Evaluation of Potential Alkali-Carbonate Reactions

The application of an integrated procedure for evaluating marginal aggregates with potentially deleterious degrees of alkali-carbonate reactivity is described. This evalation couples petrographic examination and laboratory expansion testing with a detailed field inspection of existing structures. Field inspection often indicates other sources of potential problems such as chert zones, shale pop-outs, road salt action, and the influence of high sulfate environments. In addition to providing expansion data, preparation of test prisms may indicate other problems such as poor workability. For the typical portland cements and range of alkali contents used, there was no laboratory evidence of deleterious alkali-carbonate reaction for the aggregates in question. This confirmed the field observations. It is critical that all aspects of performance, including workability and special construction precautions, be considered when examining the economics of using a marginal aggregate source.