A visual condition assessment of a reinforced concrete railway bridge subject to alkali silica reaction (ASR) deterioration in Johannesburg

Abstract

In the 1940’s, a reinforced concrete (RC) railway bridge located in central Johannesburg was constructed using Witwatersrand Quartzite, at the time, unknown to be an alkali-silica reactive aggregate. The bridge currently displays signs of distress in the form of severe map-cracking. This study presents preliminary results of a series of tests that have been conducted to characterise the severity of alkali silica reaction (ASR) deterioration in the bridge. Twelve concrete cores were extracted for testing from various locations of the railway bridge, which displayed varying degrees of distress. A visual assessment was conducted globally on the entire structure as well as locally (using modified damage rating index (DRI) approach) on the extracted cores. The findings showed that there was extensive map-cracking present on all thirteen railway bridge elements examined, revealing signs of distress in the bridge. Even elements that were sheltered from exposure to direct rain, such as the underside of three arch surfaces, also exhibited extensive map-cracking. Furthermore, the modified DRI method was a useful technique to assess and compare the relative extent of damage of concrete taken from various locations of a RC structure, using local images of the cylindrical surface of the concrete cores. Graphical Abstract

Computer-Aided Structural Diagnosis of Bridges Using Combinations of Static and Dynamic Tests: A Preliminary Investigation

“…Proper assessment and monitoring of reinforced concrete bridges, toward diagnosis and prognosis aims, requires a detailed knowledge of the material mechanical properties of the investigated structure, in case of either unknown design data or deteriorated material conditions. Examples of frequent damage scenarios for reinforced concrete bridges can be observed by environmental conditions (see, e.g., [18]), chemical processes (see, e.g., [19,20]) and dynamic loading conditions (see, e.g., [21]). Consequently, modern trends in engineering research and applications exhibit growing interest in efficient and optimized structural testing, supported by the robust calibration of a numerical model for prognosis purposes [22,23].…”