보통 콘크리트강도형 간이 인발시험법에 대한 제안

Abstract

The pullout test certified by the American Society for Testing and Materials(ASTM) is known to be more reliable for estimating concrete strength under construction of concrete structures than other nondestructive testing(NDT) methods such as rebound number, penetration resistance, break-off, and ultrasonic pulse velocity. However, existing equipment needed for the pullout test, known as Lok test or Capo test, require several complex installation steps and expensive loading systems including load cell. We propose a simplified pullout test composed of a break-off type bolt, a standard bolt with a groove on the shaft, as an insert, an insert nut, and a pullout instrument without load cell. This simplified pullout test would be more beneficial due to its low cost, simplicity and convenience. To verify the advantages of the simplified pullout test, three wall specimens were tested with two types of concrete strength, 15MPa and 24MPa, using the Lok test, a general pullout test including load cell, and a simplified pullout test. It was found that the pullout force was very similar in comparison with compressive strength. Therefore, it was verified that the simplified pullout test can be used to replace the Lok test. The prediction equation of groove diameter with the concrete strength was derived as y=6.01x-17.17(y=concrete strength, x=the groove diameter of break-off bolt) through regression analysis. An allowable error can be easily maintained within the specified value if appropriate safety factors are studied and added to the prediction equation.