Techshore Inspection Services-Kochi-official blog of Techshore Kerala: TECHSHORE INSPECTION SERVICES :Pull out test

The pullout test is a partial destructive test which falls in the transition area between a destructive test and a non-destructive test.It is destructive in the sense that a relatively large volume of the concrete is damaged but non-destructive since the damaged portion can be repaired. Pullout test is of two types as follows:

DANISH LOK TEST:

This test is used to determine near surface compressive strength. It measures the force required to pull an embedded metal insert with an enlarged head from a concrete structure. It requires the head to be cast into the concrete at the time of construction.

Figure shows the illustration of Danish Lok Pullout Test.The insert is pulled by using a loading ram which is seated on a bearing ring that is concentric with the insert shaft. The reaction force is transmitted to the concrete by the bearing ring.As the insert is pulled out, a conical shaped fragment of concrete is extracted from the concrete structure. The idealized shape of the extracted conic frustum is shown in Fig 1.The apex angle (2α) of the idealized frustum is given by the following equation:

Where,

D is the inner diameter of the bearing ring

d is the diameter of the insert head

h is the embedded depth

The pullout test is used to estimate the strength of concrete in order to help in deciding whether critical activities such as form removal or application of post tensioning can proceed.

Since the compressive strength is usually required to evaluate structural safety; the ultimate pullout load measured during the in-place test is converted to an equivalent compressive strength by means of a previously established correlation relationship.

Unlike some other tests which are used to estimate the in-place strength of concrete, the Pullout test makes the concrete subjected to a slowly applied load and measures the actual strength property of the concrete. The pullout test can be used to make reliable estimates of in-place strength using correlation curves. While implementing this method choosing the locations and number of pullout tests in a given placement of concrete is an important step to consider. Locate the inserts in the most critical portions of the structure and their number should be sufficient to provide statistically significant results. Additional inserts are recommended in the case that testing begins too soon, and the concrete has not attained sufficient strength. Maturity meters are used along with the pullout tests to assist in selecting the correct testing times and in interpreting possible low strength results.

Building Research Establishment, UK (BRE) PULLOUT TEST:

This test was developed to permit testing in an already existing construction by drilling a hole and inserting some type of expansion anchor. The advantage of this test is that it does not require a head to be cast into the concrete during the time of construction. The disadvantage is that it really measures the tensile strength and is then calibrated to compressive strength. Also the results of these tests are difficult to interpret if the correlation curve for the concrete used in the construction does not exists.

Monday, March 6, 2017

TECHSHORE INSPECTION SERVICES :Pull out test

1 comment: