1. Development of An Advance Overlay Design System Incorporating Both Rutting and Reflection Cracking Requirements
Rick Collins TxDOT

2. Development and Implementation of an Advanced overlay design system for TxDOT
TxDOT Research 5123
Products: 1) Overlay Tester
2) Overlay Thickness Design Software
Status: ) Implemented for several mixes
2) Training schools underway
Innovation: Estimation of both rutting and reflection cracking when selecting overlay type and thickness

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

4. 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

5. Lab testing: Balanced Mix design
The balance mix design requires to use the Hamburg Wheel to measure rutting potential and the Overlay tester to evaluate Cracking potential
Hamburg Wheel Tracking Device
Overlay Tester
Designing mixes with a good balance of rutting and cracking resistance

6. Balanced Mix Design Concept ( AC content window with adequate rutting and cracking resistance) Does not work for all aggregates and PG grade combinations
This graph show the rutting results in green. As the asphalt content increases the rutting increases. The cracking resistance is shown in red. The cracking resistance is measured in number of cycles to brake the sample in the overlay tester. A mix complies with a balance design when the asphalt content complies with acceptable values for rutting and cracking. This area is the yellow portion.

7. Overlay Design program HMA Rutting and Reflection Cracking
Faculty Web Pages Using Spartan Web Wizard
Overlay Design program HMA Rutting and Reflection Cracking
11/18/2018
Input
Output
Status information
CFD&S, SJSU 7

8. Overlay Life predictions
Faculty Web Pages Using Spartan Web Wizard
11/18/2018
Overlay Life predictions
Type C
Mix Type
SMA
Thickness
1.5 ins
3 ins
5 ins
CFD&S, SJSU 8

9. 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