REPORT-AGGREGATE and TYPES OF AGGREGATE (1).pptx

Aggregates, Types of Aggregates

1. AGGREGATES

2. AGGREGATES Aggregates are the important constituents of the concrete which give body to the concrete and also reduce shrinkage. Aggregates occupy 70 to 80 % of total volume of concrete. So, we can say that one should know definitely about the aggregates in depth to study more about concrete.

3. Geological Origin classification Natural Aggregate Artificial Aggregates

4. Natural Aggregate Almost all natural aggregates originate from bedrocks. Aggregates are reduced to its present size by weathering action of natural agents like temperature variation, rain, wind, etc. or crushing aggregate are obtained by deliberate fragmentation of rock. The geological formation of the parent’s rock, weathering processes, petrological structure and texture influence the physical properties of the aggregates.

5. Artificial Aggregates The first type of artificial aggregates obtained by the application of heat in order to expand clay, shale, slate, perlite vermiculite. The suitable raw material heated in a rotary kiln to a temperature of about 1000 -1200 C. Expansion of material takes place due to the generation of gases that entrapped in a viscous mass. This porous structure retained on cooling. The aggregate of suitable size obtained either by crushing after expansion or by reducing the raw material to the size before calcination. So the uses of pelletized material produce aggregates that are nearly spherical having a semi-impervious coating over the cellular interior.

6. Classification of Aggregates as per Size and Shape Aggregates are classified based on so many considerations, but here we are going to discuss about their shape and size classifications in detail.

7. Classification of Aggregates Based on Size Aggregates are available in nature in different sizes. The size of aggregate used may be related to the mix proportions, type of work etc. the size distribution of aggregates is called grading of aggregates

8. Aggregates are classified into 2 types according to size Fine aggregate Coarse aggregate

9. Fine Aggregate When the aggregate is sieved through a 4.75mm sieve, the aggregate passed through it called fine aggregate. Natural sand is generally used as fine aggregate, silt and clay also come under this category. The soft deposit consisting of sand, silt, and clay is termed as loam. The purpose of the fine aggregate is to fill the voids in the coarse aggregate and to act as a workability agent.

10. Fine aggregate Size variation Coarse Sand 2.0mm – 0.5mm Medium sand 0.5mm – 0.25mm Fine sand 0.25mm – 0.06mm Silt 0.06mm – 0.002mm Clay <0.002

11. Coarse Aggregate When the aggregate is sieved through 4.75mm sieve, the aggregate retained is called coarse aggregate. Gravel, cobble and boulders come under this category. The maximum size aggregate used may be dependent upon some conditions. In general, 40mm size aggregate used for normal strengths, and 20mm size is used for high strength concrete. the size range of various coarse aggregates given below.

12. Coarse aggregate Size Fine gravel 4mm – 8mm Medium gravel 8mm – 16mm Coarse gravel 16mm – 64mm Cobbles 64mm – 256mm Boulders >256mm

13. Classification of Aggregates Based on Shape We know that aggregate is derived from naturally occurring rocks by blasting or crushing etc , it is difficult to attain required shape of aggregate. But the shape of aggregate will affect the workability of concrete. So we should take care about the shape of aggregate.

14. Aggregates are classified according to shape into the following types Rounded aggregates Irregular or partly rounded aggregates Angular aggregates Flaky aggregates Elongated aggregates Flaky and elongated aggregates

15. Rounded Aggregate The rounded aggregates are completely shaped by attrition and available in the form of seashore gravel. Rounded aggregates result in the minimum percentage of voids (32 – 33%) hence gives more workability. They require a lesser amount of water-cement ratio. They are not considered for high-strength concrete because of poor interlocking behavior and weak bond strength.

16. Irregular Aggregates The irregular or partly rounded aggregates are partly shaped by attrition and these are available in the form of pit sands and gravel. Irregular aggregates may result 35- 37% of voids. These will give lesser workability when compared to rounded aggregates. The bond strength is slightly higher than rounded aggregates but not as required for high strength concrete.

17. Angular Aggregates The angular aggregates consist well defined edges formed at the intersection of roughly planar surfaces and these are obtained by crushing the rocks. Angular aggregates result maximum percentage of voids (38-45%) hence gives less workability. They give 10-20% more compressive strength due to development of stronger aggregate-mortar bond. So, these are useful in high strength concrete manufacturing.

18. Flaky Aggregates When the aggregate thickness is small when compared with width and length of that aggregate it is said to be flaky aggregate. Or in the other, when the least dimension of aggregate is less than the 60% of its mean dimension then it is said to be flaky aggregate.

19. Elongated Aggregates When the length of aggregate is larger than the other two dimensions then it is called elongated aggregate or the length of aggregate is greater than 180% of its mean dimension.

20. Flaky and Elongated Aggregates When the aggregate length is larger than its width and width is larger than its thickness then it is said to be flaky and elongated aggregates. The above 3 types of aggregates are not suitable for concrete mixing. These are generally obtained from the poorly crushed rocks.

21. Unit weight classification Normal weight aggregates Light Weight aggregates

22. Normal weight aggregates They have a specific gravity between 2.5 to 2.7 produce concrete with unit weight ranging from 23 to 26 KN/m3 and crushing strength at 28 days between 15 to 40 MPa are termed normal weight concrete.

23. Light Weight aggregates The lightweight aggregates having a unit weight up to 12 KN/m3 used to manufacture the structural concrete and masonry blocks for the reduction of the self-weight of the structure.

24. Characteristics Of A Good Fine and Coarse Aggregates It should consist of coarse, angular, sharp & hard grains. A Good Fine Aggregates must be clean & free from coatings of clay and silt.  It should not contain any organic matter. It should be free from hygroscopic salt. It should be chemically inert. It must be strong and durable.

25. Relative Density of Aggregate The  relative density (specific gravity)  of an aggregate is the ratio of its mass to the mass of an equal volume of water.

26. Bulk Density Bulk density of aggregates is the mass of aggregates required to fill the container of a unit volume after aggregates are batched based on volume

27. Voids Voids in unit volume of aggregate are the space between particles in an aggregate mass not occupied by solid minerals.

28. Porosity Porosity of aggregates is their dominant quality determinant.   Porosity governs specific gravity, and determines the physical durability of aggregates.

29. MOISTURE CONTENT The moisture content in aggregate is used to determine the binder content for HMA during production of the mixture in a plant. The procedure requires that a known amount of aggregate be obtained, the aggregate heated to remove the moisture, and the percentage of moisture determined. Ovens, hot plates, heat lamps or microwave ovens are used for heating the sample.

30. Deleterious Organic compounds are present in natural sand in sufficient quantities, that will be harmful, and hence is intended to show whether further tests are necessary or desirable.

31. Organic Impurities Organic substances in fine aggregate or sand: If sand is extracted from the river bed; it may contain humus, organic soil, decayed vegetation, decayed animal material, etc. These organic materials interfere with the cement setting and ultimately affect the strength of concrete. It shows that the presentence of organic materials excess of a limit in aggregates may be harmful.

32. Soundness refers to the durability of an aggregate in terms of the resistance to the action of weather and is an indication of the resistance to weathering of fine and coarse aggregates.

33. Alkali-silica reaction Alkali-silica reaction is of more concern because aggregates containing reactive silica materials are more common. In ASR, aggregates containing certain forms of silica will react with alkali hydroxide in concrete to form a gel that swells as it adsorbs water from the surrounding cement paste or the environment. These gels can induce enough expansive pressure to damage concrete.

34. Fineness modulus The Fineness Modulus (FM) is an empirical figure obtained by adding the total percentage of the sample of an aggregate retained on each of a specified series of sieves, and dividing the sum by 100.

35. Sieve analysis A sieve analysis (or gradation test) is a practice or procedure used in civil engineering and chemical engineering to assess the particle size distribution (also called gradation) of a granular material by allowing the material to pass through a series of sieves of progressively smaller mesh size and weighing the amount of material that is stopped by each sieve as a fraction of the whole mass.

36. Maximum Size and Grading Limit Grading limits and maximum aggregate size are specified because these properties affect the amount of aggregate used as well as cement and water requirements, workability, pumpability, and durability of concrete.

37. Recycled Aggregates Recycling of concrete is a relatively simple process. It involves breaking, removing, and crushing existing concrete into a material with a specified size and quality.

38. Iron and steel slags Iron and steel slags are  coproducts of iron and steel manufacturing . In the production of iron, the blast furnace is charged with iron ore, fluxing agents, usually limestone and dolomite, and coke as fuel and the reducing agent.From this and the added fluxing agents molten slag and iron are formed.

39. Lightweight aggregates Lightweight aggregates have been manufactured by sintering fly ash and crushing the product into suitable sizes.

40. Fine aggregate Fine aggregates are essentially any natural sand particles won from the land through the mining process Fine aggregates consist of natural sand or any crushed stone particles that are ¼” or smaller

41. SOURCES OF SAND Coral Sand Glass Sand Immature Sand Gypsum Sand Ooid Sand Silica Sand Pit Sand River Sand Sea Sand Green Sand Desert Sand Lithic Sand Mixed Carbonate silicate Sand Biogenic Sand Garnet Sand Olivine Sand Volcanic Sand Heavy Mineral Sand Sands with Hematitic Pigment Continental Sand Quartz Sand

42. Classification According to Mode of Origin Pit Sand River Sand Sea Sand

43. Pit Sand They are sharp and angular in outline. Translation and deposition are done by the wind. Such sand accumulation is sometimes covered by clay. It will be desirable to wash and clean this type of sand before use.

44. River SanD River sand is found in the river bed in-plane area. Grains of river sand is round in shape. This sand is clean and free from salt encrustations.

45. Sea Sand This type of sand is found on beaches and along sea-shore. These sand particles are round in shape. Grains are often found covered with salts that are not easily separated.

46. Classification of Fine Aggregates According to Composition Clean Sand Silty Sand Clayey Sand

47. Clean Sand These are well-graded sand containing quartz particles in a wide range of grain sizes.

48. Silty Sand These are poorly graded, having a considerable proportion of silt and other non-plastic fines.

49. Clayey Sand There is poorly graded sand that has a prominent clay fraction and also plastic fines.

50. BULKING OF SAND Bulking of fine aggregate or sand is the phenomenon of increase in sand volume due to the increase of moisture content.

51. Handling and Storing Aggregates Aggregates for batching of concrete are normally stored outdoors in stockpiles. Some of the factors that should be considered when planning for these stockpiles are: 1. Stockpiles should be built in thin layers of uniform thickness to minimise segregation. Stockpiling equipment should not be allowed to go over aggregates to avoid aggregates being crushed which will result in change in gradation or contamination. 2. Stockpiles should be separated from other materials to avoid contamination and to maintain integrity and gradation of aggregates. 3. Partitions separating aggregates should be high enough to prevent intermixing.

52. Handling and Storing Aggregates 4. Washed aggregates should be stockpiled in sufficient time before use so that they can drain to uniform moisture content. 5. Exposure to extreme hot weather should be taken care of through misting 6. Aggregates placed directly on the ground shall not be removed from stockpiles within 300mm of the ground.

53. THANK YOU FOR LISTENING