Until recently, heavy concrete composed of dense aggregates has been the basic building material in hydraulic construction. It was assumed that a reduction in the specific gravity of concrete by the use of porous aggregates might lead to undesirable phenomena in hydraulic construction and, above all, reduce the stability of the hydraulic structure and shorten its service life. Armenian builders were the first in world practice, however, to indicate that in a number of cases, the use of porous, lightweight aggregate is also possible in hydraulic construction, since in the case under consideration this measure improves the quality of the concrete and, among other things, increases its frost resistance, impermeability, and crack resistance. The close values of the" thermotechnical constants of the porous aggregate and mortar reduce the temperature deformations of the concrete itself~ particularly in the zones where its components come in contact. The reduced elastic-modulus indicator of lightweight concrete for a number of designs, the delayed start of shrinkage, its high extensibility, and lower strength reduction when cured in a dry and hot climate, as well as less rigid requirements for the curing of freshly placed concrete, are also favorable factors.