PULL OFF TEST- Adhesion testing

ASSESSMENT FOR EXISTING BRIDGE COATING PULL OFF TEST- Adhesion testing is addressed in ASTM D4541, “Standard Method for Pull-Off Strength of Coatings using Portable Adhesion Testers”. A Tensile Adhesion Tester will determine the bond of a coating on a substrate, or cohesion of the coating or cohesion of the substrate. Adhesion tests are DESTRUCTIVE and generally should only be conducted if a problem is suspected. Based on the previous visual assessment, the detachment was found localize on the existing bridge coating system. FILM THICKNESS CHECK

PULLING There are three factors that come into play in pulling dollies” • Manual or automatic • Rate and Evenness of pull • Squareness of pull Method of pull (applying force) is applied in 3 ways. Defelsko AT, HATE or Elcometer 108,

PROCEDURE Nadzli Bin Maliki (NACE Level 1 Coatings Inspector CIP No. 16583)

Select for the test location, the Pull out test was carried out for the existing coating system for the Batukawa existing bridge. There were total of 3 locations each location was attached with 3 dollies. Prior to start the dollies attachment, proper recording shall records for the track purpose: Location A, Span 1 outer girders, web of girder 1 -, A1, A2, A3

Clean the coating surface of the existing bridge, marked as above. Measure the dry film thickness before sanding and after sanding recorded on the steel girders

Prepared for the dollies attach by using the high performance epoxy adhesion (Araldite Rapid) squeeze out the resin and hardener to 1:1 ratio and mix thoroughly apply mix to both joint surface.

Hold the dollies by using the tape for the hardening and curing time for at least 6 hours before the adhesion test carried out. Location B

Location C

The Elcometer 108 was used as the tester (hydraulic pressure by hand or pump -Manual) Removed the tapes and connect trimmer / cutter to the dolly, turn and remove the coating surrounding the dolly, it help to prevent damaged to the surround coating and effect the pulling force.

Make sure the pulling is to provide a direct axial (perpendicular) force to the surface. Increase the pressure by manual hand until the hand pump was tight and take the readings.

Removed the dolly by using hammer, observed the failure and rate the test results.

RATING THE TEST It is not enough to record the maximum stress (tensile adhesion). Standard methods require some analysis of the material remaining on the dolly. Often the nature of the break is more important than the pressure that it pulled.

Test result Location A (Span 2) Attach dollies date: 18th Nov 2012 Pull off test date: 19th Nov 2012 Location A A1 A2 A3

Film thickness, μm Before Sand After Sand 313 298 320 310 317 308

Maximum Stress, psi 2100 2100 2000

st

1 coat -

Cohesion,% 2nd coat 95 95 100

3rd coat 5 5 -

There could be a break between layers of a coating system. One layer may be split, indicating the cohesion is less than the adhesion. The system may break from the substrate. The cause of this may be inadequate preparation or even dust. It is quite possible for the glue to break between the dolly and the surface of the coating; this does not constitute an adhesion value. Usually, most dollies have “multiple” mode failures. Record per cent adhesive, cohesive and glue failure

FAILURE TYPE 1. Adhesion Failure – defined as a failure between layers of paint or between the substrate and the paint 2. Cohesive Failure – defined as a failure or break within one coat of paint. 3. Glue Failure – Break occurs between the glue and the pant or the glue and the dolly. This is not an adhesion failure. TO SCORE OR NOT TO SCORE The specification should say whether or not to score around the dolly. ASTM D-4541 leaves it open to the owner and the person doing the test. It cautions scoring can cause micro-cracking that can cause lower adhesion but also acknowledges that not scoring can lead to higher pull rates due to the influence of the adjacent coating.