Selection of Appropriate Coarse Aggregates from Local Crushing Plants of Taxila Region

Aggregates make up about 75% of the volume of concrete, so their properties have a large influence on the properties of the concrete. Aggregates are granular materials, most commonly natural gravels and sands or crushed stone, although occasionally synthetic materials such as slags or expanded clays or shales are used. Most aggregates have specific gravities in the range of 2.6 to 2.7, although both heavyweight and lightweight aggregates are sometimes used for special concretes. The role of the aggregate is to provide much better dimensional stability and wear resistance; without aggregates, large castings of neat cement paste would essentially self-destruct upon drying. Also, because they are less expensive than Portland cement, aggregates lead to the production of more economical concretes. In general, aggregates are much stronger than the cement paste, so their exact mechanical properties are not considered to be of much importance (except for very high-strength concretes). Similarly, they are also assumed to be completely inert in a cement matrix, although this is not always true. For ordinary concretes, the most important aggregate properties are the particle grading (or particle-size distribution), shape, and porosity, as well as possible reactivity with the cement. Of course, all aggregates should be clean—that is, free of impurities such as salt, clay, dirt, or foreign matter. As a matter of convenience, aggregates are generally divided into two size ranges: coarse aggregate, which is the fraction of material retained on a No. 4 (4.75-mm) sieve, and fine aggregate, which is the fraction passing the No. 4 sieve but retained on a No. 100 (0.15-mm) sieve.

Coarse aggregates occupy almost 50-60% volume of concrete. So the shape, texture and source of coarse aggregate greatly affect the properties of concrete.
See Also: Use of waste material as aggregates

Methodology:

Coarse aggregate samples will be taken from local crushing plants around Taxila. It will be tested by the procedures given by ASTM. The results will be compared with the standards provided by different institutes around the world. Also in the end,5  concrete cylinders of dia 6 inches and height 12 inches will be made from each sample of coarse aggregate and by keeping all other variables constant. The compressive strength will be noted after performing the compressive test on UTM. The results will be compared and evaluated.

References:

•  Concrete Technolog
  y by Shetty
• ASTM C39, 1996. “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens”. Annual Book of ASTM Standards, Vol. 04. 02, the American Society for Testing and Materials, Philadelphia, USA.
•  Concrete Construction Engineering Handbook by Edward G. Nawy