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The current state of construction of concrete structures as the most labor-intensive necessitates an improvement of existing and development of new highly effective cyclic and continuous technologies of conducting works with the creation of an interrelated complex of highly productive machines and equipment completely mechanizing all elements of the works.A highly efficient technology based on the use of especially stiff, low-cement concrete mixes with the use for their placement and compaction of simple highly productive operating methods similar to the methods of constructing earth dams is presently gaining popularity for massive lightly reinforced concrete structures. The new technology has a high rate of placing the mixes (200-500 m3/h), which in many respects predetermined continuous methods of its preparation and conveyor delivery.For concrete-encased steel members and structures, especially heavily reinforced and thin-walled ones and those with a complex configuration, a progressive technology, in our opinion, is that with the use of modern concrete-pumping plants [1], which provides: combining horizontal and vertical delivery of mixes by one mechanism; the possibility of laying the concrete-delivery pipeline under the most complex and confined conditions of the construction site; movement of the concrete mix under pressure and its protection from unfavorable environmental effects; high mobility of the concrete-pumping equipment providing continuous delivery of the concrete mix; possibility of pumping the mixes through stationary piplines to considerable distances.The impetus to the creation of new economical designs and technologies of conducting concreting operations by means of concrete pumps was the intense development of superplasticizing and complex additives to concrete. Additive made it possible to obtain nonsegregating cast concrete mixes (CCMs) with a fluidity of 20-26 cm with respect to the slump of a standard cone (SSC) with prescribed physical and mechanical properties and workable in concreting blocks by nonvibration methods. Some progressive scheme of constructing hydraulic structures and members with the use of concrete-pumping techniques and CCMs are given in [2, 3, 4].Concrete-pump transport of cast concrete mixes has been studied little [5]. Rather extensive investigations of this problem as applied to the technology of constructing reinforced-concrete hydraulic structures are being carried out at the M. I. Kalinin Leningrad Polytechnic Institute (LPI) [6]. The following main technological problems have been established in the general problem of concreting technology: calculation of the maximum distance of transporting the mixes through stationary concrete-delivery pipelines; selection of the type of concrete pumps and their number; selection of the composition of the concrete mix meeting the given conditions of the delivery distance.These problems can be solved with consideration of the main characteristic of a concrete pump --the magnitude of the maximum pressure of the piston on the c...

The Zeya hydropower scheme is under construction in the middle reach of the Zcya River, a large tributary of the Amur River [1]. Included in the structures are a massive buttress dam with a spillway section, a power-station unit with a building adjoining the dam, distribution works and auxiliary operational structures, a permanent bridge over the Zeya River, and a transshipment port. Selection of Type of Concrete DamConsideration was given to gravity, massive buttress, and multiple-arch forms of concrete dams. The selection of type of concrete dam for severe climatic conditions is a complex engineering problem. An analysis was made of the construction and operation experience with the dams of the Bratsk, Mamakan and other hydropower schemes, construc~d under similar climatic conditions [2][3][4][5][6]. Full-scale observations of these dams and computations showed that the behavior and strength of a dam is most greatly affected by the forces due to external temperatures. It was necessary to select a dam of such design that it would be able to adapt itself to normal and continuous operation at a below-zero mean annual temperature and for a considerable air-temperature variation during the year. Semigravity dams with internal cavities (dams with widened joints, and massive buttress types) have this advantage, which make it possible to artificially create a required temperature regime within the dam body, both during the construction period and in service.Computations for the Zeya hydropower scheme and operational experience for the Mamakan dam have shown that this type of dam, with enclosed cavities, provides the maximum monolithicity of the structure, the minimal widening of construction joints along the periphery, an above-zero concrete temperature in the principal load-carrying components, operational stability of the drainage system, and a guarantee that the design distribution of foundation pressures will be achieved. The above considerations led to the decision to design the Zeya dam in the buttress form, with an internal artificial climate, maintained in enclosed and heated cavities.For a mass-gravity dam it would be necessary to take supplementary measures to reduce the thermal effects on its stressed state. Consideration was given to one such measure, the use of thermal insulation along its downstream boundary. However, this was not feasible at the spillway boundary. Therefore, an alternative which is the principal method for gravity dams was examined, namely, the provision of thermal protection and heating in the downstream boundary zone. This solution would be more effective than the former but would entail considerable operating expenditure.Adoption of the massive-buttress alternative for the Zeya dam not only reduced on the unfavorable thermal forces included in the dam's stressed state but also enabled its cost to be lowered 15% below that of a gravity-profile dam. Under very severe climatic conditions the massive-buttress type is superior to the mass-gravity dam, not only from the viewpoint of ensurin...