(prHWY.com) June 12, 2012 - Zhengzhou, Canada -- Aggregate is used in concrete mainly to reduce the amount of cement paste, thus decreasing the cost. Aggregate is also necessary since it reduces the volume changes of concrete and makes it more durable as compared to the cement paste. The aggregate server as filler in the concrete and consewuently has relatively small effect upon the quality. However, for good concrete, the quality and the gradation of the aggregate should be uniform. Uniform size gradation is facilitated by using aggregate in two different size tanges, fine and coarse, and combining them in the desired proportions. Fine aggregate consists of particles less than about 7 mm. Ä°n diameter. The most commonly used fine aggregate is sand. The coarse aggregate has particle diameters varying from 7mm. to 70 mm. The gravel and crushed Stone are the most commonly used coarse aggregate. The size and grading of the aggregate are studied by means of stantard sieves.
Concrete mix should be designed mainly to obtain the required strength and workability. Although many other properties may be of prime importance in certain structures (durability, permeability etc.) strength and workability are the most important ones. It should also be noted that many of the other properties are closely related to the strength.
Generally, other things being equal, the strength of concrete varies with water/cement ratio. This ratio is extremely important and is the main parameter, which determines the strength of concrete. The strength of concrete increases as its water/cement ratio decreases. However there are practical difficulties in using very low ratios since water is not only required to hydrate the cement during the chemical reaction, but helps to maket he mix workable and thus facilitate transportation and placing of the concrete. Therefore, the amount of water used in concrete mixes is much greater than the one needed for hydration. Admixture can be used to reduce the water concent without decreasing the workability. drum
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