2020. 1. 23. 02:24ㆍ카테고리 없음
Properties Of Aggregates In Concrete
Tests for geometrical properties of aggregates. Determination of shell content. Percentage of shells in coarse aggregates (British Standard) This European Standard specifies a method for the determination of shell content of coarse aggregates. It applies to gravel or mixed aggregate containing gravel.
Strength StrengthAlthough the water / cementious material ratio is an important factor affecting the strength of concrete, the aggregateproperties can not be ignored. The aggregate strength is usually not afactor except in lightweight and high strength concrete. However, aggregatecharacteristics other than strength, such as the size, shape, surface texture,grading and mineralogy are known to affect concrete strength in varyingdegrees.Size:The maximum size of a well-graded coarse aggregate of a given mineralogycan have two opposing effects on the strength of normal concrete. Withthe same cement content and consistency, concrete mixtures containing largeraggregate particles require less mixing water than those containing smalleraggregate. On the contrary, larger aggregates tend to form weaker transitionzones containing more micro-cracks. Therefore, the result of these twoopposing effects when large aggregates are used is only slight.To obtain high strength concrete, coarse aggregate size is usually heldto a maximum size of 19 mm, but additional cement is required for the additionalsurface area. The fine aggregate can generally contain less material passing300 um and 150 um sieve because of the higher cement content.
Tests For Geometrical Properties Of Aggregate Income
Proportionally,the amount of fine aggregate should also be somewhat less than that usedfor normal strength concrete.Shape:Shape refers to geometrical characteristics such as round, angular,elongated, flaky, etc. Aggregate particles that are cubicle or sphericalin shape and correct mineral composition are ideal for maximizing concretestrength. The use of flat and elongated aggregate particles should be avoidedor at least limited to a minimum of 15 percent.