AASHTO rigid pavement design methodology

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). 

The design data required for the determination of the slab thickness for an assumed subbase thickness ( 150 mm) are as follows resilient modulus of subgrade (M ), elastic modulus of sub-base (E ), modulus of rupture of concrete (S ) (or flexural strength of concrete), elastic modulus of concrete ( (.), cumulative ESAT over the design period (W ), overall standard deviation (S ) and design serviceability (APSI) as in flexible pavement design. 

In addition to the above, the effective modulus of subgrade reaction (k) and the load transfer coefficient (/) must be determined and the expected level of drainage must be considered, expressed as drainage coefficient Q. 

The methodology allows the use of other hydraulically bound material for the construction of the sub-base. 

A detailed procedure for designing rigid concrete pavements with jointed or continuously reinforced concrete slabs can be found in the AASHTO manual (AASHTO 1993). However, in the following paragraphs, a brief description for determining the thickness of the concrete slab in all cases (unreinforced or reinforced slabs) and the required quantity of reinforcement are given for the benefit of the reader. 

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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). 

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