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Heavyweight aggregates as it can be seen from the name is an aggregate that posses relatively high density and it is fundamental in a situation that high density concrete is necessary. Generally, aggregates with specific gravity of 2400 Kg/m3 and higher are considered to be heavyweight. The concrete density that can be obtained based on the aggregate type for example, concrete density would be 3900 Kg/m3, which is about 60 percent higher than normal concrete density when Magnetite is used, the concrete density would be around 3500 Kg/m3 when Barite is used that is greater by 45 percent compared with normal concrete density. Moreover, extremely heavy concrete could be produced by employing steel aggregate.
There are different types of minerals in composition of the heavyweight aggregate which includes either synthetic or natural. The compositions of natural mineral aggregates are dominated by minerals like magnetite, hematite, serpentine, ilmenite, and barite. Examples of synthetic aggregates include steel, iron, boron frit, Ferrophosphorus.
Furthermore, coarse heavy aggregate consisting of crushed ore, synthetic products or mixtures of both while fine heavy aggregate consists of high density minerals and manufactured or natural sand.
Additionally, high density grout and mortar can be achieved when it is needed by using fine heavy aggregate. Table 1 Provide specific gravity and composition for different types of heavyweight aggregate:
Contents:
Properties of Heavyweight Aggregates
Table 1 Physical properties, chemical composition of different class of heavyweight aggregate| No. | Material class | Predominant constituents | Granular bulk density (Kg/m3) | Chemical composition essential minerals |
| 1 | crushed stone, hydrous iron ore | Limonite | 2100 to 2400 | (HFeO2)x(H2O)y |
| 2 | crushed stone, hydrous iron ore | Goethite | 2100 to 2250 | HFeO2 |
| 3 | gravel or crushed stone | Barite | 2300 to 2250 | BaSO4 |
| 4 | crushed stone, iron ore | Ilmenite | 2250 to 2700 | FeTiO3 |
| 5 | crushed stone, iron ore | Hematite | 2900 to 3200 | Fe2O3 |
| 6 | crushed stone, iron ore | Magnetite | 2400 to 3050 | FeFe2O4 |
| 7 | Synthetic (Scrap steel) | Steel | 3700 to 4650 | Fe |
| 8 | synthetic | Ferrophosphorus | 3200 to 4150 | FenP |
Specifications of Heavyweight Aggregate:
- ASTM C637- 98a covers special aggregate application in concrete radiation shield that great density or composition or both of them are main consideration.
- ASTM C638- 92 (reapproved 1997) it is a nomenclature that provide accurate explanation for synthetic and naturally existing contents of aggregates that are used for radiation shield concrete.
- According to ASTM C637- 98a both fine and coarse heavyweight aggregate should be meet the requirements of ordinary concrete grading of ASTM C 33.
- Depend on the ASTM C637- 98a, aggregate specific gravity is not allowed to be differ by more than 3 percent between consecutive shipment and average specific gravity of overall shipment should not be less than minimum required specific gravity.
- Testing and sampling methods are carried out according to ASTM C 33 with numbers of exceptions for example to get enough particle numbers and required sample volume larger amount of materials are taken.
Advantages of Heavyweight Aggregates
Properties of heavyweight aggregates which are desirable for producing heavyweight concrete are:- It is advantageous that both coarse and find aggregates to be clean, strong, and inert.
- Approximately do not posses deleterious materials that may lead detrimental effects on strength and increase water for mixing.
Application of Heavyweight Aggregate:
There different and numbers of applications of heavyweight aggregates. Since heavyweight aggregates are the main and most important constituents of heavyweight concrete, it would be much clearer and easier to understand the importance of this type of aggregate through heavyweight concrete application. Various applications of heavyweight aggregate are as follows: 1. Radiation Shielding that includes nuclear or shelter bomb or medical as shown in Figure 1 , offshore structure, ballasting. Gamma and x-ray are two types of radiation that should be taken into account during designing for concrete radiation shield, see Table 2. Table 2 some aggregates that recommended for radiation shield.| Types of aggregate | Granular bulk density (Kg/m3) | Shielding capability |
| Goethite | 2100 to 2250 | Fast neutrons |
| Limonite | 2100 to 2400 | Fast neutrons |
| Barite | 2300 to 2250 | Gamma rays |
| Ferrophosphorus | 3200 to 4150 | Gamma rays |
| Boron Frit | 2600 to 2800 | Neutrons |
Figure: Heavyweight concrete that produced from hematite aggregates used to construct of floors, ceiling, and walls in order to guarantee full radiation shielding for medical building
2. Counter weights 3. Application in which high mass to volume ratio is required 4. It might be useful to attenuate vibration and sound.
