Paving Principles and Tetcniques concepts of asphalt paving .ppsx

How to start asphalt paving and paving concepsts

1. Principles And Paving Techniques

2. Role of the paver is to
meet specifications
for grade, texture &
smoothness
Principles And Paving Techniques

3. •Project Planning
•Understanding the
Paver
•Factors Affecting the
Screed
•Screed Adjustment
•Levelers
•Mat Defects
•Joint Construction
Foundamentals of Asphalt Paving

4. Project Planning
•Asphalt mix supply
–Hot plant output
–Distance from plant to jobsite
–Traffic conditions and number of
trucks available
•Paving width and
specifications
–Paving packages installation
–Feeding sensors positioning
•Grade conditions
–Leveling course
–Bumps and Low Spots
–Transitions, obstacles

5. Understanding The Paver
•Paver configurations
•Material feed
•Efficiency and
Maintenance

6. Understanding The Paver
The paver is composed of
two main parts:
•Tractor , which includes
operator’s station, engine
and all systems used for
propel and material feeding
•Screed , utilized for laying
the asphalt mix

7. Understanding The Paver
The Tractor can have
different undercarriage
configurations:
•Wheels,3 axles (1 driving rear
axle; 2 front steering axles,
driving on demand) :
–Maneuverability
–High travel speed
–Comfort
•Steel track:
–High traction capability
–Lower ground pressure
•MTS track:
–Includes best features of both

8. Understanding The Paver
Material Feed System
•Independent hoppers
•Independent augers and
feeders for each side of
machine
•Feeder sensors to ensure a
continous and constant
material flow
–Independent sensors for
each function and each side
–Mechanical (paddle) or sonic
–ON-OFF or proportional
Hopper
Feeders
Feeder
Sensor
Auger
Assembly
Auger
Sensors

9. Understanding the Paver
Efficiency and
Maintenance
•Conditions of the paver affect
paving quality
–Schedule inspections and
maintenance
–Follow maintenance
guidelines

10. Understanding the Paver
The Screed can have two
different configurations:
•Extendible width :
-2 fixed central elements and 2
hydraulically extendible lateral
elements
-possibility to add additional
mechanical paving packages
•Fixed width :
-Bolted-on modular structure

11. Free-floating Screed
•During paving operation the
Screed is connected to the
paver at the Tow points.
•Screed is free to raise and fall.
•Reachs equilibrium
•The screed vertical position
determines paving thicknessTow point
Understanding the Paver

12. Factors Affecting Screed
•Material Feed
•Asphalt mix
characteristics
•Ambient and grade
temperature
•Screed adjustments

13. Factors Affecting Screed
Material Feed
•Optimum conditions:
constant feeding
–Constant material flow from the
hoppers to the front of the screed
–Constant height of material in front
of the screed
–Material load evenly distributed in
front of the screed
–Constant paving thickness
•Correct feeder sensors
setting
Augers
Sensors
Feeder
Sensors

14. Factors Affecting Screed
Material Feed
•Sonic sensors
–Non contact with asphalt mix
–Adjustable range
–Proportional control
–Correct setting: constant feeding
•Correct sonic sensor alignment
–The sensor should
be targeted perpendicular to the material
face
•Incorrect sensor position
–Incorrect alignment causes loss of signal

15. 1/2 auger diameter
above material
level
Factors Affecting Screed
Material Feed
•Correct head of material
–Asphalt mix level should
be at 1/2 of auger diameter
•A constant head of material is
necessary to obtain a
constant paving thickness

16. Factors Affecting Screed
Material Feed
•Decreased head of material
–Resistance decreases
–Paving thickness decreases
•Increased head of material
–Resistance increases
–Paving thickness increases

17. Factors Affecting Screed
Material Feed
•Augers height adjustment
–A correct height adjustment helps for a
good paving quality
–As starting reference can be considered
50mm above the paving layer
–Further adjustments should be done
according mix design and paving results
–Augers height adjustment can be used
also for transportation (machine loading
onto the truck)

18. Screed Adjustments
•Angle of Attack
•Screed Assist and
counter-balance
system
•Tamper & Vibrators
•Crown adjustment
•Extenders height
adjustment
•Screed temperature
adjustment

19. Screed Adjustments
Screed Reaction Time
•Screed reacts to
change in angle of
attack over 5 tow arm
lengths
•65% of change occurs
in the first tow arm
length
•35% of change occurs
in the last 4 tow arm
lengths
•Factor improves
rideability

20. Screed Adjustments
Angle of Attack
•Angle of attack is the
relationship between the nose
of the screed & grade
•Screed finds its equilibrium
(floating) when the angle of
attack is positive
•Increase of the angle of attack
causes an increase of the
paving thickness

21. Screed Adjustments
Angle of Attack
Angle of attack setting points
•Tow arms adjusters
–Changes the relative angle
between tow arms and screed
–Quick reaction
•Tow point cylinders
–Raise or lower the screed tow
point
–Controlled reaction
–Controlled manually or by
automatic leveling system

22. Screed Adjustments
Angle of Attack
Tow point adjustment
•Tow point raise causes paving
thickness increase
–More material passes under screed
–Screed raises to new level
–Screed reaches new height, achives equilibrium and
resumes original angle of attack
Paving thickness value shown on tow
point scales may not correspond to
paving thickness
1
2
1
2
I I I I I I I I I
I
I I I I

23. Screed Adjustments
Angle of Attack
Tow arms adjustment
•Positive setting (+):
–Allows, in combination with
tow point adjustment, to
reach max paving thickness
–Should not be allowed to
reach “zero” even with tow
point fully lowered
+ I I I I I I I I 0 I I I I I I I I
-

24. Screed Adjustments
Screed Assist and
Counter-Balance System
•Allows to vary the specific screed
weight. Screed remains floating but
results to be lightened
•Allows to maintain the same specific
load on the paving mat
•In demanding paving conditions helps
to prevent driving wheels slippage
(tranfers weight from screed to driving
wheels)
•Helps to prevent screed sinking in
stand-by (counter-balance)
Scree
d
Assis
t
Counter-
balance

25. Screed Adjustments
Screed Assist and
Counter-Balance
System
Optimum counter-balance
pressure
•Machine stop does not
produce marks on to
paving mat
•Eventual marks are
eliminated in one roller
pass
Mark is gone
after roller
compaction
Normal
settling
marks

26. Screed Adjustments
Tamper & Vibrators
Tamper
•Pre-compact material in
front of the screed
•Help screed floating
•Adjusting frequence up to
1700 rpm according to
paving speed
•Adjustable starting ramp
Screed plate
Tamper blade
Tamper stroke
Wearing strip
Front blade

27. Screed Adjustments
Tamper & Vibrators
Vibrators
•Optimum asphalt mix
distribution
•Helps eliminate air voids in
asphalt mix layer
•Adjusting frequency up to
3400 rpm according asphalt
mix design

28. Screed Adjustments
Crown Adjustment
•Allows to reach a positive
or negative crown
•Central adjuster:
+ 4,5 % in positive
-2,5 % in negative
+ 4,5 %
-2,5 %

29. Screed Adjustments
Extenders Height Adjustment
•Allow a perfect alignment
between the central screed and
the extenders paving layers
•Adjust simultaneously both
adjusters on each screed sector
•Increasing paving thickness
could require a new height
adjustment
•Acting only on side adjusters for
sloped lateral layer

30. Screed Adjustments
Temperature adjustment
of screed plates and tampers
•Optimum screed tempersture to be set
according mix design and
environmental conditions
•Set heating system (Electric or GPL) in
order to reach the optimum
temperature at the paving start.
•After a few meters stop the machine on
to the paving layer to allow the asphalt
mix to make the temperature uniform
on all screed plates surface.

31. Automatic Leveling System
•Leveling
systems
•Leveling
devices
typology
•Grade controls
positioning

32. Automatic Leveling System
Leveling Systems
•Grade control
–Detects variations of Grade
along the longitudinal
direction
–Controls paving level on
one side of the paver
•Slope control
–Detects slope variations in
percentage
–Controls lateral slope of the
paving mat

33. Automatic Leveling System
Leveling Systems
•Grade control allow to
copy an existing profile
(example: longitudinal
joints)
•Slope control to control
lateral slope

34. Automatic Leveling System
Leveling Devices Typology
Mechanical ski
–Short reference ski
–Available also with rod
for reading the string
line

35. Automatic Leveling System
Leveling Devices Typology
Grade control application
with self-leveling long ski
–Considers reference
average along the long
ski length (6 or 9 m)

36. Automatic Leveling System
Leveling Devices Typology
Single Sensor
•Sonic grade
–No contact with hot
material
–Can read the string-
line

37. Automatic Leveling System
Leveling Devices Typology
Multiple sensors Sonic
grade
–Averages inputs from
all sensors
–Can be used to read a
string-line (to be fitted
transversally respect
the string-line)

38. Automatic Leveling System
Rotation
point
Grade Controls Positioning
Correct positioning
–Optimum is to position
the grade contol
between 1/3 and 2/3 of
the tow arm lenght
Tow point
cylinders

39. Automatic Leveling System
Leveling Devices Typology
Slope control
–Detects and controls
slope variations in
percentage
–Digital or analogic
–Stand alone unit or
integrated in the
machine leveling system

40. Solutions
•Transversal joint
•Longitudinal joint
•Paving thickness
check

41. Solutions
Transversal Joint
•Remove tapered area
•Start with square joint
•Set mat thickness on the tow
points
•Set paving width
•Set eventual crown
•Put wooden blocks under screed
plates to compensate compaction
Remove tapered
area

42. Solutions
Transversal Joint
•Release down screed on to wooden
blocks and eliminate any tension on
the tow-arms adjusters
•Introduce angle of attack
•Start manually augers and feeders
until the complete material filling in
front of the screed
•Set height of material at 1/2 auger
diameter level. Use shovel if needed
•Activate automatic leveling system
(if any). Start paving

43. Longitudinal Joint
Mat thickness
•Mat thickness of the new layer has to
be defined according to the
compaction capability of the asphalt
mix
•After compaction the two layers must
be at the same level
•A lower mat thickness causes poor
density in corresponding joint
•As a consequence the joint will wear-
out earlier (longitudinal creeps)
Solutions
Previous layer
(already
compacted)
New layer
(still to be
compacted)
Longitudinal joint

44. Solutions
Longitudinal Joint
Excessive overlap of the two layers
•Previous layer bears the screed and
affects floating
•Screed looses mat thickness control
•Concentration of fine aggregates on
the over-lapping area
•Bigger aggregates segregate on the
internal side of the joint

45. Solutions
Longitudinal Joint
•Optimum overlap of the two
layers
•A correct overlap between
the two layers should not
exceed 20 mm witdh

46. Paving thickness check
•Do not correct based on
one measurement
•Make series of
measurements
•Average measurements
•Correct based on average
Solutions

47. Mat Defects
Some of the most common
mat defects:
•Relationship between paving
thickness and aggregate size
•Material drop from the truck
•Wrong use of the truck
•Extended stop of the paver
•Existing bumps on to the
grade
•Cold screed sector
Some mat defects have been detected by using
an Infra-red camera to check variations of
temperature on to the paving mat

48. Mat Defects
Relationship between mat
thickness and aggregate size
Best quality when mat thickness is at
least two times the size of the
aggregate
•On the contrary it could happen:
–Tendency to fracture aggregates
–Screed looses thickness control
•Optimum condition: mat thickness at
least 2 or 3 times the maxuimum size
of the aggregate

49. Mat Defects
Material drop from the
truck
•Cools off quickly when
contacts the ground
•Infre-red image shows
colder areas even after
paving

50. Mat Defects
Wrong use of the truck,
could affect mat quality
•Hits paver in reverse
–Pushes the paver back,
sometimes the screed
–Rear edge of the plates generates
deep marks
–Cannot be eliminated by the roller
•Driver uses brakes
–It could generate slippage of the
paver
•Anticipate start when the
truck is not completely
empty

51. Mat Defects
Extended stop of the
paver
•Mat under the plates
remains hot
•Rear layer cools off quickly
•Material will be compacted
unevenly due to difference
of temperature
On the infra-red image can be
recognized the shape of the
screed

52. Mat Defects
Existing bumps on to the
grade
•High points can cause screed
to break aggregates
•Needs to know and carefully
evaluate original grade
conditions
•Line of open material on the
central area could be caused
by a longitudinal bump

53. Mat Defects
Cold screed sector
•Visibly open and teared
strip
•This strip will be
compacted differently
from other areas
•It will show problems in
terms of density,
smoothness and
roughness
Infra-red image shows evidence of the
colder screed sector