Computer vision-based techniques were developed to overcome the limitations of visual inspection by trained human resources and to detect structural damage in images remotely, but most methods detect only specific types of damage, such as concrete or steel cracks. To provide quasi real-time simultaneous detection of multiple types of damages, a Faster Region-based Convolutional Neural Network (Faster R-CNN)-based structural visual inspection method is proposed. To realize this, a database including 2,366 images (with 500 × 375 pixels) labeled for five types of damages—concrete crack, steel corrosion with two levels (medium and high), bolt corrosion, and steel delamination—is developed. Then, the architecture of the Faster R-CNN is modified, trained, validated, and tested using this database. Results show 90.6%, 83.4%, 82.1%, 98.1%, and 84.7% average precision (AP) ratings for the five damage types, respectively, with a mean AP of 87.8%. The robustness of the trained Faster R-CNN is evaluated and demonstrated using 11 new 6,000 × 4,000-pixel images taken of different structures. Its performance is also compared to that of the traditional CNN-based method. Considering that the proposed method provides a remarkably fast test speed (0.03 seconds per image with 500 × 375 resolution), a framework for quasi real-time damage detection on video using the trained networks is developed.

Autonomous Structural Visual Inspection Using Region-Based Deep Learning for Detecting Multiple Damage Types

Recent applications of fiber optic sensors to health monitoring in civil engineering

Enhanced matrix packing density and tailored fiber-to-matrix interface bond properties have led to the recent development of ultra-high performance fiber reinforced concrete (UHP-FRC) with improved material tensile performance in terms of strength, ductility and energy absorption capacity. The objective of this research is to experimentally investigate and analyze the uniaxial tensile behavior of the new material. The paper reviews and categorizes a variety of tensile test setups used by other researchers and presents a revised tensile set up tailored to obtain reliable results with minimal preparation effort. The experimental investigation considers three types of steel fibers, each in three different volume fractions. Elastic, strain hardening and softening tensile parameters, such as first cracking stress and strain, elastic and strain hardening modulus, composite strength and energy dissipation capacity, of the UHP-FRCs are characterized, analyzed and linked to the crack pattern observed by microscopic analysis. Models are proposed for representing the tensile stress–strain response of the material.

Properties of strain hardening ultra high performance fiber reinforced concrete (UHP-FRC) under direct tensile loading

The effects of blending fibers on the tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete (UHP-HFRC) are investigated. Four types of steel macro-fibers (of differing length or geometry) and one type of steel micro-fiber are considered. In producing the specimens, the volume content of the macro-fiber was held at 1.0%, whereas the volume content of the micro-fiber varied from 0.0% to 1.5%. The overall shape of tensile stress–strain curves of UHP-HFRC is primarily dependent upon the type of macro-fiber, although the addition of micro-fibers favorably affects the strain hardening and multiple cracking behaviors. UHP-HFRC produced from macro-fibers with twisted geometry provides the best performance with respect to post cracking strength, strain capacity and multiple micro-cracking behavior, whereas UHP-HFRC produced with long, smooth macro-fibers exhibits the worst performance.

Tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete

A comprehensive investigation into the mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC), considering various influential factors, is imperative in order to obtain fundamental information for its practical utilization. Therefore, this paper reviewed the early-age strength (or setting) development and mechanical properties of hardened UHPFRC. In connection with the latter, the effects of the curing conditions, coarse aggregate, mineral admixtures, fiber properties, specimen size, and strain-rate on the mechanical performance of UHPFRC were specifically investigated. It was obvious that (1) heat treatment accelerates the hydration process, leading to higher strength; (2) a portion of the silica fume can be replaced by fly ash, slag, and rice husk ash in mechanical perspective; (3) the use of deformed (hooked and twisted) or long straight steel fibers improves the mechanical properties at a static rate; and (4) high rate loading provides a noticeable increase in the mechanical properties. Alternatively, there are some disagreements between the results from various ‘size effect’ tests and the effectiveness of using twisted steel fibers at static and high rate loadings. Further research to reduce the production cost of UHPFRC is also addressed in an attempt to make its widespread use more practical.

Mechanical properties of ultra-high-performance fiber-reinforced concrete: A review

https://rosap.ntl.bts.gov/view/dot/38714/dot_38714_DS1.pdf

Material Property Characterization of Ultra-High Performance Concrete

An experimental program aimed at determining ultra-high performance fiber-reinforced concrete (UHPFRC) uniaxial compressive behaviors was conducted. Overall stress-strain behavior, strain capacity, modulus of elasticity, and strength of both steam-treated and untreated UHPFRC were determined by analyzing results of compression tested cylinders. Enhanced stiffness and exceptional compressive strength were exhibited by UHPFRC according to study results. The authors present modulus of elasticity as compression strength function and strength gain with time predictor equations. The authors present UHPFRC stress-strain response linearity and establish an ascending branch compressive stress-strain behavior equation.

Compressive Behavior of Ultra-High-Performance Fiber-Reinforced Concrete

The term Ultra-High Performance Concrete (UHPC) refers to a relatively new class of advanced cementitious composite materials whose mechanical and durability properties far surpass those of conventional concrete. This class of concrete has been demonstrated to facilitate solutions that address specific problems in the United States highway bridge infrastructure. Initial material development research on UHPC began more than two decades ago. First structural deployments began in the late 1990s. First field deployments in the U.S. highway transportation infrastructure began in 2006. For this study, UHPC-class materials are defined as cementitious-based composite materials with discontinuous fiber reinforcement that exhibit compressive strength above 21.7 ksi (150 MPa), pre- and post-cracking tensile strength above 0.72 ksi (5 MPa), and enhanced durability via a discontinuous pore structure. This report documents the state of the art with regard to the research, development, and deployment of UHPC components within the U.S. highway transportation infrastructure. More than 600 technical articles and reports covering research and applications using UHPC have been published in English in the last 20 years, with many more published in other languages. The report includes information about materials and production, mechanical properties, structural design and structural testing, durability and durability testing, and actual and potential applications. The report concludes with recommendations for the future direction for UHPC applications in the United States.

https://rosap.ntl.bts.gov/view/dot/26387/dot_26387_DS1.pdf

Ultra-High Performance Concrete: A State-of-the-Art Report for the Bridge Community

Routine inspection is the most common form of highway bridge inspection to satisfy the requirements of the National Bridge Inspection Standards. The accuracy and reliability of documentation generated during these inspections are critical to the allocation of Department of Transportation construction, maintenance, and rehabilitation resources. Routine inspections are typically completed using only the visual inspection technique and rely heavily on subjective assessments made by bridge inspectors. In light of this, and given the fact that visual inspection may have other limitations that influence its reliability, the Federal Highway Administration initiated an investigation to examine the reliability of visual inspection as it is currently applied to bridges in the United States. This paper will summarize results from this study related to the accuracy and reliability of routine inspection documentation. A number of important conclusions were developed from the experimental study. Generally, it was found...

Routine Highway Bridge Inspection Condition Documentation Accuracy and Reliability

Significant recent advancements in cement-based, fiber-reinforced composite materials have stretched the bounds of concrete into the realm of ultrahigh-performance concrete (UHPC). The durability of a commercially available UHPC was independently evaluated through six standardized durability tests and the results are reported herein. Regardless of the curing treatment applied, this concrete exhibits significantly enhanced durability properties as compared to normal and high performance concretes. The concrete exhibited minimal damage after being subjected to two times the normal number of ASTM C 666 freeze–thaw cycles. It was innocuous to ASTM C 1260 ASR deterioration, to ASTM C 672 scaling deterioration, and to AASHTO T259 chloride penetration. The ASTM C 1202 Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration test result was negligible if any steam-based curing treatment was applied, and was very low otherwise. Steam-based curing treatments significantly enhanced the ASTM C 9...

Benjamin A. Graybeal

Papers

Material Property Characterization of Ultra-High Performance Concrete

Compressive Behavior of Ultra-High-Performance Fiber-Reinforced Concrete

Ultra-High Performance Concrete: A State-of-the-Art Report for the Bridge Community

Routine Highway Bridge Inspection Condition Documentation Accuracy and Reliability

Durability of an Ultrahigh-Performance Concrete