Passive Magnetic Inspection Provides Quantitative Infrastructure Condition Assessment
Date & Time
Wednesday, October 6, 2021, 11:00 AM - 12:00 PM
Maurice Dusseault, P.Eng.

Sustainability and resilience principles imply quantitative infrastructure condition assessment to
permit risk management and optimum deployment of dollars and personnel in maintaining and
replacing assets. We have a new and powerful NDA technique to identify corrosion and defects in
covered reinforcing steel and tendons: Passive Magnetic Inspection (PMI) based on passive detection
and analysis of magnetic field perturbations. We demonstrated PMI by scanning rebar in parking
structures and small concrete bridges, showing that corrosion and defects can be detected quickly and

Eight years of PMI research and development have resulted in an economically attractive means of rapid
corrosion and crack detection in steel goods. PMI is not affected by the cover material (concrete,
fiberglass, polymers), moisture, temperature, or salinity; only ferromagnetic substances can perturb the
magnetic field. It works if the concrete cover is dry, warm and intact; it works if the concrete is cracked,
wet, salty and cold. Steel corrosion alters its ferromagnetic properties (destruction of magnetic domains),
leading lead to detectable perturbations in the surrounding magnetic field. Perturbations
from corrosion, cracks, or other defects are classified as severe, moderate or light, and calibration allows
us to estimate the amount of steel lost. We surveyed longitudinal rebar in the slab forming a small
bridge in Markham, Ontario, and produced a 2D map of cross-sectional area loss from corrosion, guiding
rehabilitation recommendations.

PMI allows owners to develop and maintain a quantitative condition history of their assets. For example,
a reinforced concrete bridge owner can use PMI each two years at critical-location sites where the
tensile stress is the greatest, where steel-concrete debonding is most likely to occur, where corrosion is
expected, and where critical connections exist. The time-series data allow quantitative management:
early identification of corrosion/cracking problems early; life span predictions; maintenance scheduling,
and avoidance of loss-of-service events. Acoustic and electrical NDT methods are lengthy, costly and
non-definitive in many cases, and visual assessment is severely limited and distressingly non-
quantitative. PMI allows assessment of columns, slabs and connections, and if repeated regularly, guides
risk mitigation procedures and cost/time management. PMI is also useful for condition assessment of
stressed steel tension cables under cover, I-beam evaluation, steam pipe and boiler condition, buried
steel pipelines, and other applications.