NCHRP 10-17 [Completed]
Use of Antistripping Additives in Asphaltic Concrete Mixtures
| Project Data
||David G. Tunnicliff|
||David G. Tunnicliff|
Moisture is often the major factor associated with the deterioration of asphalt concrete pavements. The most serious consequence of the adverse action of moisture is the loss of adhesion, commonly called "stripping," between the aggregate and asphalt cement resulting in substantial reduction in the tensile strength of the asphalt concrete paving material. Because the asphalt-aggregate adhesion properties of mixtures are very complex, many tests have been used to evaluate these properties. NCHRP Report 274, "Use of Antistripping Additives in Asphaltic Concrete Mixtures--Laboratory Phase," describes the development and verification of a laboratory test procedure for predicting the performance of pavements built with moisture susceptible aggregates, which was developed in the first phase of this project. Subsequent work provided information on the precision of the laboratory test.
A field evaluation phase of the research was begun in 1984 and extended in 1992 to evaluate the effectiveness of both antistripping additives and the test method (now designated ASTM D 4867). Nineteen test sections have been constructed in eight states with and without antistripping additives. Laboratory tests have been conducted using the actual aggregates, asphalts, and additives from the construction projects to predict pavement performance. The pavements were studied over a 6- to 8-year period to compare actual performance with the predictions. Antistripping additives added to asphalt concrete mixtures were effective at controlling stripping over that period, and ASTM D 4867 is an effective laboratory test for predicting moisture damage and the effects of additives.
Because the test sections have not experienced much moisture damage, the researchers recommend further evaluations to confirm performance trends. Based on this study, an interim limiting tensile strength ratio of 75 percent is suggested for test results with ASTM D 4867. This suggested interim limiting tensile strength ratio needs further research and states are encouraged to build their own sections to verify its usefulness. Because the Strategic Highway Research Program has recommended 6-in.-diameter specimens, research on specimen size is also needed to modify ASTM D 4867.
The project is now complete, and the results have been published as NCHRP Report 373, "Use of Antistripping Additives in Asphaltic Concrete Mixtures."