Investigation of Portland Cement Concrete Exposed to Automated Deicing Solutions on Colorado's Bridge Decks

The Colorado Department of Transportation (DOT) has identified potential performance problems in some portland cement concrete (PCC) bridge decks and approach slabs in the form of pattern surface cracking, spalling, and joint and crack deterioration; these problems are suspected to be materials-related distress (MRD). External factors such as deicing and anti-icing chemicals can initiate and increase the rate and magnitude of deterioration caused by MRD and thereby shorten the life of the structure. This study investigated whether highly concentrated deicer solutions that were applied through bridge deck deicing and anti-icing systems that used fixed automated spray technology disproportionately contributed to deterioration of PCC bridge decks and adjacent concrete approach slabs in Colorado and whether mitigation strategies employed by Colorado DOT addressed the problem. The investigation involved visual inspection techniques, materials sampling, and evaluation of sampled concrete by using petrographic methods. In bridge decks studied, the concrete evaluated seemed sufficiently resistant to damage from the intrusion of deicer chemicals. Where full-depth cracking was present, however, obvious signs of the movement of moisture and deicers through the deck were observed. Also, some initial signs of possible chemical attack from deicers were noted, and continued exposure to highly concentrated deicers may have contributed to long-term durability concerns. However, use of polymer-modified asphalt and fabric membranes in conjunction with a hot-mix asphalt overlay seemed effective in preventing the ingress of chlorides into the underlying concrete deck.