Using Autoclave Concrete Prism Testing to Evaluate ASR Reactivity in Concrete Using Laboratory Tests and Outdoor Exposure Blocks as Benchmark Data

Abstract

Abstract The alkali–silica reaction (ASR) occurs in concrete that contains silica in a reactive aggregate, sufficient alkalis, and sufficient moisture. Although the most widely accepted tests for evaluating ASR potential are the concrete prism test (CPT) and the accelerated mortar bar test, each test has limitations. Because of the need to test concrete mixes within a short period of time, an accelerated autoclave test method (autoclaved CPT [ACPT]) was investigated using concrete prism samples boosted to 3.0 % total alkali content subjected to an exposure temperature of 271°F (133°C) with a corresponding pressure of 29 psi (0.2 MPa) for 24 hours. A suite of aggregates was evaluated by concrete prism specimens using both the ACPT and CPT methods. The ACPT was able to classify individual aggregate fractions for ASR reactivity with 97.2 % accuracy for the proposed limit of 0.09 % expansion for 36 tested mixtures and approximately 130 specimens. Data from this test suggest that a week-long test could be considered an effective screening tool for the alkali reactivity of coarse or fine aggregate fractions. In addition, miniature CPT (AASHTO T 380, Standard Method of Test for Potential Alkali Reactivity of Aggregates and Effectiveness of ASR Mitigation Measures (Miniature Concrete Prism Test, MCPT) and 12-year outdoor exposure block results are evaluated and compared with both CPT and ACPT results. Although the data suggest a general agreement between these methods, further testing is warranted along with multi-laboratory precision evaluation.