The technology of constructing concrete dams from roller-compacted concrete (rollcrete) with elimination of sectioning or with a considerable increase of the size of the sections has been being developed increasingly more in recent years. When solving problems of the thermal crack resistance of rollcrete masses, it is important to take into consideration creep of the concrete.To study this problem, the research department of the All-Union Planning, Surveying, and Scientific-Research Institute (Gidroproekt) in 1988-1989 conducted experiments on the design composition of rollcrete of the Katun hydroelectric station (Table i). Cylindrical specimens with a diameter of 30 cm and height of 90 cm were made for studying creep.Compaction of the stiff concrete mix (S = 25-35 sec) was carried out by a vibrating plate made by fastening a 29-cm-diameter steel plate on the end of the working part of an IV-90 suspended vibrator. The mix was compacted in layers 10-15 cm thick with a vibrating time of 40-60 sec. Such compaction technology was developed by conducting systematic tests with checking the density of the concrete, which reached values of about 0.96-0.98 of the theoretical in an absolutely compact body.The cylinders were loaded in devices with a pneumatic-~nydraulic power system providing constancy of the longitudinal force in time. The deformations of the concrete were measured in the middle part of the cylinder on a base of 400 mm from four sides by means of constant deformeters (scale division of the measuring head i ~m). Shrinkage deformations of the concrete were eliminated by means of "standard" specimens. Vapor insulation was realized by adhesive polyethylene film applied on the surface of the cylinder immediately after removing the molds (age of concrete 5-7 days).The age of the concrete during loading was 7, 28, 90, and 180 days and 1 year. Two cylindrical specimens were used for the 7-and 28-day ages and one specimen in the remaining cases. One of the 7-day-old specimens was finally discarded, since a high deformability of the concrete, which was related to incomplete compaction of the stiff concrete mix, was found during loading and initial stage of the tests.
In the general case the stress relaxation coefficient Kr(t, T) is a function of ~wo variables: age of the concrete T at the time of a change in stresses and the duration of the effect of a given stage of stresses (t--T) [1]. Heretofore the data on the relaxation coefficients obtained in investigations of the authors of [1-4] were used in calculating hydraulic structures. These data, although they are considered pertinent to concrete used in hydraulic structures, were obtained by tests of small specimens in which the behavior of concrete differs from conditions in massive structures.
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