Investigation of the use of strip-prone aggregates in hydraulic asphalt concrete

A study is made of the suitability of strip-prone aggregates for use in asphalt concrete water barriers in embankment dams. Standard boiling tests were used for ranking various aggregate types with respect to water susceptibility and aggregate-bitumen adhesion. Indirect tension tests (splitting tests) were used to study the effects of aggregate-bitumen adhesion on asphalt concrete tensile strength. The test results show the significant detrimental effects of using strip-prone aggregates for open-grade porous asphalt (air void 4–10%), but that aggregate-bitumen adhesion and tensile strength could be increased by adding amine or hydrated lime to the asphalt mix. However, a similar test series on dense-grade hydraulic asphalt (air void 2–3%) shows no detrimental effects of using strip-prone aggregates. Furthermore, there were no significant differences in compressive strengths or beam bending strengths and strains at failure between specimens with or without strip-prone aggregates and with or without amine added. This was the case even for specimens having been cured by exposure to 100 freeze–thaw cycles at +25 °C to −25 °C. For hydraulic asphalt, which is virtually impervious with a significant bitumen film thickness covering the aggregate particles, it does not seem required to use additives to improve the aggregate-bitumen adhesion properties. However, further testing should be done to study any long-term effects of using strip-prone aggregates.