Optimization of Tack Coat for HMA Placement (2012)

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C-1 A p p e n d i x C Standard Test Method for Assessing Tack Coat Installation Quality Using the LTCQT

C-2 C-2 Proposed Standard Method of Test for DETERMINING THE TACK COAT QUALITY OF ASPHALT PAVEMENT IN THE FIELD OR LABORATORY AASHTO Designation: TP XX-XX Proposed test method under review before submitting to AASHTO Subcommittee on Materials American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001

C-3 C-3 Proposed test method under review before submitting to AASHTO Subcommittee on Materials – Month Day, 20XX Proposed Standard Method of Test for DETERMINING THE TACK COAT QUALITY OF ASPHALT PAVEMENT IN THE FIELD OR LABORATORY AASHTO Designation: TP XX-XX 1. SCOPE 1.1. This test method covers the determination of the tack coat spray application quality as measured by the tensile strength of tack coat materials on free surface of asphalt concrete in the field or laboratory. 1.2. This test can be performed in the field on surface of asphalt concrete or 150 mm (5.9 in.) diameter gyratory compacted samples. 1.3. This standard may involve hazardous material, operations, and equipment. This standard does not purport to address all safety problems associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standard: T 53 Softening Point Of Bitumen (Ring-And-Ball Apparatus) 3. TERMINOLOGY 3.1. Tack Coat Spray Application Quality – A measure of the uniformity of coverage of tack coat application on a pavement surface, also referred to as tack coat quality. The quality of tack coat is described by the tensile strength of the tack coat material. 4. SUMMARY OF METHOD 4.1. The standard test materials and test apparatus consist of the Louisiana Tack Coat Quality Tester (LTCQT), LTCQT software, computer, weights to hold the LTCQT in place during testing, and an Infrared Reflective Heating (IRH) device used to desiccate emulsion. A heat gun and fan are recommended to heat the surface to testing temperature. A thermometer should be used to determine the surface temperature. 4.2. The test procedure involves desiccating a tacked surface using the IRH device, adjusting the temperature of the surface with the fan or heat gun to reach testing temperature, and applying a compressive load to the tacked pavement surface for a given amount of time using the LTCQT device and software. At a prescribed displacement rate, the movement of the loading plate away from the tacked surface

C-4 C-4 results in tensile loading until failure. The maximum tensile strength reflects the tack coat quality of the material. 5. SIGNIFICANCE AND USE 5.1. This test method is suitable for field or laboratory tests to determine the tack coat quality of a tacked surface as measured by the tensile strength. The knowledge of tack coat quality serves as a tool in characterizing the tack coat material. 6. APPARATUS 6.1. Louisiana Tack Coat Quality Tester – The device shall be equipped with a closed-loop servo motor actuator for precision control of the rate of displacement during testing. It shall be capable of measuring loads of up to 446 N (100 lbf) with an accuracy of ±1%. The displacement of the actuator shall be measured using a position transducer that has a total travel of 100 mm. 6.2. Computer and Software – The software shall be designed such that it displays the time, normal load, and displacement of the actuator continuously during testing while graphically illustrating the relationship of the normal load and time. It shall allow the user to input the required compressive load, the time to hold the compressive load, and the displacement rate required. The actual holding time of the compressive load shall be displayed during testing as well as the actual displacement rate. In addition, the software shall allow the user to move the actuator manually. 6.3. Infrared Reflective Heating Source – It shall be equipped with a 250 watt, 120 volt bulb. It shall be designed such that it can be positioned six inches from the surface to be tested without contact made with the tacked surface. 6.4. Thermometer – The thermometer shall be suitable to measure the temperature of a tacked surface without directly contacting the test area. It is recommended that an infrared thermometer be utilized. 6.5. Weights – The weights used shall be equal or greater than the expected maximum normal load. Note that the normal load applied by the machine cannot exceed 446 N (100 lbf). 6.6. Temperature control devices – The mechanism of the temperature control device shall be to adjust the surface temperature to the required test temperature. It is recommended that a fan be used to cool the tacked surface and a heat gun be used to heat the tacked surface.

C-5 C-5 Figure 1. Illustration of the LTCQT device. 7. H AZ ARDS 7.1. Standard laboratory safety precautions must be observed when preparing and testing asphalt concrete specimens. 8. T EST S PECIMENS 8.1. Testing area shall be cleaned prior to tack coat application. 8.2. Tack coat material shall be applied using the appropriate method. 8.3. Emulsified tacked surfaces shall be desiccated prior to testing. It is recommended that this shall be accomplished by placing the Infrared Reflective Heating source six inches above the tacked surface for a minim um of one hour. Note that this time may be extended for bulk application rates greater than 0.05 gal/yd². 8.4. Number of test areas – a single test shall consist of at least three test areas. 8.5. Test area shall be numbered and the location shall be documented. Weight Actuator Loading Plate Driving Motor Frame Load Cell

C-6 C-6 9. PROCEDURE 9.1. Testing areas shall be conditioned to the correct testing temperature using a heat blower or fan. It is recommended that the testing temperature shall be the softening point of the tack coat material. 9.2. Device positioning – Place the LTCQT directly above the tacked surface to be tested. Lift up the front end of the device to verify that the loading plate is positioned directly above the tacked surface that will be tested. 9.3. The correct weight shall be placed on top of the LTCQT device. 9.4. The compressive load, time to hold the compressive load, and the displacement rate shall be entered into the computer by the user. The compressive load shall not exceed the weight placed on top of the LTCQT device. 9.5. Immediately following the initiation of the test, the load shall be offset such that the software displays a load of 0 N (lbf) prior to the contact between the loading plate and the tacked surface. It is also recommended that the plate be positioned as close as possible to the tacked surface prior to testing so as to minimize the change in temperature. The initial position of the loading plate shall be determined to allow sufficient time for the observation of the initial load and application of the offset. 9.6. The compressive load shall be mechanically applied to the tacked surface for the specified amount of time. Once the allotted time has ended, the loading plate shall automatically move away from the tacked surface at the prescribed displacement rate. The software shall by design record the normal load, vertical displacement, and time throughout the test. Record the ultimate tensile load, Pult, of the tack coat material, Figure 2.. 10. CALCULATIONS 10.1. Calculate the tack coat tensile strength, TS, as follows: where: TS = Tensile Strength, Pa Pult = ultimate tensile load, N D = diameter of the loading plate, m 11. REPORT 11.1. Test location. 11.2. Note the appearance of the tacked surface before and after testing including any contaminants, milling striations, stripping, tack coat streaks, etc. 11.3. Test results: 11.3.1. Loading plate dimensions – including the diameter, and the cross-section area. 11.3.2. Ultimate tensile load applied. 11.3.3. Tensile strength, Pa. TS P D ult = pi 2 4

C-7 C-7 11.3.4. Corresponding vertical deformation. 11.3.5. Average and standard deviation of tensile strength for the set of tested areas. 12. P RECISION AND BIAS 12.1. The precision and bias statements for this method have not been determined. 13. K EYWORDS 13.1. Tack Coat Quality, Tensile Strength, Asphalt Overlay, Tack Coat, Slippage Failure. Figure 2. Typical LTCQT test result. Tensile L oad Time P ult