{"id":6113,"date":"2019-02-25T09:50:02","date_gmt":"2019-02-25T09:50:02","guid":{"rendered":"https:\/\/ctech-llc.com\/en\/?p=6113"},"modified":"2019-06-19T09:21:59","modified_gmt":"2019-06-19T09:21:59","slug":"frp-tests","status":"publish","type":"post","link":"https:\/\/ctech-llc.com\/en\/wikitech\/frp-tests","title":{"rendered":"FRP Tests"},"content":{"rendered":"

Before 2009, the standard used as guidance for pull-off tests was\u00a0ASTM<\/a>(2009b). This standard was primarily created as a test method for the pull-off strength of coatings. However, because of similarities in specimen preparation and testing procedures, the standard was used by previous studies as a method for testing pull off strength of FRP materials bonded to concrete. With the increase in popularity of this specific test application, ASTM (2009a) was created specifically to determine the pull-off strength of FRP bonded to concrete. The standard is applicable to both wet lay-up and shop-fabricated or pultruded laminates bonded to concrete. The test cannot be classified as nondestructive, but owing to its relatively small scale, surface repairs are minimal.<\/p>\n

The test determines the greatest tension force (applied perpendicular to the bond) that the FRP\u2013concrete bond can resist. The method consists of adhesively bonding a metallic circular loading fixture, also referred to as a dolly or puck, to the surface being tested. The dolly contains a threaded hole in the center that allows for attachment of the fixed alignment adhesion testing device, also known as a pull-off tester. Once attached, the tester slowly applies<\/p>\n

tension to the bond until a partial or full detachment of the dolly is witnessed, at which point the load is regarded as the maximum bond force. The circular hole cutter is used to isolate the area being tested from the rest of the surface. This hole must be the same diameter as the loading fixture, commonly taken as 50 mm (2.0 in.).<\/p>\n

The test procedure consists of the following steps:<\/p>\n

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  1. Begin with a flat surface of concrete externally reinforced with FRP;<\/li>\n
  2. Drill a circular core through the FRP surface and into the concrete substrate. Keep the depth of the core between 6 and 12 mm (0.25 and 0.50 in.);<\/li>\n
  3. Prepare the FRP surface by roughening, cleaning, and fully drying it;<\/li>\n
  4. Affix the dollies to the prepared surface by means of a bonding\u00a0adhesive<\/a>\u00a0(epoxy), and allow the adhesive to cure following manufacturer instructions;<\/li>\n
  5. Carefully attach and align the pull-off tester;<\/li>\n
  6. Apply the load at the recommended rate of less than 1 MPa\/min (150 psi\/min) by slowly rotating the crank of the pull-off tester until the maximum force is reached; and<\/li>\n
  7. Report maximum pull-off force as well as characteristics of the failure mode.<\/li>\n<\/ol>\n

    Pull-Off Test method<\/h2>\n

    The adhesive strength is determined as the maximum tensile strength applied by a direct load perpendicular to the surface being tested. The tensile load is applied by means of a defined pull head plate glued to the test area. The adhesive strength is the quotient between the failure load and the test area. On all the tests described in this paper, the test area was pre-cut in situ, fitting the size of the pull-head plates. These could be square metallic plates of 50 mm x 50 mm or circular metallic plates with diameter of 50 mm. The test machine for direct pull tensile force test is in accordance with standard requirements, with the additional feature of automatic control of the applied force provided by an attached electrical engine.<\/p>\n\t

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