Pavimentos

PART II : PAVEMENT DESIGN METHOD
1. INTRODUCTION
The structural design guide developed consists of nomographs from which the thickness of
the asphaltic layers in relation to thethickness of the base and subbase layer of a flexible
pavement can be determined. The nomographs have been developed in terms of the stiffness
of the subgrade, expressed in CBR, andthe total number of Equivalent Standard Axles
(ESA).
For practical reasons the thickness of the sub-base/base untreated layer have been fixed to
200mm, 300mm and 400mm.
Since airtemperature affects the mechanical properties of the bituminous mixtures two sets
of nomographs have been prepared. One set at the almost lowest average yearly
temperature to occuralong Egnatia road which is 13 oC and one set at the almost highest
average yearly temperature to occur which is 16 oC. For intermediate temperature values
the thickness isdetermined by interpolation.
Nomographs have also been prepared not only for the standard type of bitumen used which
is the 50/70pen bitumen but also for a harder bitumen 40/50pen. Mixturesprepared with
40/50pen bitumen may be considered as heavy duty mixtures. The type of bituminous
mixtures considered in the development of the nomographs are dense asphalticconcrete
mixtures.
For the development of the nomographs, the elastic theory has been employed for multilayer
systems in which the materials are characterized by the elastic modulus(Young’s
modulus) and the Poisson’s ratio. The materials are assumed to be homogeneous and
isotropic and the layers have horizontally infinite dimensions. The calculations of thestresses and strains at the critical interlayer points and the required thickness of each layer
to sustain these strains were carried out with the BISAR-PC1 and SPDM-PC2 programmes.