Research on the service performance of CA mortar: field behaviour characterization, multi-scale testing, and performance improvement methods

The cement and emulsified asphalt (CA) mortar layer is a critical bonding component between the track slab and the base plate in the CRTS II slab track structure. This study presents a comprehensive field investigation and laboratory evaluation of the in-service performance of CA mortar after 10 years of operation in both cold (Beijing) and warm (Nanjing) regions of China. Field inspections revealed external gap damage ratios of 4.1% and 11.8% in the cold and warm regions, respectively, while internal void damage ratios reached 41.7% and 47.0%. Damage was more severe in the warm region due to higher temperatures and greater precipitation. The interlayer shear strength of track slabs decreased to approximately 60% of the initial value due to interfacial voids. Laboratory tests confirmed that the mechanical properties of CA mortar – including compressive strength, flexural strength, elastic modulus, water absorption, and freeze–thaw resistance – still met the design requirements. Microscopic analysis indicated that freeze–thaw effects were concentrated within depths of 12 mm and 3 mm in the cold and warm regions, respectively, while rainfall-induced calcium leaching occurred at depths of 1 mm and 4 mm. Asphalt ageing was slight in both regions, though more pronounced in the warm region. Two repair materials – permeable crystalline and epoxy resin – were evaluated. Epoxy resin significantly improved freeze–thaw resistance and wear resistance, while the permeable material enhanced compressive strength by 11.5%. Field tests demonstrated that epoxy resin grouting increased the interlayer shear strength of track slabs by 125%, exceeding the original design performance.