BS 7533-4-1998

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BRITISH STANDARD BS 7533 :Part 4 : 1998

ICS 93.080.20

Pavements constructed withclay, natural stone or concretepavers

Part 4. Code of practice for theconstruction of pavements of precastconcrete flags or natural stone slabs

This British Standard, havingbeen prepared under thedirection of the Sector Board forBuilding and Civil Engineering,was published under theauthority of the Standards Boardand comes into effect on15 April 1998

BSI 1998

The following BSI referencesrelate to the work on thisstandard:Committee reference B/507Draft for comment 96/103818 DC

ISBN 0 580 28652 5

BS 7533 : Part 4 : 1998

Amendments issued since publication

Amd. No. Date Text affected

Committees responsible for thisBritish Standard

The preparation of this British Standard was entrusted to Technical CommitteeB/507, Paving units and kerbs, upon which the following bodies were represented:

Brick Development Association

British Cement Association

British Ceramic Research Ltd.

British Precast Concrete Federation Ltd.

Cementitious Slag Makers' Association

County Surveyors' Society

Department of Transport (Highways Agency)

Institution of Civil Engineers

Instituton of Highways and Transportation

Interlay, the Association of Block Paving Contractors

Interpave the Concrete Block Paving Association

Landscape Institute

Society of Chemical Industry

Stone Federation

The following bodies were also represented in the drafting of the standard, through

subcommittees and panels:

British Civil Engineering Test Equipment Manufacturers' Association

Institution of Structural Engineers

National Federation of Clay Industries Ltd.

National Paving and Kerb Association

BS 7533 : Part 4 : 1998

BSI 1998 i

Contents

Page

Committees responsible Inside front cover

Foreword ii

Code of practice

1 Scope 1

2 References 1

3 Definitions 1

4 Preparation of the sub-layer 1

5 Preparation of existing bases as the sub-layer 3

6 Installation of units 3

Annexes

A (informative) Reinstatement of flag and slab areas 7

B (informative) Recommended typical layouts 7

Tables

1 Compaction plant for sub-layer 2

2 Materials for sub-layer construction 2

3 Minimum time between finishing sub-layer and laying products 2

4 Grading for laying course sand and jointing sand 6

5 Thickness of laying course 6

Figures

1 Typical section 3

2 Typical ways of cutting flags 4

3 An example of a ramped crossing and over-run area using small elementflags or slabs 5

B.1 An example of a ramped crossing 8

B.2 An example of a dropped crossing 8

B.3 An example of a runout corner 9

B.4 An example of a new town corner 9

List of references Inside back cover

ii BSI 1998

BS 7533 : Part 4 : 1998

1) In preparation.

Foreword

This Part of BS 7533 has been prepared by Technical Committee B/507, Paving unitsand kerbs. It supersedes BS 7263 : Part 2 : 1990 which is withdrawn.

BS 7533 will be published in the following Parts:

Part 11) Guide for the structural design of heavy duty pavements constructed ofclay pavers or precast concrete paving blocks

Part 21) Guide for the structural design of lightly trafficked pavementsconstructed of clay pavers or precast concrete paving blocks

Part 3 Code of practice for laying precast concrete paving blocks and claypavers for flexible pavements

Part 4 Code of practice for the construction of pavements of precast concreteflags or natural stone slabs

Part 51) Guide for the design of pavements (other than structural aspects)Part 61) Code of practice for construction of pavements Ð kerbs, channels and

edgingsPart 71) Code of practice for the construction of pavements of natural stone settsPart 81) Guide for the structural design of lightly trafficked pavements of

precast concrete flags and natural stone slabs

BS 7533 : 1992 will be withdrawn on the publication of Parts 1 and 2.

A British Standard does not purport to include all the necessary provisions of acontract. Users of British Standards are responsible for their correct application.

Compliance with a British Standard does not of itself confer immunityfrom legal obligations.

Summary of pages

This document comprises a front cover, an inside front cover, pages i and ii, pages 1to 10, an inside back cover and a back cover.

BSI 1998 1

BS 7533 : Part 4 : 1998

Code of practice

1 ScopeThis Part of BS 7533 gives recommendations forlaying precast concrete flags conforming to BS 7263 :Part 1 : 1994 Precast concrete flags, kerbs, channels,edgings and quadrants : Part 1 : Specification andnatural stone slabs, intended for use in theconstruction of carriageways, footways, pedestrianareas and pavements.

2 References

2.1 Normative references

This Part of BS 7533 incorporates, by reference,provisions from specific editions of otherpublications. These normative references are cited atthe appropriate points in the text and thepublications are listed on the inside back cover.Subsequent amendments to, or revisions of, any ofthese publications apply to this Part of BS 7533 onlywhen incorporated in it by updating or revision.

2.2 Informative references

This Part of BS 7533 refers to other publications thatprovide information or guidance. Editions of thesepublications current at the time of issue of thisstandard are listed on the inside back cover butreference should be made to the latest editions.

3 DefinitionsFor the purposes of this Part of BS 7533, thedefinitions given in BS 7263 : Part 1 and BS 6100 :Part 2 apply together with the following.

3.1 edge restraint

Device which serves to prevent lateral movement ofthe products and to prevent loss of material from thebedding layer.

3.2 joint width

The distance between two adjacent units or unitsand restraint.

3.3 laying face

Working edge of the surface course at which layingof products takes place.

3.4 laying course

Layer of material on which the units are laid.

3.5 roadbase

One or more layers of material above the sub-basethat is a structural element of a composite pavement.

3.6 sub-base

One or more layers of material between the roadbaseand/or laying course and subgrade.

3.7 subgrade

The part of the soil, natural or constructed, thatsupports the loads transmitted from the overlyingpavement.

3.8 surface course

Layer of precast concrete or natural stone flagswhich acts as the wearing surface and forms part of

the structure of the paving.

3.9 sub-layer

Layer below the laying course which may includeeither or both sub-base and roadbase layers abovethe subgrade.

4 Preparation of the sub-layer

4.1 Excavation

All topsoil and unsuitable material should beexcavated from the area to be paved and the groundshould be reduced to the specified level. Any softspots or loose spots should be replaced with sound,properly compacted and inert material, or withfoamed concrete.NOTE. Replacement material should have properties similar to theground adjacent to the soft spot.

4.2 Subsoil drainage

Any subsoil drainage required beneath the pavementshould be completed before commencing backfilling.

4.3 Backfilling

All trenches within the pavement area should bebackfilled in layers, fully compacting each layerbefore placing the next, so that the resultingreinstated ground has a similar load bearing capacityto that of the undisturbed ground (see also annex A.)

Guidance on the choice of compaction plant and theminimum number of passes for a particularcompacted layer thickness is given in table 1.NOTE. Further information is given in the requirements of theHighway Authorities and Utilities Committee (HAUC)Specification for the reinstatement of openings in highways.[1]

4.4 Drainage of laying course using naturalground as the sub-layer

4.4.1 Any drainage required to protect the layingcourse from saturation should be completed beforeplacing the laying course. Drainage inlets should beprotected from ingress of laying course material,e.g. by using filter fabric.

4.4.2 The ground should be levelled so that therequired surface level and laying course thickness,including tolerances, are achieved.

4.5 Construction of the sub-layer usingimported material

4.5.1 The sub-layer material should be placed inlayers not exceeding 150 mm in thickness or twicethe nominal maximum aggregate size, whichever isthe greater, until the specified thickness is reached.Each layer should be fully compacted before thenext layer is placed.

Suitable imported materials for sub-layerconstruction are given in table 2.

Guidance on the choice of compaction plant and theminimum number of passes for a particularcompacted layer type and thickness is given intable 1.

The sub-layer should have a close-textured surfaceafter compaction.

2 BSI 1998

BS 7533 : Part 4 : 1998

Table 1. Compaction plant for sub-layer

Type of compaction plant Mass Minimum number of passesfor compacted layerthickness

100 mm 150 mm

Vibrating plate 1400 kg/m2 to 1800 kg/m2 1) 6 Not suitable

1800 kg/m2 to 2100 kg/m2 1) 4 8

Vibrating roller 700 kg/m to 1300 kg/m2) 12 Not suitable

1300 kg/m to 1800 kg/m2) 5 12

Engine driven vibro-tamper 50 kg to 65 kg 4 8

65 kg to 75 kg 3 6

Over 75 kg 2 41) Unit area beneath the base plate.

2) Unit width of roller.

Table 2. Materials for sub-layer construction

Material Clause reference in Specification for HighwayWorks, 6th Edition, Department of Transport[2]

Granular sub-base material type 1 803 (except that 100 % should passa 37.5 mm sieve)

Granular sub-base material type 2 804

Cement-bound material category 1 (CBM 1) 1036



Wet-lean concrete 1030

Concrete grade C25P in accordance with BS 5328 Ð

Table 3. Minimum time between finishing sub-layer and laying the surface course

Sub-base material(see table 1)

Minimum time for surface coursebedded with maul

Minimum time for surface coursebedded with vibrator

h h

Natural ground 0 0

Granular sub-base materialtype 1

0 0

Bitumen-bound material 0 0

Cement-bound materialcategories 1, 2 or 3

0 72 (at ambient temperaturesabove 4 8C)

Wet-lean concreteStructural concrete

40 (at ambient temperaturesabove 4 8C)

72 (at ambient temperaturesabove 4 8C)

4.5.2 The sub-layer should be levelled so that therequired surface level and laying course thickness,including tolerances, are achieved.

4.5.3 Where the sub-layer contains cement and isnot to be covered by another pavement coursewithin 2 h, it should be protected from moisture loss,

e.g. by covering with plastic sheeting. If a curingmembrane or compound is used, the manufacturer'sinstructions should be followed.

The appropriate minimum time given in table 3should be allowed to elapse before starting to lay thesurface course.

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BS 7533 : Part 4 : 1998

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Sub-layer Subgrade

Laying coursePrecast flag or slab Edge restraint

Figure 1. Typical section

5 Preparation of existing bases as thesub-layer

5.1 Where a surface course is to be laid overexisting roads or similar types of construction,corrections to existing levels may be required.

5.2 The existing surface water drainage levelsshould be checked to ensure that the drains willcontinue to function after adjustment of levels. Anynew drains should be installed in accordancewith 4.4.1.

5.3 Any excess material should be removed to allowinstallation of a bedding course of 25 mm thicknesswhen compacted. Levels should be built up usingsuitable materials (see table 2) and compacted asdescribed in 4.5.1.

5.4 The base should be levelled so that its surfacelevel does not differ from the design level by morethan ±10 mm.

5.5 Where any regulating layer containing cement isnot to be covered by another pavement coursewithin 2 h, it should be protected from moisture loss,e.g. by covering with plastic sheeting. A bituminousemulsion membrane can be used in accordance withthe manufacturer's instructions.

5.6 The sub-base should be levelled so that itssurface level does not differ from the design level bymore than 10 mm.

5.7 The appropriate minimum time given in table 3should be allowed to elapse before starting to lay thesurface course.

6 Installation of units

6.1 Uniform support

The laying course should provide a uniform supportfor the flags and slabs and should not be used as ameans of correcting the tolerances or any minorsurface irregularities in the sub-base.

6.2 Edge restraints

Edge restraints should be capable of preventing theloss of laying course material and sidewaysmovement of flags and slabs, and of supportingdesign traffic loads, including constructional loads,before the laying material and the flags and slabs arelaid (see figure 1).

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BS 7533 : Part 4 : 1998

6.3 Cutting flags and slabs

Wherever possible, cutting flags or slabs should beavoided, e.g. by using other sizes of the samethickness. If more than 25 % of the flag or slab has tobe notched, the remaining shape (from the internalcorner of the cut-out to the external corner of theflag or slab) should be cut as shown in figure 2,(see also annex B).

a) Example 1

b) Example 2

45° desirable

Figure 2. Typical ways ofcutting flags

Concrete infill around an obstruction should be keptto a minimum. It should not exceed 25 mm in width,and should be the full depth of the flag or slab.Where concrete infill is used, it should have amaximum aggregate size of 10 mm and a concretestrength conforming to C25 as specified in BS 5328.

NOTE. Careful selection of material or pigments may be necessaryto achieve an adequate colour match. Proper curing of theconcrete is essential.

6.4 Laying details

It is recommended that flags or slabs are bonded(see figure 3). Where concrete paving blocks areused to form the bond between flags, their differingdimensions and tolerances may require the use ofwider joints. Flag and slab laying on slopes shouldcommence from the bottom upwards wheneverpossible.

6.5 Drainage channels and fittings

Where flags and slabs are laid abutting a drainagechannel or other drainage fitting, the top surface ofthe paving units should stand 3 mm to 6 mm abovethe drainage channel or fitting to reduce thepossibility of ponding.

6.6 Surface tolerances

Flags and slabs should be laid as follows:

a) Their surface level should not differ from thedesign level by more than ±6 mm.

b) The difference in level between two adjacentflags or slabs should not exceed 3 mm.

6.7 Surface falls

Longitudinal falls and crossfalls should be providedto ensure drainage of water. A minimum crossfallof 1.25 % is recommended. Falls should be formedwithin the sub-layer rather than by varying thethickness of the laying course.

6.8 Mortar laying course and wide joints

NOTE. Flags and slabs larger than 450 mm3 450 mm are generallylaid on mortar.

6.8.1 General

Flags or slabs should be laid to line and level on afull mortar bed using a paviour's maul. The flags orslabs should not rock after bedding down. Anyrocking flags or slabs should be lifted and rebeddedas necessary.

Bedding should consist of a workable mixof 1:3 cement-sand mortar (proportions by volume),or a 1:3 lime-sand mortar (proportions by volume),using sand conforming to grade M or F of BS 882.NOTE. Retarded, plasticized and pre-mixed mortars may be used.

6.8.2 Laying course thickness

The laying course material should be laid to give athickness of 25 mm after compaction. Where mortarcontaining cement has begun to set it should bereplaced with fresh mortar.

6.8.3 Joint construction: wide joints

Flags and slabs laid with wide joints, i.e. a widthof 5 mm to 10 mm, should have their joints filled tothe full depth of the unit and to within 2 mm or 3 mmof their top surface. A 1:4 cement-sand mortar(proportions by volume) using sand conforming tograde M or F of BS 882 should be used. The mortarshould be firmly pressed into the joints with a trowelor suitable rod. Alternatively, spread mortar on theside of the laid flag or slab, offer the next flag to thisand strike off any surplus mortar.NOTE. Any mortar on the surface should be cleaned offimmediately to avoid staining if this is an important consideration.

6.8.4 Joint construction: narrow joints

Flags and slabs laid with narrow joints, i.e. a widthof 2 mm to 5 mm, should be filled with dry fine sandas described in 6.9.4 or grouted with lime mortar asdescribed in 6.8.1. The joint width should be not lessthan 2 mm.

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Example of longitudinalbonding of large flags

or slabs

Back of crossing can either be in linewith back of footway or above or below

depending upon site conditions

Example of transversebonding of large flags

or slabs

Paving blocks usedas closers

Small units used in over-run area adjacentto kerb. Width depending upon site conditions

Paving blocks usedto start bond

Figure 3. An example of a ramped crossing and over-run area using small element flags or slabs

6 BSI 1998

BS 7533 : Part 4 : 1998

6.9 Sand laying course with narrow jointsNOTE. Flags of 450 mm3 450 mm or smaller are generally laid onsand.

6.9.1 General

The laying course should consist of naturallyoccurring sand graded in accordance with table 4.The moisture content of the sand should be uniform.The sand should be moist without being saturated atall stages of construction.

NOTE 1. As a guide, after sand is squeezed into a ball in the handand the pressure released it should not show free water andshould start to exhibit cracking.

NOTE 2. It may be necessary to remove and replace saturatedsand after inclement weather.

NOTE 3. Laying course material should be covered whilestockpiled.

Table 4. Grading for laying course sand andjointing sand

Nominalaperture ofsieve

Percentage by mass passing throughsieve size

Laying course sand Jointing sand

% %

10.00 mm 100 100

5.00 mm 89 to 100 100

2.36 mm 65 to 100 100

1.18 mm 45 to 100 90 to 100

600 mm 25 to 80 50 to 100

300 mm 5 to 48 15 to 60

150 mm 0 to 15 0 to 15

75 mm 0 to 3 0 to 3

NOTE. When testing for gradings, this only applies to sandstested by washing, decanting and dry sieving in accordance withBS 812 : Part 103.

6.9.2 Laying course thickness

The laying course should be spread to give athickness conforming to table 5 after being placedand fully compacted.NOTE 1. A thickness of 30 mm of uncompacted material is usuallyfound to be suitable. A trial area should be used to determine therequired surcharge.

NOTE 2. In areas of mixed paving, i.e. flags and blocks, thethickness of the sand laying course should be determined by theflags.

Table 5. Thickness of laying course

Pavement location and use Compactedlaying coursethickness

Tolerance

mm mm

Footways alongsidecarriageways and otherpavements used by vehicles

30+5210

Areas that are only used bypedestrians, i.e. no vehicleof any kind

50+15220

6.9.3 Laying practice

Flags or slabs should be laid without disturbing thescreeded sand and bedded down using a vibratingplate, compactor or a paviour's maul. Flags or slabsshould not be trafficked within at least 1 m of anunrestrained edge of the screeded sand layingcourse. Units should be laid away from previouslylaid flags and slabs whenever possible.

The surface of the sub-base should be tight anddense enough to prevent laying course materialbeing lost into it during construction and use.

NOTE 1. Some manufacturers recommend the use of a compactorwith a neoprene sole plate to protect special surfaces.

The laying course sand should be compacted using avibrator plate (see table 1) and then the top 10 mmshould be loosened using a rake. Alternatively, 25 mmof laying course material should be screeded out,compacted and then a further 10 mm of loosematerial screeded out.

NOTE 2. Care should be taken to fill voids left in the layingcourse by screed rails.

If any disturbance of the prepared laying course sandby pedestrian or wheeled traffic, etc., occurs prior toplacing flags or slabs, the area affected should berelaid.

NOTE 3. Typical examples of layouts using the products describedin this British Standard and guidance on laying details are given inannex B.

6.9.4 Joint construction

Where flags or slabs are laid with close joints, i.e. awidth of 2 mm to 5 mm, dried sand conforming totable 4 should be brushed into the joints. More sandcan be used to top up the joints after the units havebeen compacted down into the bedding material.This process should be repeated as necessary, untilthe integrity of the pavements is established. A platevibrator with the following specification should beused:

a) plate area of not less than 0.25 m2;

b) dimensions greater than those of an individualflag;

c) effective force transmission rate of not lessthan 75 kN/m2 of plate;

d) vibration frequency in the range 65 Hz to 100 Hz;

e) minimum mass of 200 kg.

NOTE 1. Joint filling should take place on the same day as layingthe flags or slabs and before the onset of inclement weather.

NOTE 2. It may be necessary to top up jointing sand early in thelife of the pavement.

NOTE 3. Sand which might stain the surface should not be used ifappearance is an important consideration.

NOTE 4. Vacuum sweepers should not be used on the wearingcourse for at least three months after laying, in order to reducethe risk of jointing sand being lost. Joint sealants may be used tostabilize the sand in joints where vacuum sweepers are likely tobe used.

BS 7533 : Part 4 : 1998

BSI 1998 7

Annex A (informative)

Reinstatement of flag and slab areasNOTE. Careful compaction of backfill in a trench can allowpermanent reinstatement to be carried out immediately. Thisremoves the need for temporary reinstatement.

A.1 Backfilling of trenches

A.1.1 Backfilling up to sub-base level may be carriedout using either suitable selected material from thetrench excavation or imported material with a gradingconforming to table 2 and as detailed by the HAUCspecification [1].

A.1.2 The material should be placed in layers andfully compacted, in accordance with table 1.

A.1.3 The sub-base should be replaced, using materialwith a grading conforming to those in table 2.

A.1.4 The sub-base should be trimmed as describedin 5.6.

A.2 Laying material

The flags or slabs should be relaid on either mortar orsand, similar to that used for the surrounding flags orslabs, in accordance with 6.8 and 6.9.

NOTE. If a trench has been open long enough to allow thesub-layer and/or adjacent flags to move, it may be necessary to liftone flag or more width on either side of the trench opening toachieve proper reinstatement.

Annex B (informative)

Recommended typical layouts

B.1 Cutting flags or slabs

Typical methods of cutting flags or slabs are shown infigure 2. Where less than 25 % of the flag or slab is cutaway it may be left as a single flag or slab, as shown infigure 2a.

Where more than 25 % of the flag or slab needs to benotched then the remaining shape should be mitredfrom the internal corner of the cutout to the edge ofthe flag or slab, as shown in figure 2b.

B.2 Vehicle crossings

B.2.1 A ramped car crossing is formed where thefootpath and driveway are at similar levels. The kerbsshould be placed into the required position and theadjacent flags or slabs ramped to the footpath level.The two corner flags or slabs should be cut diagonallyto form a mitred ramp (see figure B.1).

NOTE. Ramps should not be steeper than 1:10.

B.2.2 Dropped pedestrian crossings are formed whenthe footway crosses the carriageway. The kerbs shouldbe placed into the required position and the two linesof flags or slabs adjacent to the dropped kerbs shouldbe ramped from the footway to the top of the droppedkerb (see figure B.2).

B.2.3 Small sized paving units can be used for vehiclecrossings and in areas where footways may besubjected to over-run by vehicles (see figure 3).

B.2.4 Radial paving at the intersection of footwaysand footpaths may be carried out in a number of ways.Two examples are described as follows.

a) Runout corner. The laying pattern of the majorfootways continues through the corner, with theflags or slabs abutting the radial kerb marked andcut to fit. The flags or slabs on the minor footwaymay abut the inner edge of the major footpath(see figure B.3).

b) New town corner. This can be used with eitherequal or unequal width footways but the inner edgesof the footways may be connected with a straightline from the start points of the curves. The flags orslabs are laid from this line. The outer flags or slabsare cut to meet the curved kerbs and marked usinga template (see figure B.4).

8 BSI 1998

BS 7533 : Part 4 : 1998

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Flags or slabs cut across for

mitre and ramp

Flags or slabs ramped

Channel

Road surface

Figure B.1 An example of a ramped crossing

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Ramp flags, slabs and kerb

Channel

Dropped crossing

Precast concrete kerb

Figure B.2. An example of a dropped crossing

BSI 1998 9

BS 7533 : Part 4 : 1998

Major footpath


Minor footpath

Figure B.3. An example of a runout corner


Laying start line

Figure B.4. An example of a new town corner

10 blank

BSI 1998

BS 7533 : Part 4 : 1998

List of references (see clause 2)

Normative references

BSI publications

BRITISH STANDARDS INSTITUTION, London

BS 882 : 1992 Specification for aggregates from natural sources for concreteBS 5328 ConcreteBS 6100 Glossary of building and civil engineering terms

BS 6100 : Part 2 : 1988 Civil engineeringBS 7263 : Precast concrete flags, kerbs, channels, edgings and quadrants

BS 7263 : Part 1 : 1994 Specification

Other publications

[2] Specification for Highway Works, 6th edition. Department of Transport: The Stationery Office

Informative references

BSI publications

BRITISH STANDARDS INSTITUTION, London

BS 812 Testing aggregatesBS 812 : Part 103 : 1985 Method for determination of particle size distribution

BS 7533 : 1992 Guide for structural design of pavements constructed with clay orconcrete block pavers

Other publications

[1] Specification for the reinstatement of openings in highways, Highway Authorities and Utilities Committee(HAUC): The Stationery Office

BSI389 Chiswick High RoadLondonW4 4AL

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Documents

BS 7533-4-1998