Theresa M. Ahlborn

Evaluation of Commercially Available Remote Sensors for Highway Bridge Condition Assessment

Improving transportation infrastructure inspection methods and the ability to assess conditions of bridges has become a priority in recent years as the transportation infrastructure continues to age. Current bridge inspection techniques consist largely of labor-intensive subjective measures for quantifying deterioration of various bridge elements. Some advanced nondestructive testing techniques, such as ground- penetrating radar, are being implemented; however, little attention has been given to remote sensing technologies. Remote sensing technologies can be used to assess and monitor the condition of bridge infrastructure and improve the efficiency of inspection, repair, and rehabilitation efforts. Most important, monitoring the condition of a bridge using remote sensors can eliminate the need for traffic disruption or total lane closure because remote sensors do not come in direct contact with the structure. The purpose of this paper is to evaluate 12 potential remote sensing technologies for assessing the bridge deck and superstructure condition. Each technology was rated for accuracy, commercial availability, cost of measurement, precollection preparation, complexity of analysis and interpretation, ease of data collection, stand-off distance, and traffic disruption. Results from this study demonstrate the capabilities of each technology and their ability to address bridge challenges.

Combined Imaging Technologies for Concrete Bridge Deck Condition Assessment

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.

Bond Performance between Ultrahigh-Performance Concrete and Normal-Strength Concrete

AbstractUltrahigh-performance concrete (UHPC) exhibits several properties that make it appropriate for the rehabilitation of concrete structures. In this investigation, the application is focused on bridge deck overlays, but the study is equally applicable to other rehabilitation applications. Its negligible permeability makes this material suitable as a protective barrier that prevents any water or chemical penetration into the substrate. In addition, its ultra-high compressive strength and post-cracking tensile capacity could provide an improvement to the bearing capacity. However, for extensive acceptance, it has to be demonstrated that the bond between UHPC and normal strength concrete (NSC) offers a good long-term performance under a variety of operating conditions. The UHPC-NSC interface can experience high tensile, shear, and compressive stresses at both early and later life stages and the environmental conditions inherent to the operating environment. The success of the rehabilitation will depend ...

Characterization of Strength and Durability of Ultra-High-Performance Concrete Under Variable Curing Conditions

One of the latest advancements in concrete technology is ultra-high-performance concrete (UHPC), a fiber-reinforced, densely packed material that exhibits increased mechanical performance and superior durability compared with normal- and high-strength concretes. UHPC has great potential to be used in the bridge market in the United States. However, to gain acceptance by designers, contractors, precasters, and owners, this material needs to be tested according to ASTM International and AASHTO standards, and new practices must be developed. The variability in performance that is based on new challenges of mixing and curing must also be considered. The effects of curing regimes and specimen age on the strength and durability properties of a fiber-reinforced UHPC was investigated. Regardless of when the thermal treatment was applied, UHPC consistently attained compressive stresses above 30 ksi (207 MPa), a modulus of elasticity of approximately 8,000 ksi (55 GPa), and a Poissons ratio of 0.21. Flexural characteristics were enhanced with high-temperature curing. UHPC also demonstrated extremely high resistance to freeze–thaw cycling (with a durability factor of more than 100), coefficient of thermal expansion values only slightly higher than that of normal-strength concrete, and negligible chloride ion penetration. Furthermore, modified versions of ASTM and AASHTO standard testing methods were employed to aid in development of draft standards for testing some UHPC material properties in the United States that will eventually lead to a national design code.

Characterization of Interface Bond of Ultra-High-Performance Concrete Bridge Deck Overlays

Critical components of the nations bridge network, concrete bridge decks, are deteriorating at a rapid rate. This deterioration can be attributed to several factors; however, winter salt application, the diffusion of chlorides to the reinforcing steel, and eventual corrosion of the reinforcement are primary culprits. Multiple protection solutions, include concrete protective systems, sealers, additional cover to the reinforcement, membranes, and epoxy-coated reinforcement, but each solution has shortcomings and does not completely address the problem. Ultra-high-performance concrete, a relatively new material with exceptional strength and durability characteristics, may be a solution to these problems when it is used as a thin overlay on bridge decks. An experimental study was performed to evaluate the bond strength between an ultra-high-performance concrete overlay and a normal concrete substrate with different types of surface textures, including smooth, low roughness, and high roughness. Slant shear and splitting prism tests were performed to quantify the bond strength under compression combined with shear and under indirect tension. Test results demonstrated that under compressive loading, the bond strength was greater than the strength of the substrate when the surface texture was greater than the standard smooth finished mortar surface. For the bond strength under indirect tension, results were not highly sensitive to the surface roughness. In both cases, the measured bond strengths fell within the ranges specified in the American Concrete Institutes Guide for the Selection of Materials for the Repair of Concrete.

The Challenges Related to Interface Bond Characterization of Ultra-High-Performance Concrete With Implications for Bridge Rehabilitation Practices

Over the past decade there has been a significant increase in the number of concrete transportation structures reaching the end of their service lives, typically as a result of age and severe degradation. This deterioration is often the result of exposure to aggressive environments and substantial increases in vehicle loading. Rehabilitation is typically the most appropriate solution for these structures because of the high cost of full replacement, resulting in the need for cost-effective and suitable solutions for rehabilitation. Ultra-high-performance concrete (UHPC), one of the more recent advances in construction materials, appears to be a promising material for the repair of concrete structures. The potential benefit of UHPC is primarily derived from its negligible permeability, which prevents water or chemical penetration, and its high mechanical properties, which serve to increase the bearing capacity of the structure. Some of the primary challenges associated with the use of UHPC as a repair material are uncertainty in the bond performance and interaction with the existing substrate material. This paper focuses on the characterization of the interface bond and compatibility between UHPC and normal concrete. The testing program was conducted in the spirit of ASTM because no standard test methods currently exist for UHPC. In addition, a series of numerical models were developed to support the results obtained in the experimental investigations. The results highlight the exceptional performance of the bond, but they also demonstrate a number of challenges with respect to characterizing the bond. Specific challenges included characterization of surface roughness, premature specimen failure, material strength mismatch, and the quality and consistency of the testing methods used.

Optimization of a Prestressed Concrete Railroad Crosstie for Heavy-Haul Applications

In response to rising energy costs, there is increased demand for efficient and sustainable transportation of people and goods. One source of such transportation is the railroad. To accommodate the increased demand, railroads are constructing new track and upgrading existing track. This update to the track system will increase its capacity and make it a more reliable means of transportation compared to other alternatives. In addition to increasing the track system capacity, railroads are considering an increase in the size of the typical freight rail car to allow larger tonnage. An increase in rail car loads will, in turn, require the design of track components to accommodate these loads. This design change is especially pertinent to crossties that support the rail and serve to transmit loads down to the substructure. Today, the use of concrete ties is on the rise in North America as they become an economical alternative, competitive with the historical wood ties used in industry, providing performance that surpasses its competition in terms of durability and capacity. Because of the increased loads heavy-haul railroads are considering applying to their tracks, current designs of prestressed concrete railroad ties for heavy-haul applications may be undersized. In an effort to maximize tie capacity while maintaining tie geometry, fastening systems, and installation equipment, a parametric study to optimize the existing designs was completed. The optimization focused on maximizing the capacity of an existing tie geometry through an investigation of prestressing quantity, configuration, stress levels, and other material properties. The results of the parametric optimization indicate that the capacity of an existing tie can be increased most efficiently by increasing the diameter of the prestressing and concrete strength. Findings of the study demonstrate that additional research is needed to evaluate the true capacity of concrete ties because of the impacts of deep beam effects and inadequate development length in the rail seat region.

Comparative Bond Study of Stainless and High-Chromium Reinforcing Bars in Concrete

Concrete bridge decks in corrosive environments have used several methods to prevent corrosion of the reinforcing steel including the use of alternative steels as reinforcement. While research has been conducted on corrosion resistance, very little information is available about the bond strength of alternative metallic reinforcement such as solid stainless steels and high-strength, high-chromium (HSHC) alloys. Therefore, the tensile bond strengths of three alternative metallic steel reinforcements in concrete are compared with conventional A615 Grade 60 steel reinforcement. Two types of stainless steel were considered, 316LN and 2205 duplex. An HSHC microcomposite bar was also considered. A total of 250 bond tests were performed with beam-end specimens similar to the ASTM A944 specimen. Bonded lengths of 4 to 12 in. were used for No. 4 and No. 6 reinforcing bars. Concrete clear cover for all tests was 1½ in. to produce cracking bond failure. No transverse reinforcement was present. The normal strength concrete was typical of that used in Michigan bridge decks. Statistical comparisons of bond test results with predicted values for bond strength of A615 reinforcement revealed there was no reason to believe the bond strength of the alternative metallic reinforcing bars was less than predicted. The conservatism of the current development-length relationships generally predicted lower bond strengths than were observed. Therefore, no modifications are suggested when estimating the development length of these reinforcements as a one-to-one replacement for A615 Grade 60 reinforcement, No. 4 to No. 6 bars, using standard development-length relationships.

Unmanned Aerial Vehicle (UAV)-Based Assessment of Concrete Bridge Deck Delamination Using Thermal and Visible Camera Sensors: A Preliminary Analysis

ABSTRACT Infrared and visible cameras were mounted on an unmanned aerial vehicle (UAV) to image bridge deck surfaces and map likely concrete delaminations. The infrared sensor was first tested on laboratory validation experiments, to assess how well it could detect and map delaminations under controlled conditions. Field tests on two bridge deck surfaces further extend the validation dataset to real-world conditions for heterogeneous concrete surfaces. Performance of the mapping instrument and algorithms were evaluated through receiver operating characteristic (ROC) curves, giving acceptable results. To improve the performance of the mapping by reducing the rate of false positives, i.e., areas wrongly mapped as being affected by delamination, visible images were jointly analyzed with the infrared imagery. The potential for expanding the method to include other products derived from the visible camera data, including high density 3D point locations generated by photogrammetric methods, promises to further improve the performance of the method, potentially making it a viable and more effective option compared to other platforms and systems for imaging bridge decks for mapping delaminations.

Effect of fiber orientation on dynamic compressive properties of an ultra-high performance concrete

Abstract : Casting structural elements with ultra-high performance concrete (UHPC) tends to create preferential fiber alignment, which affects the strength and must be accounted for in design. To date, most work on fiber-orientation effects has been in tension rather than compression. This work characterizes the fiber orientation occurring in a typical UHPC beam and how that orientation affects compressive behavior at high strain rates. Specimens (36 total) were cored from the beam, and their fiber orientations were non-destructively evaluated using x ray computed tomography. Fibers showed flow-induced alignment along the length of the beam. The perpendicular orientation number was used to describe orientation, as fibers perpendicular to the load were most effective in crack bridging. Quasi-static compressive strength appeared to increase with perpendicular orientation number, but the correlation is uncertain due to data limitations. Dynamic tests at strain rates of 130 to 200 s-1 were performed with a split-Hopkinson pressure bar. Dynamic compressive strength was independent of orientation number in these tests, although results suggested that the distribution and orientation of fibers influenced crack formation. The strain at peak stress, a measure of ductility, increased up to 25 percent over the range of perpendicular orientation numbers tested.