Review of Nondestructive Testing Methods for Condition Monitoring of Concrete Structures

Table 1

Different NDT methods and parameter measured.

S. no.	Parameter measured	NDT method	Advantages	Limitations	Principle
1	Concrete quality, cracks, defects, and voids	Visual inspection	Rapid, economical	Expertise is required, superficial, and depends upon skill of viewer	Based on the visual defects on the surface
		Image Pro Plus (IPP)	Simple, rapid, cheaper	Slow results	Comparing colors of different objects
		Acoustic emission (AE)	Fast results, detect changes in materials	Costly, defects already present are not detected	Sudden distribution of stresses generates elastic waves
		Impact echo	Able to detect condition of concrete accessible from one side only, quick, accurate, and reliable	Interpretation is difficult, reliability decreases with increase in thickness, and accuracy depends on impact duration	Transmission and reflection of electromagnetic waves
		Infrared thermography	Easy interpretation, simple, safe, no radiation, rapid setup, and portable	No information about depth or thickness of defects, and results affected by environmental conditions	Surface temperature variation
		One-sided signal wave transmission measurements	Used to detect structures accessible from one side only such as pavements	Large thickness affects the results	Propagation velocity of signal waves
		Impulse response	Simple, easy to handle	Depends on the skill of user, and deep damages influence the results	Based on stress wave test method
		Radiography	Thickness and composition can be easily detected, and rebars can be located	Expensive, hazardous, and limited to low thickness	Velocity of X and gamma rays and its attenuation
		Petrographic testing	Provides information about alkali-silica reaction, alkali carbonation reaction, sulfate attack, freezing, and thawing	Required high skill for the interpretation of result	Samples are examined through a petrological microscope using reflected or transmitted light
		Lamb Wave Theory (LWT)	Relatively accurate	Difficult interpretation	Based on guided wave theory
2	Compressive strength, surface hardness, adhesion	Rebound hammer	Simple, quick, and inexpensive	Not so reliable, smoothness, age of concrete, carbonation, and moisture content can affect results	Rebound of plunger when strucked with concrete indicates strength
		Ultrasonic pulse velocity (UPV)	Quick, portable, large penetration depth, Simple interpretation, and moderate cost	Not very reliable, moisture variation and presence of reinforcement can affect results	Ultrasonic wave velocity and its attenuation
		CAPO test	Correlation between pull out force and compressive strength is reliable	Damage to the surface	Expanded ring in the cored hole is pulled out
		Probe penetration	Simple, needs less training, and low maintenance	Leave a hole in concrete surface, and coarse aggregates affect the penetration	Penetration of probe is measured and related to strength
		microcoring	Good correlation between test results and compressive strength	Depends on the preparation of specimens	Extraction of microcore samples from a concrete structure is used for analysis
		Pull off test	Fast results, evaluate adhesion, and tensile strength which can be converted to compressive strength	Damage to the surface	A disc is bonded to the testing surface, and when disc is pulled off, force required is used to obtain pull off strength
3	Chloride concentration	Quantab test	Fast and accurate	Expensive, hazardous, limited to low thickness	Reaction of silver dichromate with chloride ion produces white column on the strips
		Potentiometric titration	Reliable	Requires skilled personal	Using acid or water soluble methods, the final volume will indicate chloride content
		Rapid chloride test	Portable, simple, and quick	Variation in results by the presence of certain materials	Potential difference of unknown solution is compared with potential difference of solutions with known chloride concentration
4	Corrosion rate, percentage of corrosion, corrosion progress	Galvanostatic pulse method	Measures half-cell potential and electrical resistance simultaneously	Unstabilized readings	Based on the polarization of rebar by means of small constant current
		Linear polarization resistance (LPR)	Rapid, requires only localized damage, more detailed information	Measurements are affected by temperature and humidity	Electrical conductivity of fluid can be related to its corrosiveness
		Half-cell potential	Simple, portable, results in the form of equipotential contours	Needs preparation, saturation required, not very accurate, and time consuming	Electric potential of rebars is measured relative to half cell and indicates probability of corrosion
		Time domain reflectometry (TDR)	More robust, easy, locates corrosion, and identifies extent of damage	Less sensitive	By applying a sensor wire along side of the reinforcement a transmission line is created. Physical defects of the reinforcement will change the electromagnetic properties of the line
		Ultrasonic guided waves	Identifies location and magnitude of corrosion	Not very reliable	Based on propagation of ultrasonic waves
		X-Ray diffraction and atomic absorption	Simple and reliable	hazardous	Intensity of X-ray beams reduces while passing through a material
5	Carbonation depth, pH of concrete	Phenolphthalein indicator test	Simple, quick, and inexpensive	Inappropriate for dark aggregates, results affected by saturation	Carbonation reduces pH of the concrete
		Rainbow indicator	Quick, descriptive, and easy to use and interpret	Requires drilling of concrete surface up to rebar depth	Carbonation reduces pH of the concrete
6	Pavement inspection and subsurface condition	Ground-coupled penetrating radar (GPR)	Low cost, portable, effective	Complex results, difficult interpretations	Propagation of radiofrequency (0.5 to 2 GHZ)
		Hammer sounding	Simple, easy to handle	Depends on the skill of user, and deep damages influence the results	Surface is striked with hammer and hollow or dull tone indicates the existence of delamination
		Acoustic tomography	Useful results, moderate	Requires skill, high cost	Waves were received on opposite side, and wave velocity depends on material properties
		Falling weight deflect meter (FWD)	Useful results	Can provide misleading results and requires experience for interpretation	Load is produced by dropping a large weight to detect concrete
7	Flaw detection inside decks, delamination, location, and extent of damage in bridges	Chain drag	Simple, portable	Time consuming, tedious	Chain is dragged over surface for flaw detection
		Vibration based damage identification (VBDI)	Easy to implement, cost effective	Environmental factors, errors in measurements, and nonunique solutions	Based on changes in the dynamic characteristics of a structure
8	Entire depth of damage, percentage of damage, identification of deteriorating infrastructure	Seismic refraction method	Calibration is not necessary, more reliable	Valid for high speed for large depths	Seismic waves travel outward from a source and reach a detector
		Ultrasonic longitudinal waves (L-wave, P-wave)	Inspect also at large depths	Not appropriate as primary investigation method	Transmission and reflection of ultrasonic waves
		Ultrasonic continous spread spectrum signal	Improved sensitivity	Difficult interpretation	Signals are received by detectors and signal speed depends on defect
9	Permeability, water absorption	Water permeability test	Preparation and skill required, time consuming	Semidestructive type test	Assesses the ease with which water penetrates in concrete
		Initial Surface Absorption Test (ISAT)	Consistent results in laboratory	Problems in using in situ, affected by increase in temperature	Rate at which water is absorbed in concrete is measured
		Covercrete absorption test (CAT)	Not influenced by local surface attacks	Sensitive to W/C ratio, curing time and moisture content	Rate of absorption of concrete is measured
10	Concrete cover, rebar diameter, location of reinforcement	Cover meter	Portable	Slow, affected by deep cover and closely spaced bars	Electromagnetic induction
		Radioactive methods	Simple	Hazardous	Generates images of the structure of RC and steel
13	Load bearing capacity of bridge	Static truck load test	Reliable	Dangerous	Response of strain sensors under truck load indicates load bearing capacity
14	Relative conditions of brick masonry side walls	Multichannel Analysis of Surface Waves (MASW)	Reliable, fast and economical	Expensive, time consuming	Uses multiple sensors to record wave field
15	Detecting disbands	Microwave NDT method	Detects from one side, rapid, noncontact, and robust	Costly	Reflection and transmission coefficients are measured and related to material properties
18	Stress/strains sensor for monitoring composite beams	Fiber optic Bragg grating sensors	Suitable for long-term tests	Slow response	Monitors the response of structure subjected to full load