The urgent need for the prevention of ASR damages for new constructions has been outlined in the final report of the ASR-Colloquium of the ASTRA in November 2005. Methods of resolution for the new constructions have been developed by different cantons (VS, BE, UR) and the SBB. The committee SIA 262 has now gone about the elaboration of a guideline for the ASR prevention.
The present experiences with the test methods used in Switzerland for the determination of the alkali-reactivity of the aggregates and the ASR-resistance of concretes evidence the lack of a sufficient validation of these test methods. Therefore it is not possible to make safe statements about the ASR-risk, respectively the need of preventive measures.
The present project aims at
- examining the relevance of the actual test methods for save statements on the effective reactivity of aggregates and concrete performance in real structures;
- examining the validity of actual limit values by means of comparison with real structures;
- creating the basics for the correlation of the different test methods
The project aims at answering the following questions:
- Limits of applicability of Microbarpüfung on Swiss rocks: what rock types are reactive? Reflect the present value the effective Micro reactivity of aggregates in the concrete?
- Establishing a limit of Swiss Microbarpüfung: the existing French limits adapted to Swiss conditions (generally slow-reacting aggregates, usual life of a building)?
- Correlation of micro cash values with the results of the performance tests: why, due to the Micro cash value cannot be derived the necessary concrete modification to suppress AAR? Can the inclusion of the petrographic composition of aggregate lead to a usable interpretation of micro cash value?
- Validation on the structure of the limit value for the performance test: confirms comparison with the field observations the French limit?
- Specifications for the petrographic evaluation of the alkali reactivity of aggregates: how can be correctly identified with reference to the petrographic analysis alkali reactive aggregates? What additions to the standard VSS 670 115 are needed?
Following activities are provided during the project:
- Laboratory tests: Petrographic analyzes, chemical and physical tests, microscopic analysis (optical and electronic)
- Structural inspection: detection of AAR damage Correlation with laboratory tests
Thse are results of the project:
- Verification of the practicability of the Microbar-test for Swiss aggregates.
- Definition of a Swiss limit value for the Microbar-test.
- Correlation of the Microbar-test values with the results of the Performance-tests.
- Validation of the limit value of the Performance-test based on the comparison with concrete performance in real structures
- Guidelines for the petrographical evaluation of the reactivity of granulates after VSS 670 115
The results form a basis for the elaboration of guidelines and recommendations for avoiding AAR damage if new.
The studies provide previously missing supplements to standard VSS 670 115