Coal-burning powerplants generate over one billion tonnes of coal combustion by-products per year in the United States. These include fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) by-products from advanced clean coal technology combustors. Each tonne of by-products used in instead of portland cement in concrete saves about 7,600,000 kJ of energy, and prevents 1 t of CO2 released in the air due to avoided cement manufacture. This paper presents results of a research to study the shrinkage of no-ash concrete and fly ash (FA) concrete as influenced by the use of shrinkage reducing admixture (SRA). A polyoxyalkylene alkyl ether based SRA was used at 0%, 1.8%, and 2.5% by mass (0, 1.8, and 2.5 L/100 kg) of cementitious materials in the concrete mixtures. The fly ash concrete was made by replacing 30% (by mass) of cement with Class C fly ash. In most cases, the SRA had an effect similar to water-reducing admixtures and often improved the strength of concrete. The SRA decreased much of the initial drying shrinkage of concrete. The 4-day drying shrinkage was reduced by up to 85%, and the 28-day drying shrinkage was reduced by up to 63%. When compared with the no-ash concrete, use of 30% Class C fly ash had the following effects: autogenous shrinkage of concrete was lower at early ages and higher at later ages; drying shrinkage of concrete (after 28 days of moist curing) was somewhat higher; and, a higher dosage of SRA was required to achieve comparable reduction of the drying shrinkage. © Sila Science.