EXPERIMENTAL STUDY ON THE ACCURACY OF CRACK DETECTION ON CONCRETE AND ASSESSMENT OF QUALITY OF REPAIRED CONCRETE WITH ULTRASONIC PULSE VELOCITY

Abstract

Concrete cracks are frequently discovered in structures made of concrete. They should be avoided because they may result in serious issues. Therefore, the prompt identification of cracks and the implementation of preventive measures are essential for ensuring structural durability. Cracks formed on the concrete cover pave the way for structural problems. The concrete cover varies according to the purpose of the structural member and the environment in which it is exposed. These cracks make the structural member less resistant to weathering, corrosion, and fire. To detect the extent of these visible cracks on plain concrete, it is better to start with a non- destructive test. This method is cost-effective and quick, making it preferable before using more advanced equipment that may be expensive and time-consuming. To detect the extent of these visible cracks that are on plain concrete, the Ultrasonic Pulse Velocity (UPV) Test can be used. The PUNDIT 7 apparatus of frequency of 54 kHz was used to detect the prefabricated cracks of 2cm, 4cm, and 6cm deep while keeping the width of the cracks fixed. Concrete beams of size 100 × 100 × 950mm were used. The accuracy of these crack detections was studied by varying the transducer distances from the crack. Identifying the most effective transducer distance would save time and cost in detecting the cracks by reducing the labour cost involved. For all three depth variations, the effective transducer distance range with high accuracy, higher than 85% was observed for 80 to 140 mm, and the most effective transducer distance was 100 mm with an accuracy of 97.04% for a 2 cm crack, 94.45% for a 4 cm crack, and 98.02% for a 6 cm crack. The identified cracks in any structure should be repaired. Otherwise, it may end in huge structural problems over time. In the market, many filling materials are available to fill cracks. Among various crack- filling materials, cement grout remains the most widely utilized due to its availability and compatibility with concrete. Therefore, in this study, cracks were filled with cement grout, and the efficiency, which is a measure of how much the filling comes closer to behaving as the original concrete, was checked. For cracks with depths of 2cm, 4cm, and 6cm, the percentages of efficiency were 94.39%, 90.90%, and 88.05%, respectively. These results show that cement grout is effective in reinstating the performance of cracked concrete, especially for shallower cracks. This study was focused on varying the depth of cracks while maintaining a constant crack width. For future research, it is recommended to investigate the influence of crack width variation at a fixed depth.