• Quality Control of Field Asphalt Mixtures and Compatibility of Aggregates and Emulsions using Asphalt Compatibility Tester (ACT)

    NCDOT Research Project Number: 2020-15

 Executive Summary

  • ​Asphalt mixtures used in pavement construction are required to meet the North Carolina Department of Transportation (NCDOT) moisture sensitivity specifications. To improve resistance to moisture damage various antistrip additives are used by the asphalt plants producing asphalt mixtures. These antistrip additives help improve the adhesion between asphalt and aggregate and thus improve the resistance of the asphalt mixtures to moisture damage. The antistrip additives are added to the asphalt mixture at the plant by various mechanisms based on the type of antistrip additive being used or they come premixed with the asphalt liquid. The additive is usually added to the asphalt liquid. A problem in the mechanism used to add the antistrip additive to the asphalt might lead to a lesser amount, or no antistrip additive being added into the asphalt mixture. This might lead to the asphalt mixture not meeting the NCDOT moisture sensitivity specifications. Since the additive is added to the asphalt liquid, any problem in the mechanism will not be noticed until the asphalt mixture is tested for its moisture sensitivity.

    NCDOT currently uses Tensile Strength Ratio (TSR) with modified AASHTO T283 conditioning procedure to test the moisture sensitivity of asphalt mixtures. The current test method uses the ratio of the indirect tensile strength of the conditioned and unconditioned specimens (TSR). TSR test is a time-consuming test which takes anywhere between 3 days to a week to complete the test. The variability involved in TSR test results is also observed to be high. Because of the time required to complete the testing and the variability involved in the test, the TSR test is not used for regular quality control of moisture sensitivity of the asphalt mixtures produced in the plant. Hence, there is no test which is used to do quality control of moisture sensitivity of the asphalt mixtures produced in the plant. There is a need for a quicker test method(s) that is quantitative, has less variability, and simple enough to be used as a quality control test method for moisture sensitivity of plant-produced asphalt mixtures.

    Asphalt mixtures used for pavement rehabilitation which use emulsion such as chip seals are required to meet the NCDOT compatibility criteria. The current method to conduct compatibility test uses procedures as per NCDOT M&T Asphalt Procedure A-24, Rev 2 which is a modified version of AASHTO T-59. This current method is qualitative measure of compatibility as it is based on visual inspection to grade the aggregate and emulsion mix. However, since visual inspection is used to grade, it is difficult to get consistent and quantifiable results. There is a need for a standard test method that is quantitative and has less user variability. The proposed test method will use two color measuring device, Asphalt Compatibility Tester (ACT) and Colorimeter device to the compare the amount of uncoated material in the aggregate and emulsion mixture. The effect of antistrip additives on aggregate-emulsion mix and conducting boil test to determine aggregate-emulsion compatibility will be done in this proposed research.
    The overall objectives of the proposed research are – (1) Develop a procedure to identify the optimum antistrip additive content for each antistrip additive, in the laboratory; (2) Quantify the stripping potential of the plant produced asphalt mixtures using the ACT device and the colorimeter device; (3) Develop L* and percentage stripping limits using the Asphalt Compatibility Tester (ACT) device for plant-produced mixtures; (4) Develop a limit based on ER ratio using Impact Resonance Test; (5) Determine the frequency of ACT, TSR test using Moisture Induced Stress Tester (MIST) conditioning, and Impact Resonance Testing; (6) Quantify the compatibility between aggregate and emulsion for chip seals; (7) Develop guidelines to use ACT and colorimeter device as quality control tool in the field for chip seal mixes; (8) Explore the potential to use antistrip additives in aggregate-emulsion mix; and (9) Explore the potential for boil test (ASTM D3625) for aggregate-emulsion mix using color measuring devices.

    ​The results from this testing will provide a guideline for quality control of moisture sensitivity of plant-produced asphalt mixtures and a modified compatibility test for aggregate-emulsion mixtures.

Akhtarhusein A. Tayebali
Akhtarhusein A. Tayebali; Cassie A. Castorena
Tony D. Collins
Mustan Kadibhai, PE, CPM
NC State University

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 Report Period

  • August 1, 2019 - July 31, 2021


  • In Progress


  • Pavement, Materials and Maintenance

 Sub Category

  • Asphalt Mix Design

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