Inter Connected Paving Blocks (ICPB)

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
       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