In recent years, MnDOT has seen an increase in cracking of low slump overlays. Cracking of overlays allows chlorides to get into the bridge deck which leads to deterioration of the reinforcement and eventual delamination or spalling. This means that the bridge deck needs to be repaired or even replaced before the service life has been reached.
What is a low slump overlay? A low slump overlay is a technique used by DOTs to extend the life of bridge decks. They are typically 2″ thick and designed to provide low permeability.
In a new research project, investigators will modify the low slump overlay mixture to maintain a low permeability while reducing the cracking, improving sustainability, and lowering the cost.
It is suspected that the individual materials that make up the mix have evolved over the years resulting in different behavior compared to the past mix compositions thus resulting in more cracking.
“This project aims to redesign our low slump overlay concrete mix to crack less leading to longer lasting overlays which means fewer service interruptions, better ride quality, and ultimately money savings,” said Kyle Fritz, MnDOT bridge scoping coordinator.
Objectives
The objectives of the research include:
- Reviewing mixture designs and specifications from other states
- Examining the most promising mixtures and documenting their performance
- Implementing the most promising mixtures on a field project and documenting their performance
Project Details
- Estimated Start Date: 7/27/21
- Estimated Completion Date: 4/30/24
- Funding: MnDOT
- Principal Investigators: Tyler Ley, Dan Cook, Neal Berke
- Technical Liaison: Kyle Fritz, Maria Masten
Details of the research study work plan and timeline are subject to change.
To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.
Crossroads 
Many overlay experts agree that the most typical crack-inducing culprit in concrete is the substrate. There could be numerous factors involved here. I appreciate it when you pointed out that individual materials that make up the mix have changed over the past few years, leading to various behavior, unlike the previous mix compositions. Therefore, it leads to more cracking. It is essential to implement the most promising mixtures on a field project and document their performance.