International Concrete Abstracts Portal

Structural health monitoring (SHM) is a process aimed at providing accurate and timely information concerning structural health condition and performance. The information obtained from monitoring is generally used to plan and design maintenance activities, increase the safety, verify hypotheses, reduce uncertainty, and widen the knowledge concerning the structure being monitored. The technologies used to perform the SHM are continuously developing, and researchers and practitioners are not always aware of their market maturity, performances, and applicability. The papers included in this CD, 1) Identify the state-of-the-art SHM technologies, including their performances, applications, and market maturity; 2) Generalize the use of SHM technologies for various classes of problems and structures; 3) Examine how the SHM technologies can be used in evaluation of the current conditions and performances of concrete structures; and 4) Analyze the benefits of SHM technologies regarding the preservation and safety of concrete structures and long-term management activities in general. This CD consists of 10 papers that were presented at a technical session sponsored by ACI Committee 444 at the ACI Convention in Cincinnati, Ohio in October 2011. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-292

Needs for structural health monitoring in the last decades were rapidly increasing, and these needs stimulated developments of various sensing technologies. Distributed optical fiber sensing technologies have reached market maturity and opened new possibilities in structural health monitoring. Distributed strain sensor (sensing cable) is sensitive at each point of its length to strain changes and cracks. Such a sensor practically monitors one-dimensional strain field and can be installed over the entire length of the monitored structural members, and therefore provides for integrity monitoring, i.e. for direct detection and characterization of local strain changes generated by damage (including recognition, localization, and quantification or rating). The aim of this paper is to help researchers and practitioners to get familiar with distributed sensing technologies, to understand the meaning of the distributed measurement, and to learn on best performances and limitations of these technologies. Hence, this paper briefly presents light scattering as the main physical principle behind technologies, explains the spatial resolution as the important feature for interpretation of measurements, compares performances of various distributed technologies found in the market, and introduces the concept of integrity monitoring applicable to various concrete structures. Two illustrative examples are presented, including applications to pipeline and bridge.

From the very beginnings of time mankind has been intrigued with the potential applications of light and the possibilities that it could bring about. The origins of optical fibers probably go back to mid 19th century when the scientists tried to guide, bend, and transmit the light from one location to another. Now, optical fibers have found widespread usage in telecommunications as well as in medical and sensing applications. This article provides a summary review of principles involved in sensing with discrete optical fibers such as Bragg gratings and specific methods more prevalently employed in monitoring of bridges. The focus will be in application examples including monitoring of the masonry vaults of the Brooklyn Bridge, deformation of cable stays, and fiber optic accelerometers for testing of bridges.

This paper describes three electrically-based methods of damage detection in concrete materials. The first approach describes the use of EIS as an electrical sensing method for concrete. The results indicate that the electrical impedance spectroscopy of concrete can be used to detect cracks in concrete materials. Furthermore, this method can be used to obtain information on the geometry of the crack such as crack width and crack depth, however, the measurement are sensitive to the materials inside the crack. The second approach is the use of electrically conductive thin film that is applied to the surface of the concrete. The electrical resistance of this film increases due to cracking of the film and substrate. By monitoring the electrical resistance of this thin film, information about the time and location of cracking can be obtained. To evaluate the feasibility of using this method, it was used to detect cracking in restrained concrete elements while cracking was monitored with acoustic emission and strain measurements. The third approach presented in this paper describes the development and use of frequency selective circuit. A frequency selective circuit (FSC) has been developed to rapidly and simultaneously interrogate the response of multiple conductive surface elements. The response of the FSC is analyzed using numerical methods and the use of the FSC is demonstrated using a pilot study in which conductive films were used to simultaneously monitor the time of cracking of multiple restrained concrete rings.

The protection and health monitoring of deteriorating concrete infrastructure requires a new generation of self-sensing structural materials that possess intrinsic damage tolerance but offer self-sensing capabilities that are tailored to diagnose states of cracking. Engineered Cementitious Composites (ECC) doped with carbon black (CB) nano-particles are proposed as highly damage-tolerant materials whose electrical properties can be correlated to strain and cracking. This study investigated the effect of CB dosage on the CB-ECC rheological, mechanical and electrical properties. By incorporating CB nano-particles into the ECC system while simultaneously controlling the rheological properties of the fresh mix, the fully cured CB-ECC elements achieved close-to-uniform PVA fiber and carbon black dispersion, reduced bulk resistivity by an order of magnitude, strain hardening behavior with tensile strain capacity of 0.26 to 1.38%, and reduced crack widths of 30 to 40 m during tensile loading. Furthermore, all of the CB-ECC specimens exhibited prominent piezoresistive behavior with resistivity increasing in tandem with applied tensile strain, thereby indicating the potential of CB-ECC for strain and damage sensing.