Mohamed K. ElBatanouny

Corrosion Damage Quantification of Prestressing Strands Using Acoustic Emission

AbstractSteel degradation due to corrosion in prestressed concrete bridges has been of major concern as it presents a threat to the integrity of structures adjacent to marine environments or where deicing salts are regularly used. To assess the potential for monitoring of the corrosion process, an accelerated corrosion testing program has been conducted. A series of specimens with dimensions 114×114×508  mm (4.5×4.5×20  in.) were subjected to constant potential application through the embedded steel strand while being continuously monitored with acoustic emission (AE). Depassivation of the strand was detected by monitoring the fluctuations in applied anodic current. Half-cell potential measurements assessed the probability of corrosion, and all results obtained were compared to acoustic emission data. The mass loss of the corroded strands was correlated to acoustic emission intensity analysis to quantify the degree of damage. Results show that acoustic emission is as sensitive as half-cell potential for d...

Acoustic-Emission-Based Characterization of Corrosion Damage in Cracked Concrete with Prestressing Strand

An accelerated corrosion study to assess the feasibility of acoustic emission (AE) for the detection of active corrosion in prestressing strand is described. Concrete prisms with an embedded steel strand were corroded by supplying a constant potential between the strand and a copper plate while the specimens were immersed in a 3% sodium chloride (NaCl) solution. Corrosion was detected using the half-cell potential (HCP), steel section loss, and visual inspection, and the results were compared to AE data. The location of active corrosion was determined experimentally based on the characteristic wave speed. An intensity analysis approach was used to plot the relative significance of the corrosion damage and a classification chart is presented. Results indicate that AE is a useful, nonintrusive technique for the detection and quantification of corrosion damage and may be developed as a structural prognostic tool for maintenance prioritization.

On-Site Acoustic-Emission Monitoring for Assessment of a Prestressed Concrete Double-Tee-Beam Bridge without Plans

AbstractAcoustic emission was used in this study to assess the condition of a simple-span, prestressed concrete bridge located in southern New Mexico during a proof test. The 40-year-old bridge is county owned and no design plans were available. Acoustic emission (AE) data were collected under several loading conditions from two groups of sensors placed near the support and midspan of an interior double-tee beam. Strain measurements were also taken at midspan and used to direct the test and determine the maximum loading. AE data analysis methods were applied to evaluate the response of the structure under increasing loads and to develop crack maps. Analysis of the AE data showed signs of internal beam microcrack development near the supports (shear region) as well as in the midspan (moment region). The AE data indicated that damage in the form of crack growth was more prevalent in the region near the supports.

Assessing Corrosion Damage in Post-Tensioned Concrete Structures Using Acoustic Emission

AbstractThe ingress of chlorides into posttensioned (PT) concrete structures is a leading cause of corrosion of the prestressing strands. This reduces the strength, durability, and service life of the structure and may result in catastrophic failure. A structural health monitoring (SHM) method is needed to improve the maintenance procedures associated with this method of construction. To evaluate the potential of acoustic emission monitoring for this application, long term corrosion monitoring tests were performed on specimens that were representative of internal and external posttensioning methods. Corrosion was induced in the specimens by adding chlorides to the grout and by performing wet/dry cycling with NaCl solution. The corrosion process was monitored by half-cell potential measurements (HCP) and acoustic emission (AE). Results show that AE has the ability to detect corrosion damage in the PT specimens with similar accuracy to HCP measurements. Furthermore, intensity analysis of the AE data shows t...

Plain Pile Embedment for Exterior Bent Cap Connections in Seismic Regions

AbstractFour full-scale exterior bent cap connections utilizing plain pile embedment were evaluated for suitability in seismic regions. A self-reacting test setup was used to investigate the special case of reverse axial tension and compressive loading expected to occur in the exterior portions of bridge bents. The current state of practice design detail was first evaluated and performed unsatisfactorily. Three additional specimens were then specially designed and evaluated. Specimen variables include embedment depth of the prestessed pile, bent cap reinforcement design, and bent cap dimensions. Specimens were evaluated in terms of moment capacity, plastic hinge length, ductility, and damage to the bent cap. Design alternatives include an idealized hinge connection and two moment transfer connections. The results indicate that the use of plain pile embedment is feasible for regions similar in level of seismicity to South Carolina, provided that the embedment depth is sufficient.

Determining Slipping Stress of Prestressing Strands in Confined Sections

Development length and slipping stress of prestressing strands subjected to confining stress is not well-quantified and the appropriateness of the ACI 318-11 equation under such conditions can be questioned. In 1992, a test was performed on nineteen 14 in. (356 mm) square prestressed concrete piles with a clamping force applied during testing under lateral load. The findings indicated that the ACI 318-11 equation for development length of prestressing strands may not be suitable when used for sections subjected to confining stress. In this study, a modified equation that accounts for the effect of concrete confinement is discussed and compared to the published 1992 results and the ACI 318-11 equation. The moment strength of the sections is also compared using moment-curvature analysis by comparing three different slipping values: 1) those obtained from experimental results; 2) the ACI 318-11 equation; and 3) the modified equation.

Assessment of corrosion rate in prestressed concrete with acoustic emission

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.

Detection of crack formation and stress distribution for carbon fiber–reinforced polymer specimens through triboluminescent-based imaging

This article demonstrates the ability of surface-coated triboluminescent materials to detect damage in carbon fiber–reinforced polymer specimens. An experimental protocol was developed to test the efficiency of the triboluminescent-based diagnostic method using carbon fiber–reinforced polymer coupons under combined bending–compression conditions. Luminescence, emitted from the triboluminescent coatings under quasi-static loading, was detected by capturing digital images. We employed image processing software to quantify change in luminescence as a function of triboluminescent concentration. We observed that 10%, 20%, and 30% triboluminescent coating resulted in 25.3, 27.9, and 40.4 (arbitrary units) total luminescence, respectively, which shows a positive correlation of triboluminescent concentration with luminescence. Finite element simulation was also performed to understand the stress and strain distribution and to aid in understanding and correlating light emission regions on the carbon fiber–reinforced polymer coupons under bending deformation. This work represents a step toward the development of a robust technology that employs triboluminescent materials for early damage detection, consistent with theoretical predictions of damage occurrence.

Bent-cap confining stress effect on slip of prestressing strands

Cast-in-place (CIP) reinforced concrete bent caps are often used in combination with precast/prestressed piles in bridge construction. Previous studies have shown that the actual development length of prestressed strands used in piles embedded in CIP bent caps was less than the theoretical length. An increase in the bond between steel and concrete due to confining stress produced as a result of bent-cap shrinkage is responsible for the increase in strand slipping stress. In the current study, reverse cyclic load tests were conducted to determine the moment capacity and ductility of the pile-to-bent cap connections as well as the slipping stress of the strands. Four prestressed concrete pile specimens embedded into CIP reinforced concrete bent caps were tested. The piles used were 18 in. (457 mm) square x 18 ft (5.5 m) long and were plainly embedded into the bent cap to depths of 18, 22, and 26 in. (457, 560, and 660 mm). The authors created analytical models in which the slipping stress of the strands was calculated using the ACI 318-08 equation for development length. The findings showed that the connection achieved more moment than expected due to the confining stress produced from the bent cap, which tends to decrease the development length of the strands. A modified equation that accounts for the beneficial effect of concrete confinement due to shrinkage is introduced. This equation is used to suggest a possible modification to ACI 318-08, Equation (12-4) by including the effect of confinement. Directions for future research are discussed.

Crack Detection and Evaluation in Grout Structures with Passive/Active Methods

AbstractThis paper presents piezoelectric-based passive/active methods to reliably detect and quantify defects in mass concrete or grout structures. A dual-mode sensing methodology that makes use o...