Pavement

The Australian polymer modified binder (PMB) specification currently includes two tests, segregation of PMBs and ease of remixing of PMBs, which are included in the specification to determine whether the polymer in a PMB will separate out under conventional storage and transport conditions.  A storage stability test is used in Europe to determine whether polymer separation will occur during storage of PMBs. This study compared results in the Australian and European tests.

A series of PMBs with different segregation propensities were subjected to each of the three tests to determine the sensitivity of each test to the separation of the polymer in PMBs. The sensitivity of the tests to polymer separation was found to be in the order storage stability tests > segregation tests > ease of remixing tests.

Field mixing simulation studies were conducted in the laboratory to ascertain which of these tests best predicted whether typical field mixing protocols could redisperse the polymer in segregated PMBs.  Field mixing simulations indicated that the polymer in segregated PMBs could be redispersed by mixing in the case of PMBs which showed satisfactory results in the storage stability and segregation tests.  The polymer in segregated PMBs could not be redispersed by mixing in the case of PMBs which showed satisfactory results in the ease of remixing test.

A literature review was conducted to investigate the chemical processes that occur when styrene‑butadiene‑styrene (SBS) PMBs degrade during hot storage and the effects of PMB degradation on field performance.  A review of international PMB specifications was not able to identify any country where a specific test was used to limit the degradation of PMBs during storage.  Based on the information obtained during the literature review, it is recommended that further work be conducted to determine the effects of PMB degradation on the field performance of PMBs.