Coarse Aggregate

1. GS.Mohan 1011210335 1 COARSE AGGREGATE

2. INTRODUCTION:- Aggregate are the important constituent in concrete. Aggregate are granular material, derived from the most part from the natural rocks, crushed stones, or natural gravels and sands. Aggregate generally occupy about 70% to 80% of the volume of concrete and can therefore be expected to have an important influence on it properties. 2

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4. CLASSIFICATION OF AGGREGATE:- a)CLASSIFICATION BASED ON SIZE: >Coarse aggregate: Aggregate which retained on the No.4 (4.75mm) sieve. The function of the coarse aggregate is to act as the main load-bearing component of the concrete. >Fine aggregate: Aggregate passing No.4(4.75mm) sieve and predominately retained on the No.200 (75µ) sieve. The fine aggregate serve the purpose of filling all the open space in between the coarse particles. 4

5. b)CLASSIFICATION BASED ON SOURCE: >Natural aggregates: This kind of aggregate is taken from natural deposits without changing their nature during the process production such as crushing and grinding. >Manufactured (synthetics) aggregates: This is a kind of man-made materials produced as a main product or an industrial by-product. Some example are blast furnace slag, air cooled slag and broken bricks. Synthetics aggregates are produced by thermally processed materials such as expanded clay and shale used for making light weight concrete. 5

6. c)CLASSIFICATION BASED ON UNIT WEIGHT: A ggregates are classified as Light-weight, Heavy-weight and Normal-weight aggregate depending on weight and specific gravity. 6 AGGREGATE SPECIFIC GRAVITY UNIT WEIGHT (kN/m3) BULK DENSITY (kN/m3) EXAMPLE normal-weight 2.5-2.7 23-26 15.20-16.80 sand heavy-weight 2.8-2.9 25-29 >20.80 Scrap iron light-weight 12 <11.20 dolomite

7. d)CLASSIFICATION BASED ON SHAPE: The shape of aggregates is an important characteristic, since it affect the workability of concrete. 7 CLASSIFICATION EXAMPLE Rounded River or seashore gravels Partly rounded Pit sands & Gravels Angular Crushed Rocks Flaky Laminated rocks

8. 8 FLAT ELONGATED ROUND ANGULAR

9. e)CLASSIFICATION BASED ON SUFACE TEXTURE: Surface texture is a measure of the smoothness and roughness of aggregate. The grouping of aggregate is broad and is based on visual examination of the specimen. As per IS:383-1970 the aggregates are classified into five groups, namely, Glassy, Smooth, Granular, Crystalline, Honeycombed and Porous. 9 CLASSIFICATION EXAMPLES Glassy Black flint Smooth Gravel, Marble Granular Sandstone Rough Basalt Crystalline Granite Honeycombed & Porous Brick, slag

10. 10 SMOOTH ROUGH

11. GOOD QUALITYIES OF AN IDEAL AGGREGATE: An ideal aggregate used for the manufacturing of concrete and mortar, should meet the following requirements. (1) It should consist of natural stones, gravels and sand or in various combinations of these materials. (2) It should be hard, strong and durable. (3 ) It should be dense, clear and free from any coating. (4) It should be free from injurious vegetable matters. (5) It should not contain flaky (angular) and elongated pieces. (6) It should not contain any material liable to attack steel reinforcement in case of reinforced concrete. 11

12. TESTS ON AGGREGATE:- The test usually conducted on coarse aggregates are >PARTICLE SIZE >FLAKINESS &ELONGATION INDEX >MOISTURE CONTENT >SPECIFIC GRAVITY AND WATER ABSORPTION >TEN PERCENT FINE VALUE >AGGREGATE CRUSHING VALUE >AGGREGATE IMPACT VALUE > AGGREGATE ABRASION VALUE 12

13. IMPACT VALUE TEST The aggregate impact value gives a relative measure of the resistance of an aggregate to sudden shock or impact. The impact value is some times used as an alternative to its crushing value . Material passing 12.5mm and retained on 10mm sieve is taken. 13

14. AGGREGATE CRUSHING VALUE:- The aggregate crushing value gives a relative measure of resistance of an aggregate to crushing under a gradually applied compressive load. The aggregate crushing strength value is useful factor to know the behavior of aggregates when subjected to wear. CRUSHING VALUE= weight of fraction passing the sieve total weight of sample 14

15. AGGREGATE ABRASION VALUE:- The aggregate abrasion value gives a relative measure of resistance of an aggregate to wear when it is rotated in a cylinder along with some abrasive charge 15

16. SIEVE ANALYSIS Sieve analysis is also called as Particle size value. In determination of the proportions of the particles with in certain ranges in an aggregate by separation o n various sieves of different size openings , may be defined as sieve analysis . FINENESS MODULUS = cumulative % of agg retained on each sieve 100 16

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18. 18 SPECIFIC GRAVITY OF AGG. Sp.Gr. is used in certain computations for concrete mix design or control work, such as, absolute volume of aggregate in concrete. It is not a measure of the quality of aggregate. Sp.Gr.= Weight of Agg. (W A ) Weight of an equal volume of water (V A * ρ w ) = W A V A * ρ w = ρ A ρ w Density of Agg. Density of Water

19. FLAKINESS & ELONGATION INDEX FLAKINESS INDEX= weight of particle passing through the gauge weight of sample ELONGATION INDEX= weight of particle retained on length gauge weight of sample 19

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