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Introduction to Bond Strength tensile Test of Mortar

Introduction to Bond Strength tensile Test of Mortar

1. Standard test conditions

1.1 Test temperature: (23±2)

1.2 Relative humidity: 45-75%

2. Test equipment

2.1 Tensile testing machine: The breaking load of the tensile testing machine is within the range of 20% to 80% of its range, the accuracy is 1%, and the minimum indication value is 1N

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2.2 Special fixture for tensile testing: It meets the requirements of JG/T3049 "Putty for Building Interiors", as shown in the following figure:

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2.3 Forming frame: the outer frame size is 70x70mm, the inner frame size is 40x40mm, the thickness is 6mm, and the material is rigid PVC or metal, as shown in the figure below:

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2.4 Steel backing plate: outer frame size 70x70mm, inner frame size 43x43mm, thickness 3mm, as shown below

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3. Specimen Preparation

3.1 Preparation of base cement mortar specimens

3.1.1 Raw materials: cement conforms to grade 42.5 cement in accordance with GB175; sand conforms to sand in JGJ52; water conforms to water standard of JGJ63

3.1.2 The mixing ratio is cement:sand:water=1:3:5 (mass ratio)

3.1.3 Forming: pour the cement mortar prepared according to the above mixing ratio into a 70x70x20mm hard polyvinyl chloride or metal mold, vibrate or artificially form, and the inner wall of the test mold should be painted with water-based mold release agent in advance, and it should be dried and used for later use. .

3.1.4 Demould after 24 hours of molding, put it in (23±2) water for 6 days, and then put it under the test conditions for more than 21 days. Before the test, use 200# sandpaper or grindstone to shape the cement mortar specimen Grind the surface and set aside.

3.2 Preparation of mortar slurry

3.2.1 Preparation of dry-mixed mortar slurry

1) The sample to be tested should be placed under test conditions for more than 24 hours

2) Weigh a sample of no less than 10kg to be tested, and weigh the water according to the proportion provided by the product manufacturer. If a range of values is given, the average value is used.

3) Put the sample to be tested into the mortar mixer, start the machine, slowly add the specified amount of water, and stir for 3 to 5 minutes. The mixed material should be used up within 2 hours.

3.2.2 Preparation of wet-mixed mortar slurry

1) The sample to be tested should be placed under test conditions for more than 24 hours

2) Weigh the material according to the proportion provided by the product manufacturer, and the total amount of dry material shall not be less than 10kg

3) Put the weighed material into the mortar mixer, start the machine, slowly add the specified amount of water, and stir for 3 to 5 minutes. The mixed material should be used up within the specified time.

3.2.3 Preparation of freshly mixed mortar

1) The sample to be tested should be placed under test conditions for more than 24 hours

2) Weigh the materials according to the mixing ratio required by the design, and the total amount of dry materials shall not be less than 10kg

3) Put the weighed material into the mortar mixer, start the machine, slowly add the specified amount of water, and mix for 3 to 5 minutes. The mixed material should be used up within 2 hours.

3.3 Preparation of tensile bond strength test pieces

Place the forming frame on the forming surface of the cement mortar test block prepared in accordance with 3.1, pour the dry-mixed mortar prepared in accordance with 3.2 or the wet-mixed mortar sample directly taken from the site into the forming frame. The rod is evenly inserted and pounded 15 times, artificially tamped 5 times, then turned 90°, and tamped 5 times, then smooth the surface of the mortar with a scraper in the direction of 45°, gently demould, at a temperature of (23±2) , Cured to the specified age in an environment with a relative humidity of 60% to 80%. Prepare at least 10 test pieces for each mortar sample.

4 Tensile bond strength test

4.1 Tensile bond original strength test

4.1.1 Curing the test piece for 13 days under standard test conditions, coat the surface of the test piece with a high-strength adhesive such as epoxy resin, then place the upper fixture on the adhesive, and ensure that the upper fixture is not Skew, continue to maintain for 24 hours.

4.1.2 Determination of tensile bond strength on the tensile testing machine, the schematic diagram is as follows:

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4.1.3 Sleeve the steel backing plate on the base mortar block, install the tensile bond strength fixture on the testing machine, place the test piece in the tensile fixture, and connect the fixture to the tensile testing machine with a ball hinge movable connection, loading at ( 5±1) mm/min until the specimen fails. The failure surface should be inside the inspection mortar, then it is considered to be valid and record test value. If the failure is tensile fixture or adhesive, the test results are invalid.

5 Test results

The tensile bond strength should be calculated as follows

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Note: fat------ Tensile bond strength of mortar (Mpa)

          F------The load when the specimen fails (N)

         AZ------bonding area(mm2)

The tensile bond strength value of a single specimen shall be accurate to 0.001Mpa, and the average value of 10 specimens shall be calculated. If the difference between the strength value of a single specimen and the average value is greater than 20%, the test value with the largest deviation shall be discarded successively until the difference between each test value and the average value does not exceed 20%. When there are no less than 6 valid data in the 10 specimens, the average value of the remaining data is taken as the test result, and the result is accurate to 0.01Mpa. When there are less than 6 valid data in the 10 specimens, the test results of this group are invalid. The test piece should be re-prepared for the test.

7. For the tensile bond strength required by special conditions, after processing as required, repeat the above test.

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