DARWIN AC/AC Overlay Design

Course Materials Tables and Design Procedures for this manual

Why have a Pavement Course? Pavements are among the most complex structures that an engineer can design!

Overlay Designs Minor Overlay (Final elevation is maintained) Mill 2”/Overlay 2” Mill 4”/Overlay 4” Major Overlay Overlay adds structure to the pavement Mill 2”/Overlay 4”

Overlay Thickness

Effective Structural Number, SN eff The existing pavement structure is based on adjustments based on: Visual Distress Observations FWD Deflections Analysis

Layer Coefficients, a i Materialaiai Polymer Modified HMA0.5 HMA (surface and stabilized base)0.44 Granular Base0.14 Granular Subbase0.10

FWD Analysis

FWD

Sensor Spacing SensorD1D2D3D4D5D6D7D8D9 9-Sensor Configuration Sensor Configuration n/a

8” 12” 24” 36” 48” 72” - 12” Sensor Spacing

Loads HeightTarget Load Seating9,000 lbs 16,500 lbs 29,000 lbs 312,000 lbs 416,000 lbs

FWD Test Spacing Project Size (miles)Test Spacing (feet) Minimum Number of Tests < – – >

Subgrade Resilient Modulus, M R C=0.33, convert backcalculated modulus to estimate of lab modulus P = applied load, lbs d r = deflection at r inches from center of the load plate r = distance from the center of the load plate use deflection at r = 60 or 72 inch

Effective Modulus of Pavement, E p

d o = deflection at center of the load plate, inch p = load plate pressure applied load, lbs (applied load/load plate area) a = load plate radius, inch D = total thickness of pavement above subgrade M R = subgrade resilient modulus, psi E P = Effective modulus of pavement layers above subgrade, psi Effective Modulus of Pavement, Ep

dodo EPEP EPEP dodo 5,000d o 5,000 … 100,000d o 100,000 d o from FWD EPEP

Temperature Adjustment of E P (mid-depth of AC layers) Darwin adjusts E P to 68 degrees, F o

SN eff From FWD Analysis D = Total thickness of the pavement layers above the subgrade, inch E P adj = Temperature Adjusted Effective modulus of pavement layers above the subgrade, psi

SN eff From FWD Analysis * E P Adjusted

DARWIN EXAMPLE

7 “ HMA = 6” after milling 12 “ DGABC Subgrade Mill 1 “ MR=11,880

DARWIN EXAMPLE

Traffic Requirements

Traffic Mix

DARWIN EXAMPLE F1 for Help

DARWIN EXAMPLE

After milling

DARWIN EXAMPLE >1 inch

DARWIN EXAMPLE

> 1 “

DARWIN EXAMPLE

      Data Limits (AASHO Road Test) CurrentDesigns >100 million <2 million AXLE LOAD REPETITIONS PAVEMENT THICKNESS Projection A Projection C Projection B Current design traffic is far beyond AASHO road test limits Dilemma – How to project traffic beyond AASHO limits?

Input Requirements 1993 AASHTO Design Guide 5 flexible inputs 10 rigid inputs M-E Design Guide (200X) 100+ Total Inputs 35+ Flexible 25+ PCC