# Evaluation of Condition of Concrete Structures Using Ultrasonic Pulse Velocity Method
## 3 Ultrasonic Pulse Velocity Method
The Figure 6 shows that there is a certain correlation between the ultrasonic pulse velocity and the compressive strength. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Age** & \multicolumn{6}{c}{**Ultrasonic Pulse Velocity**} & \multicolumn{3}{c}{**Aver.**} & \multicolumn{3}{c}{**Compressive Strength (MPa)**} & \multicolumn{1}{c}{**Aver.**} \\ \cline{2-11}  & **(h)** & & & & **(m/s)** & & & & **Aver.** & **Compressive Strength (MPa)** & **Aver.** \\ \hline \multirow{4}{*}{360} & 3362 & 3446 & 3413 & 3362 & 3327 & 3535 & 3250 & 3327 & 3413 & 3362 & \multirow{4}{*}{19.96} & \multirow{4}{*}{20.59} \\ \cline{2-11}  & 3362 & 3327 & 3413 & 3250 & 3327 & 3535 & 3250 & 3446 & 3413 & 3250 & & \\ \cline{2-11}  & 3362 & 3327 & 3413 & 3362 & 3446 & 3413 & 3250 & 3446 & 3413 & 3446 & & \\ \cline{2-11}  & 3250 & 3446 & 3535 & 3250 & 3327 & 3413 & 3362 & 3446 & 3413 & 3446 & & \\ \cline{2-11}  & 3362 & 3327 & 3535 & 3362 & 3446 & 3413 & 3362 & 3327 & 3535 & 3413 & & \\ \cline{2-11}  & 3250 & 3327 & 3413 & 3362 & 3327 & 3413 & 3250 & 3446 & 3535 & 3413 & & \\ \hline \multirow{4}{*}{672} & 3410 & 3362 & 3396 & 3410 & 3482 & 3283 & 3410 & 3482 & 3283 & 3410 & & \\ \cline{2-11}  & 3410 & 3482 & 3396 & 3293 & 3362 & 3283 & 3410 & 3362 & 3283 & 3410 & & \\ \cline{2-11}  & 3410 & 3362 & 3283 & 3410 & 3362 & 3396 & 3410 & 3362 & 3396 & 3482 & & \\ \cline{2-11}  & 3293 & 3362 & 3283 & 3293 & 3482 & 3283 & 3410 & 3362 & 3396 & 3482 & 3381.12 & 21.84 & 22.17 \\ \cline{2-11}  & 3410 & 3362 & 3283 & 3410 & 3482 & 3283 & 3410 & 3482 & 3283 & 3283 & & \\ \cline{2-11}  & 3410 & 3482 & 3396 & 3410 & 3362 & 3283 & 3537 & 3482 & 3283 & 3396 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 5: Compressive strength with age (24 MPa). For the designed concrete compressed strength of 30 MPa, the ultrasonic pulse velocity in each specimen was measured at the ages of 16, 20, 24, 48, 72, 120, 168, 360, and 672 h, and compressive strength testing was conducted. The measurement results are listed in Table 3. The measured ultrasonic pulse velocity was 96.4 m/s at 16 h of age, 96.0 m/s at 20 h, 1010.03 m/s at 24 h, 2451.8 m/s at 48 h, 2867.2 m/s at 72 h, 3118.3 m/s at 120 h, 3240.3 m/s at 168 h, 3529.8 m/s at 360 h, and 3389.2 m/s at 672 h. Figure 7 shows the ultrasonic pulse velocity according to age. As shown in the Figure 7, the wave velocity sharply increased from 16 to 72 h of age. It slowly increased to 120 h and then maintained a very slow increasing tendency up to 672 h. Figure 8 shows the concrete compressive strength according to age. As shown in the figure, the concrete compressive strength was 2.07% of the designed strength at 16 h of age, 2.07% at 20 h, 3.73% at 24 h, 13.07% at 48 h, 30.67% at 72 h, 69.70% at 120 h, 84.70% at 168 h, 92.77% at 360 h, and 95.40% at 672 h. In particular, the compressive strength increased as the age increased. Figure 6: Relationship of ultrasonic pulse velocity and compressive strength (24 MPa). Figure 7: Ultrasonic pulse velocity with age (30 MPa). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Age (h)**} & \multicolumn{10}{c}{**Ultrasonic Pulse Velocity (m/s)**} & \multicolumn{1}{c}{**Aver. **} & \multicolumn{1}{c}{**Compressive Strength (MPa)**} & \multicolumn{1}{c}{**Aver.