A four-lane rural highway pavement is designed to last 25 years with an initial serviceability index of 4.5 and terminal index of 2.5. The estimated first year traffic is 144,000 equivalent single axles and the growth rate is 3.5%. The subbase has a modulus of 110 psi and drainage is fair. The concrete strength is 4900 psi with a modulus of rupture of 600 psi. The required pavement thickness is determined to be slightly less than 9 inches and is rounded up to 9 inches.

1. A pavement for four-lane rural divided highway is to be
designed to last 25 years. During the first year, the estimated
two-way equivalent single axle application are 144,000. The
expected traffic growth rate is 3.5 percent. The design
reliability is 95 percent, and the overall standard deviation is
0.35. The initial serviceability po is expected to be 4.5, and
terminal serviceability, pt is 2.5.
The PCC pavement is to be laid on a granular subbase material.
The average compressive strength fc’ = 4900 psi, and average
modulus of rupture is 600 psi.
The drainage was judged to be fair and will be subjected to
moisture levels, approaching saturation, 10 % of time. The
effective modulus of subgrade reaction, (corrected for loss of
support) k is 110 psi.
Determine the design thickness.
Example
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2. Solution
1. The effective modulus of subgrade reaction = 110 psi.
(corrected for loss of support) k
2. The concrete elastic modulus Ec = 57000 * (fc’)0.5
= 3.99 * 10 6 psi
3. The concrete modulus of rupture Sc
’ = 600psi
4. The load transfer coefficient, J, = 3.2 (from table 20.10)
5. The drainage coefficient CD = 0.95 (from table 20.11)
6. R = 0.95
7. So = 0.35
8. Design Serviceability loss, ΔPSI =Po –Pt = 4.5 -2.5 = 2.0
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4.  Traffic in the design lane
W18 = DD * DL * w18
W18 = 0.5 * 0.9 * 144000 = 64800
Design ESAL =
[((1.35)25 – 1)/ 0.035] 64800 = 2.52*106
using the inputs given above in the nomograph, Figure 20.13
The design thickness can be determined
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6. The design thickness is
slightly less than 9 inches
Round up to 9 inches.
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