Due to the heterogeneous nature of the cement-based materials, the ultrasonic waves in concrete exhibit highly scattering and attenuation, leading to the difficulty of concrete damaged detection. This paper presents a dual mode ultrasonic array imaging methodology that can map damage using Rayleigh surface waves and permanently installed piezoelectric sensors. The dual mode sensing integrates passive acoustic emission and active ultrasonic wave inspection. When a crack is developing, acoustic emission (AE) occurs and the disturbance can propagate outwards along the structure surface. A novel AE source imaging algorithm has been developed to detect and locate the AE source. Once the AE source is located, the sensor array switches to its active mode. For active sensing, one sensor in the array is used to generate Rayleigh wave for interrogation, while all the others are used as the wave receivers. All the sensory data are processed by the active ultrasonic array imaging algorithm. The proof-of-concept testing was performed on a grout specimen with representative dimensions. The passive array imaging algorithm was able to locate the AE source simulated by pencil lead break while active sensing imaging was able to detect the damage simulated by a hole. The duel mode imaging method is promising and economically beneficial for solving a key source localization problem in damage detection on large concrete structures.
The corrosion of reinforced concrete structures is a major issue from both a structural safety and maintenance
management point of view. Early detection of the internal degradation process provides the owner with sufficient options
to develop a plan of action. An accelerated corrosion test was conducted in a small scale concrete specimen reinforced
with a 0.5 inch (13 mm) diameter prestressing strand to investigate the correlation between corrosion rate and acoustic
emission (AE). Corrosion was accelerated in the laboratory by supplying anodic current via a rectifier while
continuously monitoring acoustic emission activity. Results were correlated with traditional electrochemical techniques
such as half-cell potential and linear polarization. The location of the active corrosion activity was found through a
location algorithm based on time of flight of the stress waves. Intensity analysis was used to plot the relative significance
of the damage states present in the specimen and a preliminary grading chart is presented. Results indicate that AE may
be a useful non-intrusive technique for the detection and quantification of corrosion damage.
Early detection of corrosion can help reduce the cost of maintenance and extend the service life of structures.
Acoustic emission (AE) sensing has proven to be a promising method for early detection of corrosion in reinforced
concrete members. A test program is presented composed of four medium-scale prestressed concrete T-beams.
Three of the beams have a length of 16 ft. 4 in. (4.98 m), and one is 9 ft. 8 in. (2.95 m). In order to corrode the
specimens a 3% NaCl solution was prepared, which is representative of sea salt concentration. The beams were
subjected to wet-dry cycles to accelerate the corrosion process. Two of the specimens were pre-cracked prior to
conditioning in order to examine the effect of crack presence. AE data was recorded continuously while half-cell
potential measurements and corrosion rate by Linear Polarization Resistance (LPR) were measured daily. Corrosion
current was also being acquired constantly to monitor any change in the concrete resistivity. Results indicate that the
onset of corrosion may be identified using AE features, and were corroborated with measurements obtained from
electrochemical techniques. Corroded areas were located using source triangulation. The results indicate that
cracked specimens showed corrosion activity prior to un-cracked specimens and experienced higher corrosion rates.
The level of corrosion was determined using corrosion rate results. Intensity analysis was used to link the corrosion
rate and level to AE data.
Acoustic Emission (AE) sensing was employed to assess the rate of corrosion of steel strands in small scale concrete
block specimens. The corrosion process was accelerated in a laboratory environment using a potentiostat to supply a
constant potential difference with a 3% NaCl solution as the electrolyte. The embedded prestressing steel strand served
as the anode, and a copper plate served as the cathode. Corrosion rate, half-cell potential measurements, and AE activity
were recorded continuously throughout each test and examined to assess the development of corrosion and its rate. At
the end of each test the steel strands were cleaned and re-weighed to determine the mass loss and evaluate it vis-á-vis the
AE data. The initiation and propagation phases of corrosion were correlated with the percentage mass loss of steel and
the acquired AE signals. Results indicate that AE monitoring may be a useful aid in the detection and differentiation of
the steel deterioration phases, and estimation of the locations of corroded areas.