Assessment of Aggregate Reactivity Using Slurry Tests
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The testing and screening of aggregates for their alkali-silica reactivity (ASR) is generally carried out initially by petrographic analysis. If reactive aggregates are identified by petrographic analysis then a rapid screening of the aggregate’s potential to cause expansion using the accelerated mortar bar test (AMBT, AS-1141.60.1) is carried out to determine further reactivity potential. Aggregates that are found to be reactive in the AMBT method may be further screened using the concrete prism test (CPT, AS-1141.60.2). Both AMBT and CPT methods are a compromise between introducing accelerated and reactive conditions and monitoring the expansion over short and long periods of time but with conditions that are more closely aligned with field conditions. Given that these tests are empirical estimates of reactivity potential, alternate testing may be developed for the screening of aggregates. Alternate laboratory tests are rapidly carried out using slurry tests on small samples of ground aggregate (e.g. ASTM C289). Simulating storage temperatures used in the AMBT (80°C) and CPT (38°C) in 1 M NaOH (1.25% Na2Oe) is an alternate approach to the development of new rapid screening tests. To assess the degree of aggregate reactivity a co-reactant, calcium hydroxide (CH), may be added to the reaction mixture aiding reactivity assessment through the consumption of CH. The results of a laboratory trial into the reactivity of aggregates using a ground aggregate slurry test of this nature are reported in this paper. The results are correlated with standard test method data using AMBT and CPT (AS-1141.60.1 and 2) with a view to assessing this method (or methods of this type) as an alternative rapid screening approach in the identification of aggregate reactivity for ASR potential.
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