PAST AND PRESENT DESIGN PRACTICES

Tables 4 through 13 are used to overview past and current design practices for flexible and rigid pavements.

Mahoney, Monismith, Coplantz, Harvey, Kannekanti, Pierce, Uhlmeyer, Sivaneswaran, and Hoover 91

TABLE 3 Snapshot of Traffic Levels for the Three States (2004 Data)

Trucks per State

(urban or rural)

29,000 California I-80 Berkeley (U)

I-5

Los Angeles (U)

159,000 6% 10,000 I-5 Portland (U)

136,000 9% 12,000 Oregon I-84

5,000 I-5 Seattle (U)

Hood River (R)

5,000 ADT= average daily traffic

I-90 Snoqualmie Pass (R) 30,000 18%

TABLE 4 Comparison of Current West Coast Flexible Design Practices

Features California 2 Oregon Washington Thickness design

AASHTO 93 Design process

Gravel equivalent

AASHTO 93

Hveem equations

DARWin

DARWin/State computer software

Design period

20 or 40 years (40 years

20 years (30 years in

50 years

used if AADT

Traffic index = 9.0

ESALs ESALs

(ESAL/10 6 ) 0.119

Subgrade strength

M R (mostly from FWD M P (mostly from FWD design parameter

R -value

deflections) 1 Caltrans (2006); 2 WSDOT (2005); FWD = falling weight deflectometer

deflections)

TABLE 5 Comparison of 1960s West Coast Flexible Design Practices

Feature California Oregon Washington Thickness design Gravel equivalent Gravel equivalent Gravel equivalent

Design process

Charts Design period

Hveem equations

Charts

20 years Traffic

20 years

Traffic index = 9.0

Traffic index

(ESAL/10 6 ) 0.119

Subgrade strength

R -value design parameter

R -value

92 Pavement Lessons Learned from the AASHO Road Test and Performance of the Interstate Highway System

TABLE 6 Comparison of Current West Coast Rigid Design Practices

Feature 2 California Oregon Washington Thickness design

State procedure but

AASHTO 93

adopting M-E procedures

Design process Design tables (Chapter 600 DARWin DARWin series)

Design period

20 yrs (if 20-year AADTT

30 years

50 years

<150,000) 40 years (otherwise)

Type of PCC pavement Primarily JPCP and CRCP CRCP CRCP

to a lesser extent 1

Transverse joints

For JPCP, straight joints

Not applicable

Straight joints with

either 12 or 15 ft with avg

15-ft spacing

= 13.5 ft

Use dowels

Traffic

Traffic index =9.0

ESALs ESALs

(ESAL/10 )

Base types

Mostly LCB and HMA

Stabilized base

HMA

(generally HMA)

Subgrade strength

k -value design parameter

R -value

k -value (estimate from

FWD data)

1 Caltrans (2006); 2 WSDOT (2005) AADT = annual average daily traffic; PCC = portland cement concrete; M-E = mechanistic–empirical; HMA = hot-

mix asphalt; LCB = lean concrete base

TABLE 7 Comparison of 1960s West Coast Rigid Design Practices

Feature California Oregon Washington Thickness design

State process (modified

State process

State process (combination

of more than one) Design process

PCA from 1967–1983)

Tables

Design period

Type of PCC

(No dowels)

CRCP (>1963)

Subgrade strength

R -value

design parameter Traffic

Traffic index = 9.0

Traffic index

(ESAL/10 6 ) 0.119

Base types

HMA or crushed stone Transverse joints

Cement-treated base

Crushed stone

1950s: 15-ft joints, skew Not applicable

1940s and 1950s: 90-degree

optional

15-ft joints

1964: Skewed random

1966: Random, skewed

spacing of 12, 13, 18,

spacing ranging from 14 to

and 19 ft

18 ft

1983: Skewed random

1967–1992: Random spacing

spacing of 12, 15, 13,

between 9 and 14 ft

and 14 ft

Mahoney, Monismith, Coplantz, Harvey, Kannekanti, Pierce, Uhlmeyer, Sivaneswaran, and Hoover 93

TABLE 8 California Flexible Pavement As-Builts—1950s to Current

Feature HMA Thickness (in.) Subgrade 1950s

Minimum HMA depth

Min. allowed: 1.2

Subgrade strength was characterized by

Min. used: 3.0

R -value

Maximum HMA depth

Max. allowed: 24.0 Max. used: 12.0

Current Minimum HMA depth

Min. allowed: 1.2

Subgrade strength was characterized by

Min. used: 3.0

R -value

Maximum HMA depth

Max. allowed: 24.0 Max.used: 12.0

TABLE 9 Oregon Flexible Pavement As-Builts—1950s to Current

Feature HMA Thickness (in.) Subgrade

1950s Minimum HMA depth

3.5 Characterized by R-value. Maximum HMA depth

5.0 12–18 in. of select material was often specified over silty or clayey subgrades.

Current Minimum HMA depth

12.0 6.0-in. aggregate base over 18.0-in. subbase

Maximum HMA depth 13.0 12.0-in. aggregate base

TABLE 10 Washington Flexible Pavement As-Builts—1950s to Current

Feature HMA Thickness (in.) Base/Subgrade 1950s Switched from CBR to R-value due to

Minimum HMA depth

issues with clean sands and clayey gravel characterization about 1951

Maximum HMA depth

Some bases were CTB Current Minimum HMA depth

9.6 Use of R-value continued from early 1950s to 1990s. Then with AASHTO

Maximum HMA depth 10.8 86, switch to M R was made. CTB = cement-treated base

94 Pavement Lessons Learned from the AASHO Road Test and Performance of the Interstate Highway System

1 TABLE 11 California Rigid Pavement As-Builts—1950s 2 to Current

Traffic PCC slab (in.) Base (in.) Other Factors 1950s

Light traffic (design ESALs <2.5 million)

PCC not used if subgrade Heavy traffic (design ESALs

8.0 4.0 CTB

R <10; same for all >2.5 million)

climate regions Current

9.0 4.0 CTB

Lightest traffic (design

4.2 HMA, LCB, or

Slab thicknesses for Heaviest traffic (design

ESALs <1,000,000 or TI<9)

8.4 12.0 granular base

Inland Valley location, ESALs >200 million or

Type 2 subgrade (10 ≤R- TI >17)

13.8 6.0 HMA or LCB

value ≤40)

1 Harvey, et al. (2000); 2 Caltrans (2006)

TABLE 12 Oregon Rigid Pavement As-Builts—1950s to Current

Traffic PCC slab (in.) Base (in.) Traffic 1950s Minimum rigid section

PCC primarily used for Maximum rigid section

8.0 9.0 crushed stone

8.0 12.0 crushed stone

most new alignments starting in 1959

Current Minimum rigid section

LCCA used to determine Maximum rigid section

11.0 4.0 HMA

pavement type LCCA = life-cycle cost analysis

13.0 4.0 HMA

TABLE 13 Washington Rigid Pavement As-Builts—1950s to Current 1

Traffic PCC Slab (in.) Base (in.) Traffic 1950s Minimum rigid section

PCC considered only Maximum rigid section

8.0 Crushed stone

9.0 Either HMA or crushed

when 10 year TI = 6.5 (or

about 500,000 ESALs) Current Minimum rigid section

stone

LCCA (mostly) used to (design ESALs

determine pavement type <25,000,000)

10.8 HMA

Doweled transverse Maximum rigid section

joints (design ESALs

Reliability = 95% >50,000,000)

12.6 HMA

Thinner slabs allowed for ramps, rest areas, etc.

1 WSDOT (2005)

Mahoney, Monismith, Coplantz, Harvey, Kannekanti, Pierce, Uhlmeyer, Sivaneswaran, and Hoover 95

TABLE 14 Typical Rigid Pavement Designs [NCHRP 1-32 (1996)]

Feature

Slab Thickness (in.)

Design ESALs

2.5 million ESALs

7.5 million ESALs

30.0 million ESALs

PAST AND PRESENT DESIGN PRACTICES