Airfield pavements with smaller slabs I.e. (225 to 278 sf) have lower warping stresses and are less prone to mid-slab cracking. Google Earth the PHX airport for a visual example.
The old Terminal 1 apron (no building just pavement slabs in a radial configuration at the west end of the terminal area was built in 1952 using then Navy criteria, 12.5 x 15 foot slabs, 3000 lb concrete, 9-inch with thickened edges.
Compare the pavement condition and mid-slab fractures with that of Terminal 2 apron, built in 1960 using then FAA design criteria, 20 x 25 foot slabs, 650 flex concrete, 11-inches thick.
Both areas have the same soil type, and 50 plus years of primarly Group III aircraft.
Current FAA design (cumulatiive stress) methods are based on aircraft loadings and ignore the daily warping stresses that created by environmental variations.
My preference is to select slab size (ie joint spacings) so that the warping stresses never exceed 50% of the design flexural strength.
In my opinion, the reason that some organizations have such a problem with joint maintenance is becaiuse of poor joint design (no chamfered joints), insufficient curing, and permitting any construction traffic on the pavement prior to the time that the concrete has cured to at least 75% of the design strength. See the following paper "Improved Methods for Specifying and Placemnet of Hot Weather Pavement in Desert Environments, Transportation Systems Workshop, Austin, 2012 for detail based on experience of over 4.2 million square yards of pavement at Ft. Bliss TX.
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Jon Girand P.E., L.S., F.ASCE
Vice Pres
Arvada CO
(303) 658-0777
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Original Message:
Sent: 02-27-2017 15:56
From: Manuel Bejarano
Subject: Maintaining joints in concrete pavements
Maintaining joints in our concrete pavements is expected, but we question why we need to maintain so many linear feet. Seems reasonable that slabs could be bigger in plan dimension (currently 20ft x 20ft and/or 25ft x 25ft) to minimize the amount of joints we need to maintain. FAA set the standard on joint spacing, but couldn't there be some technical justification to go to bigger spacings? Many of today's wide body aircraft have gear loading that fall along the longitudinal joint line, perhaps that is justification to increase slab dimensions? Your thoughts? - #SpacedOut
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Manuel Bejarano P.E., M.ASCE
Engineer IV
Atkins
Orlando FL
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