This session will present research findings and test method development using alkali content of aggregate and concrete composites to determine the potential for alkali-silica reaction in structures, and mitigation strategies. ssessing the role of alkali in alkali-silica reaction - alkali related test methods for alkali threshold, alkali loading, affect of SCMs, alkali release of aggregate, predictive models and interpretations.
Learning Objectives:
(1) The role of alkalies in alkali-silica reaction and where the alkalis are coming from;
(2) How to determine alkali content, what is and how to measure alkali threshold and alkali loading of concrete;
(3) What is the role of aggregate in alkali content;
(4) Use of predictive models and interpretation of data.
What We Learned from 25 Years of Outdoor Exposure Sites
Presented By: Thano Drimalas
Affiliation: University of Texas at Austin
Description: The industry now has a 25 year history of outdoor exposure sites for alkali-silica reaction research. This presentation will present recent exposure site data in relation to accelerated lab tests, challenges with assessing chemical admixtures, and need for a new approach.
Laboratory vs Field Performance of AAR Affected Concrete: Data Driven Assessment of Risks Associated with Accelerated Test Procedures
Presented By: Leandro Sanchez
Affiliation: University of Ottawa
Description: This presentation will explore how advanced statistical analysis and machine learning techniques can be used to better understand the risks and limitations associated with using laboratory accelerated test methods to predict long term field performance of Alkali–Aggregate Reaction (AAR) in concrete. By integrating datasets from laboratory expansion tests, material characterization, and field monitored structures, the study evaluates the ability of current tests to capture key variables such as alkali availability, binder chemistry, moisture regimes, and temperature histories. The goal is to provide engineers and researchers with improved tools and a more robust analytical framework for interpreting test results, reducing false predictions, and supporting more reliable performance based decision making for AAR mitigation.
Mitigating Potential Alkali-Silica Reaction (ASR) Expansion in Airfield Concrete Pavements
Presented By: Jason Ideker
Affiliation: Oregon State University
Description: This presentation provides an overview of the ongoing research to identify and assess approaches for prevention of ASR in mixtures containing reactive aggregates. A performance and novel mechanistic approach has been recommended and is being validated.
Test Methods for Mechanistic Determination of Alkali Threshold of Aggregates and Alkali Availability from Cement and Supplementary Cementitious Materials
Presented By: Ashlee Hossack
Affiliation: University of New Brunswick
Description: Two test methods have been developed to determine an alkali threshold value (in kg/m3 Na2Oeq) below which there is a low risk of developing deleterious ASR. First the alkali sensitivity of aggregates was evaluated by modifying two different existing testing methods (ASTM C1260 and AASHTO T380). From this work the sensitivity of a specific aggregate type to alkalies can also be observed. A new test procedure, the Method of Determining Alkali Threshold (MDAT) is introduced. In the second step a new test method called the Method of Determining Alkali Release from Cementitious Systems (MDARC) was developed based on the concept of available alkali testing in ASTM C311.
Effect of SCMs on Concrete Pore Solution: Experimental Evaluation and Thermodynamic Modeling
Presented By: Moe Sharbaf
Affiliation: Pennsylvania State University
Description: Alkali–silica reaction (ASR) in concrete is strongly influenced by pore solution chemistry, particularly hydroxyl and alkali ion concentrations. While supplementary cementitious materials (SCMs) are widely used to mitigate ASR, non-traditional SCMs—such as volcanic ash, ground glass, and off-spec coal ash—may contain elevated alkali contents, making their influence on pore solution uncertain. This study investigates the effect of 14 SCMs on pore solution composition in sealed cement pastes from early ages to one year. Despite large differences in total and soluble alkali contents, all SCMs reduced pore solution pH relative to plain cement paste. Several high-alkali SCMs produced substantial pH reductions, due to alkali binding associated with pozzolanic reactions. A thermodynamic modeling framework incorporating phase assemblage simulations, pore partitioning, dissolution kinetics, and alkali binding in C–S–H was also developed. Model predictions were compared with experimental results to assess the ASR mitigation potential of these SCMs.
A Large-Scale Field Exposure Study of ASR Using Pennsylvania Aggregates
Presented By: Farhad Kooban
Affiliation: Pennsylvania State University
Description: Alkali–silica reaction (ASR) remains a major durability concern for concrete infrastructure worldwide. To better understand ASR development under realistic environmental conditions, a large-scale outdoor exposure site has been established in Pennsylvania through a collaborative effort involving multiple academic and industry partners. The site includes nearly 200 concrete blocks produced using 22 aggregates representing a range of reactivity levels, multiple cement types (IL, IT, LC3) with varying alkali contents, multiple SCMs (slag cement, fly ash, volcanic ash), and selected ASR inhibiting chemical admixtures. The objectives of this long-term field study are to: (1) evaluate the field performance of reactive aggregates and new ASR mitigation strategies; (2) improve the predictive capability of accelerated ASR tests by correlating laboratory results with field performance; and (3) support improved prescriptive and performance-based approaches for ASR mitigation in concrete infrastructure.