Encasement and overlays

After milling, and deeper removal where cracking and spalling has occurred, the deck is then patched in the delaminated areas and a dense cementitious overlay of microsilica, polymer modified or low slump, low water/cement ratio concrete is put back on. This will slow the corrosion rate and the appearance of further delaminations. 

These techniques are popular in the United States for delaying, or preventing chloride induced delamination on substructures and bare concrete bridge decks. A recent review of highway bridge deck maintenance practice in the United States (Russell, 2004) found overlaying to be far more popular than the application of cathodic protection. 

There was no indication of any problem with the reinforcement until the encasement was removed and it was found that there was steel left to restrain any sideways movement in the piles. 

However, several DOTs in Northern States are having some success with encasement. There are also trials of carbon fibre wraps used for strengthening as a method of suppressing corrosion. 

Concrete overlays or encasement may absorb some of the chlorides, reducing the level at the concrete surface. They will certainly reduce the high chloride gradient that drives chloride further into the concrete if they are coupled with removal of some or all of the old cover concrete. This has been measured on bridge decks. 

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