On-site inspection of the construction quality of concrete structures reinforced with carbon fiber sheets

1 Test equipment and specimens

1.1 The bond strength tester should comply with the relevant provisions of the current industry standard "Digital Bond Strength Tester". The bond strength tester should be calibrated once a year, and should be repaired and calibrated at any time when abnormalities are found.

1.2 Sampling shall comply with the following provisions:

1 On-site inspection shall be carried out on the surface of the structure where the carbon fiber sheet has been pasted and reinforced.

2 According to the actual surface area of the reinforced structure where the carbon fiber sheet is pasted, one group of samples shall be taken for projects below 500m, with 3 samples in each group; two groups of samples shall be taken for projects from 500m to 1000m; two groups of samples shall be taken for every 1000m of projects above 1000m:

3 Samples shall be randomly selected by the inspectors, and the spacing between samples shall not be less than 500mmm.

1.3 On-site sample preparation shall comply with the following provisions;

1 The reinforced surface of the measured part shall be cleaned of stains and kept dry.

2 Pre-cut seams shall be cut from the reinforced surface to the inside of the concrete matrix, and the depth of the cut into the concrete shall be 2mm~3mm and the width shall be 1mm~2mm. The shape of the pre-cut seam shall be a circle with a diameter of 40mm.

3 A circular steel standard block with a diameter of 40m shall be pasted with sampling adhesive resin (as shown in the figure). The positive tensile bond strength of the sample bonding resin should be greater than the positive tensile bond strength of the carbon fiber sheet bonding resin. The steel standard block should be fixed after bonding.

1-Reading table；2-Carbon Fiber Bond Strength Tester；3-Steel standard block；4-Carbon fiber sheet; 5-Concrete; 6-Resin sample;  7-Pre-cut seam 2-3mm

2 Test steps

2.1 The steel standard block should be connected according to the instruction manual provided by the manufacturer of the bond strength tester.

2.2 During the test, the load should be loaded at a hook speed of 1500N/min~2000N/min, and the load value at the time of failure should be recorded and the failure form should be observed.

3 Experimental results

Classification of failure forms

The judgment of construction quality shall comply with the following provisions:

1  When the failure form is AF, the construction quality shall be judged as qualified

2  When the failure form is BF, CF, DF, the average value of the positive tensile bond strength test of each group of specimens shall not be less than 2.5N/mm², and the minimum value of the positive tensile bond strength of a single specimen shall not be less than 2.25N/mm², and the construction quality shall be judged as qualified.

3  When the failure form is BF and CF, if the average value of the positive tensile bond strength test of each group of specimens is not less than 2.5N/mm², and the minimum value of the positive tensile bond strength of a single specimen is not less than 2.25N/mm² is not met, the construction quality shall be judged as unqualified, or the number of samples shall be increased and re-inspected according to the actual project situation.

4  When the failure form is DF, if the average value of the positive tensile bond strength test of each group of specimens is not less than 2.5N/mm², and the minimum value of the positive tensile bond strength of a single specimen is not less than 2.25N/mm² is not met, the specimens shall be re-prepared and inspected.