Development of An Advance Overlay Design System Incorporating Both Rutting and Reflection Cracking Requirements

Rick Collins TxDOT

Development and Implementation of an Advanced overlay design system

for TxDOTTxDOT Research 5123

Products: 1) Overlay Tester2) Overlay Thickness Design Software

Status: 1) Implemented for several mixes2) Training schools underway

Innovation: Estimation of both rutting and reflection cracking when selecting overlay type and thickness

Everyday TxDOT designers are often designing HMA overlays for Cracked pavements Products developed help to optimize design

Key steps for Successful Overlays

Project Evaluation Is an overlay the answer ? Performance Evaluation + NDT Identification of pretreatments

Mix design (balance of properties) Thickness Design Quality Control in the Field

Lab testing:Balanced Mix design

Hamburg Wheel Tracking Device

Overlay Tester

Designing mixes with a good balance of rutting and cracking resistance

Balanced Mix Design Concept ( AC content window with adequate rutting and cracking resistance) Does not work for all aggregates and PG grade combinations

Balancing Rutting and Cracking

0

2

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4 4.5 5 5.5 6 6.5 Asphalt Content (%)

Ru

t Dep

th (m

m)

0

100

200

300

400

500

600

700

800

Cra

ckin

g L

ife (c

ycle

s)

Rut

Crack

Acceptable Rutting &Cracking

Acceptable Rutting

Acceptable Cracking

Overlay Design programHMA Rutting and Reflection Cracking

Input

Output

Status information

Overlay Life predictions

Type C

SMA

1.5 ins

3 ins

5 ins

Mix Type

Thickness

Summary Overlay Tester developed to measure crack

resistance of new overlay materials Overlay Tester implemented for several Texas

mixes New pavement design software developed to

predict overlay performance based on Existing Pavement condition and distress Traffic Environment Proposed overlay type and thickness

Default material properties available for all standard TxDOT mixes

Training schools underway