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ASR testing : a new approach to aggregate classification and mix design verification : technical report.
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2014-04-01
[PDF-57.50 MB]
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Abstract:The main objective of this study was to develop a fast, reliable test method to determine the aggregate alkali-silica reactivity
(ASR) with respect to the overall alkalinity of the concrete. A volumetric change measuring 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 is modeled to determine activation energy (Ea) based on the rate theory. The VCMD-based test can reliably predict
aggregate alkali silica reactivity in a short period of time (5 days) in terms of measuring activation energy. A representative Ea can
be determined by testing as-received aggregates (i.e., field aggregates) with 0.5N NaOH + Ca(OH)2 solution (similar to concrete
pore solution) and with permissible repeatability. Researchers have developed an Ea-based aggregate classification system, which
can serve as a potential screening parameter in an aggregate quality control program. A relationship between Ea and alkalinity is
developed, which became the basis to determine threshold alkalinity. The proposed method has the potential to be considered as an
alternative method to the current AMBT method.
An effective way of tailoring mix design depending on the level of protection needed is developed based on activation
energy, threshold alkalinity, pore solution chemistry, and concrete validation testing. A new accelerated concrete cylinder test
(ACCT) using VCMD (60°C, leaching-proof conditions) was developed to test concrete mixes in a short time. Although the testing
period is not yet fully established, the ACCT method takes around 1 month to test a reactive straight cement concrete mix with
varying alkali loadings (i.e., 8.9–4.5 lb/yard3) and around 3–4 months to test a slowly reactive straight cement mix with lower
alkali loadings (e.g., 3.0–4.0 lb/yard3). The ACCT method has the ability to emerge as a potential method to test job mix.
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