Report on the Diagnosis, Prognosis, and Mitigation of Alkali-Silica Reaction (ASR) in Transportation Structures
7.0 Concluding Remarks
This document described an approach for the diagnosis and prognosis of alkali-aggregate reactivity in transportation structures. A preliminary investigation program is first proposed to allow for the early detection of ASR; the program involves a condition survey aiming at detecting typical visual symptoms of ASR in the structures, along with a quantitative assessment of the extent of cracking in those structural members most susceptible to ASR. The assessment (diagnosis) of ASR is then completed by a sampling program followed by the petrographic examination of a limited number of cores collected from selected structural members.
In the case of structures showing evidence of ASR that justifies further investigations, an integrated approach involving the quantification of the contribution of critical parameters with regards to ASR. For instance, the expansion attained to date by the concrete, the current expansion rate and the potential for future expansion, including the temperature and humidity conditions at the site, the water soluble alkali content in the concrete and the restraint conditions in the structural member, is proposed. It is generally recognized that the potential for future distress in ASR-affected members is best evaluated through a fairly extensive in-situ monitoring program; however, such a program generally requires years to generate reliable data. Consequently, the approach proposed in this report analyses the results from a series of selected laboratory investigations, which are used to provide the best estimate possible of the current condition and future behavior of the structure under study, thus allowing one to select reasonable remedial/mitigation actions (summarized in Section 6.0).