Question

A three-lane northbound section of interstate (with
the design lane conservatively designed) has rigid
pavement (PCC) and was designed with a 10-inch slab,
90% reliability, 700 lb/in2 concrete modulus of rupture,
4.5 million lb/in2 modulus of elasticity, 3.0 load transfer
coefficient, and an overall standard deviation of 0.35.
The initial PSI is 4.6 and the TSI is 2.5. The CBR is 2
with a drainage coefficient of 1.0. The road was
designed exclusively for trucks that have one 24-kip
tandem axle and one 12-kip single axle. It is known
from weigh-in-motion scales that there have been 13
million 18-kip–equivalent single-axle loads in the entire
northbound direction of this freeway so far. If a section
of flexible pavement is used to replace a section of the
PCC that was removed for utility work, what structural
number should be used so that the PCC and flexible
pavements have the same life expectancy (the new life
of the flexible pavement and the remaining life of the
PCC)?

Answer 1