Performance of Hydraulic Asphalt Concrete with Acidic Aggregates in Severe Cold Regions

[Objective] To facilitate the construction of asphalt concrete core walls in the severe cold regions of Western China, this paper undertakes a systematic investigation into the influence of acidic gravel aggregates on the performance characteristics of hydraulic asphalt concrete. [Methods] The research methodology and evaluation framework were strictly guided by two pivotal Chinese technical standards: Test Code for Hydraulic Asphalt Concrete (DL/T 5362-2018) and the more recent Technical Specification for the Application of Acidic Aggregates in Hydraulic Asphalt Concrete (DL/T 5876-2024). The key performance indicators (mechanical properties, deformation behavior, impermeability, and overall durability) of asphalt concrete incorporating crushed gravel aggregates were evaluated through asphalt concrete water stability tests, direct tensile tests, bending tests, pressure-based impermeability tests for dense-graded asphalt concrete, triaxial compression tests, long-term water immersion stability tests, and long-term freeze-thaw splitting tests. [Results] (1) Complex Composition and Durability Challenge: Gravel aggregates typically exhibited a complex mineralogical composition, encompassing alkaline, neutral, and acidic aggregates, with acidic rock types often being predominant. A primary concern identified was the inherently weak interfacial bonding force between asphalt binder and acidic aggregate surfaces. Under prolonged water immersion, this weak bond facilitated a gradual displacement process where water molecules infiltrated and substituted the asphalt at the aggregate interface, leading to stripping or detachment of the asphalt film from the aggregate surface. This mechanism posed a substantial threat to the long-term durability of the asphalt concrete. Consequently, a thorough durability assessment should be required when considering the application of gravel aggregates-based hydraulic asphalt concrete in critical structures. (2) Enhancement Mechanisms via Cement Filler and Anti-Stripping Agents: The study identified effective methods to mitigate the adhesion issue. Metal ions present in cement, such as Ca2+ and Mg2+, engaged in chemical bonding with oxygen atoms within the asphalt. In the mixing process, this interaction promoted a more robust and durable bond between the asphalt and the aggregates. Furthermore, the use of anti-stripping agents was found to be highly beneficial. These agents operated through multiple synergistic mechanisms, including chemical bonding with the aggregate surface, modification of the interfacial properties, and the creation of a physical barrier against water intrusion. Collectively, these actions significantly enhanced both the durability and the mechanical performance of asphalt concrete made with acidic aggregates. Incorporating cement filler alone, or using a combination of cement filler and non-amine anti-stripping agents, effectively strengthened the adhesive bond between the gravel aggregates and the asphalt matrix, thereby markedly improving the durability of the resulting acidic gravel aggregate hydraulic asphalt concrete. (3) Mechanical Behavior and Modeling: Asphalt concrete was recognized as a temperature-sensitive material. Analysis of triaxial test data revealed that the relationship between lateral strain and axial strain approximated a linear relationship. Specifically for the gravel aggregate asphalt concrete studied, its strength demonstrated a well-defined and favorable linear increase with rising confining pressure. The material's strength could be effectively characterized using the parameters of a linear strength model, namely the cohesion and the angle of internal friction. (4) Overall Performance Improvement: Incorporating cement filler or adding non-amine anti-stripping agents substantially improved the comprehensive performance profile of acidic gravel aggregate asphalt concrete. These enhancements directly translated to superior mechanical properties, increased resistance to water-induced damage, and extended long-term durability. [Conclusion] The application of acidic gravel aggregates in the construction of asphalt concrete core wall dams is demonstrated to be technically feasible. Key performance parameters evaluated in this study, including the long-term water immersion stability coefficient, the freeze-thaw cycle splitting tensile strength ratio, and the failure tensile strain, provide a robust theoretical foundation and essential technical support for the engineering application of this material.