1. The strength of concrete according to control samples and cores at an age of 360 days is considerably higher than the analogous indices at an age of 180 days. In this case mainly the compressive strength of concrete substantially increases after an age of 180 days; the values of the coefficients of variation decrease at a considerably smaller rate. 2. When designing and constructing the largest dams the assignment of the design strength grade of the main volume of concrete to an age of 360 days is a technically and economically expedient method, saving about 20 kg/m3 cement. This method should be regulated as mandatory for concrete of large dams by all hydrotechnical construction standards.