Virginia’s Approach to Evaluation of Concrete Resistant to Alkali-Silica Reactions

Beginning in the late 1980s, the Virginia Department of Transportation (VDOT) observed that concrete made with aggregate containing micro-crystalline, strained, or highly fractured quartz was failing earlier than expected due to alkali-silica reactions (ASR). These reactive constituents are widespread in the aggregate resources available for use in Virginia. Difficulties have been encountered in accurately classifying aggregates with regard to their potential reactivity. Consequently, VDOT instead is attempting to identify and use cementitious materials that prevent or hinder ASR. These materials, pozzolans and slag, have been shown to reduce both ASR and permeability, resulting in a more durable concrete. Two newly developed tests were used to evaluate the effects of cementitious materials (ASTM C1260 and ASTM C1293) on the ASR potential of construction aggregates. The results of these tests were compared with the results of a more accelerated test (ASTM C441) that uses an extremely reactive synthetic aggregate. Differences in test results were noted: the C441 test, using more stringent criteria, predicted higher replacement levels for a given pozzolan or slag with a portland cement of a given alkali content than are interpreted from the C1260 or the C1293 tests. However, although a greater degree of confidence in long-term performance can be placed in material levels that “pass” the C441 test, the material replacement levels that meet the criteria specified in the C1260 and C1293 tests have been generally observed to provide acceptable performance in the field.