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Heavyweight concrete is used for radiation shielding, for both medical and nuclear purposes. The increased density is generally achieved by the use heavy natural aggregates such as barites or magnetite. The density achieved will depend on the type of aggregate used. Typically using barites the density will be in the region of 3,500kg/m3, which is 45% greater than that of normal concrete, while with magnetite the density will be 3,900kg/m3, or 60% greater than normal concrete.
Cement contents and water/cement ratios are similar to those for normal concretes, but the aggregate/cement ratios will be significantly higher, because of the higher density of the aggregates. Heavyweight concrete can be batched, transported and placed using conventional equipment, though there are obviously certain aspects, such as the amount that can be carried by a ready-mixed truck or handled in a skip, that will be limited by the density. Because of the higher density, formwork pressures will be increased. The rate of wear of mixers and pumps will also be increased. Compaction will require more energy than normal concrete and poker vibrators will have to be inserted at closer centres. There may be a greater tendency for the mix to bleed.
Acknowledgement: The Concrete Society