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A STUDY OF INTERLOCKING BEHAVIOUR OF CONCRETE BLOCK USED INPAVEMENTS Viveka Nand
Department of Civil Engineering, School of Engineering and Technology, K.K. University, Nalanda (Bihar), 803115
Deepak Kumar
Assistant Professor, Department of Civil Engineering, School of Engineering and Technology, K.K. University, Nalanda (Bihar), 803115
Abstract - In interlocking concrete block pavement, the blocks make up the wearing surface and are a major load-spreading component of the pavement. It differs from other conventional form of pavement that the wearing surface is made from small paving units embedded and joined in sand rather than continuous paving. Beneath the bedding sand the substructure is similar to that of a flexible pavement.
Concrete Block Pavement (CBP) is getting popularity in areas where normal flexible pavement does not last long. Application of CBP is developing very fast for various reasons such as high resistance to deformation, durability, easy and rapid quality construction, ability to carry traffic immediately after construction, compatibility with the environment and aesthetic features etc.
The structural behaviour of CBP is similar to flexible pavement. However, the performance of CBP depends upon on block shape, size, thickness, type of bedding and jointing sand, joint width. The laying pattern of blocks is also important which affects the overall performance of the CBP. The edge restraint is one of the features which are essential to stop mitigation of the block outward. The interlocking mechanism is one of the unique characteristics of the CBP. The performance of CBP largely depends on how well the interlock has achieved. It is an established fact that the block share the structural member of the CBP and is instrumental in load spreading to its neighbor.
Keywords- CBP, bedding sand, jointing sand, edge restraints, interlock.
1 INTRODUCTION
Concrete block pavement (CBP) was introduced in The Netherlands in the early 1950s as a replacement for baked clay brick roads. The general world wide trend towards beautification of city pavements , the rising cost of bitumen as a paving material and the rapid increase in construction and maintenance cost have encouraged designers to alternate paving material such as concrete blocks.
The strength, durability and aesthetically pleasing surface of pavers have made CBP ideal for many commercial, municipal and industrial applications. For the past 50 years, significant research activities for the development and refinement of CBP technique have been going on many on in many countries like Argentina, Australia, Canada, France, The Netherlands, UK and USA. The CBP is now a standard surface in Europe, where over 100,000,000 m2 are placed annually.
In interlocking concrete block pavement, the blocks make up the wearing surface and are a major load- spreading component of the pavement. It differs from other conventional form of
pavement that the wearing surface is made from small paving units‟ embedded and joined in sand rather than continuous paving. Beneath the bedding sand the substructure is similar to that of a flexible pavement.
1.1 Components of an interlocking concrete block pavement
The main components of a concrete block pavement are shown in figure 3.1.1.
1. Paving blocks. (Made of cement concrete with sufficient compressive strength, available in various size and shapes)
2. Bedding sand which supports the block layer.
3. Jointing sand provided in joint of blocks.
4. Edge restraint.
5. Sub-base.
6. Sub grade.
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Fig. 1 Main components of a concreteblock pavement 1.2 Terms Used
Pavement Structure - A combination of sub base, base course, and wearing surface placed on a sub grade to support the traffic load and distribute it to the road bed.
Base Course - A material of a designed thickness placed on a sub base or a sub grade to support a surface course. A base course can be compacted aggregate, cement or asphalt stabilized aggregate, asphalt, concrete, or flow able fill.
Bedding Sand - A layer of coarse, clean, sharp sand that is screeded smoothly for bedding the pavers. The sand can be natural or manufactured (i.e. crushed from larger rocks) and should conform to the grading requirements.
Edge Restraint- A curb, edging, building or other stationary object that contains the sand and pavers so they do not spread and lose interlock. They can be exposed or hidden from view.
Joint Sand- Sand swept into the openings between the pavers.
Joint Spacing- The distance between pavers subsequently filled with joint sand.
Laying pattern-The repetitive geometry created by the installed units. Laying patterns may be selected for their visual or structural benefits.
Rutting- Permanent deformation from repetitive traffic loading that exceeds the ability of pavement structure to maintain its original profile.
1.3 Merits of Interlocking Concrete Block Pavement over Asphalt Pavement
Flex without cracking.
Do not require expansion joints.
Resistant to spilled fuel and oil.
Resistant to freeze/thaw damage.
Resistant to de-icing compounds.
Virtually unlimited combination of solid and blended colors, shapes and laying patterns.
May be used immediately upon completion of installation.
May be disassembled to repair sub grade or underground services then reinstalled with no unsightly patch.
Skid and slip resistant surface.
Cooler surface.
Easy to work to grade transitions.
Long design life.
Low life cycle costs.
Virtually maintenance free 1.4 Scope of Work
The present work has been taken up to study the structural behavior of ICBP by varying the different block parameters. In this study experimental investigations have been done by taking laboratory scale models and effects of size, shape and compressive strength on pavement deflection were investigated
2 LITERATURE REVIEW 2.1 Literature Summary
The surface of ICBP comprises concrete blocks bedded and joined in sand .It transfer the traffic loads to the substructure of the pavement .the load spreading capacity of concrete blocks layer depends on the interaction of individual blocks with joining sand to build up resistance against applied load.
The shape, size, thickness, laying patterns are important block parameters which influences the block parameters.
Ahmed and Singhi (2013) make a study with title” Overview on Structural behaviour of Concrete Block Pavement”
and they found that the structural behaviour of CBP is similar to flexible pavement. However, the performance of CBP depends upon on block shape, size, thickness, type of bedding and jointing sand, joint width. The laying pattern of blocks is also important which affects the overall performance of the CBP. The edge restraint is one of the features which are essential to stop mitigation of the block outward. The interlocking mechanism is one of the unique characteristics of the CBP. The performance of CBP largely depends on how well the interlock has achieved
Shackel (1993) established that shaped blocks exhibited smaller deflection than rectangular blocks of similar
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thickness installed in same laying patternunder same applied load.
Jacobs and Houben( 1988) found that, in their early life, block pavements stiffen progressively with an increase in load repetitions. However they clarified that the progressive stiffening did not influence the magnitude of resilient deflection of ICBP.
A study by Panda and Ghosh (2001) has done and they found that tendency of rotation and translation of the smaller block is higher than larger block.
Again, the tendency of translation is not distinct near edge of the pavement because of the edge restrain. It is conclusive that the pavement experiences larger deflection in case of smaller size block than the larger size. Larger block would improve the performance of the pavement within the size.
Shackel (2000) gets a result that by means of accelerated trafficking studies established that complex shaped block perform better than the rectangular or square one. The complex shaped blocks developed larger frictional forces to transfer load to adjacent blocks. The shape of the block has significant influence on the performance of CBP under load.
Shackel and Lim (2003) which demonstrated that a reduction in the loose thickness of the bedding sand from 30 mm to 50 mm was beneficial to the defor- mation(rutting) behaviour of block pavements. Experience gained from more than twenty-five accelerated trafficking tests of prototype blockpavements in South Africa has confirmed that there is no ne- cessity to employ bedding sand thickness greater than 30 mm in the loose(initial) condition, which yields a compacted typically close to 20 mm .
Ali Jamsidi et.al.(2019) dealing with pavements and experts on materials have been increasingly focused on the structural strength of the pavement materials without paying sufficient attention to the environment and cultural norms. In the 21st century, the concept of pavement design and rehabilitation needs to be modified owing to new requirements such as the additional structural loads derived from the climate change, environmental challenges, social requirements, and aging population.
Therefore, the concept of post-modern
pavement (PMP) was proposed to address the structural, sustainability, and socio- psychological requirements. In this review of the state-of-the-art, the potential of the interlocking concrete block pavement (ICBP) was evaluated based on its laboratory and field structural performance, sustainability, and social acceptance as a PMP in Japan. Therefore, the relevant literature in English and Japanese, including journals, conference proceedings, technical reports, books, and theses, over a span of 47 years (1971–
2018), were studied. It was found that the structural and functional performances of the ICBP in different facilities were satisfying. Furthermore, owing to its waste material use, less noise emission, air purifying characteristics, and heat island reduction, the environmental performance of ICBP was in harmony with sustainable practices. In addition, pavements users, both able and differently abled, rated the ICBP as a more appropriate pavement system owing to its physical appearance, serviceability, aesthetic features, lower heat island effect, rapid maintenance, and positive psychologic effects after earthquake and tsunami events. As a result, the ICBP can be recommended as a PMP for the design and development of resilient transportation infrastructure assets in Japan.
A.V. Bahiense et.al.(2021) studied with title „Dosage of interlocking paving with ornamental rock waste: An experimental design approach, particle packing and polluting potential‟ and they found that a dosing procedure for interlocking concrete pavements that incorporate ornamental rock waste, with a view to meeting mechanical and molding criteria and ensuring the sustainability of the mineral industry, an economically important sector in Brazil despite environmental issues surrounding its waste generation. The procedure involves evaluating the packing density of the sand, coarse aggregate and waste fines via the minimum void ratio. A simplex lattice experimental design and the theoretical particle size distribution (Alfred) model were used, followed by a 22 factorial with a center point to determine the influence of the factors (proportions) and different water-cement (w/c) ratios (levels). The full cubic model obtained a 95.62%
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adjustment index for optimal particle sizeof the aggregates and waste fines, and the lowest MVR (1.961 103kg/m³). This trend was confirmed by the theoretical Alfred model, with a coefficient of 0.29, and the factorial experiment, with an adjustment index of 97.50 %. Dosing indicated an ideal cement content of 20 %, 15.2 % for sand, 44.8 % for the coarse aggregate and waste fine incorporation of 20 % of the total mass (25 % of the aggregate mass), achieving compressive strength of 36.70 MPa for w/c and water/aggregate ratios of 0.5 and 0.123, respectively, and a carboxylate super plasticizer content of 6% of cement consumption, as well as adequate molding and demolding conditions. An ecotoxicological assessment was conducted, which found that waste fine incorporation posed no risk to the environment. Scanning electron microscopy (SEM) demonstrated that this mixture exhibited the best mechanical performance, with adequate aggregate particle size distribution and paste coverage, as well as waste fine stability in the cement matrix.
Vahid Taheri et.al.(2021) studied with title „Evaluation of airfield concrete block pavements based on 3-D modelling and plate loading test‟ and found The use of concrete block pavement is a more suitable option at aprons. Fewer studies have been done on this type of pavement in the airfields than on roads. For further studies, the performance of this pavement was examined by making a 3D model and a test track with dimensions of 2 m × 2 m.
This sample was composed of subgrade, subbase, base and Cement-Treated Base (CTB) layers, with 15 cm thickness, for each layer, bedding sand with 3 cm thickness and a Unipave-shape (zig-zag) concrete block pavers with 8 cm thickness and herringbone pattern. Then their quality was controlled, based on Federal
Aviation Administration (FAA) regulation.
At the next step, Plate Load Test (PLT), was conducted on this sample. For this purpose, a setup including a concrete foundation and a reaction beam was built. For the first time in related research, several 3D models of concrete block with all its angles and corners representing their actual dimensions were made using ABAQUS software. The field studies' experiments result on the materials were used to define the characteristics of the model components, and then the force–deflection curve, as a guidance chart was presented. Studies have shown differences in opinion about the amount of elastic modulus of block and jointing sand. The 3D model analysis result showed that the elastic modulus of the concrete block surface could be taken into account at 2000 MPa to achieve the most coordination between finite element analysis and PLT results.
Some early plate load studies suggested that load spreading ability was not significantly affected by block shape.
Latter accelerated trafficking studies established that shaped blocks exhibited smaller deflection than rectangular blocks of similar thickness installed in same laying pattern under same applied load.
found that, in their early life, block pavements stiffen progressively with an increase in load repetitions. Elastic deflection is decreased with an increase in number of load repetition, rather than an increase, as observed in flexible and rigid pavements.
2.2 Objective of this Study
It was felt necessary that the phenomenon of block interaction under applied load needed investigation. Such test could then provide insights into load- spreading ability and other structural characteristics of block pavement .
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3 METHODOLOGY AND MATERIAL USED3.1 PAVING BLOCKS
3.1.1 Shape and size of block, material testing
Table 3.1 The materials used for
manufacture of the blocks were 1.Portland cement 2. Crusher dust (fine) 3. Crusher chips 4. Fine aggregate (river sand). The manufacturer used the proportion of material as 1:3:3:2 and approximately 30 liters of water per 1/3
bag of cement (one gamula).They got nearly 150 blocks per bag of cement.
Some sample of the blocks and materials were collected for testing.
Sieve analysis of crusher dust fine (1 kg).
Table no 2.3.2
3.2 Expeimental Setup 3.2.1 Block strength
The blocks of the in-service CBP undergo compressive stresses due to traffic loading. The bending stresses develop in blocks are negligible because of block size and its aspect ratio. As we all know that the concrete has many a times higher modulus of elasticity than the under laying layers. Hence the concrete blocks behave as rigid bodies in CBP. Loads
transfer to the adjacent blocks is by virtue of its geometrical characteristics rather than strength of blocks. The load associated performance of block pavements was essentially independent of compressive strength of the blocks. The effect of block strength on load-deflection behaviour of block pavement.
The compressive strength of paving blocks (ordered from manufacturer) is tabulated as below.
Table 3.2 4 RESULTS AND DISCUSSIONS
4.1 Load and dial gauge readings The results of load and corresponding deflection under loading and unloading
for different types of blocks have been presented in following tables.
Saw toothed edged blocks 1st repetition
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eTable 2.4.1 2nd repetition
Table 2.4.2 3rd repetition
Table 2.4.3
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I-shaped blocks 1st repetitionTable 2.4.4 2nd repetition
Table 2.4.5 3rd repetition
Table 2.4.6
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Hexagonal shaped blocks 1st repetitionTable 2.4.7 2nd repetition
3rd repetition
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4.2 Effect of block shape on deflection.Fig 3.4.2 shows the effect of load and deflection on the blocks of different shape.
The block types used have same thickness, size and are laid in a stretcher bond. The shape of load deflection is similar for all the blocks. The first one is for saw toothed shaped, second one for I- shaped and third one for hexagonal shape. From the graph it is clear that I- shaped blocks gives lower deflection because of the vertical surface area (friction area) which is more for I-shaped blocks.
4.3 Effect of Loading and Unloading on Deflection
The effect of loading and subsequent on loading and deflection for saw toothed edged block is shown in Fig 3.4.3.
For the saw toothed edged blocks laid in herringbone pattern the pavement was subjected to load repetition three times at 10 KN intervals. For each load repetition the deflection during loading and recovery of deflection during unloading are determined. It may be seen from the graph that the response is non linear. The deflection is not fully recovered. In other words, permanent residual deformation develops due to load repetition.
Load repetition vs deflection curve
Fig. 3.4.2
During loading, additional compaction of sand under blocks occurs, and some part of the energy is lost in that way. As a result the recovery is not full. In accelerated trafficking test Shackle found
that the range of load repetition to achieve fully elastic property varies from 5000 to 20000, depending upon the magnitude of load.
5 CONCLUSION
CBP differs from the other form of pavement in many ways. In the CBP, the wearing surface is made up of segmental paving blocks, bedding sand and jointed sand rather than a continuous paving sur- face. The edges are restrained by providing rigid kerbs sufficiently high enough to restrained movement of the blocks. In CBPs the blocks are the principal components which act as a load spreading member. The bedding provides necessary level surface for block paving. It also absorbed considerable amount of stresses before transmitting the stresses to succeeding layers originated due to traffic load. The jointing sands are the major components which initiate interlocking mechanism amongst the block and act as a single unit and transfer the loads to the under-laying structure as well as significance in terms of load spreading ability but the thickness of the blocks is important in transferring the load. The intra-block load transfer is developed due to friction between the jointing sands and the block surface area.
Hence with the increase of the thickness of the block the increment in the surface area results increased frictional force. The high resistance to deformation and durability of the CBP has made it a popular alternative to the pavement engineers. The loading of the pavement is essential to acquire elastic property of the pavement layers. When loads are applied through static plate load the elastic property yields at 150 to 200 repetitions.
The elastic property under repeated load acquires at 5000 to 20000 repetition depending upon the magnitude of loads.
The higher repetition is requires in case of trafficking conditions because of alternate bulging and compression of sand due to wheel movement. The interlock is the essential property of CBP.
The herringbone pattern performs better than other pattern.
Also the following points should be include in conclusion of this study-
1. A simple laboratory-scale test setup can be utilized to assess the behavior of concrete blocks with
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respect to their shape, thicknessand laying pattern, etc.
2. The effectiveness of load transfer depends on the vertical surface area of individual blocks.
3. Block shape influences the deflections of blocks. Shaped blocks perform better than rectangular blocks of similar thickness installed in same laying pattern.
4. Blocks with larger size produce lower deflection.
5. Strength of blocks has no significant influence on deflection.
6. Block pavements stiffen more progressively with an increase in load repetition, but gain full elastic property after some repetitions.
REFFERENCE
1. Shackel B. (1993)," Design and constructions of interlocking concrete block pavement". First International Conference on Concrete Paving, Newcastle-upon-time,U.K,113-120
2. Panda B.C., and Ghosh A.K., "Structural behavior of concrete block pavement". ASCE Journal of Transportation Engg, 128(2), 123- 129.
3. Barber, S.D., and Knapton, J. (1976) "An experimental investigation of the behavior of a
concrete block pavement". Cement Concrete Association, U.K.
4. Australian Road Manual (1991) "A guide to design and construction of interlocking concrete block pavement ".
5. Clark A.J. (1987), "Block paving research and development". Concrete, July, 24-25.
6. ASTM C-936. "Standard specification for solid concrete interlocking paving units".
7. ICPI "Design guidelines for Interlocking concrete block pavement". (Part 1 to Part 10).
8. T. Muraleedharan, R.V.K. Rao. Prasant Kumar and P.K. Nanda, “Structural Evaluation of Interlocking Concrete Block Pavement in the la- boratory and guidelines for design of ICBP for low volume roads”, CRRI, New Delhi- 110020
9. B.K. Panda and A.K. Ghosh, “Structural Behaviour of Concrete Block Paving. 1. Sand in Bed and Joins”, Journal of Transportation Engi- neering, Vol. 128,No. 2, March 2002, ASCE
10. J. Guidelines for the use of Interlocking Concrete Block Pavement, IRC: SP 63-2004, The Indian Road Congress, New Delhi 110011 11. Clark., A.J., “Block Paving Research and
development”, Concrete, Ju- ly 1998, 24-25 12. S.D. Barber and J. Knapton, “An Experimental
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Of Civil Eng.,69(2), 139-155 (1999)
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