Quantitative Determination of Asphalt Antistripping Additive

About the report:

A small device (StripScan) has been developed by InstroTech, Inc., that uses litmus paper and a spectrophotometer to analyze vapors from hot liquid asphalt binders and mixtures to determine the percentage of antistripping additive present. Approximately 60 five-point additive content-color index count regressions were performed on binders and mixtures to determine how well the StripScan device measured additive content. The regressions basically fit the quadratic format that is used by the manufacturer in the recommended calibration process. The regressions were best when the litmus color index count was calculated by subtracting the initial count of the blank strip from the final count after exposure for the mixtures. Changes to the instrument software and testing temperature were necessary as the investigation progressed to accommodate different grades of binders. After the planned testing was completed, some retesting of the binders was performed using modified equipment and procedures. The changes appeared to improve the consistency of the results; therefore, the author believes that additive content in binders can be determined within +0.2 percent 95 percent of the time using the modified equipment and procedures. Test results for mixtures were less accurate than for binders; however, if the vapor trap is modified as described the accuracy for mixtures should be improved substantially. Since the test can be performed quickly, multiple tests on a sample are possible. This would increase the confidence of the test results. Additional research and development are recommended and necessary before the device can be used for quality assurance testing. An accuracy of +0.1 percent is a worthy goal.

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