBRPC was evaluated based on the AE parameter direct analysis method, and the failure mode of SBRPC was investigated through the AE indirect calculation analysis method. In addition, the distribution of the shear cracks and tensile cracks of SBRPC was investigated through the defined parameter.