What Went Wrong, and Why

Forensic Studies Give Clues to Pavement Failure

By Tom Kuennen, Contributing Editor

Whether the pavement is black or white, flexible or rigid, asphalt or concrete, pavement forensic testing is the key to preventing future pavement failures in either paving medium.

In the lab or in the field, engineers examine pavement condition, cores or entire cut-out sections to ascertain what went wrong, and why.

“Forensic pavement analysis is a core function of every department of transportation,” say Paul E. Krugler, Carlos M. Chang-Albitres and Robert L. Robideau, Texas Transportation Institute, in their paper Development of a Rigid Pavement Forensics Knowledge Management System to Retain TxDOT Corporate Knowledge.

“Excellence in this technical area allows selection of proper and most cost-effective rehabilitation options, with potential monetary benefits to the department of millions of dollars annually,” they write. “Capturing and disseminating corporate forensic pavement knowledge will help assure exceptional performance in this area in the future.”

Acknowledging that staff turnover and retirements were depleting the acquired engineering expertise of Texas DOT, the writers in 2005 outlined creation of a knowledge database of rigid (portland cement concrete), and later, in 2007, flexible (bituminous concrete) pavements, all accessible to Texas DOT employees via the Texas i-Way learning content management system.

Tools for Detective Work

Poor quality construction can occur due to a number of complex and sometimes competing variables, reports the Texas DOT, including reduced inspection staffing, employee turnover, variability of inspectors’ and project managers’ experience levels, incompatibilities between new admixtures and construction materials, implementation of new technologies and construction methods, environmental constraints, recycled materials and other issues unforeseen during design and construction phases.

“To prevent, and to reduce the probability of premature pavement failures and poor long-term pavement performance, the root causes of these problems have to be identified,” Texas DOT says in its Pavement Design Guide. “In conducting forensic studies, a thorough review and analysis of existing quality construction records and tests, nondestructive testing like ground penetrating radar (GPR) and the falling weight deflectometer (FWD) are essential to identify problematic areas and probable causes.”

“When a pavement fails earlier than expected – with early cracking or rutting – we conduct forensic investigations to determine why that happened so soon,” says Timothy R. Clyne, P.E., MnROAD forensic engineer for Minnesota DOT’s MnROAD pavement test facility.

MnROAD – a full-scale accelerated pavement test facility – tests pavement materials, structural designs and construction techniques. It’s unique in that in addition to a low-volume roadway test track that simulates conditions on rural roads, it includes an actual test section of I-94 that carries live Interstate traffic.

“We will do a forensic investigation on good roads to find out what we did right, or what were the conditions that made things go so well with that section,” Clyne says. “But most of the time our forensic investigations are on early failures.” MnROAD also will conduct forensic investigations for pavements throughout the state, either for Minnesota DOT or local agencies.