The structural design of the ‘standard’ pavement construction for the 5th runway of AAS,
being a 200 mm PMA on top of 700 mm CTB and 500 mm thick sand layer, is based on the
reflective cracking criterion and secondly on primary deformation (rutting). The CTB layer in
this case is the by AAS adopted standard recycled mix of 60% concrete and 40% milled asphalt
rubble. Secondary deformation should at all times be avoided and therefore the vertical subgrade
strain should not be the failure mode that will govern the design. The drawback of a thick bound
base layer in combination with a soft subsoil (with intermediate 500 mm thick sand layer) is its
structural sensitivity for the horizontal tensile stresses at the bottom of this layer. This stress level
is defined by the variation in subsoil strength, the variation of the mechanical parameters of the
CTB and the aircraft loading. A pre-analysis showed that the design life of this type of pavement
structure is extremely sensitive for a variation in allowable flexural tensile strength of the CTB
material. The use of more cement to increase its strength does make this material more sensitive
for cracking due to shrinkage or temperature variations. This in turn will create the need for an
asphalt mix having better characteristics regarding reflective cracking. Either making the CTB
layer thicker than required or using in the design a lower strength based on a cracked layer can
increase the safety factor. However, like all cement bound materials, structural cracking can be
introduced by one single heavy load. This unwanted situation is likely to be introduced by the
new multiple-wheel gear layouts. As the development of even larger aircraft models of existing
types can not be ruled out, the need for pavement structures less sensitive for overloading and
easier to adjust in a most economical way is desirable. This wish has led to the development of an
alternative pavement structure for the new runway of AAS designed for a fleet-mix containing
NLA/A380 type of aircraft.