Concrete placement at the Naghla hydroelectric station

Conclusions

• 1. In concreting work under climatic conditions similar to those of the Naghla hydroelectric plant, it is neccessary that the temperature of the concrete at the time it leaves the mixer be not higher than 17–18°C. The composition of the concrete must be established so that a minimum amount of cement is used, with mandatory incorporation of an air-entraining admixture of the SNV type, to provide uniformity, segregation resistance, and work-ability of the mix.

• 2. The concrete plants must be equipped with special proportioners for the SNV admixture, to permit the incorporation of small amounts of this admixture directly into the water batching tanks. It must be borne in mind that if the established amounts of the SNV admixture are exceeded, the strength of the concrete is sharply reduced.

• 3. Under hot, dry climatic conditions, the concrete in place must be adequately protected against drying. In this connection, continuous spraying and curing by means of wet materials (mats, tarpaulin), especially during the day, are recommended. Intense, evaporation of moisture from the concrete in the earlier stages sharply reduces its strength.

• 4. The use of precast elements, instead of wood panels, as forms for the external surfaces of the structures and for the joints between the sections, facilitates and simplifies the erection of the blocks, but requires careful compaction of the mix along the internal perimeter of the precast elements, at the time it is placed in the blocks.

• 5. According to the results of the tests performed on the control samples, for strength and impermeability, the concrete in the Naghla dam exhibits high indexes and meets the requirements established in the project.