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

Sponsor: Transportation Research Board

PI: Karl Peterson

The Colorado Department of Transportation (CDOT) 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/crack deterioration, which are suspected to be materials-related distress (MRD). External factors, such as the use of deicing/anti-icing chemials, have the potential to initiate and increase the reate and magnitude of deterioration due to MRD, thereby shortening the life of the structure.

This paper details the results of a study conducted to investigate whether the application of highly concentrated deicer solutions through fixed automated spray technology (FAST) automated bridge deck deicing/anti-icing systems is disproportionately contributing to the deterioration of PCC bridge decks and adjacent concrete approach slabs in Colorado and whether the mitigation strategies being employed by CDOT are addressing the problem. The approach to this investigation involved the use of visual inspection techniques, materials sampling, and the evaluation of the sampled concrete using petrographic methods.

In the bridges studied, the concrete evaluated appears to be sufficiently resistant to damage from the intrusion of deicer chemicals, though where full-depth cracking was present, obvious signs of movement of moisture and deicers through the deck were observed in addition, some initial signs of possible chemical deicer attack were noted, and continued exposure to highly concentrated deicers may contribute to long-term durability concerns. However, the use of polymer-modified asphalt/fabric membranes in conjunction with a hot mix asphalt (HMA) overlay appears to be very effective in preventing the ingress of chlorides into the underlying concrete deck.