Bridge Expansion Joint Drainage Design: Preventing Chloride Attack

Chloride-contaminated drainage from bridge decks is the primary cause of premature bridge deterioration. Proper expansion joint drainage design is essential for long-term bridge durability. Chloride Sources: Deicing salt (sodium chloride, calcium chloride, magnesium chloride). Marine spray in coastal environments. Industrial contamination. Damage Mechanisms: Chloride ions penetrate concrete and initiate reinforcement corrosion when concentration exceeds threshold (0.4% by weight of cement). Corrosion products expand, causing concrete cracking and spalling. Drainage System Components: Primary drainage at joint must collect water passing through the joint. Drainage trough should be stainless steel or HDPE, minimum 200mm wide, 100mm deep. Downpipes minimum 100mm diameter, spaced <=3m apart. Secondary drainage below joint discharges water away from bearings and substructure with minimum slope 2% toward discharge point. Drainage Maintenance: Drainage systems must be inspected and cleaned annually. Blocked drainage is a leading cause of bearing corrosion and substructure deterioration. Design Standards: EN 1337-1 covers drainage requirements for expansion joints. AASHTO LRFD covers drainage design for bridge decks.