METHOD FOR DETERMINING THE TENSILE ADHESIVE STRENGTH OF ASPHALT PAVEMENT TACK COAT (Kansas Test Method KT-78)

Transcription

1 METHOD FOR DETERMINING THE TENSILE ADHESIVE STRENGTH OF ASPHALT PAVEMENT TACK COAT (Kansas Test Method ) 1. SCOPE This method covers the test procedure used to measure the tensile adhesive strength of asphalt pavement tack coat. This test procedure may involve hazardous materials, operations, and equipment. Follow all safety precautions when performing the test. This test is similar to ACI 503R, Appendix A, of the ACI Manual of Concrete Practice. 2. REFERENCED DOCUMENTS 2.1. Part V, Section , Random Sampling ACI Manual of Concrete Practice 503R, Appendix A Use of Epoxy Compounds with Concrete. 3. APPARATUS 3.1. Grinder or sander Core drill with a 2 inch (50 mm) inside diameter diamond tipped core barrel and a 6 inch (150 mm) nominal diameter diamond tipped core barrel Ice Markers suitable for marking asphalt samples Standard 1 1/2 inch (37 mm) diameter pipe caps, where the bottom surface has been machined flat and the shoulder has been cut to provide a 2 inch (50 mm) diameter bonding surface. See Figure 1 below. The surface of the pipe cap should be textured to provide good adhesion to the adhesive. This may be achieved by sandblasting, scoring or any method that produces a roughened bonding surface. The surface of the cap must be clean and free of any rust or oil prior to use. Cleaning with acetone prior to each use is recommended A rapid curing adhesive with strength and viscosity properties suitable for bonding the pipe caps to the overlay. A high viscosity, rapid setting epoxy with a pot life of 3 to 25 minutes is recommended Mixing utensils for adhesive. Small plastic cups and tongue depressors are suitable for mixing Electric fan A mechanical testing device for pulling a bonded pipe cap in tension similar to that shown in ACI 503R, Appendix A, of the ACI Manual of Concrete Practice. The device used for this test shall have a feature that eliminates torque being applied to the test specimen. See Figure A tension link scale, crane scale or dynamometer with a capacity of 500 lbf (200 kg) with resolution and accuracy to 1 lbf (0.5 kg) or better and an ability to retain and display the peak load. The scale must have been calibrated or normalized to a NIST traceable standard within the previous 12 months. Page 1/

2 3.11. A table-like fixture with an adjustable shelf below the top surface and with a 3 inch hole in the top surface. See Figure A digital thermometer with probe, readable to 0.1 F (0.1ºC) Ruler or measuring device An oven or propane torch A stiff putty knife or scraper Calipers Framing square Wire brush Wire rack x8 pan with fine aggregate. Note: Test equipment for this procedure may be available in various forms and may be used with the approval of the Engineer. 4. OBTAINING SAMPLES 4.1. Select the station at which the samples will taken by method described in Part V, Section , Random Sampling. Record the time at which the pavement is placed at the selected station. Record the surface condition on which the overlay is placed, i.e. milled surface, existing surface, new pavement Sand, grind or wire brush at the coring locations to provide a finish suitable for the adhesive to bond to the surface. The use of right angle grinder with a 36 grit sanding disk to remove surface asphalt and expose the aggregate has proved to be suitable Using the 2 inch core barrel, core to a depth ¼ to ¾ inch deeper than the expected overlay depth. The core drill must be oriented perpendicular to the pavement surface to within ¼ inch in 12 inches. Use a framing square to check the perpendicularity at two points 90 degrees apart around the circumference of the core barrel. Core three times in a triangular pattern so the set of two inch cores may be circumscribed by a six inch circle. It is necessary to core to a depth slightly below the overlay but not so deep as to penetrate the layer of pavement on which the overlay is placed. It may be necessary to use ice placed on the sample location for a period of time prior to coring to prevent damage to the sample. The core should remain attached to the pavement. DO NOT remove the cores from the pavement. Coring should be done at slow pace with little downward pressure to avoid damage to the specimen If the overlay separates from the base during coring, examine the surface of the base layer. Note the location and presence or absence of visible tack. Repeat the steps in 4.2 through 4.3 at a point 3 feet away in the direction of paving. If the overlay separates at the new location the test result is considered a failure and both locations, presence or absence of tack, and the separation during coring should be recorded. Page 2/

3 If one of the cores separate in the base layer during coring, note the location and repeat the steps in 4.2 through 4.3 at a point 3 feet away in the direction of paving. If the cores separate at the new location, the base layer is not strong enough for this test method or the coring technique needs to be evaluated. Both locations and the separation during coring in the base layer should be recorded If one or two of the cores separate as noted in or but a total of three intact cores are obtained, note the separations in the test report and continue with the remainder of the test procedure Using the 6 inch core barrel, center the drill over the set of 2 inch cores and core to a depth of nine inches or to the depth of the pavement, whichever is less. Any length of six inch core removed from the hole that includes the substrate on which the overlay was placed and the intact 2 inch cores is acceptable for testing Remove the 6 inch core from the pavement using the minimum amount of lateral force necessary to break the core loose Gently turn the core over to drain water from the 2 inch cores Verify that the 2 inch core barrel reached a depth below the overlay interface by inserting a thin steel ruler or wire witness between the 2 inch cores and the remainder of the 6 inch core. Note that waste material may be present at the bottom of the core in the form of mud or particles that must be gently pushed aside to reach the full depth of the core. Use care not to apply any lateral force to the 2 inch core Transport the samples to the field laboratory in an upright manner taking care to avoid any shock that might loosen or dislodge the 2 inch cores. 5. TEST PROCEDURE 5.1. In a field laboratory with a controlled air temperature maintained less than 77 F (25ºC) place the sample on an elevated wire rack in front of a fan so that air can circulate around the entire sample. Acclimate the sample to room temperature until the temperature at the bottom of the 2 inch core is less than 77 F (25ºC). If the sample is cold and damp allow extra time for temperature acclimation Bond a 1 1/2 inch (37 mm) pipe cap to the cored overlay disk. The adhesive used to bond the pipe cap to the overlay should be a rapid curing adhesive with a minimum working life of approximately 3 minutes. Apply a thin layer of adhesive to both the pipe cap surface and the cored disk. Attempt to evenly cover the overlay surface and cap filling in all voids. Do not allow any adhesive to flow over the edge of the cored disk down into the cored area. If adhesive reaches the interface of the overlay and the substrate or bonds the cored disk to the remainder of the overlay, do not record the test result. If samples are to be tested from more than a single location it will save time to bond one cap to each sample at the same time. The cap may be bonded during the temperature acclimation period in Determine the temperature by allowing a probe type thermometer to stabilize at room temperature, recording the temperature and then carefully placing the probe in contact with bottom of the 2 inch core. The temperature of the probe must be stable to 0.2 F (0.1ºC) for a period of 3 minutes before either reading is taken. Do not apply any lateral pressure to the 2 inch core when inserting the probe. Page 3/

4 The use of infrared thermometers is specifically prohibited Perform the tensile adhesion test at the time required by the relevant specification Place the test specimen on the fixture shelf so that the cap is centered under the hole in the table. If the bottom of the core is not flat a shallow pan filled with fine aggregate may be used to help keep the specimen in an upright position. Raise the shelf until the top of the core is seated flat against the bottom of the table and the pipe cap is centered in the hole Gently screw the eyebolt loosely into the pipe cap. Do not over tighten or apply torque to the sample. Place the apparatus on top of the table centered over the specimen and attach the scale to the apparatus and to the eyebolt in the pipe cap. Set the scale to peak load mode. Without tension on the specimen, zero the scale Apply a preload of approximately 10 lbf (5 kg). Position yourself so that a ¾ turn of the handle can be made in a smooth continuous motion. Apply a load with a travel rate of 0.8 +/- 0.1 inches per minute. With a thread pitch of 11 threads per inch this corresponds to a rotation rate of the handle of one turn in 6 to 8 seconds or 3 to 4 seconds per half turn. DO NOT exceed the capacity of the scale Record the peak load for each test core to the nearest 1 lbf (0.5 kg). If the load exceeds the scale capacity, record the load as 500+ lbf with a note that the capacity of the scale was exceeded Record the location of failure for each test core and percent failure in the asphalt layer that failed. Various types of failures: Failure at the interface of the top layer and substrate. Failure in the top layer. Failure in the substrate. Failure in the top layer and substrate, record a percentage of top layer vs. substrate. Failure in the top layer or substrate and the interface, record a percentage of top layer or substrate vs. interface. Failure of the adhesive Measure and record the diameter of the core at the failure location. Take two measurements to the nearest inch (0.025 mm) at right angles with the calipers Repeat 5.2. through for all three specimens Clean the pipe caps by heating in an oven set to 350 F for one hour or by heating with a propane torch until the adhesive degrades to the point that it can scraped from the cap with a putty knife or scraper. Thoroughly clean the cap surface with a wire brush or sand paper to remove the remainder of the adhesive. Page 4/

5 5.10. Motorized test equipment may be used with the Engineer s approval. 6. CALCULATIONS 6.1. Calculate average diameter for each specimen to the nearest inch (0.025 mm) Calculate cross sectional area to the nearest 0.01 inch 2 (0.25 mm 2 ) for each 2 inch specimen Calculate the stress at failure to the nearest 0.1 psi (0.7 kpa) for each specimen If a specimen fails at more than 50% in the surface layer or the substrate and with a value less than required by the specification do not use that sample to calculate the average stress at failure If the adhesive fails with a value less than required by the specification do not use the test result to calculate the average stress at failure. If the adhesive fails with a value less than required by the specification in all three specimens, the test is inconclusive If all specimens fail at more than 50% in the surface layer or the substrate and with a value less than required by the specification the test result is inconclusive. This does not indicate a tack coat failure Calculate the average stress at failure for the three specimens. 7. RECORD AND REPORT 7.1. Record the average stress at failure to the nearest 0.1 psi (0.7 kpa) Report the average stress at failure to the nearest 1 psi (7 kpa) Record all test data required on the report form in this method. Figure 1. Page 5/

6 Figure 2. Figure 3. Page 6/

7 REPORT FORM METHOD FOR DETERMING THE TENSILE ADHESIVE STRENGTH OF ASPHALT PAVEMENT TACK COAT Project Number: Date Placed: Time Cored: Station: Time Placed: Surface: Sample Id Location In/Between Wheel Paths Notes Sample Id: Date Tested: Time Tested: Core Temp F: a Load lbf: b Dia. 1 in.: Failure Type: Area: c Dia. 2 in.: e f a/e Stress PSI: Avg. Dia.: d Sample Id: Date Tested: Time Tested: Core Temp F: a Load lbf: b Dia. 1 in.: Failure Type: Area: c Dia. 2 in.: e f a/e Stress PSI: Avg. Dia.: d Sample Id: Date Tested: Time Tested: Core Temp F: a Load lbf: b Dia. 1 in.: Failure Type: Area: c Dia. 2 in.: e f a/e Stress PSI: Avg. Dia.: d Average Stress: PSI Page 7/