Post-Installed Tests

A drawback of the cast-in-place pullout test is that the locations of the inserts have to be planned in advance of concrete placement and the inserts have to be fastened to the formwork. This limits the

Number of Tests Acceptable Range (Percent of Average) 5 7 10 31 34 36 n n V V 1 2 1 2 2 £ ¤ ² ¥ ¦ ´

applicability of the method to new construction. In an effort to extend the application of pullout testing to existing structures, various “drilled in” or “post-installed” techniques have been investigated.

Spurred by the need to evaluate distress in structures made with high alumina cement, the Building Research Establishment (BRE)52,53_{developed a technique based on commercial anchor bolts with expand-}

ing sleeves, as shown in Figure 3.25. A 6-mm (1/4-in.) hole is drilled into the concrete, the hole is cleaned, and an anchor bolt is inserted into the hole so that the split-sleeve is at a depth of 20 mm (0.8 in.). After applying an initial load to expand and engage the sleeve, the bolt is loaded in tension and the maximum load during the extraction is recorded. Reaction is provided by three “feet” located along the perimeter of a ring 80 mm (3.1in) in diameter. The expanding sleeve applies to the concrete a force having vertical and horizontal components, as indicated by the inclined arrows in Figure 3.25. The concrete fracture differs from that in the standard pullout test, and the test is referred to an “internal fracture test” rather than a “pullout test.” The reported strength relationship between ultimate load and compressive strength has a pronounced nonlinearity, indicating that the failure mechanism is probably related to the tensile strength of the concrete. The within-test variability was found to be greater than that of the standard pullout test, and the 95% confidence limits of the strength relationship were found to range between (30% of the mean curve.

In the BRE test system, the pullout force is applied by turning a nut on the end of the anchor bolt and measuring the maximum torque achieved during the test. Bungey54_{developed a mechanical loading}

system with the aim of reducing the scatter of test results compared with using the torque loading system. Using the mechanical loading system, the 95% confidence intervals for the estimated compressive strength were estimated to be (20%, which is a significant improvement. The comparatively low precision of the internal fracture test has been attributed to two principal causes:54_{(1) the variability in the hole drilling}

and preparation; and (2) the influence of aggregate particles on the load transfer mechanism and on the failure initiation load.

Mailhot et al.55_{investigated the feasibility of several drilled-in pullout tests. One of these used a split-}

sleeve and tapered bolt. In this case, the bolt assembly was placed in a 19-mm (3/4-in.) hole drilled into the concrete. As shown in Figure 3.26A, this technique differs from the BRE method because the reaction to the pulling force acts through a specially designed high-strength, split-sleeve assembly. Thus, the force transmitted to the concrete is predominantly a lateral load due to the expansion of the sleeve. The developers claimed that failure occurred by shear. The author, however, believes that failure is more likely to occur by splitting as in the standard splitting tension test of a cylinder. Similar to the BRE test, the variability of this test was reported to be rather high.55 _{A second successful method involved epoxy-}

grouting a 16-mm (5/8-in.) threaded rod to a depth of 38 mm (1 1/2 in.) in a 19-mm (3/4-in.) diameter hole. After the epoxy had cured, the rod was pulled using a tension jack reacting against a bearing ring. This method was also reported to have high variability. The study concluded that these two methods

FIGURE 3.25 BRE internal fracture test.52,53

20 mm 80 mm Split Sleeve Internal Force 6-mm Hole

have the potential for assessing the strength in existing construction. Additional research was recom- mended to enhance their reliability.

Domone and Castro56_{developed a technique similar to that shown in Figure 3.26A, except that the}

load was applied by a torque meter and the embedment was 20 mm (3/4 in.) as in the BRE method. Based on a limited number of comparative laboratory tests, it was concluded that the new method resulted in better correlations than the BRE method.

Another method was developed by the manufacturer of the LOK-TEST system and is referred to as the CAPO test (for cut and pullout).33_{The method involves drilling an 18-mm (0.7-in.) hole into the}

concrete and using a special milling tool to undercut a 25-mm (1-in.) diameter slot at a depth of 25 mm (1 in.). An expandable ring is placed into the hole, and the ring is expanded using special hardware. Figure 3.26B shows the ring after expansion. The entire assembly used to expand the ring is then pulled out of the concrete using the same loading system as for an ordinary pullout test. Thus, unlike the other methods discussed above, the CAPO test subjects the concrete to the same type of loading as the standard pullout test. The performance of the CAPO test in laboratory evaluations has been reported to be similar to the LOK-TEST.33_{In early field trials of the CAPO test, the variability of results was higher than for}

cast-in-place tests. This was attributed primarily to difficulties in obtaining a flat bearing surface per- pendicular to the axis of the post-installed insert. With improvement in the hardware and technique, the

FIGURE 3.26 (A) Post-installed pullout test using spilt-sleeve and tapered bolt.53_{(B) The CAPO test by undercutting}

and using an expandable ring.33

Split Sleeve A B 51 mm Internal Force Tapered Rod 25 mm 25 mm Expandable Ring

variability was reduced and results comparable to cast-in-place tests were reported.57_{In 1999, ASTM C}

900 was revised to include pullout tests with post-installed inserts. The procedure calls for careful attention to surface preparation before testing.

3.5.7 Summary

This section has discussed some of the practical considerations in the application of the pullout test. Considerable information has been published on laboratory and field experience involving the method, and standard test procedures and recommended practices have been established.

Prior to using the pullout test to estimate in-place strength, a relationship between ultimate pullout load and compressive strength must be established for the particular test system and concrete materials. The maximum size and type of coarse aggregate can have a significant influence on the strength rela- tionship. Although no standards currently exist, recommendations for establishing this relationship have been published. The preferred procedure is to perform the pullout tests on cube specimens. Correlation data should span as wide a strength range as is practicable, and the strength level that is expected to be measured in the field should fall within this range. At least six data sets should be used to develop the strength relationship.

In implementing pullout testing in the field, the number of pullout tests and statistical analysis of the results are critical. The number of tests should be chosen so that the average value and the variability of the pullout strength are established with a reasonable degree of confidence. Most practitioners use more than the minimum number required by the current ASTM standard. The inserts should be located in critical portions of the structure. Test results should be subjected to statistical analysis so that the estimated in-place strength will be exceeded by a large fraction of the concrete in the structure. Several statistical methods have been proposed, but there is no consensus on which should be used. Danish practice has promoted the tolerance limit approach, but there are more rigorous methods that can be implemented using a personal computer.

Finally, there has been a brief discussion of recent developments related to drilled-in tests that do not require the installation of inserts prior to concrete placement. Some of these methods load the concrete in a different manner compared with the standard pullout test, and higher within-test variability have been reported. One of these methods loads the concrete in a manner similar to the standard cast-in- place test, and comparable performance has been reported in laboratory and field evaluations. This post- installed pullout test is included in ASTM C 900.