The RILEM Approach to Mitigate Alkali Aggregate Reactions (AAR) in Concrete

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Evaluation of laboratory test methods for assessing the alkali-reactivity potential of aggregates by field site tests

Field site tests were carried out to assess the reliability of the tests developed by RILEM and some regional tests to evaluate the alkali-reactivity potential of aggregates (eight tests were included). One hundred concrete cubes made with 13 different European aggregate combinations were stored on eight different European field sites to compare their expansions with the laboratory test results. All highly reactive aggregate combinations caused significant expansion of concrete cubes within the first six years on all field sites from Norway to Spain. These and the non-reactive aggregate combinations were correctly identified with all laboratory tests. Concrete cubes with moderately reactive aggregate combinations expanded very slowly and mainly in the outdoor exposure sites with warm climate conditions. The RILEM test method AAR-4.1 (60°C accelerated concrete prism test) and the Norwegian concrete prism test at 38°C seem to be best suited to identity the potential reactivity of moderately reactive aggregate combinations.publishedVersio

Evaluation of different methods for the determination of the free alkali metal content in the pore solution of concrete

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Alkali leaching from an ASR-affected dam

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Alkali–silica reactions (ASR): Literature review on parameters influencing laboratory performance testing

Utilisation of potentially alkali–silica reactive aggregates requires reliable performance tests to evaluate the alkali–silica reactivity of various aggregate combinations, including their alkali threshold dependence on binder type. Several such performance tests have been used worldwide for more than 15 years, but none of the methods have proven to be reliable for use with all aggregate types and all binders. One of the objectives of RILEM TC 219-ACS (2007–2012) is to develop and validate one or more of such performance tests. Several parameters may influence the results obtained in an accelerated performance test compared to the field behaviour. Based on a state of the art literature review, this paper discusses which parameters must be considered to be able to develop reliable ASR performance testing methods and provides some tentative recommendations. The internal humidity in the test specimens, the extent of alkali leaching and the storage temperature are of particular importanceACKNOWLEDGEMENT. We greatly acknowledge all RILEM TC 219-ACS members and the TC Chairman and Secretary. We are particularly thankful to the authors that took part in the literature survey report performed within the task group “Performance testing”, in which has formed the basis for this review paper. The authors would also like to acknowledge COIN, the COncrete INnovation centre (www.coinweb.no) for the financial support to the PhD study of the principle author.acceptedVersio

The EU "PARTNER" Project - European standard tests to prevent alkali reactions in aggregates: Final results and recommendations

This paper presents the main findings in the EU PARTNER Project (2002–2006) providing the basis for a unified European test approach for evaluating the potential alkali-reactivity of aggregates. The project evaluated the tests developed by RILEM and some regional tests for their suitability for use with the wide variety of aggregates and geological types found across Europe. The project had 24 partners from 14 countries, covering most of Europe, from Iceland to Greece. 22 different types of aggregates from 10 different European countries were evaluated. It was found that in most cases the RILEM tests could successfully identify the reactivity of the aggregates tested. They were most successful with normally reactive and non-reactive aggregates, but with aggregates that react very slowly an extended test period may be necessary for some of the RILEM methods. Overall, the accelerated mortar bar test and the accelerated concrete prism test seemed most effective and to have the best precision.acceptedVersio

Alkali metal distribution in composite cement pastes and its relation to accelerated ASR tests

Accelerated testing of alkali silica reaction (ASR) in concrete at elevated temperatures of 38 and 60 °C has an unknown impact on the alkali metal distribution in the cement paste. This paper investigates how the alkali metals released from hydrating Portland cement, limestone, and SCMs distribute between non-reactive and unreacted phases, C-A-S-H, and the pore solution. The SCMs investigated were fly ash and a volcanic pozzolan. The hydrate assemblage and pore solution of cement pastes cured at 20, 38 and 60 °C were analysed and related to the expansion of concrete prisms. There is little difference in alkali metal distribution at 20 and 38 °C, whereas curing at 60 °C has a large impact for the SCM containing blends. At alkali metal concentrations in the pore solution below 0.5 mol/L (Na + K) expansion of concrete was suppressed. Pore solution analysis could be used to screen new SCMs for ASR mitigation.publishedVersio

Proceedings of the XXIII Nordic Concrete Research Symposium, Aalborg, Denmark 21-23 August, 2017

Development and assessments of test methods, to avoid deleterious AAR in concrete, have been the focus of three previous RILEM Technical Committees (TC) in the period 1989 to 2014. The 4th RILEM TC on AAR, TC 258-AAA, was established in 2014, and will until 2019 focus on the following Work Packages: WP1- Performance based testing concepts; WP2 - Relationship between results from laboratory and field and the establishment of field exposure sites; WP3 - Testing of potential alkalis released from certain types of aggregates and measurement of internal concrete alkali content; WP4 - Verification of alkalis released from aggregatespublishedVersio

Characterization of amorphous and crystalline ASR products formed in concrete aggregates

Amorphous and crystalline alkali silica reaction (ASR) products formed in aggregates of two different concrete mixtures exposed to the concrete prim test both at 38 °C and 60 °C have been analysed by scanning electron microscope with energy dispersive X-ray spectroscopy and by Raman microscopy. Additionally, amorphous ASR products were synthesized and analysed with Raman microscopy and 29Si nuclear magnetic resonance. Amorphous ASR products display a higher Na/K-ratio than crystalline ones. Both types of products display a structure dominated by Q3-sites (Si-tetrahedra with three bridging oxygen atoms typical for a layer structure) with a secondary amount of Q2-sites (Si-tetrahedra with two bridging oxygen atoms typical for a chain structure). Temperature in the CPT alters the structure of the crystalline ASR. While the Raman spectra of the product formed at 38 °C is identical to the one formed in concrete structures, the one of the 60 °C product corresponds to K-shlykovite.publishedVersio

Alkali‐silica reaction (ASR) – Performancetesting

Whether or not concrete prism tests developed for assessment of alkali‐silica reactivity of aggregates is suitable for general ASR performance testing of concrete has been evaluated. The work has been part of the Norwegian COIN program (2007‐2014), and has been performed in co‐operation with the "performance testing" task group of RILEM TC 219‐ACS. Thus, the RILEM aggregate concrete prism tests (CPTs) form the basis for the laboratory program. As a foundation for the experimental work, an introductory study focused on the following: • Summary and assessment of the main findings in the EU "PARTNER" project (2002–2006), in which the author participated actively. • Summary and discussion of the experience gained from more than 15 years of performance testing in Norway. • A comprehensive literature review, with the main objective to assess how various parameters might influence the laboratory/field correlation with respect to ASR performance testing. Based on the introductory work, the experimental part of the study focused on the effect of specimen "pre‐treatment", "ASR exposure conditions" and prism size on: • Porosity and internal moisture state of the concrete prisms. • Concrete transport properties (with respect to mobility of water and ions). • Alkali leaching (rate and amount) from the concrete prisms during the ASR exposure. • Concrete prism expansion (rate and ultimate expansion). Additionally, the effect of water‐to‐cementitious‐materials ratio (w/cm) and type of binder have been assessed. The results clearly show that parameters of importance for the development of ASR are significantly influenced by the specimen "pre‐treatment", "ASR exposure conditions" and prism cross‐section. Most test conditions included are representative test procedures used in various "commercial" CPTs. The extent of the impact depends on the concrete quality, i.e. w/cm ratio and cement type. Consequently, the conclusion from a concrete performance test will differ depending on the test procedure used. Generally, a high fraction of the in‐mixed alkalis was leached out of the concrete prisms during the ASR exposure. In fact, the rate of alkali leaching during the first weeks of exposure is the parameter found to have the highest impact on the development of ASR expansion. When exposed to 60°C, it completely controls the prisms expansion. However, a modified test procedure was developed (cotton cloth with added alkalis) in the study which might be a promising tool to mitigate alkali leaching during accelerated laboratory testing. For less permeable concretes, with a high degree of self‐desiccation, the lower internal RH for the 38°C test series contributes together with the lower rate of diffusion to reduce the rate and extent of ASR. The main part of the thesis is the papers enclosed. However, the summary gives an overview of the work and the main findings. Furthermore, some supplementary results are included together with an overview of a follow‐up project initiated based on the results of the PhD study. The thesis also gives some general recommendations for performance testing