Research on key technologies of vacuum grouting for post-tensioned precast box girders in large-temperature-difference environments

To enhance the construction quality and extend the service life of post-tensioned precast box girders in environments with large temperature differences, key technologies for vacuum grouting construction under such conditions are investigated. Three grouting material mixtures with different proportions are prepared using cement, fly ash, water-reducing agents, and other materials. Three types of vacuum grouting material test blocks - with strengths of C40, C50, and C60 - are fabricated under cyclic high-low temperature, low-temperature, and normal-temperature environments. Compressive strength and dynamic elastic modulus tests are conducted to determine the most suitable grouting material for vacuum grouting construction in post-tensioned precast box girders. Employing this selected material, vacuum grouting construction is carried out through equipment preparation, electric heat tracing, grouting, and curing processes. After construction, quality is evaluated using the impact-echo method. A comparative experimental verification of the three vacuum grouting materials shows that the C60 test blocks demonstrate higher compressive strength and dynamic elastic modulus across all temperature conditions. Therefore, the C60 mix proportion is adopted for construction. Post-grouting inspections under varying temperatures indicate negligible deviations in reflected sound time compared with the standard, with no significant voids or defects observed, confirming the reliability of the proposed technique.