## 4 Conclusions  
The purpose of this study was to develop a method for evaluating the pavement condition and durability of functional damage on concrete pavement as soundness through the ultrasonic velocity measurement method and by estimating the depth of deterioration of the surface of the slab. To achieve this, the standard of the ultrasonic velocity of concrete pavement was used as a method of a repeated ultrasonic velocity test to remove the deteriorated areas of concrete core specimens, and the test was devised to verify the assumption of progress of the deterioration of the spalling damage part. The main results of this paper are provided below:  
1. The variability due to equipment error and proficiency of the ultrasonic velocity measurement method was analyzed and found to be 0.36%. In the case of the ultrasonic velocity measurement method used in this study, the tester's skill required in using the equipment was low, and a direct method was used in which the transmitter and receiver of the ultrasonic pulse passing through the core specimens were arranged in a straight line. Therefore, the results were lower than the general variability of other NDT instruments. 2. The relative difference between the results of ultrasonic velocity measurement of the half-cutting core specimens was evaluated at 2.04% to the effect of the thickness on the results of ultrasonic velocity measurement. As the half-cutting core specimens have gone through the process of cutting the surface, it is judged that the result is due to the micro structural difference between the surface conditions that came into contact with the probe before cutting and the surface conditions after cutting. 3. A soundness grade of ultrasonic velocity standard of concrete pavement was derived. The corresponding soundness criteria categorized ultrasonic velocity as 4400 m/s, 4100 m/s, 3500 m/s, and 3000 m/s, and the soundness of the concrete pavement was graded from \"very good\" to \"very poor\" with a grade of 5. 4. In order to estimate the depth of deterioration, a method of measuring the repetitive ultrasonic velocity of removing the deterioration areas was developed. As a result of analyzing the change in ultrasonic velocity depending on the depth of the deterioration removal of the core collected at the spalling damage point, it was confirmed that the tendency of the ultrasonic velocity increases according to the depth of the deterioration part removal. 5. According to the test method that was developed, the deterioration of the depth of the slab was analyzed to be from a minimum of 3 cm to 6 cm for spalls with widths < 150 mm, 7 cm to 10 cm for spalls with widths of 150 mm to 200 mm, and 9 cm to 13 cm for spalls with widths greater than 200 mm. 6. Referring to the results of this experiment, if the administration and road managers determine the depth of the degradation removal of the existing pavement for repair of the PCC pavement, three methods can be proposed according to the management level. The first method is cutting and repairing the existing pavement surface by more than 7 cm in the simplest way. The second is to determine the repair range in consideration of the predicted degradation depth according to the spalling severity presented above. The third is to directly measure the depth of degradation at the target point by means of repeated ultrasonic velocity testing of coring and degradation removal of the pavement in a way that can be used to determine the repair range based on quantitative test results at the target site. 7. This study conducted an ultrasonic velocity test by collecting cores from pavement under various conditions in South Korea to estimate the depth of deterioration of PCC pavement and develop a methodology to determine the repair range.