Ten days after GIP's purchase of EDI was announced, NATS published revised PCNs for EDI. Amongst these revisions, the centre (original) section of Taxiway Alpha had its PCN revised from 72/R/C/W/T to 70/F/A/W/T despite no significant works having been carried out. The "/F/A" part of this revised PCN represents a very substantial increase in the strength of the pavement. The slight drop from 72 to 70 is relatively unimportant from a strength perspective; I think it just reflects the fact that the pavement needs to be resurfaced. I believe the resurfacing works will commence on 29th July according to a recent NOTAM.
My assumption is that GIP have carried out a new technical analysis of the pavement, and reclassified it from having a rigid surface to it being flexible and have re-analysed the subgrade and reclassified it to be high strength (A grade) rather than low strength (C grade).
Taxiway Alpha at EDI was built in the mid-70s and was originally concrete. At some point it was topped with asphalt. Is it normal for a pavement's subgrade to be reclassified to be a higher grade after a period of use / settlement / consolidation and, if so, how long typically does it take for a subgrade to settle / bed down to become a higher sub grade?
Typically, what depth of asphalt on top of a concrete pavement (lets say 72/R/C/W/T) is needed before the pavement’s characteristics become flexible rather than rigid? Is there a rule of thumb or are there too many variables?
Having revised the PCN of taxiway alpha from 72/R/C/W/T to 70/F/A/W/T how likely is it that a revised technical analysis of Runway 06/24, which was constructed at the same time as taxiway alpha and had the same original PCN, would result in a similar PCN increase?
Last edited by Porrohman; 24th July 2012 at 11:40.