Properties and Testing of Aggregates:
Aggregates are extremely important ingredients of concrete due to the following reasons:
(a) They gives body and strength to the concrete (role of aggregates is similar to that of bones in human body).
(b) They occupy about 75% volume of concrete and being comparatively cheaper as compared to the other ingredients, they govern economy of concrete.
(c) Not just the strength of concrete but also other properties are governed through aggregates such as durability, workability, shrinkage, volume, stability, etc.
Earlier it was believed that aggregates are inert material but later on it was established that some of the aggregates (depending upon their chemical composition) are chemically active. Thus, it is necessary to study each and every property of aggregates namely, size, shape, grading, surface texture, specific gravity, density, impact and abrasion value, crushing strength, soundness and chemical composition.
Aggregates, used in concrete, can be natural or artificial type and are broadly classified as coarse aggregates (size > 4.75 mm) and fine aggregates (size < 4.75 mm). The coarse aggregates, locally known as 'gitti', are generally available in 80, 40, 20, 10 or 4.75 mm sizes. A fine aggregates (i.e. sand) popularly known as 'ret' or 'bajri' can be conveniently grouped into coarse, medium and fine sand.
In this unit, various important properties of aggregates namely, water absorption, density and specific abrasion resistance, soundness, crushing strength, gravity, impact strength, grading, etc. and the several tests to determine the similar have been described in brief. In addition, the effect of these properties of aggregates on the strength of concrete has also been discussed.
Objectives
After studying this unit, you should be able to
- Elaborates the importance of several properties of aggregates in manufacturing the concrete.
- Get obtained with some of the related technical terms in defining these properties of aggregates like, bulking of sand, saturated surface dry (SSD) condition, flakiness and fineness modulus, elongation index, alkali-aggregate reaction, etc., and
- Determine these characteristic in laboratories or at site.