Interlocking Paving Concrete

A

REPORT

ON

“INTERLOCKING CONCRETE

BLOCK PAVEMENT”

1.INTRODUCTION

As historical background the first record of stone paving dates back to 4000 B.C. in Assyria cobble stones was the traditional method of stone paving. Over two thousand years ago, the mighty Romans developed a simple system for building roads which helped them to control much of their world a marvel of its time, some of these roads are still in use today. Perhaps the most famous of all Roman roads is the Appian Way, built by Roman engineers in 312 BC. The 377 kilometer road was surfaced with tight-fitting paving stones that still carries traffic between Rome and Italy’s south-eastern port of Brindisi. Romans used natural cut stone for their surface.

Though pavers made out of concrete may be a new product. Today’s modern paving stone is manufactured high strength “no-slump” concrete in precast concrete plant, under controlled conditions which produce units in many shapes & colours.

Over the past 50 years, worldwide, CBP has gained rapid popularity as an alternative to conventional concrete & asphalt pavement. Interlocking concrete block pavement has been extensively used in a number of countries for quite sometimes as a specialized problem solving technique for providing pavement in areas where conventional type of construction are less durable due to many operational & environmental constraints.

ICBP technology has been introduced in India in construction, a decade before for specific requirement viz. footpaths, parking areas etc. But is now being adopted extensively in different uses where the conventional construction mix or cement concrete technology is not feasible or desirable.

Segmented concrete paving is a system of individual shaped blocks arranged to form a continuous hardwearing Surface overlay.(2)(6)

1.

HOW ICBP DIFFERS?

ICBP differs from other forms of pavement where wearing surface is made from small paving units bedded & jointed in sand, between edge restraints rather than paving continuously. Beneath the bedding sand & substructure is similar to that of a conventional flexible pavement. The surface of CBP transfers the load to the substructure of pavement. The load spreading capacity of concrete blocks layer depends on the interaction of individual blocks with jointing sand to built up resistance against applied load.(7)

2. APPLICATION OF ICBP TECHNOLOGY

Concrete pavers are a versatile paving material, which due to the availability of many shapes, sizes and colors, has endless streetscape design possibilities. The use of concrete block paving can be divided into the following categories: (4) (6)

• Non-traffic areas

• Light traffic areas

• Medium traffic areas

• Heavy & very heavy traffic areas

Some of the proven areas where ICBP technology is being applied listed below

ROADS

• Factories and warehouses

• Container depots

• Military applications

• Mines

• Wastewater reduction works

• Quarries

• Airports and harbours

DOMESTIC PAVING

• Pool surrounds

• Driveways

• Patios

• Townhouses and cluster homes

SPECIALISED APPLICATIONS

• Cladding vertical surfaces

• Storm water channels

• Embankment protection under freeways

INDUSTRIAL AREAS • Main roads • Residential roads • Urban renewal • Intersections • Toll plazas • Pedestrian crossings • Taxi ranks • Steep slopes • Pavements (sidewalks) COMMERCIAL PROJECTS • Car parks

• Shopping centers and malls

• Parks and recreation centers

• Golf courses and country clubs

• Zoos

• Office parks

• Service stations

• Bus termini

• Indoor areas

3. SHAPES & CLASSIFICATION

There are four generic shapes of paver blocks

a) Type A : Paver blocks with plain vertical faces, which do not key into each other when paved in any pattern

b) Type B : Paver blocks with alternating plain & curved/corrugated vertical faces, which paved in any pattern.

c) Type C : Paver blocks having all faces curved or corrugated, which key into each other along all the vertical faces when paved in any pattern.

d) Type D : ‘ L ’ & ‘ X ‘ shaped paver blocks which have all faces curved or corrugated & which key into each other along all the vertical faces when paved in any pattern.(6)

Corolink Unique Aristocrat Satinpave Coneleaf

Clover Tiffany Classic Cobble Honey style Double zigzag

Bevel Brick Country Block

Fig . 1 Different Shapes of Paver Blocks

5. MATERIAL

5.1 CONCRETE BLOCK

The quality of materials, cement concrete strength, durability and dimensional tolerance of paving blocks etc. is of great importance for the satisfactory performance of block pavements. These aspects and the block manufacturing process itself, which immensely affect the quality of paving blocks. The recommended thickness of block & grades of concrete for various applications & specification for paving i.e. material used in the preparation of blocks, there physical requirements. These are the factors we have to consider while preparing blocks.

Preparation of block depends on the situation of site, loading. As it varies the proportion of block also changes. Also it depends on the locally available materials. It is to be explained with the example of case of sandy soil subgrade .

Nominal 1:1.5:3 mixes by weight was adopted, using 25 mm & down aggregate. The coarse aggregate was quartzite & fine aggregate was local sand of fineness modulus 2.8. The slump was kept close to 15mm. The resulting flexural strength was in the range of 4.15 to 4.83 N/sq.mm (42.3 to 49.3 kg/sq.cm) with a mean value of 4.49 N/sq.mm (45.8 kg/sq.cm). The blocks were prefabricated using m.s. moulds and adopting normal precasting techniques including 28 day curing of blocks. Block design details are shown in table 1(3)(4)

5.2 BEDDING AND JOINTING SAND

Bedding sand provides four main functions that include: • Bedding the pavers during installation

• Initializing interlock among the pavers

• Providing a structural component for the system

• Facilitating water drainage that infiltrates through the paver joint sand.

It is well established that if proper attention is not paid to the quality of bedding sand and if the thickness of bedding sand layer is not uniform enough, serious irregularities in surface profile can result. Excessive differential deformation and rutting can occurs early in service life of the block pavement. The gaps in between two adjacent paving blocks (typically about 3mm wide) need be filled with material. Sand, relatively finer than the bedding sand itself. The desired gradation for bedding and joint filling sands is as shown in table 2

sr. no. Dimension Interior Block Edge Block

1 Shape Uniform Hexagon Pentagon obtained

by omitting one corner in the Uniform Hexagon 2 Edge 56cm --3 Shorter Edge -- 56cm 4 Longer Edge -- 97cm

5 Distance between opposite edges 97cm

--6 Distance between opposite edges 112cm

--7 Area of top surface 0.8148 sq.m 0.679 sq.m

8 Thickness of top slab 7.5cm 11cm

9 Depth of ribs beneath top slab 7.5cm

--10 Depth of ribs beneath top slab,

except at longer edge -- 4cm

11 Depth of ribs beneath top slab,

at longer edge -- 11.5cm

12 Solid Volume 0.091cu.m. 0.092cu.m

13 Number of hollows 6 5

14 Volume of hollow compartments 0.058cu.m. 0.0096cu.m. 15

Number of 20 mm dia holes on the top of the hollow

compartment 6 5

16 Average weight 210kg 213kg

17 Dimensions of m.s. half-dowel Common for IB & EB

(a) Diameter 22mm

(b) Length 250mm

(c) Size & length of threading Male,

at one end M22*2.5*52 mm

(d) Size of rectangular m.s. strip

welded at other end 40mm*28mm*3mm 18 Dimensions of m.s. sleeve used

for interconnection of half-dowels (a) Diameter 40mm (b) Length 44mm (c) threading Feamale, M22*2.5*44mm (d)Grooves,equally spaced on

outer cylindrical surface

6mm deep,7mmdia., 6 nos.

Table 2 Sand Gradation (4)

It is necessary to restrict the fines (silt and/or clay passing 75 micron sieve) to 10 per cent, since excessive fines make joint filling very difficult. It is not advisable to use cement in the joint filling sand, which may not only make it difficult to completely fill the joints, but may also adversely affect the desired flexibility characteristics of the paving block layer. The joint filling sand should be advisably as dry as possible; otherwise completely filling of joints may be difficult.

The quality of bedding sand and jointing sand, the joint width and thickness of bedding sand in concrete block pavement have an important influence on the performance of entire pavement. Jointing sand is the main component of CBP which plays the major role of promoting load transfer between blocks and ultimately larger areas of lower layers. For optimum load spreading by friction, it is necessary to provide uniform, narrow and fully filled joints width in between 2mm to 4mm. In practice, joint width ranging from 2 to 8mm are obtained depending upon the shapes of blocks, laying pattern, aesthetic considerations and application areas.

Jointing sand provides two primary functions in an interlocking concrete pavement. First it creates interlock and second it helps seal the pavement. ICBP recommends either finer mortar sand conforming to ASTM C144 or CSA A179 in the joints or coarser bedding sand. Over time the joints become filled with detritus, providing some degree of sealing. Regardless of the sand used, segmental concrete pavements will always allow some water penetration through the joints. The same coarse graded sand in the bedding layer facilitates the drainage of this water.

In some cases, smaller joint widths may require the use of finer graded sand. In this case, the use of mortar sand is permitted. Mortar sand should confirm to the gradations of either ASTM C144 or CSA A179. Although joint sand selection is an important factor, design and construction play a more important role. Considerations such as joint width, ensuring that sand is swept in dry,

Gradation of Bedding And Joint Filling Sand

IS Sieve Size mm

Bedding Sand Joint Filling Sand (% Passing) (% Passing) 9.52 100 --4.75 95-100 --2.36 80-100 100 1.18 50-95 90-100 0.6 25-60 60-90 0.3 15 30-60 0.15 0-15 15-30 0.075 0-10 0-10

degree of compaction and ensuring the joints are fully filled are critical to the long term success of interlocking concrete pavement performance.(2)(4)(8)

5.3

BASE AND SUB-BASE MATERIALS

The engineering properties of base materials are the load spreading properties to disperse stresses to the subgrade and the desired drainage characteristics and have an important bearing on the performance of a block pavement. Although, local availability and economics generally dictate the choice of base material at the design stage, yet the commonly used materials considered suitable for base courses are unbound crushed rock, water bound macadam, wet mix macadam, cement bound crushed rock/granular materials, and lean cement concrete/dry lean concrete etc.

Where the subgrade is weak (having CBR value below 5) use of bound granular materials, like, cement treated crushed rock, requiring a relatively thinner base, should be preferred while for high strength subgrade, unbound crushed rock may be used. The climatic and environmental factors also need be considered during the choice of a base material. Sub base is essential where commercial traffic is expected. The quality of base material is inferior to the base materials and natural gravels cement treated gravels and sands and stabilized subgrade materials. (4)

6. CONSTRUCTION OF INTERLOCKING CONCRETE BLOCK

PAVEMENT

SEQUENCE OF OPERATIONS

The sequence of operations for construction of block pavement should be as follows

a) Installation of sub-surface drainage structures

b) Leveling and compaction of subgrade

c) Provision and compaction of sub-base course (where needed)

d) Provision and compaction of base course and checking for correct profile

e) Installation of edge restraints

g) Laying of blocks and interlocking

h) Application of joint sealing sand and compaction

i)Cleaning of surface

j)Filling any remaining empty portions in the block layer especially near edge restraint blocks with in-situ concrete

Fig 4. SECTION WITH LEYING KERB (6)

6.1 CONSTRUCTION OF SUBGRADE

This is the foundation layer over which the block pavement is constructed. Like in conventional pavements, the water table level should not be at a level of 600 mm or higher, below the subgrade level. It should be compacted in layers of either 150 mm or 100 mm thickness as per IRC guidelines.

The prepared subgrade should be graded and surface dressed to a tolerance of 20 mm of the design levels, and its surface evenness should have a tolerance of within 15 m straight edge.

6.2 CONSTRUCTION OF BASE AND SUB-BASE LAYERS

Base course and sub-base course are constructed in accordance with standard procedures contained in relevant IRC specification IRC SP: 11 shall apply. Constructing the lower layers to proper level and grade is very essential to maintain the top surface level and surface regularity of the block pavement surface.

Concrete blocks on trafficked pavements tend to move sideways and forward due to braking and maneuvering of vehicles. The tendency to move sideways has to be counteracted at the edges by special edge blocks and kerbs. The edge block should be designed and anchored to the base such that the rotation or displacement of blocks is resisted. These are to be made of high strength concrete for withstanding the traffic wheel-load without getting damaged.

As far as possible, the edge blocks should have vertical face towards the inside blocks. The road kerbs provided on edges of roads also serve the purpose of edge blocks. In case the kerbs are not provided, it has to be replaced by edge strips. In case of heavy traffic, plain cement concrete (M-25) may also be provided over dry lean concrete to give further confinement of blocks. In between the edge restraint blocks, cement mortar 1:6 (cement: coarse sand) may be used in place of sand for sealing of blocks.

6.4 PLACING AND SCREEDING OF BEDDING SAND

The thickness of the sand bed after compaction should be in the range of 20-40mm. It is preferable to restrict the compacted thickness to 20-25mm to reduce the risk of any localized over compaction, which would affect the final block surface level. Bedding sand should not be used to fill up local depressions on the surface of a base or sub-base. The depressions if any, should be repaired with same base or sub-base material in advance before placing sand. The sand of specified gradation to be used, should be uniformly in loose condition and should have uniform moisture content. The processed sand so obtained is spread with the help of screed boards to the specified thickness.

6.5 LAYING OF BLOCKS

Blocks can be laid generally by manual labour but mechanical aids like hand pushed trolleys can expedite the work. Normally laying should be commence from the edge strip and proceed towards central line. When dentate blocks are used, the laying done at to fronts will create problem for matching joints in the middle. Hence, as for as possible, laying should proceed in one direction only, along the entire width of area to be paved. Rectangular units should be layed in a herringbone pattern to prevent "creep" under traffic, permitted by the opening of joints. Interlocking units may be laid in running or stretcher bond as their interlocking design resists the forces that cause "creep." Each block is place against the adjacent units without disturbing the sand or other units, (Developments are taking place at this time relative to mechanized placement of individual units or clusters of block that are tied together with break-away webs.) The order of laying should be such that it is never necessary to force a block between those already laid.

While locating the starting line, the following should be considered:

a) On a sloping site, starting from the lowest point and proceed to up slope on a continuous basis, to avoid down slope creep in incomplete areas.

b) In case of irregular shaped edge restraints or strips, it is better to start from straight string line.

6.6 ESTABLISHING THE LAYING PATTERN

Patterns are determined by the shape of a specified paving block. The three patterns shown below are basic patterns for the more traditional oblong or interlocking blocks. The laying pattern is an important factor in the performance of block pavements and, based on tests and field observations, it is widely accepted that blocks laid in herringbone bond do perform better under traffic loads than pavements laid in stretcher bond or basket weave. Other blocks, because of their different geometry, can produce a far greater variety of patterns. Even the simplest block, however, is perceived to produce a multitude of patterns when two or more colours are used.(4)(6)

HERRINGBONE STRETCHER

BASKET WEAVE

Fig 5. DIFFERENT LYING PATTERNS

7.

TYPICAL PAVEMENT COMPOSITION

Typical composition normally used in ICBP are given below Table 3 TYPICAL PAVEMENT COMPOSITION (4) CATALOGUE FOR PAVEMENT THICKNESS

Traffic / Road type Materials

Subgrade CBR (%) >10 5-10 < 5

Thickness (mm)

Cycle tracks, pedestrian Blocks 60 60 60

Base 200 200 200 Commercial traffic (axle load Blocks 60-80 60-80 60-80 repetitions less than 10 msa), Sand bed 20-40 20-40 20-40

residential streets WBM/WMM base 250 250 250

Granular sub-base 200 250 300 Commercial traffic (axle load Blocks

80-100 80-100 80-100 repetitions between Sand bed 20-40 20-40 20-40 10-20 msa), collector street, WBM/WMM base 250 250 250 bus and truck parking areas Granular sub-base 250 300 350 Commercial traffic (axle load Blocks

80-100 80-100 80-100 repetitions between Sand bed 20-40 20-40 20-40 20-50 **msa), arterial WBM/WMM base 250 250 250

streets or

WBM / WMM base 150 150 150 and DLC over it * 75 75 75 Granular sub base 300 350 380 * in case of roads having inadequate drainage or heavy rainfall areas (above 1500 mm per annum).

** msa denotes repetitions in million standard axles

8. BLOCK PAVEMENTS AT TYPICAL LOCATIONS

Essentially, there are three important aspects in detailing.

1) Curves

It is necessary to cut the paving units to fit the edge restraints. Rectangular blocks of similar or contrasting colour as an edging have been used to minimize the visual effects of small errors in block cutting. To avoid unsightly and potentially weak joints, it is often preferable to change laying pattern at the curves. The curve itself can be installed in Herringbone bond and yet the pavement can revert to stretcher bond on the approaches.

2) Pavement intrusions

around the both sides of the intrusions simultaneously so that closure is made away from the starting work face, rather than carrying the pavement around the intrusion to return to the original laying face to avoid accumulation of closing error.

3) Change in alignment

Changes in alignment of a road pavement can sometimes be achieved by the use of special blocks. Choose herringbone bond through simply cutting the blocks to fit into the edge restraints. Whereas 90 degree shape change in alignment can be achieved without cutting the blocks. At intersections, if herringbone bond laying pattern is adopted, the block laying can proceed without need for construction joints. (4)

9.

COMPACTION

For compaction of the bedding sand and blocks laid over it , vibratory plate compactors are used over the laid paving blocks; at least two passes of the vibratory plate compactors are needed. It is not a good practice to leave compaction till the end of the day, as some blocks may move under construction traffic resulting in the widening of joints and corner contact of blocks, which may cause spalling or cracking of blocks. During vibratory compaction of the laid blocks, some amount of bedding sand may get filled up into the joints between them; the extent of sand getting filled up into the joints will depend on the degree of compaction of sand.

The vibrating action compacts the sand and also forces some sand up between the joints. After the initial vibration, sand is brushed over the surface and is vibrated into the joints by an additional two passes of the vibrator. This locks the block together so that they no longer act as individual units but as a group in distributing loads. Vibration also evens out any minor variations in level between units. The vibrator should not be passed closer than about one yard from and unrestrained edge. After surplus sand is removed the pavement is completed and ready for traffic. If heavy trucks are used to deliver materials close to the work, the sanding and vibrations should be done before the trucks are permitted to enter that section of the pavement. (4)(7)

10. MECHANISMS OF PAVER INTERLOCK

Even block pavements which are judge to be well layed typically exhibit small rotations of the pavers relative to one another. The rotations develop both during construction and under traffic. Such small moments are almost imperceptible to the naked eye but can be measured using profilometers to map the surface of the paving. Measurements shows the rotations are usually less than 10 degrees and are associated with surface displacements typically less then 5mm. accordingly, the may appear to be of little practical import.

However, because concrete pavers are manufactured to much higher and more consistent dimensional tolerances than any other form of segmental paving they tend to be laid so that the joints between the pavers are consistently narrow and relatively uniform in width. With such narrow and consistent joints rotations of

a paver soon results in it wedging against its neigbhours as shown schematically in cross section. As shown in this figure, the wedging action caused by rotation of paver B around a horizontal axis leads to the

development of horizontal forces within the paving. Lipping is the movement along a joint between one paver and next as shear displacement. (5)

Fig 6 ROTATION OF PAVER B CAUSING OUTWARD WEDGING IF A & C

Fig 7 EFFECT OF ROTATION ON WEDGING ACTION

As the vehicles are travelling on the pavement with different loading and different travelling path. Such type of vehicle which follows their own path are having different impacts on the paver block which results into the cracking of paver block. As the maneuvering of vehicles to left, right and straight will gives different cracking patterns on the paver blocks, which is shown in figure below. (3)

12. PERMEABLE ICBP

One of the main concerns related to the use of concrete blocks as road pavement in a northern environment is the water infiltration through the joints which is very damaging for base and sub base layers. For this reason, it is recommended to provide an adequate slope (transversal profile) for water draining purposes and to reduce the permeability of joints, or, even better, to seal them. Ishai et al. (1999) has shown that the choice of sand grading for the laying of blocks must take into account.

Fig 8 Typical crack pattern of

blocks Left wheel path Right wheel path Centre

The mechanical strength and especially the water infiltration. Water infiltration can wash away the sand if the speed of flow is elevated which result in shifting of the blocks. Indented blocks (multidirectional blocks) remain better in place than rectangular blocks (unidirectional) under water infiltration or water flow at high speed. Tests carried out have shown that coarse particle sands (5 mm in diameter) are less susceptible to being washed away than finer particle sands. It has been shown that many parameters affect the performance of interlocking concrete pavement. (9)

13. ICBP– AN ENVIRONMENT FRIENDLY TECHNIQUE

Interlocking Concrete Block Pavement (ICBP), an environment friendly and labour intensive technology, has been developed at CRRI for providing pavements in areas where conventional types of construction are less durable due to many technical and environmental constraints.

ICBP has many advantages as detailed below: 1. No need for heavy construction equipment

2. Factory production facilitates centralized quality control 3. Labour intensive construction

4. Instant opening to traffic

5. No thermal expansion and contraction of concrete 6. Accommodates higher elastic deflection without failure 7. Pavement not damaged due to fuel and oil spillage

8. High salvage value – almost all blocks can be recycled / reused 9. Least life cycle cost due to low maintenance cost

10. Environment friendly technology

Concrete pavers act as a zipper in the pavement. When the need arises to make underground repair, interlocking concrete pavement can be removed and replaced using the same materials. Unlike asphalt or poured-in-place concrete, paving blocks can be opened and closed without jack hammers and with less construction equipment. The process of reusing the same paving units is called reinstatement. (10)

Guidelines for design of ICBP for roads have been included in a recent IRC publication. The essential design requirements and applicability indicated in the publication are listed below:

a) 60 mm block using minimum M-25 grade concrete can be used for non- traffic areas, like footpaths.

b) 80mm blocks using minimum M-30 grade concrete should be used for roads subjected to traffic.

c) The grading of bedding sand should be as per Zone-II of IS:383-1970 d) The compacted thickness of bedding sand should be 30 mm

e) The grading of joint filling sand should be as per Zone-IV of IS: 383-1970.

f) Cement-treated aggregates, lime-fly ash bound macadam and lime-fly ash concrete can also be used in place of granular base, by assuming an equivalence factor of 1.5.

g) A good drainage layer should be provided over the compacted subgrade before provision of base course. (1)

15. CONCLUSIONS

1. ICBP technology can provide durable and sustainable road infrastructure where construction and maintenance of conventional pavements are not cost effective.

2. Difference in the performance of segmental paving associated with paver shape or the choice of laying patterns both during construction and under traffic.

3. ICBP is much cheaper than rigid pavement design for identical locations. Compare to bituminous pavement for low traffic volumes and high strength subgrade, the initial

construction cost of ICBP is likely to be equal to or marginally higher. For high traffic volumes and low strength subgrade, ICBP will be cheaper than flexible pavement.

4. A hypothetical case application of ICBP for a road subjected to medium traffic road (5 msas; CBR: 4) indicates that, for urban and semi-urban conditions, ICBP is likely to be cheaper by as compared to the conventional flexible pavement about 10 % initially, and by about 27 % after 20 years.

5. Specification on pre-cast concrete block for paving is under preparation by Bureau of Indian Standards, which will be very useful for Indian industries and highway professions for adoption of block pavement technology.

REFERENCES

1. Highway Research Bulletin, June 2003, Evaluation of ICBP

By T.Muraleedharan, R.V.K.Rao, Prashant Kumar & P.K.Nanda

2. Highway Research Bulletin, June 2001

Bedding & Jointing Sand for Concrete Block Pavement By Biksha Chandra Panda, Ashok Kumar Ghosh

3. Highway Research Bulletin, June 2000

Field Experiments on Precast Concrete Block Pavers-An Interim Appraisal By T.Muraleedharan, S.P.Pokhriyal, Sudesh Kumar, P.K.Nanda

4. Civil engineering and construction review, November 2005

Interlocking Concrete Block Pavement: New trend In Construction By Dr.S.D.Sharma, Prashant Kumar, P.K.Nanda

5. Mechanism Of Paver Interlock, Volume 133,Issue 5, pp. 318-326, may 2007 By Brain Shakel and Daniel Oon Ooi Lim

6. Concrete Block Paving, Ideal Concrete block company, 2006 By Concrete Manufactures Association

7. Deformation Development Under Highway Accelerated Loading Instrument (HALI) Special Report, 20 April 2007

By Chow Ming Fai

8. Beddig Sand Selection,The Engineers View

Interlocking Concrete pavement Magzine, November 2006 By Rob Burak

9. Permeable Pavements, 2007

By David R Smith, Kelly A. Collins and William F Hunt

10. ICBP –Environment technique, from Icbp.com