RILEM TC 258-AAA Round Robin Test: Alkali release from aggregates. Critical review of the test method AAR-8
Bibliographic record
Abstract
The aim of this work is to introduce the method and modifications proposed by several laboratories after carrying out the Round Robin Test based on the AAR-8 method “Determination of alkalis releasable by aggregates in concrete”, which started in July 2015 [1]. This method was based on a literature survey on the subject, on a method first developed at Univ. Laval (Quebec City, Canada) and on other works developed at Institute Eduardo Torroja IETcc-CSIC (Spain), LNEC (Portugal) and LCPC (France). Five aggregates with different mineralogy and origin (phonolite, cataclasite, granodiorite, granite and a sea dredge basalt) were immersed in specific volumes of NaOH or KOH solutions with excess calcium hydroxide maintained at 38 °C and 60 oC. At 2, 6, 13, 26 and 52 weeks, samples of the immersion test solution were removed by pipetting and chemically analysed for potassium (NaOH test solution) or sodium (KOH test solution). The amount of alkalis released were expressed in grams of Na2O, K2O, and Na2Oe per kilogram of aggregates. In this article, the results obtained of alkalis releasable by the tested aggregates are presented and, based in the obtained data, several changes are proposed in the test method in order to improve it. The main subjects of discussion were to avoid the agglomeration of fine aggregates and the alkali precipitation by reaction especially with fine aggregates, to promote the stabilization of the solution, to reduce the errors related to the method and mainly, to reduce the test time to 26 weeks instead of to 52. In addition, the test temperature is set at 38 °C due to no significant differences in the results obtained at 60 °C. The obtained results show that most of the aggregates tested release higher quantity of alkalis at 60 oC than at 38 °C, except for cataclasite and granodiorite which present similar results at both temperatures. Also, it was observed a higher release of Na+ than K+, except for granodiorite and granite. Moreover, after 52 weeks of testing, the alkali release from aggregates has still not reached a plateau. The obtained results show a high dispersion between laboratories, which was attributed to the different amount of excess of calcium hydroxide used, the variation in the acidification of alkaline solutions before the chemical analysis, and the different analytical methods used by different laboratories as well as the calibrating method.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.016 | 0.018 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.006 | 0.002 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.004 | 0.001 |
| Research integrity | 0.003 | 0.003 |
| Insufficient payload (model declined to judge) | 0.003 | 0.006 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".