Enhancing frost resistance of cement-stabilised macadam base layers through synergistic effects of multiple additives

Low temperatures and frequent freeze–thaw cycles in permafrost areas weaken cement-stabilised macadam (CSM), requiring improved frost resistance. This study investigates four modifiers – re-dispersible latex powder (RDP), water-absorbent resin (WAR), expansion agent (EA), and polypropylene fibre (PPF) – through orthogonal testing with range analysis and analysis of variance. Five frost-related mechanical indices were evaluated, and the optimal mix was compared with ordinary CSM. WAR had the strongest effect on mass loss, PPF dominated the decline of unconfined compressive strength (UCS), resilient modulus, and elastic modulus, and EA primarily influenced splitting-strength loss. The optimal formulation (3% EA, 2% RDP, 1% WAR, 0.2% PPF) markedly enhanced frost resistance, reducing the loss of UCS, resilient modulus, elastic modulus, and splitting strength across freeze–thaw cycles. X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry verified the multi-component synergy. Synergistic improvement resulted from void filling, calcium-ion complexation, water absorption, and fibre anchoring within the matrix.