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 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 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.

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.

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.

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.

Applications of ground penetrating radar (GPR) in bridge deck monitoring and assessment

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.

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.

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

Remote sensing of concrete bridge decks using unmanned aerial vehicle infrared thermography

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.

This paper describes a novel approach to detecting shape features of non-metallic anti-personnel land mine using certain attributes of wavelet packets and wavelets in general. Data sources included 2GHz and 10 GHz pulse ground penetrating radar (GPR) data, and 6 GHz stepped-frequency GPR data, from laboratory measurements. Targets are chosen to include rocks and other non-lethal clutter which normally present false alarms to the GPR. The GPR signals are first de-noised with an adaptive wavelet packet de-noising method, then the shape features of the APL are determined form exploiting the regularity properties of wavelets. Results are shown which indicate that the method may be applied to pulse GPR processing, but not for frequency-stepped GPRs. Preprocessing the GPR signal for clutter reduction may not always be necessary, thus simplifying the detection process.