Damage to Anchoring Systems and Sleepers Caused by Bolt Corrosion and Expansion
Q1: Why does bolt corrosion expansion damage the anchorage structure?
A1: The volume of rust is about 2 to 4 times that of original iron, and the expansion produces huge extrusion force on the anchoring agent and sleeve. Under the action of continuous expansion force, the anchoring agent cracks and pulverizes, losing bonding force with bolts, and the pull-out resistance of spikes or bolts drops sharply. Eventually, the anchorage system completely fails and cannot restrain rail displacement.
Q2: What harms does corrosion expansion cause to concrete sleepers?
A2: Expansion force generates radial micro-cracks inside sleepers, which gradually expand into through cracks. In severe cases, the surface of sleepers chips and falls off, greatly reducing bearing capacity. Rainwater and salt further penetrate into cracks, accelerating corrosion of internal steel bars and bolts, forming a vicious circle of "corrosion – expansion – cracking – more serious corrosion".
Q3: Why is bolt corrosion more destructive in curves and low-lying sections?
A3: Curved sections have poor drainage and high humidity, leading to faster corrosion. Meanwhile, complex stress and strong vibration make cracks easier to propagate under dynamic loads. Low-lying sections accumulate water for a long time, keeping bolts in a humid environment, and the expansion force continues to grow, causing faster and more serious damage to sleepers and anchorage.
Q4: How does early bolt corrosion affect fastening torque?
A4: Initial corrosion increases thread friction, resulting in false high torque during retightening. Spalling of the rust layer leads to unstable preload and easy loosening. Corrosion products entering thread gaps prevent bolts from bearing force normally, resulting in a seemingly tightened but actually failed state, laying potential safety hazards.
Q5: How to prevent structural damage caused by bolt corrosion expansion?
A5: Select long-term anti-corrosion bolts such as galvanized and Dacromet ones. Apply anti-corrosion grease to threads during installation. Drain water in time to keep sleeper areas dry. Regularly remove surface rust and repair slightly corroded areas. Replace bolts with serious corrosion and signs of expansion immediately.