We're the contractor on a large concrete repair project, and the mix proportions for the repair concrete include replacing 18% of the portland cement with fly ash. A co-worker told me that fly ash increases drying shrinkage and now I'm concerned about potential cracking. What effect does fly ash have on the drying shrinkage of concrete?
According to the Portland Cement Association's Design and Control of Concrete Mixtures, the effect of fly ash on the drying shrinkage of concrete is of little practical significance when used in low to moderate amounts.