Pavement design and
Structure
General points regarding
design of pavement
• Quality of sub grade is
often measured by special test known as CBR. Moisture content and density of
materials will change the CBR values.
• Depending upon the
traffic loading and ability of sub grade to carry the load, the thickness of
sub base or base course is decided.
• The base course
thickness can vary with the design conditions from 0 to 300 mm but most widely
used are 75 mm to 200 mm.
• Before starting of
construction two other aspects materials and drainage are required to be
considered
Advantages of ICBP
• Mass production, ensures
availability of block having consistent quality and high dimensional accuracy.
• Good quality blocks
ensures durable pavement when constructed as per design and specification.
• ICBP tolerates higher
deflections without structural failure, will not get affected by thermal
expansion and contraction.
• ICBP does not require
curing and hence pavement can be put into service immediately.
• Construction of pavement
is labour intensive and requires very few equipments.
• The system provides
ready access to underground utilities without damage to pavement.
• Maintenance of ICBP
pavement is easy and simple.
• Use of coloured blocks
facilitates permanent markings.
• Low life cycle cost.
• Provides resistance to
punching loads and horizontal shear force caused by movement of heavy vehicles.
Limitations of ICBP
• Quality control of block
at the factory premises is very much necessary.
• Any deviations of base
course profile will get reflected on ICBP. Hence proper supervision is
required.
• High quality, graded
coarse sand and joint filling sand are essential for good performance.
• ICBP over unbound
granular base course is susceptible to the adverse effects of poor drainage and
will deteriorate faster.
• ICBP is not suitable for
high speed roads (Speeds over 60 Km/Hr)
Applications of ICBP
Technology
• Non traffic areas -
Building premises, Footpaths, malls, Pedestrian plaza, Monument premises,
Public gardens/Parks, Shopping complex, Parking areas, and railway platforms.
• Light traffic - Car
park, Office driveway, Housing colony roads, rural roads, Residential colony
roads, Farmhouses etc.
• Medium traffic - City
streets, small market roads, Intersection, Low volume roads, Service stations
etc.
• Heavy and Very heavy
traffic – Container, Bus terminals, Port/Dock areas, Roads in Industrial
buildings, Airport pavement.
Materials- Paver Block
• Produced with zero slump
concrete.
• Available in different
shapes and colours.
• Quality of the block
will depend upon capacity of compaction, grade of cement used, water content,
quality of aggregates used and their gradation and mix design, admixtures used,
handling equipments used, curing method adopted, level of supervision during
production, workmanship and quality control achieved etc.
• Specification of
materials used for preparation of block, physical test method, sampling and
acceptance criteria has already been formulated in IS 15658:2006, & IRC SP
63:2004
Shapes and colours for
paving block
• Type A – Paver block
with plane vertical face, which do not key into each other when paved in any pattern.
• Type B – Paver block
with alternating plain and curved/corrugated vertical face, which key into each
other along the curved/corrugated vertical face when paved in any pattern.
• Type C – Paver block
having all faces curved/corrugated which key into each other along all vertical
faces when paved in any pattern.
• Type D – ‘L’ & ‘X’
shaped paver block which have all faces curved or corrugated and which key into
each other along all vertical faces when paved in any pattern.
Bedding and Joint
filling sand
• The selection of
material as bedding and joint filling sand is very vital.
• Joint filling sand must
be relatively finer than the bedding sand.
• It is necessary to
restrict the fines (clay and silt) to 10 % in joint filling sand.
• Don’t used cement to
fill the joints.
• Joint filling sand must
be dry.
Base and Sub base
materials
• Base and sub base
material requirements will depend upon traffic loading expected and sub grade
strength.
• Grading- For better
interlock and ease of construction, Number of broken faces - For better
interlock, Crushing resistance- to prevent breaking of stone particles,
Soundness- For durability, Nature and quantity of fine particles in the
aggregate or sand, desired drainage characteristics are need to be considered.
• Factors like local
availability, economy, climatic and environmental factors will detect the
selection of materials
• Commonly used materials
are
– Unbound crushed rock
– Water bound macadam
– Wet mix macadam
– Cement bound crushed
rock
– Lean cement concrete
• Quality of sub base
material should be in conformance with IRC-37.
• Commonly used
materials for sub base are
– Cement treated gravel
– Sand
– Stabilized materials
Sequencing of operations
for ICBP
• Step 1 - Installation of
sub surface drainage works
• Step 2 - Leveling and
Compaction of sub grade
• Step 3 - Provision and
Compaction of Sub base course (When needed)
• Step 4 - Provision and
Compaction of base course & Checking of correct profile
• Step 5 - Installation of
edge restraints
• Step 6 - Provision and
Compaction of coarse bedding sand
• Step 7 - Laying of
blocks and interlocking
• Step 8 - Application of
joint filling sand and compaction
• Step 9 - Cleaning the
surface
• Step 10 - Filling any
remaining empty portions in the block layer especially near edge restraints
block with in situ concrete.
Step 1 - Installation of
sub surface drainage works
• Normally drains are sub
surface drains and must be surrounded by either filter aggregate or geotextiles
to avoid washing of bedding and joining sand.
• Except pedestrian open
areas the pavement surface should have a cross fall of at least 3 % and top of
the blocks next to drainage channels should be at least 10 mm above lip of the
channel.
• In pedestrian open areas
the pavement surface should have a cross fall of at least 1.25 % and top of the
blocks next to drainage channels should be at least 3 mm above lip of the
channel.
Step 2 - Leveling and
Compaction of sub grade
• Importance of sub grade
• Importance of compaction
of sub grade
• Compaction near
trenches, back fills etc.
• The preparation of sub
grade should be graded to a tolerance of ± 20 mm of design levels and its
surface evenness should have tolerance of 15 mm under a 3 m straight edge.
• Moisture content in the
sub grade material will affect the strength. Hence water table should not be at
a level of 600 mm or higher below the sub grade level. In case of soils like
clay and silt moisture must be removed before further rolling. After that it is
covered with a thin layer of dense base course. The layer is then rolled.
• Stabilization of sub
grade with lime or cement may also increase the strength of sub grade.
• Sub grade should
be compacted in layers either 150 or 100 mm thickness as per IRC guidelines.
Step 3 & 4 Provision
and Compaction of Base and Sub base course & Checking of correct profile
• Base course and Sub base
course are required to be constructed with IRC:SP:49-1998, IRC:SP:50-1973,
IRC:SP:63-1976, IRC:19-1997, IRC:37-2001.
• Quality control
specified in IRC:SP:11 for construction of lower layers.
• The base course is
directly laid over the sub grade with the thickness of each layer should not be
more than 100 mm compacted thickness.
• For weaker sub grades
there are other options
– Improved drainage
– Cement of Lime
stabilization
– Use of Geotextiles
• Base course should be
finished within +0 mm to -10 mm for level. It should not pond water and should
be well shaped. Do not rely on sand bedding for removal of unevenness.
• For compaction usually
vibratory plate compactors are used. The selection of vibratory plate
compactors is very vital.
• Number of passes for effective
compaction will depend upon the various factors like compactor capacity, speed
of compactor, base course material properties, moisture content and layer
thickness.
• Normally vibratory
compactors will loose top material of base course and hence after applying the
required number of passes, 4 passes of regular roller or plate compactor
without vibratory motion should be given.
• The compaction of
material around manholes, kerbs, service boxes must be done carefully.
Step 5 - Installation of
edge restraints
• Must be produced with
high quality concrete with at least 28 day characteristic compressive strength
of 30 N/mm2 and Flexural strength 3.8 N/mm2
• Road kerbs, Edge strips,
PCC of 150 mm X 150 mm can also be used as edge restraints.
• The gap between the two
edge restraint block is required to be closed with cement mortar of 1:6
proportion.
Step 6 - Provision and
Compaction of coarse bedding sand
• Thickness of bedding
sand in loose form must be 25-50 mm and in compacted form 20-40 mm.
• Sand must be laid in
uniform thickness
• Grades and cambers must
provided in the sub grade and base course it self and not in the bedding sand.
• Sand is required to be
spread with screed board.
• Bedding sand must have
uniform moisture content of 6 to 8 %. Hence regular checking of moisture
content in sand is important.
• Before placing the sand
take a trial to decide the surcharge for a typical sand.
• Required quantity of
sand for a days work must be stored in advance and must be covered with
tarpaulin sheets or any other suitable material.
• After laying
proper compaction of bedding sand is required
Step 7 - Laying of
blocks and interlocking
• Block should be laid on
5 mm screed provided with bedding sand material.
• Don’t place block on
compacted or saturated sand.
• Normally laying should
commence from edge strip and proceed towards centre. Also as far as possible
laying should be done only from one direction along the entire width of the
area paved.
• While locating the
starting line following points must be considered
– On a sloping site start
from lowest point and proceed to up slope.
– In case of irregular
shaped edge restrains or strips it is better to start from straight string line
as shown in fig
• Gap between the two
blocks are not less than 2 mm and not more than 4 mm. The blocks very popularly
laid in three patterns
Step 8 - Application of
joint filling sand and compaction
• Don’t use wet block and
wet sand.
• Joint filling sand must
be properly graded as per guidelines.
• For compaction vibratory
plate compactors are used. Heavy plate compactors with a weigh between 300 to
600 kg and apply a centrifugal force in the range 30 to 65 KN are preferred
over standard plate compactors (90 Kg Weight, 15 KN force, 0.3 m2 plate
area)
• Alternative to this is
apply 2 passes of standard plate compactor and then apply 2 to 6 passes of a
roller, Vibrating roller (With static weight less than 4 tonne, amplitude less
than 0.6 mm), Or Pneumatic tyre roller (6 tonne or heavier)
• There should not be
delay in compaction after laying of paving blocks.
• The surface tolerance of
individual layers must be as per table
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