Experimental Research On Magnesium Phosphate Cement For Rapid Repair Of Ballastless Track In High-speed Railway

Slab ballastless track is the main type of high-speed railway in China. In the complex operating environment, service condition and differences in loading and climatic conditions, different damages such as gap of mortar layer and track slab, mortar layer and concrete injuries most likely occur. The strength of repair materials should meet the requirements for opening in 4 hours and its properties should be compatible with former materials. The traditional repair materials have some drawbacks, such as poor durability, complex operating process and high price.Magnesium phosphate cement(MPC) is a new kind of cementitious repair material of which the strength is based on acid-base neutralization. It has the advantages of quick setting, high strength, strong adhesion, good durability and low dry shrinkage. Using dead burned magnesia oxide, ammonium dihydrogen phosphate, fly ash, sand and borax as materials, MPC was prepared in the study. The influence of M/P, sand-binder ratio and the variety and dosage of retarders was discussed. On the basis of proposed optimal mix proportion, fly ash, polymers and polypropylene fiber are added for the modification of MPC. According to the rapid repair requirements of ballastless track, its adhesive property, water resistance, corrosion resistance, frost resistance, dry shrinkage and other engineering properties were studied and evaluated. Finally the repair process of gap, crack and defect damages was proposed. The operation feasibility and maintenance effectiveness of MPC were tested in construction.Experimental results indicate that the properties of MPC completely meet the requirements of slab ballastless track. The developed MPC has the setting time of 10~13 minutes, 1 h compressive strength of above 40 MPa, the fluidity of 280 mm, the shrinkage rate of ±0.004% and the bond strength of about 2.5 MPa. It has good durability, operation feasibility and maintenance effectiveness. It’s an ideal repair material of slab ballastless track which has good social and economic benefits.