Testing of field-cured cylinders to determine whether concrete strength is satisfactory for either removal of forms or application of post-tensioning has been required by many codes and specifications. However, it is difficult to be sure that field-cured cylinders have received the same protection or curing conditions that were provided for parts of the structure they are supposed to represent.
A pullout test measures the force required to pull a specially shaped steel rod or disc out of the hardened concrete into which it has been cast. Because of its shape, the steel rod is pulled out with a cone of concrete whose surface slope is approximately 45 degrees to the vertical. A hollow tension ram bearing on the concrete surface exerts the necessary pull on the steel rod, with power supplied by a hand-operated hydraulic pump. The force required for pullout is then related to the compressive strength of the concrete.
Pullout testing lends itself to accelerated construction programs and if properly applied can be used in conjunction with selected concrete mixes to help build multistory frames more rapidly than normal. A reduction in construction time can result in significant financial benefits to the owner and other parties to a contract.