Regulating drying shrinkage behavior of cement-based materials in low vacuum environments and developing a predictive model

Low-vacuum pipeline transportation is essential for surpassing train speed limits, but the lowvacuum environment can intensify the drying shrinkage of cement-based materials, impacting their structural durability. Leveraging existing shrinkage mitigation strategies, this study examines the influence of various shrinkage-reducing components and surface coating treatments on cement-based materials' shrinkage and mass loss behavior under low-vacuum condition. The findings indicate that the shrinkage strain of mortar and concrete under low-vacuum drying could reach more than 1.35 and 1.2 times that of standard drying, respectively. For mortar, fly ash (FA) and shrinkage reducing admixture (SRA) can minimize shrinkage. Silica fume (SF), nano-silica (NS), polyvinyl alcohol (PVA), and polypropylene (PP) fibers can all reduce the early shrinkage rate to varying degrees. The combined addition of FA, SF, and SRA can significantly alleviate the drying shrinkage behavior of concrete. Surface coating treatments can reduce specimen shrinkage by approximately 20 % and early shrinkage rates by about 30 %. The mass loss test results indicate that under low-vacuum drying condition, the mass loss rate of the mortar can exceed twice that of standard drying condition, with the drying rate being over three times higher. A linear fitting relationship between shrinkage strain and mass loss rate reveals a strong correlation. In low-vacuum environments, specimen shrinkage is less affected by mass loss than in standard drying condition. Shrinkage-reducing components make shrinkage less sensitive to water loss, while coatings increase this sensitivity. A new predictive model for concrete shrinkage strain has been developed based on existing models. This model incorporates the effects of shrinkagereducing components and low-vacuum environments, demonstrating high precision. The research findings offer valuable insights for the improvement of drying shrinkage performance in low-vacuum environments for cement-based materials.