# Evaluation of Condition of Concrete Structures Using Ultrasonic Pulse Velocity Method  
[PERSON]  
1 Department of Architecture, Woosuk University, 66 Daehakro, Jincheoneup, Jincheongun, Chungcheong bukdo 27841, Korea; [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Architectural Engineering, Hanbat National University, 125 Dongseodero, Yuseonggu, Daejeon 34158, Korea; [EMAIL_ADDRESS] (S.Y.); [EMAIL_ADDRESS] (J.K.); [EMAIL_ADDRESS] (C.L.); [EMAIL_ADDRESS] (S.K.)  
[PERSON]  
2 Department of Architectural Engineering, Hanbat National University, 125 Dongseodero, Yuseonggu, Daejeon 34158, Korea; [EMAIL_ADDRESS] (S.Y.); [EMAIL_ADDRESS] (J.K.); [EMAIL_ADDRESS] (C.L.); [EMAIL_ADDRESS] (S.K.)  
[PERSON]  
2 Department of Architectural Engineering, Hanbat National University, 125 Dongseodero, Yuseonggu, Daejeon 34158, Korea; looter2000@nate.  
with happiness and welfare through building safety, it is extremely important to establish a method of estimating the strengths of materials more accurately using nondestructive testing methods related to safety diagnosis. This is the first step of various methods to prevent accidents in concrete buildings and establish standards on precision safety diagnosis for buildings or for nondestructive testing methods.  
The ultrasonic pulse velocity method estimates the compressive strength of concrete by measuring the ultrasonic pulse velocity from the pulse passing time between the transmitter and receiver at certain distances in a concrete structure, as described in ASTM C597-09 and KS F 2731. The ultrasonic pulse velocity can be used for evaluating concrete quality factors such as the elastic modulus, crack depth, and internal defects, and is applied by obtaining a correlation between the ultrasonic pulse velocity and the compressive strength.  
This study proposes a compressive strength estimation equation from the correlation between the ultrasonic pulse velocity and the compressive strength according to the age of the concrete by applying the ultrasonic pulse velocity method, which is one of the nondestructive testing methods. Thus, the equation ultimately provides important data for establishing standards. The proposed concrete compressive strength estimation equation is expected to provide information on formwork removal at new construction sites by estimating the compressive strength of concrete structures at early ages. Further, it enables the quality control of materials at remodeled construction sites by accurately estimating the concrete compressive strength of the existing structures. Concrete specimens were fabricated to achieve the purpose of this study. Then, compressive strength testing and a nondestructive testing experiment were conducted using the specimens. In the experiment, a concrete compressive strength estimation equation was proposed by applying the ultrasonic pulse velocity method, one of the nondestructive testing methods, to identify the compressive strength estimation accuracy according to the age of the concrete structure. A total of 123 concrete specimens were fabricated by setting nine variables based on the ages of 16, 20, 24, 48, 72, 120, 168, 360, and 672 h for the designed strengths of 24, 30, and 40 MPa. To calculate the average ultrasonic pulse velocity according to the age of the concrete, an experiment was performed in accordance with KS F 2731, ACI 228-2R, and ASTM C 597-16. The concrete compressive strength testing was conducted in accordance with KS F 2405. Based on this, a method of evaluating the compressive strength estimation for concrete structures using the nondestructive testing method was established.