Hammer Sounding Research Articles

Detection of Sub-surface Delamination and Moisture Penetration in Unlined Rock Tunnels Using Passive Thermography and Tapping

An unlined rock-blast tunnel constructed by the drill and blast method is susceptible to frequent deterioration, including sagging beds, water ingress and loose rock masses. Thus, assessing potential damages above the roadway that may impact the safety of tunnel users is of utmost importance. While tapping, a conventional nondestructive method, is typically used to predict sub-surface delamination, water ingress can be identified with the naked eye. In this research, we utilized a modern-technology approach called passive thermography, together with a high-resolution digital camera and tapping. The study encountered two primary challenges; namely, the absence of direct solar radiation during the inspection and the groove-exposed surface of the unlined tunnel. The results demonstrated that passive thermography was able to detect delaminated areas and water infiltration on the tunnel's walls and ceiling, even without direct sunlight. Large delaminated areas can be detected with just a 2°C change in atmospheric temperature twelve hours before testing. Additionally, the results of image post-processing significantly contributed to enhancing the results of passive thermography. The thermal image was processed into a grayscale image prior to HE processing, which enhances contrast by over 50%. The combination of tapping, digital camera and passive thermography was proven to be effective in periodically inspecting unlined rock tunnels, while significantly reducing time and cost. KEYWORDS: Tunnel safety, Passive thermography, Old rock-cut tunnel, Hammer sounding, Non-destructive evaluation, Image post-processing.

Bridge deck surface damage assessment using point cloud data

Bridge deck condition assessments are typically conducted through visual inspections and by incorporating traditional contact sensors for Non-Destructive Evaluation techniques such as hammer sounding and chain dragging, which require the keen expertise of trained inspectors. The accuracy of these inspections is proportional to the level of deterioration of the bridge deck, as the ability of the inspectors is correlated to the apparent level of damage. This study aims to improve the accuracy of bridge deck inspection processes by utilizing non-destructive evaluation techniques, including analyzing point cloud data gathered via Light Detection and Ranging (LiDAR) as a geometry-capturing tool for identifying surface irregularities. This research aims to evaluate and quantify the effectiveness and efficiency of LiDAR sensors in contributing to the suite of technologies available to perform bridge deck condition assessment. To achieve this, the research proposes to understand the deterioration pattern of New Jersey bridges, evaluate the results gathered from point cloud data collected on a full-scale bridge deck, and quantify the information gained from deploying LiDAR on operating bridges in New Jersey. Two data processing approaches were chosen to measure the gross and fine dimensions of the evaluated bridge decks, such as the Curvature Extraction and Slope Analysis method, and the Least Square Plane Fitting method, resulting in an accuracy of 97.92% in reference to the results gathered from reports generated through the analysis of state-of-the-art NDE technology data and visual inspection.

Bridge deck surface distress evaluation using S-UAS acquired high-spatial resolution aerial imagery

ABSTRACT Bridge decks need to be routinely inspected to ensure their serviceability, capacity, and safety under current traffic conditions. Traditionally, bridge deck inspection is performed on the ground by having inspectors either visually inspect surface conditions or interpret the acoustic feedback from hammer sounding or chain dragging to determine subsurface conditions. These traditional methods have many limitations, including but not limited to, expensive, labour-intensive, time-consuming, subjective, can exhibit a high degree of variability, requiring specialized staff on a regular basis, and unsafe. Recent advancements in remote sensing, especially small-uncrewed aircraft systems (S-UAS) based airborne imaging techniques and advanced image analysis techniques, have shown promise in improving current bridge deck inspection practices by providing an above-ground inspection method. This research explored the utility of S-UAS-based airborne imaging techniques and image processing techniques to develop a complete aerial data acquisition and analysis system to accurately detect and assess bridge deck wearing surface distresses in a timely and cost-effective manner. As part of the research project, a robust tool was also developed with the aim of being able to detect, extract, and map bridge deck wearing surface distresses with an adequate degree of accuracy while maximizing the ability to assist bridge inspectors with varying expertise. Research results revealed that the developed tool is able to effectively detect and map bridge deck wearing surface distresses at a high accuracy.

A self-referencing non-destructive test method to detect damage in reinforced concrete bridge decks using nonlinear vibration response characteristics

Several non-destructive test (NDT) methods, namely visual inspection, hammer sounding, chain drag, impulse response testing, impact echo testing, ultrasonic (array) echo testing, and under certain conditions ground penetrating radar (GPR) are currently used to detect and estimate the extent of damage such as delaminations in reinforced concrete bridge decks. In this article, we present a self-referencing NDT method that builds on impulse response (IR) testing to detect damage using nonlinear vibration characteristics. The hypothesis is that for an undamaged deck, varying the impact force applied to a specific test point does not affect the corresponding frequency response function (FRF) for frequencies that lie within the measurement system’s linear operating range. On the other hand, the FRF for a test point that contains damage changes when the impact force is increased, indicating a nonlinear vibration response. To demonstrate that the concept works theoretically, two 2D finite element (FE) models of a bridge deck, one containing a shallow delamination, were developed and their responses to impact forces of increasing amplitude compared. IR data from an in-service bridge deck was processed and analyzed. Visual inspection results and ultra-high-pressure hydro-blasting performed on the deck for rehabilitation purposes provided an opportunity to compare the obtained results with common inspection methods and actual damage extent. Based on the observations, a new damage index, referred to as nonlinear vibration index (NVI), is proposed and shown to be sensitive to damage, including shallow delaminations that were missed by means of visual inspection.

Effects of rebars on the detectability of subsurface defects in concrete bridges using square pulse thermography

The ability to predict critical conditions on highway concrete bridges is important for the avoidance of unpredictable collapses during the operation period. Potential deteriorations can develop, such as terms of cracks, air voids, and subsurface delaminated areas that are usually detected through nondestructive testing (NDT) techniques together with conventional sounding methods, i.e. hammer sounding and chain dragging. Of these deteriorations, delamination is one of the major indicators of concrete bridge health, i.e., the measurement of the percentage of delaminated area. Due to vehicle loading, changes in weather and environment, and corrosion of reinforcing steel bars, delamination can occur above or even below the rebar layer, and it can be difficult to identify and determine the size and depth of delamination, especially for delamination below the rebars. In this study, two concrete specimens were analyzed in the laboratory as used with a wide range of different concrete covers that are commonly applied in bridge structures, from 2 to 8 cm at near surface. Square Pulse Thermography (SPT), one of the active infrared thermography (IRT) techniques, is used to analyze the specimens in terms of their various heating regimes and environmental conditions. This study aims to comprehensively investigate the effect of steel reinforcement on the detectability of delamination when the delaminations have a width-to-depth ratio equal to or smaller than 2.0. The results show that delamination above the rebars indicates a higher absolute contrast than that below the rebars. In addition, the observation time of delamination below the rebars decreases significantly. As a result, the predicted depth of a delamination will be less than the value of the real depth.

Computerized Hammer Sounding Interpretation for Concrete Assessment with Online Machine Learning.

Developing efficient Artificial Intelligence (AI)-enabled systems to substitute the human role in non-destructive testing is an emerging topic of considerable interest. In this study, we propose a novel hammering response analysis system using online machine learning, which aims at achieving near-human performance in assessment of concrete structures. Current computerized hammer sounding systems commonly employ lab-scale data to validate the models. In practice, however, the response signal patterns can be far more complicated due to varying geometric shapes and materials of structures. To deal with a large variety of unseen data, we propose a sequential treatment for response characterization. More specifically, the proposed system can adaptively update itself to approach human performance in hammering sounding data interpretation. To this end, a two-stage framework has been introduced, including feature extraction and the model updating scheme. Various state-of-the-art online learning algorithms have been reviewed and evaluated for the task. To conduct experimental validation, we collected 10,940 response instances from multiple inspection sites; each sample was annotated by human experts with healthy/defective condition labels. The results demonstrated that the proposed scheme achieved favorable assessment accuracy with high efficiency and low computation load.

On the Use of Ground Penetrating Radar for Bridge Deck Assessment

Many transportation agencies require the condition assessment of concrete bridge decks as part of scheduled maintenance programs. Traditional bridge deck inspection methods include: hammer sounding and chain drag techniques. The interpretation of such techniques' results depends on the operator and may produce highly variable results. Ground Penetrating Radar (GPR) has been extensively used and become an invaluable technique due to its high level of accuracy, being Non-destructive testing (NDT), low cost and simple operation. GPR technique is used for detecting the steel rebars embedded in the concrete, determining the concrete slab thickness, the asphalt layer thickness as well as developing a corrosion map for the steel rebars. This study presents the recap of using GPR technique in inspection of a bridge deck located in El- Kobba suburban in Cairo. A clear methodology for the data collection, processing and analysis of collected raw data is presented. Data is first processed, then Numerical amplitude method is used in the analysis. The study also clearly shows how to determine: 1) the slab thickness, 2) asphalt layer thickness, and 3) the arrangement of steel rebar of the slab. Thus, GPR technique can be used to make structural assessment and obtain the structural information without destruction to the element as well as structural checks and analysis can be performed for the bridge decks.

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

The present study explores the potential application of unmanned aerial vehicle (UAV) Infrared Thermography for detecting subsurface delaminations in concrete bridge decks, which requires neither traffic interruption nor physical contact with the deck being inspected. A UAV-borne thermal imaging system was utilized to survey two in-service concrete bridge decks. The inspection process involved the acquisition of thermal images via low altitude flights using a high resolution thermal camera. The images were then enhanced and stitched together using custom developed codes to create a mosaic thermal image for the entire bridge deck. Image analysis based on the k-means clustering technique was utilized to segment the mosaic and identify objective thresholds. Hence, a condition map delineating different categories of delamination severity was created. The results were validated using data generated by other non-destructive testing technologies on the same bridge decks, namely hammer sounding and half-cell potential testing. The findings reveal that UAV with high-resolution thermal infrared imagery offers an efficient tool for precisely detecting subsurface anomalies in bridge decks. The proposed methodology allows more frequent and less costly bridge deck inspection without traffic interruption. This should enable rapid bridge condition assessment at various service live stages, thus effectively allocating maintenance and repair funds.

Damage Assessment of Tunnel Lining by Mobile Laser Scanning: Pittsburgh, Pennsylvania, Implementation Phase of FHWA SHRP 2 R06G Project

This paper presents the results of a nondestructive (NDT) laser scanner investigation that was conducted in one night by using the SPACETEC TS3 laser scanner in one tube of each of the Liberty and Armstrong Tunnels in Pittsburgh, Pennsylvania. A portable seismic property analyzer (PSPA), a hand-held NDT ultrasonic seismic device, was used to investigate a 200-ft-long segment of the lining of the Liberty Tunnel, for which results are also presented. The investigation was complemented with a limited inspection with traditional techniques (e.g., hammer sounding, coring) to validate NDT findings. This work was funded by FHWA under the auspices of Round 4 of the Implementation Assistance Program of the SHRP 2 R06G project. Both technologies incorporated in this study were also used and reviewed in the original SHRP 2 R06G project. With the use of the SPACETEC TS3 scanner and the supporting suite of software, the study obtained high-resolution imagery, thermal imagery, and three-dimensional profiles for the full length of the tunnels. The deliverables included complete mapping and inventory of distresses and moisture intrusion behind the lining. In the Armstrong Tunnel, SPACETEC technology was successful at detecting cold anomalies (tile debonding, water intrusion, etc.). However, in the Liberty Tunnel, detection of debonding or delamination was less effective as a result of the insufficient temperature gradient at the time of scanning within this particular tunnel. The PSPA results correlated well with results obtained from traditional techniques. Areas with a lower seismic modulus correlated well with areas showing debonding or delamination. Areas of severe debonding were also clearly identified with the PSPA device.

Assessment of the degree of heating of lightweight concrete

Estimating the fire severity and temperature of structural elements in buildings during fire action is one of the primary factors for assessing their condition after a fire. Some existing traditional methods for assessing this temperature, such as visual inspection, hammer sounding and petrographic analysis, are well established. However, owing to the significant variation of the results it is highly advisable to conduct cross-checking by using parallel approaches. The aim of this paper is to offer initial information about the development of a novel approach, in addition to the traditional methods for estimating the degree of heating of normal and lightweight (lightweight expanded clay aggregate) concrete, which could be beneficial for cross-checking. This approach is based on results from an experimental study concerning the reduction of compressive strength of concrete after high-temperature exposure. Developed analytical correlation between the reduction of strength and the degree of heating is presented by way of parabolic equations. Further verification and consequent testing of the proposed methodology will allow a good estimation of the maximum temperature of different parts of fire damaged buildings to be obtained. It will provide an opportunity to use this information, as an additional tool, to estimate the condition of the remaining structure after a fire, in order to propose appropriate repairing methods.

The Inspection Method Research on Air Voids of Externally Bonded FRP for Strengthening Concrete Structures

Externally bonded FRP for strengthening concrete structures is widely used in concrete structures strengthening field. Many factors affect the strengthening quality, in which delaminations and air voids are two especially important factors. At present the most popular method of inspecting delaminations and air voids is hammer sounding, but this method is slow, the inspection result is easily influenced by the inspector’s experience, and the defect area can’t be measured accurately. In this paper infrared thermal imager is used, according to the inspection results with infrared thermal imager in different conditions, the influence factors to the inspection effect including surface infrared radiation rate, wind, heat source type, heating time and the test environment are analyzed. The research shows that under right conditions using infrared thermal imager to inspecting the delaminations and air voids is a convenient, quick and accurate method.

Understanding and Detecting Bridge Deck Deterioration with Ground-Penetrating Radar

Properly timed preventive maintenance and rehabilitation can extend the life of a bridge deck and reduce life-cycle costs. To implement such an effort, owners need to decide which decks are in good condition, which need work (and what type of work), and which are not economical to repair and need to be replaced. These decisions require accurate assessment of the subsurface deck condition. Traditional methods to evaluate deck condition are not economically feasible to implement on a large number of structures. Recently, ground-penetrating radar (GPR) has been implemented to scan bridge decks rapidly and to provide the necessary information. However, the relationship between GPR measurements and the state of deck deterioration is not well understood, and thus the full acceptance and adaptation of GPR has been limited. The goal of the work reported in this paper was to establish a clearer connection between the data produced by GPR equipment and the elements and stages of the deterioration process. This goal was advanced by an evaluation of bridge deck slabs, saw-cut out of a heavily deteriorated deck during demolition, and brought into the lab for evaluation. The slabs were subjected to hammer sounding, ultrasonic impact–echo, half-cell potential for corrosion, and multiple ground- and air-coupled GPR systems, which ranged from 1.0 to 2.6 GHz. The paper describes the results of experimental testing and the correlations between the deterioration process, identified through traditional testing and the measured and processed GPR signal responses.

Image Based Crack Identification in Real Concrete Surface Using Watershed Segmentation

Crack detection is important for the inspection, diagnosis and maintenance of concrete building. However, conventional image based approaches cannot achieve precise detection since the image of concrete surface contains various types of noises like concrete blebs, stain, insufficient contrast and shading. Visual inspection and hammer sounding are the traditional tools used in concrete inspection. The condition rating assigned to a concrete surface is based largely on the results of visual inspection and on an estimate of defect size. Defects hidden from view typically are not picked up, especially defects that are more than a couple of inches from the surface. Additionally, this method is slow, qualitative and potentially hazardous for the inspector. The imaging approach proposed herein is to apply optical inspection techniques in a new way to develop accurate, global bridge inspection techniques. The proposed techniques are based on an optical inspection methods, namely: Watershed Segmentation. The watershed segmentation technique recognizes and measures defects and structural flaws by means of detection and visualization of intensity gradients on the surface of the target. Analysis of the segmented images provides a quantitative signature specific to various types of defects. Additionally noise reduction based on percolation model is proposed. The validity of the proposed technique has been evaluated by means of some experiments on concrete surfaces

Effects of Environmental Variables on Infrared Imaging of Subsurface Features of Concrete Bridges

Deterioration of concrete due to corrosion of embedded steel reinforcing bars and prestressing strands represents a significant challenge for inspection and maintenance engineers. Delaminations develop in the concrete manifest as spalling, which further exposes the steel to the corrosive environment and accelerates the deterioration process. The typical method for detecting these delaminations is hammer sounding, which requires hands-on access to the material under inspection. Specialized equipment and lane closures are frequently necessary to achieve the required access. Application of infrared imaging to detect the subsurface features in concrete can image such defects from a distance, such that direct access to the surface of the concrete is not required. However, the method relies on environmental conditions to create thermal gradients in the concrete so that these subsurface features can be detected. A study examined the optimum environmental conditions for detection of subsurface features in concrete. The goal was to provide guidance on the practical application of infrared imaging for inspection of concrete bridge components. The effects of solar loading from direct sunlight and wind speed have been examined to determine their impact on the detectability of subsurface features in concrete. The optimum time of day for detection of subsurface defects and the effect of their depth is discussed. Characteristics of optimum inspection conditions for using infrared cameras in the field are described.

Repair of an Earthquake Damaged Building Façade in Coordination with FEMA: A Case Study Including Stabilization, Evaluation, Historically Sensitive Restoration, and Hazard Mitigation

Abstract The Nisqually Earthquake struck Washington State in February 2001, damaging the facade of the historic Bush Hotel, located in Seattle’s International District. During the seismic event, sections of exterior cement plaster parge cladding and clay block infill fell from the structure onto the sidewalk below. This paper outlines the failures of the 1920s era concrete frame and hollow-core clay block infill exterior wall assembly, the multi-faceted approach designed to implement a historically sensitive repair in coordination with FEMA regulations, and addresses mitigation of potential future hazards. Prompt evaluation of the life safety threat was conducted, and sprayed-in-place polyurethane foam was used as a unique method to stabilize and temporarily weatherize portions of exterior walls. Various techniques were used to evaluate exterior walls and quantify the extent of damage including hammer sounding, invasive testing, mapping, and CAD-assisted measurements in a rigorous process to meet FEMA funding requirements. Damage to the exterior walls included delaminated and cracked stucco cladding, crushed hollow-core clay block infill panels, and cracked and spalled concrete. A multitude of factors were addressed in the Construction Documents including: restoring exterior walls to pre-earthquake conditions; maintaining the historical fabric of the building’s appearance; coordination with FEMA and historic review agencies; repair to hollow-core clay block without in-kind material readily available; restoration of an exterior mural; performing work in a busy downtown setting with the building fully occupied; and addressing removal of lead-containing coatings. Importantly, a plan for mitigation of potential hazards was designed and implemented utilizing anchors to secure clay block infill panels to the structure, in order for wall sections to better resist possible future earthquakes. Methodology and examples for the synthesis of well-coordinated Contract Documents for such a complicated project are addressed. Evaluation of successes and challenges in coordination with FEMA, design, and repair methods are also provided.

Inspection of Quebec Street Bridge in Denver, Colorado: Destructive and Nondestructive Testing

Nondestructive testing techniques have been historically and commonly used to evaluate the quality of existing concrete structures. Several traditional nondestructive testing techniques were applied to the pier caps of the Quebec Street Bridge over Air Lawn Road, constructed in 1971, which is located in Denver, Colorado. The techniques utilized included visual inspection, hammer sounding, Schmidt hammer rebounding, and ultrasonic pulse velocity testing, including tomographic imaging. Results of the nondestructive tests were used to determine areas to be tested with local destructive tests. These tests included concrete compressive strengths, chloride testing, and petrographic testing. This paper presents the application and interpretation of common nondestructive testing techniques and the consequent repair, rehabilitation, and maintenance decisions. The overall results indicate that inside cores of all the pier caps are healthy, sound concrete. On all of the pier caps, extensive exterior concrete layer rehabilitation needed to be completed.

Effect of Stay-in-Place Metal Forms on Performance of Concrete Bridge Decks

The primary objective of this research was to investigate the effect of stay-in-place metal forms (SIPMFs) on corrosion of steel reinforcement in concrete bridge decks. The study included 12 concrete bridge decks located within the Interstate 215 corridor in the vicinity of Salt Lake City, Utah. All decks were subject to similar traffic loading, climatic conditions, and maintenance treatments, including applications of deicing salts during winter months, and had been constructed during 1984–1989 with epoxy-coated rebar. Test methods included visual inspection, chain dragging, hammer sounding, Schmidt hammer testing, half-cell potential testing, and chloride-concentration testing. An analysis of covariance (ANOCOVA) was performed to evaluate the effect of SIPMFs on each of the 13 deck properties measured. Five of the 13 analyses yielded significant results, including age, cover, Schmidt rebound number, half-cell potential, and chloride concentration at 2-in. depth. While differences in age and cover resulted from limitations associated with the deck selection process and were accounted for in the ANOCOVA, the differences in Schmidt rebound number, half-cell potential, and chloride concentration were attributed to elevated moisture contents in decks with SIPMFs. While higher moisture contents lead to enhanced curing conditions that ultimately provide higher concrete strengths, they also facilitate greater ionic current flow necessary to sustain higher reinforcement corrosion rates and cause accelerated diffusion of chlorides into the concrete. Given these findings, SIPMFs should be used with caution in concrete bridge deck construction.

Effect of Stay-in-Place Metal Forms on Performance of Concrete Bridge Decks

The primary objective of this research was to investigate the effect of stay-in-place metal forms (SIPMFs) on corrosion of steel reinforcement in concrete bridge decks. The study included 12 concrete bridge decks located within the Interstate 215 corridor in the vicinity of Salt Lake City, Utah. All decks were subject to similar traffic loading, climatic conditions, and maintenance treatments, including applications of deicing salts during winter months, and had been constructed during 1984-1989 with epoxy-coated rebar. Test methods included visual inspection, chain dragging, hammer sounding, Schmidt hammer testing, half-cell potential testing, and chloride-concentration testing. An analysis of covariance (ANOCOVA) was performed to evaluate the effect of SIPMFs on each of the 13 deck properties measured. Five of the 13 analyses yielded significant results, including age, cover, Schmidt rebound number, half-cell potential, and chloride concentration at 2-in. depth. While differences in age and cover result...

Windsor Bridge Pier Repairs

This paper discusses a bridge reconstruction project that included a most unusual repair of two main river piers. The bridge, built in 1935, is owned by Broome County, N.Y. and is located in the village of Windsor. It provides a two-lane highway crossing over the Susquehanna River. In the early 1980s, the piers exhibited spalling, cracking, and efflorescence indicating surface deterioration on the 2.13 m (7 ft) thick shafts that was confirmed by hammer sounding. Routine surface preparation for shotcrete repairs discovered deteriorated concrete at depths of up to 610 mm (24 in.). Hence, the construction was halted until more intensive examination and investigation could establish a different approach. The adopted solution was the installation of a new concrete shell around the perimeter of the piers with through-shaft posttensioning to clamp the shell to the shaft. The design was prepared to accommodate various stages of deterioration of the existing piers. Through-shaft posttensioning is considered rare (if not unique) in the United States. Many unusual issues and forces were confronted during the design and detailing process.