Deck waterproofing

[Zambo]

We have a problem with the bridge deck waterproof membrane blistering during asphalting of the deck. The waterproof membrane is a mineral finished bitumen sheet membrane which is torched to the cut-back bitumen tack coat. The asphalt is 80mm thick and is laid in 2 layers, but blistering is happening during compaction of the first layer.

 

[wiktor]

Yoy have excessive cut back tack coat, not dried, which is boiling when you are rolling 130-135 C hot asphalt. Puncturing few tiny went holes could help controlling the blisters, and not create any big problem.
Otherwise allow for enough time for the cut back to solidify, or use uncut hot 80 to 100 bitumen for tack coat.

 

[Zambo]

wiktor,

thank you fpr your input. We have investigated further and found that although blistering is becoming more evident during asphalt there is already a lack of adhesion and blisters before laying the asphalt. We have also found that there is a lack of bond between the compacted asphalt and the mineral finished bitumen sheet.

We are trying bitumen emulsion instead of cut back and taking more care with the torch application of the membrane. We will also try to increase the temperature of the asphalt to 170 deg at delivery and 130 deg at the time of compaction.