Aggregates for Concrete

The importance of using the right type and quality ofaggregates cannot be overemphasized. The fine andcoarse Aggregates generally occupy 60% to 75% of theconcrete volume (70% to 85% by mass) and strongly influ-ence the Concrete s freshly mixed and hardened proper-ties, mixture proportions, and economy. Fine Aggregates (Fig. 5-1) generally consist of natural sand or crushedstone with most particles smaller than 5 mm ( in.).Coarse Aggregates (Fig. 5-2) consist of one or a com-CHAPTER 5 Aggregates for Concretebination of gravels or crushed stone with particlespredominantly larger than 5 mm ( in.) and generallybetween mm and mm (3 8in. and 11 2in.). Somenatural aggregate deposits, called pit-run gravel, consistof gravel and sand that can be readily used in concreteafter minimal processing. Natural gravel and sand areusually dug or dredged from a pit, river, lake, or stone is produced by crushing quarry rock, boul-ders, cobbles, or large-size gravel.

ings of clay, and other fine materials in amounts that could affect hydration and bond of the cement paste. Aggregate particles that are friable or capable of being split are unde-sirable. Aggregates containing any appreciable amounts of shale or other shaly rocks, soft and porous materials, Fig. 5-1. Closeup of fine aggregate (sand). (69792 ...

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