Temperature Cycling–Induced Degradation of Dynamic Mechanical Properties of CA Mortar in Slab Ballastless Track Systems: Distinct Difference between Dry and Water-Saturated States

Abstract

Cement asphalt (CA) mortar, widely used as the filling layer in railway ballastless track systems, is frequently subjected to repeated temperature cycling during service. To explore the property evolution patterns of the dry and water-saturated CA mortar under temperature cycling (TC), the degradation behaviors of dynamic mechanical properties were investigated by temperature cycling tests within the range of − 40 ° C to 60°C, combined with dynamic temperature scanning, mercury intrusion porosimetry (MIP) for pore structure characterization, and viscoelastic constitutive modeling. Results showed that the moisture condition critically affects the effect of TC on CA mortar. The dry CA mortar following TC exhibited an increase in storage modulus accompanied by a decrease in loss factor, whereas the water-saturated mortar showed the opposite tendency. The asphalt-to-cement (A/C) ratio has a substantial impact on the dynamic mechanical properties. Higher A/C ratios accelerate the growth rate of storage modulus in dry specimens, whereas they slow the degradation of storage modulus in water-saturated specimens until the ratio exceeds 0.7, beyond which the decay accelerates. This contrasting behavior arises from different mechanisms. The increase in dried specimens is mainly attributed to intensified asphalt aging at higher A/C ratios. Specimens in a water-saturated state benefit from the toughening effect of asphalt and the cement’s inhibition of asphalt aging at lower A/C ratios, whereas excessive asphalt content ( A / C > 0.7 ) promotes the degree of aging, increases brittleness, aggravates freeze–thaw damage, and ultimately intensifies modulus deterioration. A viscoelastic constitutive model based on the fractional differential three-parameter solid model provides an accurate fit to the dynamic test curves under different TC conditions, with parameters E 0 and E 1 effectively characterizing the elastic behavior. This study provides valuable theoretical insight into the mechanical behavior evolution of CA mortar under extreme temperature and moisture conditions, and offers practical guidance for enhancing the long-term safety and durability of railway infrastructure in harsh climates, while also supporting the prediction of their long-term service life.