Germann Instruments

CAPO-TEST

Purpose

The CAPO-TEST permits performing pullout tests on existing structures without the need of pre-installed inserts. CAPO-TEST provides a pullout test system similar to the LOK-TEST system for accurate on-site estimates of compressive strength. Procedures for performing post-installed pullout tests, such as CAPO-TEST, are included in ASTM C900 and EN 12504-3.

Typical applications of the CAPO-TEST include the following:

• Quality assurance testing of the finished structure
• Verification of in-place strength if strength of standard-cured specimens fails to meet acceptance criteria
• Estimating strength of concrete in existing structures
• Evaluation of fire-damaged structures

Principle

When selecting the location for a CAPO-TEST, ensure that reinforcing bars are not within the failure region. The surface at the test location is ground using a planing tool and a 18.4 mm hole is made perpendicular to the surface using a diamond-studded core bit. A recess (slot) is routed in the hole to a diameter of 25 mm and at a depth of 25 mm. A split ring is expanded in the recess and pulled out using a pull machine reacting against a 55 mm diameter counter pressure ring. As in the LOK-TEST, the concrete in the strut between the expanded ring and the counter pressure ring is in compression. Hence, the ultimate pullout force F is related directly to compressive strength.

The test is performed until the conic frustum between the expanded ring and the inner diameter of the counter pressure is dislodged. Thus there is minor surface damage, which should be repaired for aesthetic reasons or to avoid potential durability problems.

Correlation and Accuracy of Estimated Strength

Several investigations have shown that the pullout strength measured by the CAPO-TEST is essentially the same as the pullout strength measured by LOK-TEST. This equality is illustrated in the graph to the right, which includes data from four independent studies. The maximum aggregate size varied from sand up to 40 mm. Thus the general correlations for the LOK-TEST are also valid for the CAPO-TEST.

Based on testing experiences and laboratory studies, it has been found that the accuracy of the compressive strength estimated by the CAPO-TEST using the general correlations shown on page 85 is similar to results obtained with the LOK-TEST. For normal density concrete, the coefficient of variation of individual CAPO-TEST results is about 8 %.

Comparison with Core Strength

An investigation on 10 bridges compared the strength of cores with strengths estimated on the basis of the CAPO-TEST and the rebound hammer test (ASTM C805, EN 12504-2). As shown in the following figure, strengths estimated by the CAPO-TEST were on average within 6 % of the core strength. This study confirms the inherent reliability of pullout testing for estimating in-place compressive strength.

Reference: Moczko, A., “Comparison Between Compressive Strength Tests From Cores, CAPO-TEST and Schmidt Hammer,” Wroclaw Technical University, Poland, 2002.

Example Applications

Routing recess for the expandable ring in preparation for CAPO-TEST to evaluate surface strength of an industrial floor slab

View of valid CAPO-TEST of a slab. Note the well-formed failure ring on the surface of the slab

CAPO-TEST being performed in parking garage to evaluate in-place strength of suspect concrete

CAPO-TEST Equipment and Ordering Numbers

Inserts and Resizing Tool
C-112 CAPO expandable inserts

C-111 Resizing Tool for resizing C-112 insert 2 to 3 times

CAPO-TEST Kits
The CAPO-TEST kit includes C-101 Preparation Kit, the C-102 DSV-Kit, and a C-104 pull machine kit with the 0 to 100 kN digital gauge.

C-101 CAPO-TEST Preparation Kit
This kit is used to drill the center hole and to cut the recess to accommodate the expandable insert. The kit also contains the unit for expanding the CAPO-TEST insert and other miscellaneous tools for conducting the test.

C-102 DSV-Kit

The kit includes the diamond planer, the suction plate, a vacuum pump, and the necessary tools for planing the surface so that it is flat before drilling the center hole and routing the recess. The diamond planer, the diamond core drill unit, and the recess router are positioned in the recess of the suction plate for proper alignment and dimensional control.

C-104 CAPO Pull Machine Kit

The hydraulic pull machine has a calibrated 0 to100 kN precision electronic gauge with memory for storage of test results (peak-value, time and date of testing). The peak-value is shown after a test has been terminated. The internal resolution of the gauge is 0.01 kN, but the pull force is displayed to the nearest 0.1 kN. The same pull machine can be used for the BOND TEST and the LOK-TEST.

Note: The calibration of the pull machines needs to be verified at least once a year, or sooner, if serviced or damaged. The L-30 Load Verification Unit is available for this purpose.