Analysis of Bridge Deck Cracking Data

Presentation byDavid L. Rettner, PE

American Engineering Testing, Inc.

Since 2005 Mn/DOT has been collecting bridge construction information

The data is collected using a standardized “Bridge Deck Placement Data Form”

The forms, along with a map of the early age cracks in newly constructed bridge decks are sent to the Mn/DOT Bridge Office and the information is stored in a central database.

Project Overview

The purpose of this project was to evaluate the information contained in the database and determine if there were statistically valid conclusions that could be developed relating to causes of bridge deck cracking as well as design or construction methods or environmental considerations that could reduce cracking.

Project Overview

The original scope of the project had two primary subtasks◦ Subtask (1)was to evaluate the completeness of current

MnDOT data and determine if the data needs some cleansing or clarification and will contact the appropriate Mn/DOT staff to assist in this effort.

◦ Subtask (2) Was to develop an analysis framework that made the best use of available data.  The enhanced data set developed through the previous steps could be subdivided into subsets for analysis by controlling for variables that are known to affect incidence of deck cracking.  For example, two ranges of evaporation rate might be identified (high and low) and the dataset could be divided into corresponding subsets.  These subsets could be further divided into sub-subsets based on mix design parameters such as paste content, water-cementitious ratio, etc.

Project Overview

Two major issues were identified during the data evaluation Subtask◦ (1) The data was inconsistent for each structure.

Most “Bridge Deck Data Forms” were missing several data elements such as mix design information, curing duration, environmental information.

◦ (2) The initial bridge deck cracking maps were not completed in a uniform manner. Some decks were mapped within a few days of the completion of curing while others were completed weeks after curing was completed. The TAP agreed that follow-up crack surveys should be

conducted on approximately 20 bridges to get consistent cracking data for the statistical analysis

Project Overview

The initial resurveys identified an additional data collection issue:◦ Most bridges had low-slump overlays on

them.◦ The overlays had generally cracked into

some type of a uniform block crack pattern 2’x2’ to 4’x4’

◦ The crack pattern in the low-slump overlays did not transfer into the structural deck – and therefore a crack survey from the surface could not be performed.

Crack Surveys

The follow up crack surveys were performed on bridges that could be viewed from underneath.

This significantly limited the bridges that could be surveyed

Cracks with efflorescence visible were determined to be full depth cracks.

Crack Surveys

Crack Surveys

Crack Surveys

The follow up crack surveys showed that there were few new full depth cracks in the bridges even after 5-7 years

They also showed that there was no relationship between the crack pattern seen in low-slump overlays and in structural cracks

Crack Surveys

The primary conclusion of the project was:◦ The data as collected was insufficient to allow any

conclusions to be drawn

Conclusions