Appendix F 4 Standard Procedure
The Austroads Stripping potential of asphalt: tensile strength ratio (AGPT/T232) test is a standardised procedure for evaluating stripping potential. It should be noted that the Austroads procedure has an optional freeze-thaw component.
Tensile strength ratio (TSR) is the test parameter reported for the test. The broken faces are inspected after testing to determine the percentage of stripped aggregate.
Briefly, the test is performed as follows:
- Specimens are prepared from the mix design formula to an air voids content in the range of 7 to 9%. This air voids content is within the pessimum range as described previously. This will require compaction to set density as explained in Section B.6.2.
- The specimens are divided into two subsets of approximately equal voids content. One subset is conditioned by being partially saturated with water in the range of 80 to 85%, while the other subset is conditioned in a dry state. A further two specimens may be required in order to establish the partial saturation conditions that need to be applied to ensure that the correct degree of saturation is attained. There is an optional freeze-thaw cycle permitted that will in some instances decrease the tensile strength of the conditioned subset.
- The tensile strength of each specimen within a subset is determined by the tensile strength test. The potential for damage by moisture is indicated by the ratio of the tensile strength of the moisture-conditioned subset divided by that of the dry subset expressed as a percentage.
- The broken faces of all specimens are visually assessed to determine if the coarse and fine aggregates show evidence of minimal, moderate or severe stripping.
A minimum TSR value of 80% is used in a number of specifications for the acceptance of an asphalt mix having a satisfactory resistance to stripping.