International Concrete Abstracts Portal

Editor: Yail Jimmy Kim

This CD contains 15 papers that were selected from three special sessions sponsored by ACI technical committees 345 and 440 at the ACI Spring 2013 Convention in Minneapolis, MN. The papers emphasizes the concept, performance, evaluation, and repair of concrete bridges in conjunction with smart materials and sensors.

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-298

Recently, several infrastructure failures have highlighted the importance of structural inspection and increase awareness of the need for efficient structural health monitoring and damage detection techniques. The Development of non-contact monitoring technique that is efficient and requires little preparation to implement would greatly benefit the civil engineering and construction community. Close range photogrammetry is a non-contact measurement technique that can be used to monitor a specimen’s deformation as it undergoes loading. This research investigates utilising an image matching algorithm to measure the deflection profile of concrete beams. The present paper illustrates the efficiency of the image matching algorithm (digital image correlation) in measuring the full deflection profile along a concrete beam. Five reinforced concrete beams, 2400 mm (94.48 in.) long, 250 mm (10 in.) deep and 150 mm (6 in.) wide were tested under 4-point bending. Three different surface treatment configurations for the test specimen’s side faces as well as two types of longitudinal flexural reinforcement, steel and CFRP, were used. Two LVDTs were used to measure the deflection to validate the proposed digital image correlation algorithm. It was concluded that the image matching algorithm can be used efficiently to measure deflection profile of a flexural member. Despite all existing health monitoring techniques, image matching has the potential to reconstruct the deflection profile along the whole member length to evaluate its current structural behaviour.

This paper presents an initial experimental result concerning the behavior of near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) strips embedded in a concrete substrate at elevated temperatures. Thermal stresses varying from 25°C [77°F] to 200°C [392°F] are applied for three hours. The experimental program is comprised of 48 CFRP-concrete specimens bonded with an ordinary or high-temperature epoxy adhesive and their comparative performance is of interest in the present investigation. Emphasis is placed on the residual capacity of the conditioned NSM CFRP-concrete interface and corresponding failure mode. Test results show that the interfacial strength of the specimens bonded with the ordinary epoxy is maintained until 75°C [167°F] is reached, while the strength noticeably decreases with an increasing temperature above this limit. The specimens with the high-temperature epoxy preserve interfacial capacity up to 200°C [392°F] despite a trend of strength-decrease being observed. The failure of the test specimens is brittle irrespective of adhesive type. Interfacial damage is localized along the bond-line with the presence of hairline cracks that further develop when interfacial failure is imminent.

The most advanced method of investigating the performance of a structure is to continuously track the strain, deflection, and acceleration by analysing data collected from a series of wireless sensors installed on the structural member. Before analysing the data, it is important to assure the reliability of the data by verifying that all sensors are working properly. For an instance, in the reinforced concrete structure sensors are attached to the reinforcement bars and might be destroyed while pouring the concrete. Besides, sensors might malfunction due to excessive variation of temperature, load, or any other causes. Data-driven and structural models-based are two damage detection techniques in civil structures. In this study, the data driven method, a direct approach to damage assessment, was followed; this approach does not require structural modeling, such as finite element analysis. In this method, the existence of damage and its location are interpreted by pattern matching of the data series at different time ranges. The objective of this study was to develop new techniques to detect defective sensors based on the pattern matching method that included the Auto Regression Xeogeneous model. As a case study, Portage Creek Bridge was selected, located in British Colombia, Canada. Data sets of strain and temperature gages were downloaded from a database connected to the instrumented pier of the bridge and filtered and normalized continuously. The condition of a set of sensors installed in the pier was determined, using a method developed based on the concept of the sequential and binary search techniques. Using sensitivity analyses of the developed models, defective sensors were detected by pattern matching of simulated and measured or real data.

Corrosion of prestressing steel strands in concrete bridge members may lead to the rupture of single strands and catastrophic collapse before visual inspection uncovers evident signs of damage, and well before the end of the design life. Recognizing corrosion in its early stage is critical to plan maintenance and repairs and prevent premature failures. The acoustic emission (AE) technique is a rational means to develop structural health monitoring and prognosis systems for the early detection and location of corrosion in prestressed concrete. It is sensitive to micro- and macro-damage, non-intrusive, and suitable for remote monitoring. However, there is little understanding of the correlation between AE and the extent of early damage in prestressing strands. This paper presents recent advances in AE monitoring of corrosion for prestressing strands embedded in concrete. The state of the art is reviewed, and results from recent research efforts are reported, in which prestressed concrete specimens representative of scaled bridge girders and piles were exposed to salt water through wet/dry cycles. The acoustic emission activity resulting from the early corrosion of strands was studied by evaluating AE data vis-à-vis electrochemical measurements and evidence from scanning electron microscopy.