A New Performance-Based Approach of ASR Aggregate Reactivity Prediction and Development of ASR-Resistant Concrete Mix

The main objective of this study is to develop a rapid, reliable test method to determine the aggregate reactivity due to alkali-silica reaction (ASR) with respect to the overall alkalinity of the concrete. A volumetric change measurement device (VCMD) developed at the Texas A&M Transportation Institute was used in this research. The VCMD simulates the aggregate-pore solution reaction in concrete and measures free solution volume contraction due to ASR over time. The solution volume change over time at multiple temperatures was modeled to determine ASR compound activation energy (CAE) based on the Arrhenius equation. The CAE-based test can reliably predict aggregate alkali silica reactivity in a short period of time (5 days) in terms of measuring CAE. A representative CAE can be determined by testing as-received aggregates (i.e., field aggregates) with 0.5N NaOH (NH) + Ca(OH)2 (CH) solution (similar to concrete pore solution) and with permissible repeatability. A CAE-based aggregate classification system is developed, which can serve as a potential screening parameter in an aggregate quality control program. A relationship between CAE and alkalinity is also developed, which became the basis to determine threshold alkalinity (THA). The proposed method has the potential to be considered as an alternative method to the current ASR test methods (e.g., accelerated mortar bar test (AMBT)).

An effective way of tailoring ASR mix design depending on the level of protection needed is developed based on CAE, THA, pore solution alkalinity (PSA), and concrete validation testing. An accelerated concrete cylinder test (ACCT) using VCMD at 60?C is developed with no involvement of errors due to operation and temperature change along with arresting alkali leaching to test concrete mixes in a short time. Composite spherical and finite element modeling where relevant gel properties and free strain of ASR are the main inputs were developed for prediction of the measured linear ACCT expansion in a pure phase system as a proof of concept. An expansion limit of 0.04% using 0.82% Na2O equivalent (Na2Oe) cement without alkali boosting after a testing period of 28 days is proposed for the ACCT to diagnose ASR aggregate reactivity. The ACCT method has the ability to emerge as a potential method to test job mix and to validate the ASR-resistant mix design.