Strength Criteria for Cement-Treated Large-Size Macadam Base to Control Fatigue Failure

With a low cement dosage and a well-formed skeleton-dense structure, super-large-particle-size cement-stabilized macadam (CTB-50, maximum particle size of 53 mm) can effectively reduce base course cracking and construction costs. Nevertheless, the existing literature lacks research on the strength design criteria for CTB-50, and the absence of dedicated strength specifications currently limits its practical application. This study investigates the mechanical properties of CTB-50 and the stress levels in the (sub)base course under construction vehicle loading, based on the vertical vibration compaction method (VCM) and Miner's fatigue cumulative theory. Aiming to prevent ultimate failure under a single load during construction and fatigue failure under repeated loading during both construction and operation, this study proposes strength criteria for CTB-50 to control fatigue damage. The 7-day compressive strength of CTB-50 specimens prepared using the VCM is approximately 90% of that of field core samples, whereas that obtained using the static-pressing method is less than 70% of the field core sample value. The mechanical strengths of CTB-50 specimens prepared via the VCM are highly correlated with those of on-site core samples. Based on the strength criteria for controlling ultimate failure during construction and fatigue failure during service, this paper proposes strength criteria for controlling the fatigue failure of CTB-50. Specifically, the 7-day splitting and compressive strengths of the base course for expressways and first-class highways should exceed 0.77 MPa and 7.6 MPa, respectively, while those of the sub-base course should exceed 0.71 MPa and 7.0 MPa, respectively.