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Concrete Constituent and Mix Design
Engineering and Construction
Pages 6 (1506 words)
Concrete Constituent and Mix Design Q-1 Concrete is basically made up from cement, aggregate and water. Aggregate occupy about 65 – 80% of the total concrete volume. Hence, its role/function and properties influence the overall performance of concrete. a) Describe briefly the three different types of aggregate.
Natural heavyweight aggregates include materials such as goethite, limonite, barite, illmenite, magnetite, and hematite, with specific gravities (SGs) ranging from about 3.5 up to about 5.3, leading to concretes with unit weights up to about 4100 kg/m3 . For higher unit weight concretes, synthetic materials such as Ferro phosphorous (SG 5.8 to 6.8) or scrap iron and steel punching (SG 7.8) can be used, with resulting concrete unit weights of up to 6100 kg/m3. High-density aggregates are good attenuators of gamma rays and of fast neutrons, hence their use in radiation shielding. Although heavyweight concretes can be proportioned in much the same way as ordinary concretes, the aggregates tend to be harsh and have a tendency to segregate from the rest of the mix. As a result, both higher than usual cement contents and a higher ratio of fine to coarse aggregates are recommended. Normal Weight Aggregates Aggregates make up about 75% of the volume of concrete, so their properties have a large in?uence on the properties of the concrete (Alexander and Mindess, 2005). Aggregates are granular materials, most commonly natural gravels and sands or crushed stone. ...
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