Graphic for the evaluation and prevention of concrete damage due to an alkali-silica reaction
Source: BAM, division Building Materials
The alkali-silica reaction (ASR) is a chemical reaction in concrete between the alkali-sensitive silicate components of the aggregate and the alkali and hydroxide ions of the pore solution, which can lead to cracking and spalling over time. The complex damage mechanism has been the subject of international research for 80 years and many damages can now be safely avoided. Problems still exist in concrete structures where late and slow reacting alkali-sensitive aggregates have been used and unfavorable exposure and usage conditions (external supply of moisture and alkaline, dynamic loading by traffic) are present. Against this background, hydraulic and bridge structures as well as concrete road pavements are particularly affected by this damage mechanism worldwide. The focus of BAM's research in this area has been on concrete pavements for many years.
In the publication for the anniversary issue of BAM, the interdisciplinary and cross-scale research of the last 20 years is presented from the macro to the micro level. First, the methods used at BAM to characterize and assess ASR risks and reaction products are explained and placed in the international context. In particular, the advantages and disadvantages of the aggregate classification approach, which is only pursued in Germany, are elaborated.
Subsequently, the added value of the research approach by combining different, preferably non-destructive methods across all scales is explained and illustrated using specific examples from a variety of research projects.
A new test setup for assessing the reactivity of aggregates is then presented. In addition, the use of microscopic, spectroscopic and X-ray techniques, which can be combined for the analysis of the microstructure and the reaction products depending on the specific problem, is explained. Furthermore, a test methodology for the condition and damage analysis of existing concrete pavements with suspected ASR is presented. This also includes the analysis of the cause of the visual ASR damage indicator “darkening of the concrete pavement surface” and the analysis of deicing salt input using innovative testing techniques.
Finally, a novel ASR prevention strategy based on internal hydrophobing of the pavement concrete is presented.
A multiscale and multimethod approach to assess and mitigate concrete damage due to alkali-silica reaction
Frank Weise, Julia von Werder, Tanja Manninger, Bärbel Maier, Matthias Fladt, Sebastian Simon, Andre Gardei, Desirée Höhnel, Stephan Pirskawetz, Birgit Meng
published in Advanded Engineering Materials, Vol. 24, issue 6, article no. 2101346, pages 1 - 36, 2022
BAM division Building Materials