Defect Detection in Concrete Bridge Decks Using Radar

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.

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

Bridges throughout the nation are continuously deteriorating, and current improvement efforts have not been sufficient for closing the investment gap. Without investing in bridge condition today, the structural integrity of the bridges, as well as the comfort, cost, and most importantly safety of motorists is compromised. During routine bridge deck inspection, simplistic methods for assessing deterioration in concrete bridge decks are substandard and only capable of detecting deterioration in its moderate to severe stages. To provide a more thorough assessment of deterioration in concrete bridge decks, advanced technologies should be incorporated into bridge inspection. Using advanced technologies like surface roughness and ground penetrating radar, deterioration hidden from the naked eye or missed using traditional assessment methods can be more accurately detected, evaluated, and reported. When accurately reported, present condition can be compared to past condition to determine what improvement efforts should be made and when. Maintaining bridges in good condition presently is more cost-effective than rehabilitating or replacing bridges in poor condition in the future. This study aims to demonstrate that a more thorough assessment of surface and subsurface deterioration in Rhode Island concrete bridge decks can be obtained through the use of advanced technologies like surface roughness and ground penetrating radar. Three Rhode Island concrete bridge decks, visually in good, moderate, and poor condition, are initially tested to generate surface and subsurface deterioration maps, then tested a second time 2 years later (the length of time of a typical routine bridge inspection) to study the change in subsurface condition over time. Both initial and secondary findings are compared to reported bridge inspection deck conditions to assess accuracy in reported bridge deck condition. The subsurface conditions of the original test in 2015 will be compared to those of the secondary test in 2017, to determine change in subsurface condition over time using mean attenuation. Change in mean attenuation over time allows for the determination of rate of deterioration without the need for corroborative testing and without using a deterioration threshold. It is important to obtain a full picture of surface and subsurface deterioration, to determine rate of deterioration, and to accurately report findings during routine bridge inspection, to best determine what management strategies should be implemented and when, for preservation purposes.

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.

Visual inspection is the commonly used method for bridge deck inspection. However, this method depends on the intuition of the inspector and his experience. The deteriorated condition of the nation's infrastructure requires better techniques for evaluation. Nondestructive evaluation can verify the integrity of a structure or any of its components without compromising its ability to perform in service. Several nondestructive techniques are implemented on concrete bridge decks evaluation. However, ground penetrating radar (GPR) is one of the promising methods in this area. Radar scans are collected and transferred into images where information about the subsurface can be extracted. This paper discusses the basis of GPR along with the advantages and disadvantages of the method. In addition, a case study of a bridge deck with asphalt overlay will be presented.

Improved concrete bridge deck evaluation using GPR by accounting for signal depth–amplitude effects

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.

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.

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.

Ground-penetrating radar method used for the characterisation of ornamental stone quarries

Ultrasonic seismic methods can be used in the condition assessment of bridge decks by evaluating changes in material characteristics and detecting the development of defects and zones of deterioration. The impact-echo method is of special benefit in the evaluation of corrosion-induced deck delamination because of its nondestructive nature and ability to detect delaminated zones at various stages of deterioration: from initial to progressed and developed. The traditional approach in the condition assessment of bridge decks by impact-echo is based on a review of individual test-point records. A new approach based on three-dimensional data visualization is proposed. The developed three-dimensional visualization platform allows for both the advanced presentation and an automated interpretation of impact-echo data. The data presentation is provided in terms of three-dimensional translucent visualizations of reflectors in a bridge deck section and horizontal and vertical cross sections through all distinctive zones, including a zone of delamination. The associated interpretation platform enables the overall assessment of the condition of the deck, through cumulative distributions of reflection intensity of different reflective layers, and the identification of deteriorated zones of the deck to be repaired or rehabilitated in an efficient and intuitive way.

As ground-penetrating radar (GPR) is increasingly used for assessing the condition of bridge decks, quantifying and controlling the quality of GPR measures becomes an important challenge. A methodology developed to assess the accuracy of deck condition measures is presented, and its use in a case study involving real data is demonstrated. The latter are generated during GPR applications on a large bridge deck and are processed with a commercial image-processing algorithm. The measures extracted from the processed GPR data are the rebar reflection amplitude and the dielectric constant of the deck material. The accuracy of the GPR assessments is evaluated by comparing core data (ground truth) with the GPR measures. The methodology uses appropriate statistical characteristic curves for quality control. It is based on a use of data to plot the probabilities of true detection versus false detection. Image interpretation requires using a threshold value (typically established from experience) selected to optimize true and false detection rates. The results of the case study indicate that rebar reflection data detect defects of the bridge decks at a 75% true detection rate with a 15% false detection rate. The dielectric data generated during field testing appear not to adequately represent the condition of the bridge deck because of the presence of latex-modified concrete overlay. The details of this finding and important conclusions are presented and discussed.

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.

Mapping Soils under Water

Ground Penetrating Radar (GPR) is widely utilized as a Non-destructive technique by transportation authorities for inspection of bridge decks due to its ability to identify major subsurface defects in a short span of time. The attenuation of recorded signal at rebar level form a characteristic hyperbolic shape in profiles obtained from GPR scans and corresponds to the corrosiveness state of concrete. The detection of these hyperbolic regions is of paramount importance and is a precursor to successful interpretation of GPR data. This paper aims to automate the detection of hyperbolic regions or hyperbolas in GPR profiles based on Viola-Jones Algorithm. A custom detector is obtained through training with numerous samples of hyperbolas over multiple stages. The detection is achieved through the developed detector and it was applied over a complete bridge deck for validation purpose. The eventual goal of such detection is to facilitate the automation of GPR data analysis.