Rigid pavement design methodologies

Various methodologies have been developed for the design of rigid pavements, the majority of which are semi-empirical and mainly based on results from experimental pavements. 

The design criteria of rigid pavements are far more complicated than those of flexible pavements. The horizontal tensile stresses causing cracking of the slab are generated by the combined effect of wheel loading and thermally induced internal and warping stresses. 

All pavement design methodologies assume that rigid pavement failure due to load related distresses occurs at the end of the design period. 

The type of load-related distresses considered in the design of jointed reinforced or CRCPs are longitudinal, transverse and corner cracks, crack width and punchouts. 

The distress level considered as failure, per type of distress, varies among methodologies. 

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The plate bearing test is used for the determination of soil bearing capacity with respect to the modulus of surface reaction (k value). The subgrade bearing capacity in terms of k value is used, mainly, in rigid pavement design methodologies. 

The AASHTO rigid pavement design methodology (AASHTO 1993) was developed at the same time as the AASHTO flexible pavements design methodology and is described analytically in the same design guide (AASHTO 1993). 

Unlike UK rigid pavement design methodology, the CRCP with asphalt overlay is not enforced to be used in all new constructions. However, the use of lean concrete, cement-stabilised crushed aggregate or dense asphalt concrete as a sub-base material in moderate to heavily trafficked roads is necessary for lightly trafficked roads, unbound granular sub-base may also be used. 

In a pavement design methodology such as the AASHTO methodology (AASHTO 1993), the elastic modulus, E (ASTM C 469 2010), or alternatively, the unconfined compressive strength (7 days) (ASTM D 1633 2007) of the CTA base, needs to be determined. With either value, the structural coefficient (<72) is derived and the thickness of the corresponding layer as well as of all layers of a flexible pavement is determined (see Section 13.4.4.3). For a rigid pavement design, the elastic modulus of the sub-base is used (see Section 14.11.1). 

However, in the Australian pavement design methodology for rigid pavements (Austroads 2012), the axle loads determined as in flexible pavement (using the equivalency law) are multiplied by a load safety factor (LSE). The ESP is related to project reliability, which varied from 80% to 97.5%. Eor a reliability of 95%, the LSE for an unreinforced slab is 1.3, while that for a doweled or continuously reinforced slab is 1.25. 

The methodology has introduced the concept of the foundation and of the pavement structure being either flexible or rigid. The design criteria used to develop the design charts are as follows for the foundation design, the deflection of the foundation surface and the minimum thickness of the upper foundation layer (Chaddock and Roberts 2006), and for the pavement design, the strain of the asphalt layer and the stress of the hydraulically bound layer (Nunn 2004). 

The methodology covers the design of jointed (unreinforced and reinforced), continuously reinforced and fibre-reinforced concrete pavements. The case of pre-stressed rigid pavement... 

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