Specialist Paving
This page contains recommendations relating to the use of clay pavers in flexible and rigid pavement systems, together with permeable pavement systems. It also has information on the specification, design, installation and maintenance of clay pavements.
2. Definitions
Figure 1 Section through a typical clay pavement and edge detail
Bedding course: This is the layer of coarse sand on which the pavers are bedded to form the pavement surface.
California Bearing Ratio (CBR): An indicator of the shear strength of sub-grade material.
Chamfers: A bevelled or rounded arris (as an alternative to the ‘square edge’).
Clay Pavers: Fired clay units complying with BS EN 1344:2002
Co-ordinating Size: Dimensions adopted to maintain bond patterns e.g. 200 x 100 (including nibs)
Edge restraint: An existing or constructed element forming a boundary to the paved area to prevent lateral movement of the pavers and material loss from the bedding course. Failed edge restraint leads to a failed pavement.
Flexible pavement: A pavement that does not rely on a rigid layer, such as a concrete slab, to distribute superimposed loads to the subgrade.
Formation: The final shape of the subgrade surface following completion of earthworks.
Herringbone bond: A laying pattern of the general form illustrated in Figure 2. This is the preferred laying pattern for flexible pavements used by vehicles.
Interlock: The effect of frictional shear forces induced in the sand filled joints between pavers that inhibits paver movement and transfers loads between adjacent pavers. Interlock accounts for the load spreading capability of pavers.
Jointing sand: Fine sand that is swept and vibrated to fill the vertical joints between pavers (see Figure 1). Please note that bedding sand is not always satisfactory as jointing sand.
Laying face: The working edge of the pavement during construction, i.e. where they are being laid.
Light vehicular traffic: Areas subject to light vehicular traffic, typically cars in applications such as off-street car parks. Access driveways, loading bays and other areas used by commercial vehicles with axle loads greater than 2.7 tonnes are excluded.
Nibs: A small extrusion (or pressing) of a profile on the side face of a paver. This nib is intended to project into the joint and should not be used to set the distance between adjacent pavers.
Rigid pavement: A pavement that relies on a rigid layer, such as a concrete slab, to distribute superimposed loads to the subgrade.
Road-base: Design considerations may require the inclusion of a road-base (for extra strength) which would be between the bedding course and the sub-base.
Sub-base or base course: A structural course or layer of granular material beneath the bedding course (see Figure 1).
Subgrade: The upper part of the soil, natural or constructed, that supports the loads transmitted by the overlying pavement layers.
Surface course: A layer of pavers on a bedding course that act as a wearing course and a major structural element of the pavement (see Figure 1).
Wearing surface: The surface that the clay manufacturer has designated to be laid uppermost and trafficked.
Work size: The dimensions adopted for manufacture e.g. the length and width of rectangular pavers not including the nib dimensions.
3. Specifying Clay Pavers
3.1 General
This section contains relevant standards and supportive documents for further reading.
3.2 Relevant standards
BS EN 1344:2002 Clay Pavers – Requirements and Test Methods
BS 7533: Part 3:1997 Table D2 – Bedding Sand
BS 7533: Part 3:1997 Table D3 – Jointing Sand
BS 7533: Part 3:1997 – Pavements constructed with clay, natural stone or concrete pavers-Code of Practice for laying precast concrete paving blocks and clay pavers for flexible pavements
3.3 Relevant tests
3.3.1 Dimensional Deviation
Whenever possible the random sampling method shall be used, in which every paving unit in the consignment has an equal chance of being selected for the sample. The test sample shall comprise 10 pavers. Measure each paver, using a calliper gauge, for length, width and thickness as close to the mid point of each dimension as possible avoiding the nib. The mean value for a given dimension of a sample of 10 pavers shall not differ from the declared work dimension by more than 0.4 x square root of the dimension (d) rounded to the nearest mm, where d is the work dimension in millimetres.
Basically, for a 200 x 100 x 65mm paver
Length +/- 6mm
Width +/- 4mm
Height +/- 3mm
However, the Range, or difference between the largest and smallest measurement of any given measured dimension shall be stated as follows:-
Class Range
(not greater than)
R0 no determination
R1 0.6 x square root d
So, the max deviation allowed on a length of 200mm is 9mm
3.3.2 Flexural strength
Transverse breaking load provides a direct indication of the ability of a paver to withstand flexural loading.
This test represents more accurately what happens to the paver in work and replaces the previous crushing strength test.
Basically, the paver is set on two cylindrical bearers at a set distance from each end and a load is applied through a third steel cylindrical bearer placed mid-way centrally from above until failure occurs, which effectively breaks its back.
Class Transverse breaking load not less than (N/mm)
Mean value Minimum individual value
T0 No declaration No declaration
T1 30 15
T2 30 24
T3 80 50
T4 80 64
3.3.3 Slip/skid resistance
Clay pavers have satisfactory slip/skid resistance provided that their whole upper surface has not been ground and/or polished, or manufactured, such that a very smooth surface is produced.
The unpolished slip/skid resistance value relates to pavers as manufactured and helps to ensure adequate slip/skid on installation.
Class Mean SRV
U0 No determination
U1 35
U2 45
U3 55
A pendulum value of 40-74 has a low potential for slip, above 75 is extremely low.
3.3.4 Other tests
Freeze/thaw resistance measures the durability of a paver under extremes of temperature, a classification of FP100 indicates that the paver has successfully undergone 100 consecutive freeze/thaw cycles and is deemed to be freeze/thaw resistant.
Abrasion resistance is the materials resistance to general wear and tear and denotes the hardness and suitability for that product to be used as a paver.
Class Mean abraded volume
(not greater than)
mm3
A1 2,100
A2 1,100
A3 450
3.4 Supporting documents
www.dft.gov.uk/adobepdf/259428/tactilepavement -Guidance on the use of Tactile Paving Surfaces
www.resiblock.com – ‘’Resiblock 22’’ a suitable sealant for clay pavements though not essential.
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