Using Advanced Technologies to Assess Deterioration in Concrete Bridge Decks

The condition of the transportation network in the United States is Deteriorating and will require enormous efforts to significantly improve its state. Out of the 600 thousand bridges, almost 14% is structurally obsolete and another 14 % is functionally obsolete. Concrete bridge condition assessment is a challenge to bridge inspectors because of the variety of problems that may exist. Therefore, the need for innovative inspection and maintenance programs is rising and new technologies are being applied to facilitate the detection of different defects that affect concrete bridges. An important component of the inspection and rehabilitation of concrete bridges is the ability to assess the condition of the bridge’s deck. The advent of nondestructive evaluation techniques aided this task. Several nondestructive techniques have been successfully utilized to detect common defects in concrete bridge decks. This paper will study Ground Penetrating Radar (GPR) and Impact Echo (IE) abilities in the detection of the most common concrete bridge deck defects faced by inspectors using fabricated bridge decks with simulated defects. These simulated decks will be used to validate and compare the abilities of both methods in detecting the presence of cracks, delaminations, and voids.

Concrete bridge decks are prone to ice accumulation. Bridge decks freeze before the roads approaching them freeze, making wintry highway travel treacherous. Road salts and deicing chemicals are effective for ice removal but cause damage to concrete and corrosion of reinforcing steel in concrete bridge decks. The resulting rapid degradation of existing concrete pavements and bridge decks is a major concern to transportation and public-works officials. The use of insulation materials for ice control and electric or thermal heating for deicing have been attempted, with unsatisfactory results. Conductive concrete is a cementitious admixture containing electrically conductive components to attain high and stable electrical conductivity. Due to its electrical resistance and impedance, a thin conductive concrete overlay can generate enough heat to prevent ice formation on a bridge deck when connected to a power source. In 1998, Yehia and Tuan, at the University of Nebraska–Lincoln, developed a conductive concrete mix specifically for bridge deck deicing. In this application, a conductive concrete overlay is cast on the top of a bridge deck for deicing or anti-icing. The mechanical and physical properties of the conductive concrete mix after 28 days have met ASTM and AASHTO specifications. Two concrete slabs were constructed with a 9-cm (3.5-in.) conductive concrete overlay for conducting deicing experiments in the natural environment. Deicing and anti-icing experiments were conducted in five 1998 snowstorms. Average power of about 590 W/m2 (55 W/ft2) was generated by the conductive concrete overlays to prevent snow and ice accumulation.

Different Characteristics of Radar Signal Attenuation Depending on Concrete Condition of Bare Bridge Deck

Evaluating the condition of concrete bridge decks is an increasingly important challenge for transportation agencies and bridge inspection teams. Closing the bridge to traffic, safety, and time consuming data collection are some of the major issues during a visual or in-depth bridge inspection. To date, several nondestructive testing technologies have shown promise in detecting subsurface deteriorations. However, the main challenge is to develop a data acquisition and analysis system to obtain and integrate both surface and subsurface bridge health indicators at higher speeds. Recent developments in imaging technologies for bridge decks and higher-end cameras allow for faster image collection while driving over the bridge deck. This paper will focus on deploying nondestructive imaging technologies such as the three-dimensional (3D) optical bridge evaluation system (3DOBS) and thermal infrared (IR) imagery on a bridge deck to yield both surface and subsurface indicators of condition, respectively. Spall and delamination maps were generated from the optical and thermal IR images. Integration of the maps into ArcGIS, a professional geographic information system (GIS), allowed for a streamlined analysis that included integrating and combining the results of the complimentary technologies. Finally, ground truth information was gathered through coring several locations on a bridge deck to validate the results obtained by nondestructive evaluation. This study confirms the feasibility of combining the bridge inspection results in ArcGIS and provides additional evidence to suggest that thermal infrared imagery provides similar results to chain dragging for bridge inspection.

In today's economic climate - of making every infrastructure dollar count — it is critically important to properly inspect and maintain our older long span bridges. Routine bridge inspections and maintenance not only provide the user with a safer structure, but also provides the owner with a bridge that will stand the test of time. Bridge inspection/maintenance procedures, however, can be costly to the owner and a major inconvenience to the user when access to the underside of the structure can only be achieved from inspection vehicles parked on the bridge deck. Travel lane closures to complete the required work can cause significant safety and traffic problems, especially on narrow bridges. To address these concerns, the Burlington County Bridge Commission made the decision to install a motorized rolling traveler platform beneath its Burlington-Bristol Bridge. The Burlington-Bristol Bridge is a long span moveable toll structure that crosses the Delaware River, connecting southeastern Pennsylvania with New Jersey. The bridge carries two 10' travel lanes and a 4' sidewalk, thus requiring a night time bridge closure when inspection or construction access vehicles, such as snoopers, are required. The traveler system was installed on the Burlington-Bristol Bridge during the summer of 2009. When suspended from the underside of the bridge, the traveler platform will be guided by motorized carriages that will travel along steel track beams. The total travel range of the platform is 940' and includes access to the 540' moveable vertical lift main span and the two adjacent 200' tower spans. When needed, the traveler platform will be lifted in place from a small boat along the river, eliminating traffic disruptions on the bridge, and used for bridge inspection, maintenance and repairs. It will only occupy the underside of the bridge when being used; once work is complete it will be removed. The traveler platform will greatly benefit the owner as well as the user by providing a more economical, safer and non-disruptive underside inspection and repair alternative when compared to past procedures that required travel lane closures.

This paper summarizes the findings of a study on the use of Ground Penetrating Radar (GPR) for nondestructive evaluation of concrete bridge decks. GPR has been found to be a proven technique for condition assessment of bridge decks [1]. However, most GPR studies have involved testing in the field, where the conditions are complex [2]. The objective of the present study is to assess the effect of isolated anomalies on the radar waveforms and determine the capabilities and limitations of the GPR technique under controlled laboratory conditions. Also, a radar data analysis model previously developed by Halabe et al. [3] was further improved, and its accuracy of prediction was compared to the actual conditions existing in the laboratory specimens.

There is an urgent need to develop methods for rapid identification of major deterioration in bridge decks and pavements. As traditional methods are slow and cumbersome, the focus has shifted to the use of modem nondestructive techniques such as Ground Penetrating Radar (GPR). GPR is a fast, non-contact technique, but interpretation of the radar datais difficult and requires complex analysis. Recently, great improvements in the analysis of radar data have been made and theoretical models for the prediction of subsurface condition of concrete structures have been developed. This paper describes models for predicting the velocity and attenuation of electromagnetic waves in concrete as a function of frequency, temperature, moisture content, chloride content and concrete mix constituents. The electromagnetic properties of concrete are predicted by aggregating the individual properties of its constituents: water, salt, air, cement paste, and aggregate solids. This mixture model, in conjunction with a rebar model developed to account for the reflection produced from reinforcing bars embedded within the concrete, has been utilized to synthesize radar waveforms for representative reinforced concrete bridge deck geometries. A least squares inversion procedure has been applied to the computer generated synthetic waveforms. This paper demonstrates the use of this inversion procedure to predict the spatial variations in volumetric'water content, salt content, and rebar cover.

Reinforced concrete bridge decks are exposed to several types of deterioration processes: corrosion, alkali–silica reaction, carbonation, shrinkage, freeze–thaw actions, and so forth. The most commonly found problem is corrosion-induced bridge deck delamination. Previous studies have shown that surveys of bridges relying on a single nondestructive evaluation (NDE) technology provide limited information about the condition of concrete bridge decks. To overcome limitations of individual technologies, a complementary approach using several NDE technologies should be used in bridge deck evaluation. The presented approach utilizes a suite of NDE technologies, namely, impact echo (IE), ultrasonic surface waves (USW), ground-penetrating radar (GPR), half-cell potential (HCP), and electrical resistivity (ER). The suite of NDE technologies was implemented in the evaluation of bridge decks on nine bridges in Iowa. The NDE was complemented by ground-truth measurements on the cores extracted from all nine bridge decks. Condition assessment with the five NDE technologies has clearly shown their advantages and limitations. For example, the GPR surveys provided assessment of concrete deterioration at relatively high speeds of data collection. In contrast, IE provided high accuracy in detection and characterization of delaminations in the deck but at a lower testing speed. HCP and ER tests provided assessment of the likelihood of corrosion, whereas the USW test provided accurate assessment of the effects of deterioration processes and defects on mechanical properties, primarily the degradation of the elastic modulus. Most important, the survey showed the advantages of use of multimodal NDE surveys in the comprehensiveness of condition assessment of concrete bridge decks.

The most expensive part to maintain throughout the lifespan of a reinforced concrete bridge is the deck, largely because rehabilitation occurs after degradation is visible on a surface. However, the mechanisms that are the cause of deterioration, such as reinforcing bar corrosion, are initiated long before damage is detected via visual inspection. If rebar corrosion can be detected in its early stages, before severe deterioration has resulted, maintenance costs can be significantly reduced and the life cycle extended. Recent studies have shown that ground penetrating radar (GPR) rebar reflection amplitude attenuation correlates with active corrosion in reinforced concrete bridge decks. A significant advantage of GPR over other non-destructive evaluation (NDE) methods is its ability to be operated at highway speeds so that traffic is not disrupted. However, a well-defined GPR amplitude threshold allowing the operator to distinguish non-corroded from corroded areas of the deck has yet to be established. Because reinforcing steel corrosion is the most predominant cause of bridge deck deterioration, this research seeks to quantify the thresholds relating GPR signal amplitudes and rebar corrosion. One bridge deck removed from service, seventeen artificially corroded slabs, and one in-service bridge deck were analyzed using GPR and half-cell potential (HCP), which measures the amount of active corrosion and is currently considered the standard NDE method. A significant correlation between these two methods was found for each case. To systematically determine a threshold for the GPR so that deteriorated areas of the deck can be identified, receiver operating characteristic (ROC) curves were utilized. With an accuracy of over 87% for each scenario, this method clearly demonstrates the use of GPR for distinguishing corrosion in bridge decks.

The presence of chloride ions in New England bridge decks has caused severe damage and has contributed greatly in reducing service life. The source of the chloride ions is mainly from deicing salts applied for snow and ice removal to enable safer driving during the winter. The chloride ion acts as an accelerator in the corrosion of reinforcing bars causing expansion and therefore deterioration of the bridge deck concrete.At present the method of determining the percentage of chloride present in bridge decks is a very time consuming, expensive and destructive process. The need for a fast nondestructive procedure to determine the amount of chloride in a concrete bridge deck is apparent. This paper introduces a means of utilizing ground penetrating radar as a viable nondestructive means of detecting areas of high chloride concentration in concrete bridge decks. The technique is based on the attenuation of a radar signal emitted from a radar unit in the presence of chloride.

Accurate assessment of the quality of concrete bridge decks and identification of corrosion induced delamination leads to economic management of bridge decks. It has been demonstrated that ground penetrating radar (GPR) can be successfully used for such purposes. The growing demand on GPR has brought into the challenge of developing automatic processes necessary to produce a final accurate interpretation. However, there have been few publications targeting at automatic detection of bridge deck delamination from GPR data. This paper proposes a novel method using partial differential equations (PDEs) to detect rebar (or steel-bar) mat signatures of concrete bridges from GPR data so that the delamination within the bridge deck can be effectively located. The proposed algorithm was tested on both synthetic and real GPR data and the experimental results have demonstrated its accuracy and reliability, even for diminished contrast and low signal-to-noise ratio.

Recent research has shown a relationship between track geometry defects and track subsurface conditions as measured by Ground Penetrating Radar (GPR). This paper presents the results of a comprehensive study looking at the development of a probabilitic model for the prediction of track geometry defects as a function of key subgrade parameters as measured by GPR. Specifically, several Logistical Regression (LR) analyses were performed, to include conventional LR modeling as well as a hybrid LR modeling approach based on Hierarchical Clustering Analysis with Histogram Data. The result was a higher order polynomial Logistic Regression model for determination of the probability of a track geometry surface defect occurring at locations with measured ballast fouling and measured ballast thickness. The results showed that there was a statistically significant relationship between high rates of geometry degradation and poor subsurface condition as defined by the GPR parameters: Ballast Fouling Index (BFI) and Ballast Layer Thickness (BLT). Furthermore, a predictive model was developed to determine the probability of a high rate of geometry degradation as a function of these key GPR parameters.

The limitations of the standard two-year interval for the visual inspection of bridges required by the U.S. National Bridge Inspection Standards have been well documented, and alternative approaches to bridge inspection planning have been presented in recent literature. This paper explores a different strategy for determining the interval between inspections and the type of inspection technique to use for bridges. The foundational premise of the proposed approach is that bridge inspections are conducted to increase knowledge about the bridge’s current condition, and therefore, are only required when uncertainty about the knowledge of the bridge condition is too high. An example case of a reinforced concrete bridge deck was used to demonstrate how this approach would work. The method utilized deterioration models for predicting corrosion and crack initiation time, considering the uncertainty in the models’ parameters. Bridge inspections were used to update the current condition information and model parameters through Bayesian updating. As this paper presents a new idea for inspection planning, not all of the data or models necessary to fully develop and validate the approach currently exist. Nonetheless, the method was applied to a simulated example which demonstrates how the timing and means of bridge inspection can be tailored to provide the required data about individual bridges needed for effective bridge management decision making.

Bridge deck condition assessments in Indiana are primarily reliant on visual inspection. The condition of bridge decks, however, is highly dependent on deterioration under the surface, which includes the corrosion of steel reinforcement and concrete delamination. The implementation of reliable nondestructive testing (NDT) methods can provide information about such internal deterioration, but considering the multiple NDT methods currently available, guidance is needed to find the best approach for assessing bridge decks in the state’s bridge inventory. A research program was conducted to examine various NDT methods with the objective of recommending an effective NDT strategy for network-level and project-level bridge inspections in Indiana that will complement information from traditional bridge inspections and provide asset engineers with improved information for long-term programming decisions. For the study, several consultants used various NDT methods to inspect a set of bridge decks that represented a range of desired test variables. Based on the test results, it was determined that aerial infrared thermography (IRT) is a good network-level method that is capable of scanning a large number of bridges and providing an initial assessment of bridge deck conditions. If significant delamination activity is detected, then follow-up network-level scanning limited to the problematic bridge decks should be performed using vehicle-mounted IRT. For project-level scanning of individual bridge decks, impact echo was found to be reliable and repeatable. For bridges with high-traffic volume for which project-level scanning is needed, a pole-mounted IRT system was found to be effective for evaluating the deck condition.

This study presents a rehabilitation method for the bridge deck pavement which has been damaged due to a moisture related failure of the asphalt concrete. In order to quickly drain the water which has infiltrated into the bridge deck pavement, this rehabilitation method adopts a new drainage system including a porous asphalt concrete layer and a polymer concrete based waterproofing layer so that the water cannot stay and cause moisture-related failure on the bridge deck. The most important factors for this drainage system are to meet satisfactory performance of the repairing material for the damaged concrete bridge deck, the waterproofing layer, and to develop a fast-track construction technique with a limited traffic blocking time. The porous asphalt mixtures for the new drainage system was suggested with the maximum aggregate size of 10mm, and was validated through various physical and mechanical laboratory tests to confirm its performance characteristics. In this study, methyl methacrylate (MMA)-type material was introduced for the water-proofing on the concrete bridge deck and damaged bridge deck repairing, and the results from a series of mechanical tests for evaluating the performance of the MMA material shows it has good capability for waterproofing and repairing of the concrete bridge deck which is subject to a moisture-induced neutralization of the cement concrete. In addition, to evaluate the field performance of the new rehabilitation method, a field study was conducted on a real bridge. Field performance observations on both the MMA and pavement materials indicated that the new method performs much better than traditional methods in draining water that has infiltrated into pavement layers.