Equivalency factors for rigid pavements

For rigid pavements, the conversion of vehicle axial loads to ESAL is carried out with the similar equivalency coefficients derived from the AASHTO road test. The values of serviceability index, p used were the same as in flexible pavements, but instead of the pavement structural number variable, the thickness, D, of the slab was used. The values of slab thickness considered were 6, 8, 10, 12 and 14 inches. 

The equivalency factors derived from complex equations (AASHTO 1986) have been tabulated and are given in the AASHTO pavement design manual (AASHTO 1993). 

The higher value of coefficient y confirms the predominant role of axle load magnitude and, hence, heavy loads or overloads in rigid pavements. This in turn signifies that rigid pavements are relatively insensitive to load repetitions. 

No unique value of coefficient y has yet been proposed for the calculation of the daily, or cumulative, ESAL using the equivalency law. 

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. 

---