Echanization of concreting the slope revetment slabs of the Leningrad flood-control levees

Abstract

The selection of the correct technological scheme of concreting is especially essential and should be regarded as a necessary element of leading technological development in the area of constructing hydraulic structures.A technical of conreting reinforced-concrete elements of the Leningrad flood-control levees, including thick slabs (more than 30 cm thick) of the revetment of its slopes, was examined in [i]. The proposed technology, whlchwas notpresented for coordination to the Design and Construction Materials Office of the Leningrad Hydroelectric Station Administration (PSMO LenGESS), calls for using concrete placing and compacting equipment not being produced by Soviet industry. Not concerning ourselves with the technology of concreting seawalls, which can be solved by various methods, we will examine the characteristics of the placement and compaction of the concrete mix when concreting slope revetment slabs, since this problem is common also for earth dams with reinforced-concrete facings and revetting the slopes of pumped-storage station dikes.For this purpose sliding formwork was proposed [i], which permit placingconcrete mixes with a cone slump of 1-3 cm, which is a more progressive method than the use of removable panel formwork. However, the given design (as far as it can be judged from the schematic diagram) is rather complex and does not consider the main process of concreting--compaction of the mix--which first of all should be mechanSzed, since undercompaction markedly reduces the life and strength of the structure. Withoutdwelling on the technological inconveniences of the proposed scheme of the sliding formwork (the need for sufficiently even lanes along the crest of the slope, complexity of readjusting the equipment upon a change in the length and steepness of the slope, etc.), we note the complete vagueness in the methods of delivering the mix and its compaction. In [i] mention is made of the use of rther stiff mixes (with a slump of 1-3 cm) and at the same time it is suggested to deliver the mix by a concrete pump, whereas Soviet equipment operates with concrete mixes with a slump of 6-8 cm. The increased fluidity of the mix in this case, not saving the need to compact it, slows the rate of rearranging the formwork, i.e., reduces productivity and increases the consumption of cement. Simultaneously, the use of plasticizing and air-entraining additives needed for providing the necessary frost-resistance index delays the setting time.Taking into account the aforesaid, the B. E. Vedeneev All-Union Scientific-Research Institute of Hydraulic Engineering together with the PSMO LenGESS developed a technology of concreting thick reinforced-concrete slope revetment slabs based on experimental data of investigations and experience of world dam construction [2, 3]. The following requirements were taken as the initial ones: all concreting operations should be mechanized; the possibility of concreting reinforced slabs up to 1 m thick of any length with a steepness up to 1:1.3 is necessary; compaction of the...