Lecture 5 Bitumnous Mixes Production.pptx

bituminous mixes production

1. HMA Production CE60136 Highway Construction Practice (3-0-0) IIT Kharagpur, Spring 2020-21

2. Books/References MORTH- Specifications for Roads and bridge works, 5th edition, New Delhi, 2013. Relevant Codes of IRC and Other Hot-Mix Asphalt Paving Handbook, 2000. Construction of Hot Mix Asphalt Pavements, MS Series 22, Asphalt Institute Hot Mix Asphalt Materials, Mixture Design and Construction, Freddy L. Robets, Prithvi S. Kandhal, E. Ray Brown, Dah-Yinn Lee, Thomas W. Kennedy, National Asphalt Pavement Association, Maryland, USA, 2 edition, 2010.

3. The purpose of HMA plant to blend, dry, heat and mix aggregate with bitumen at an elevated temperature to produce a homogeneous HMA that meets the required specifications. All asphalt plants can be categorized as either a batch plant or a drum mix plant. Batch plants produces one batch of HMA mix at a time Drum plant HMA production is continuous. HMA Production Types of Production Plants

4. HMA Production Types of Production Plants: Batch Plant

5. HMA Production Types of Production Plants

6. HMA Production Operation steps in an HMA plant Regardless of the type of the HMA plant, the basic operations involved in the HMA production is same. These operations include; Step 1: Material storage and handling (Aggregate, Bitumen, filler, RAP etc.) Step 2: Proportionating and feeding of the cold aggregates to the dryer (Cold bins, conveyor belts) Step 3: Drying and heating of the aggregate (Dryers) Step 4: Control and collection of the dust from the dryer (Emission control systems) Step 5: Mixing of bitumen with aggregate Step 6: Storage and handling of HMA

7. HMA Production Operation steps in an HMA plant The basic difference in batch and drum pants is how they mix bitumen and aggregate after it has been dried and heated (Step 5). Batch plants screen and separate the aggregate into separate bins after it has been dried and then recombine the aggregate and mix it with asphalt, one batch at a time in a separate mixer. Drum mix plants dry the aggregate and blend it with asphalt in a continuous process within the dryer drum.

8. HMA Production Operation steps in an HMA plant

9. HMA Production Operation steps in an HMA plant

10. HMA Production Material storage and handling Adequate supply of material be available prior to and during mixing operations Aggregates Avoid contamination and minimize segregation Stockpile on a free draining grade (if possible under roof) Coarse aggregate composed of several aggregate sizes require special handling If stockpiles in a cone shape, segregation occurs as large particles roll down the slope.

11. HMA Production Material storage and handling: Aggregates Avoid Segregation O Horizontal stockpiling: Each end-dump trailer load should be dumped into an individual pile. A loader should be used to push the pile together by raising the material to full bucket height and dumping, which will blend the material. O Building a stockpile in layers. This type of stockpile can be built with the aid of a dozer.

12. HMA Production

13. HMA Production Material storage and handling Bitumen Some plants may use vertical storage tanks to handle modified bitumen. At least one take required for each grade of bitumen if plant handles multiple HMA production. The tanks have a heating system to keep bitumen fluid enough. All transfer lines, pumps and weigh buckets should also have heating system.

14. HMA Production

15. HMA Production Material storage and handling Mineral filler It is subjected to hardening when exposed to moisture. Separate storage should be provided

16. HMA Production Proportionating and feeding of the cold aggregates Cold-feed system consists of cold-feed bins, feeder conveyors, a gathering conveyor, and a charging conveyor. Cold feed bins O Multiple bins to handle the different sizes of new aggregate used in the mix O A divider should be used between each cold-feed bin to prevent overflow of the aggregate from one bin into another. O Each cold-feed bin is equipped with a gate to control the size of the aggregate discharge on to feeder conveyor belt. O The gate opening and the feeder belt speed for each bin are set to deliver an proportionate aggregate required for the mix.

17. HMA Production

18. HMA Production Proportionating and feeding of the cold aggregates Feeder Conveyors Collecting Conveyor

19. HMA Production Proportionating and feeding of the cold aggregates Charging Conveyor For drum mix plant, the charging conveyor contains a weigh bridge system that measures the amount of aggregate being fed to the mixer

20. HMA Production Proportionating and feeding of the cold aggregates Quality Control Checks O Correct size of aggregates in cold bins O No segregation and intermixing of aggregate O Calibrated and set feeder gates (opening) and belts (speed) O Accurate weight of aggregate charging the drum O Moisture content of the aggregate

21. HMA Production Aggregate Drying and Heating The aggregates enter the drum and begins to move down the inclined drum by gravity action. O Dryer drum has two functions Dries the aggregate Heats the aggregate to required temperature O Consists of Burner: Exhaust fan Flights: Longitudinal troughs or channels elements bolted or welded to the inside circumference of the drum – designed to lift the aggregate and drop it in veils through the drum

22. HMA Production Aggregate Drying and Heating Dryer Drum Flights

23. HMA Production Aggregate Drying and Heating The time the aggregates spend in the drum (dwell time) depends on: O Length (6 to 12 m) and Diameter of the drum (1.5 to 3 m) O Rotational speed of the drum O Design and number of flights O Slope of the dryer Two basic types of dryers Parallel flow : The aggregate and the air flow in the same direction Counter flow: the aggregates and the air flow in the opposite direction

24. HMA Production Aggregate Drying and Heating Typical Counter-Flow Dryer

25. HMA Production Aggregate Drying and Heating Typical Counter-Flow Dryer

26. HMA Production Control and collection of the dust from the dryer Emission control equipment must be present to capture the hot exhaust gases from the aggregate dryer. These emissions which contains fine dust must not exceed the air pollution limits. The emission control equipment generally consists of primary and secondary dust collectors. These dust collectors are situated at the end of the dryer and filters the air that exits at the exhaust.

27. HMA Production Control and collection of the dust from the dryer Centrifugal Dust Collector

28. HMA Production Control and collection of the dust from the dryer Primary and Secondary dust collectors

29. HMA Production Control and collection of the dust from the dryer Primary collectors Collects and remove the large dust particles. Two types of primary collectors predominantly used are knockout box and the cyclone (centrifugal) dust collector

30. HMA Production Control and collection of the dust from the dryer Knockout Box: Exhaust gases flows through an expanded chamber causing the air speed to decrease. The velocity of the larger particles decreases such that the slow-moving particles drop to the bottom of the expansion chamber.

31. HMA Production Control and collection of the dust from the dryer Cyclone (centrifugal) dust collector: The exhaust gases forced to swirl inside the collector such that the large particles in the gases hit the walls and drop to the bottom.

32. HMA Production Control and collection of the dust from the dryer Secondary Collectors: To filter out fine dust particles. Two types are common; the baghouse and the wet scrubber.

33. HMA Production Control and collection of the dust from the dryer Baghouse A large metal housing containing hundreds of heat resistant filter fabric bags. Operates same as vacuum cleaner.

34. HMA Production Control and collection of the dust from the dryer Wet Scrubber Entraps dust particles in water droplets by spraying into the chamber from nozzles around the periphery. Requires a settling basin. Dust can’t be reincorporated into the system.

35. HMA Production Mixing of bitumen with aggregate The basic operations of both batch and drum plants are similar except for the aggregate and asphalt mixing procedures .

36. Mixing of bitumen with aggregate Batch Plant Screening and Storage of Hot Aggregates The heated and dried aggregate is deposited into hot elevator. The hot elevator carried the aggregate to “ batching tower ”. The hot aggregate than passes over a screening unit that separates hot aggregate into various size fractions and deposit into hot bins

37. Mixing of bitumen with aggregate Batch Plant Screening Unit

38. Mixing of bitumen with aggregate Batch Plant Screening Unit

39. Mixing of bitumen with aggregate Batch Plant Hot Bins S creens P ugmi l l Mixer Hot Bins Overflow pipes Weigh Hopper

40. Mixing of bitumen with aggregate Batch Plant Hot Bins: electronic high bin indicators

41. Mixing of bitumen with aggregate Batch Plant Drawing Materials from Hot Bins The aggregate is drawn from each hot bind into the weigh hopper Usually coarse aggregate first and fine aggregate last Introducing the asphalt

42. Mixing of bitumen with aggregate Batch Plant Aggregate Weigh Hopper Asphalt Binder Weigh Bucket

43. Mixing of bitumen with aggregate Batch Plant Pugmill Mixing Avoid Dead Zones

44. Mixing of bitumen with aggregate Batch Plant

45. Mixing of bitumen with aggregate Drum Plant

46. Mixing of bitumen with aggregate Drum Plant

47. Mixing of bitumen with aggregate Drum Plant : Parallel Flow Drum Mixer

48. Mixing of bitumen with aggregate Drum Plant : Parallel Flow Drum Mixer

49. Highway Construction Practices HMA Production Storage and handling of HMA Surge and storage silos Purpose: Batch mix plant and drum mix plant Difference between surge and storage: Four - purpose, insulation, heating, sealing

50. Highway Construction Practices HMA Production Storage and handling of HMA Surge and storage silos Insulation and heating -Insulation: manufacturer –required for both -Heating (cone/vertical wall) : electrical -Surge : not necessary

51. Storage Silo: 165 t Capacity Highway Construction Practices

52. Storage -overnight storage- No heat loss- well insulation -Large quantity- less ageing -Other factors- initial temp; gradation and environmental conditions -Coarse aggregate more- drain down -Open graded aggregate- low temp storage – to avoid drain down- Not advisable to store overnight Surge and storage silos Highway Construction Practices

53. Storage - Long period- 2/3 days- remove some mix every day from bottom to avoid hardening- use as RAP -- Test for required specifications Surge and storage silos Highway Construction Practices

54. Conveying Devices- HMA HMA - drum Mix/Batch mix to Silo Slat conveyor/ Belt conveyor /Bucket elevator Continuous set of Flights Highway Construction Practices

55. Buckets, belt/chain, casing, pulley etc Highway Construction Practices

56. Silo- Bin geometry Different shape- circular, elliptical, rectangular, square -Circular generally preferred- not much on segregation - Segregation - silo operation (loading/unloading) - Silo cone-funnel/cone- 55 to 75 degree angle -- angle and gate opening –large to avoid segregation - Less gate opening- larger particles donot roll to centre of cone (rathole)- causes segregation -To avoid- steep angle, larger gate opening Highway Construction Practices

57. Low bin indictor system- warn plant operator- To reduce Segregation Segregation - Coarse aggregate mixes, gap-graded mixes, conveyor system to silo thrown one side, silo operation…etc -Leads to differential cooling of mix Silo- Bin Highway Construction Practices

58. Mix delivery delivered –top of silo from conveyors(bucket/slat /belt) - leads to segregation without a batcher Top-of-Silo segregation Highway Construction Practices

59. T o r e duce Centre of silo; baffles ( to change direction of mix delivery), splitter (split mix in parts in silo) -Do not totally eliminate segregation - Use of batcher- better means to avoid segregation Top-of-Silo segregation ..con t d Highway Construction Practices

60. T op -o f -S i lo segr e gat i on ..con t d Batcher system- temporary holding hopper- momentarily store the mix When full- deposited in to silo in mass Mass- hits empty bin/existing mix- spreads uniformly in all directions Highway Construction Practices

61. Top-of-Silo segregation ..con t d Highway Construction Practices

62. Top-of-Silo segregation ..con t d Batcher system- functions well when silo is not full When full- lack momentum and not dispersed T o ov er co m e t hi s - High silo indicator- warns the operator to cut off inflow Highway Construction Practices

63. Top-of-Silo segregation ..con t d Timing device- batcher system- opens the gate before full and closes being emptied -To Match with production rate -Improper operation- timer leads to problems - More time- Stop function of conveyor system - Less time- conical shape- segregation Highway Construction Practices