STATE-OF-THE-ART APPLICATIONS OF THE PULL-OFF TEST IN CIVIL ENGINEERING

In 1973-1974 the collapse of the roofs made of prestressed High Alumina Cement (HAC) in the UK resulted in an immediate need for evaluating the conditions of the existing structures made from HAC, leading to an increasing awareness of the need for an in-situ test that would not seriously weaken members under investigation but would give a reliable estimate of the concrete's compressive strength. In 1974, the concept of using pull-off test as a means of predicting the compressive strength of concrete was patented in the UK by Professor Long at Queen's University Belfast. Substantial continuous developments have been taking place since then in Queen's University Belfast in the past 30 years. Initially, the pull-off test was developed primarily aiming at unplanned in-situ strength determination. It was found later that it is also particularly suited for assessment of bond strength of repairs. The pull-off test has now been accepted in British Standards, BS 1881-207:1992 as one of the standard tests for assessing the in-situ concrete strength in structures and BS EN 1542:1999 as a standard test for assessing the bond strength between overlays and substrate concrete in patch repairs. BS 1881-201:1986 recommends that the pull-off test is also useful in quality control and long term monitoring. It has also been accepted in North America (ASTM C1583-04), Holland and some other countries as a standard test for similar applications. This paper reviews the development history of the pull-off test, its principle, factors affecting the test results as well as its current applications in civil engineering fields.