The danger of segregation of a concrete mix is the reason why the Construction Specifications and Regulations (SNIP) limit its free drop height to 2 m. The limitation of the free drop height of the mix into blocks being concreted stipulated bythe standards serves to prevent segregation of the mix being placed, which can cause increased inhomogeneity of the physical and mechanical properties of the concrete in the structure (Fig. 1). At the same time, for example when delivering concrete to the blocks of hydraulic structures in the winter, the drop height limitation does not permit placing the mix without uncovering the protective tent, which complicates and increases the cost of construction.The main means for controlling segregation is to reduce the falling speed of the concrete mix by using "snouts" and to reduce the free fall height of the mix during discharge. Since the limitation of the mix drop height specified by SNiP is based on expert evaluations and since it is extended to all types of structures and construction conditions, it was necessary to investigate an increase in the drop height of concrete mixes for the specific conditions of the Sayano-Shushenskoe hydroelectric station. The design of the main blocks in the dam differs from the designs of industrial buildings, to which SNiP III.G-1.70 is mainly oriented, by a smaller amount of reinforcement, which actively influences segregation of the mix x,,hen it falls. The concrete is placed in the blocks by buckets with a greater capacity than those used in industrial construction, as a result of which the mix leaves the buckets as a heavy, dense flo~,, ~, kich can prevent segregation of the coarse aggregate from the mix.Experimental work was carried out under construction conditions on blocks of the main structures of the Sayano-Shushenskoe station without any changes in the general technology of placing the mix (with the exception of its drop height) or additional requirements on the concrete design. The working compositions of the mix (3-4-cm slump) used during the experiments are presented in Table 1. The concrete mix was delivered to the blocks by buckets with a capacity of 3.2 m s loaded from dump trucks.The experimental methodology called for taking samples and wet screen sizing of the mix after its discharge from various heights (3 and 6 m) with complete opening of the bucket flap, leveling, and compaction by deep vibrators. The samples were taken in the center and along the edges of the discharged portion of the mix. The holes for taking the samples were formed by vibratory driving of hollow steel cylinders into the freshly placed layer of concrete to a depth equal to the layer of placed mix (0.5 m). In all. seven experiments were conducted~ in six of which the mix was discharged from a height of 6 m and in one, the control, from 3 m. Samples from 21 holes in four blocks with different compositions of the mix were tested. The mobility of the mix was 1.5-2 cm and 5-6 cm with respect to the slumps of a standard cone.The sampling schematics are shown...
The constructional features of arch dams, together with the desire to reduce both the time and the cost of the work required to achieve a monolithic structure, demand increases in the lift height and cementation cross section.In order to prescribe a sound figure for the optimum lift height, which is limited by the carrying capacity of the nonmonolithic dam columns and sections, it is necessary to know the general pattern of grout flow in the joint for various types of grouting systems. Hydraulic investigations* of the tubular grouting system with point outlets, which was employed in the construction of the dams for the Bratsk and Krasnoyarsk hydroelectric stations, showed that, for a lift height of even 9 m and a cross-sectional area of 135 m z (Fig.
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