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Sub Base Specification

The laying course should be 50mmof 2-6mm clean crushed stone. All granular sub base must comprise Crushed gravel or rock possessing well defined edges. The 100mm deep upper layer of subbase material should be graded 5mm-20mm to

BS EN 13242: 2002. Grading of lower layer of sub-base stone:

BS EN Sieve size % passing 80mm 100
63mm 90-100
40mm 60-80
20mm 15-30
10mm 0-5

Kerbs

Standard kerb system or Forest Edging: both to be haunched with concrete.

Laying course*

50mm depth of 2-6mm. single size clean crushed stone to BS EN 13242: 2002.

Depth of Sub-base

It is recommended that a subbase depth of 350mm should be used. The depth of sub-base may be varied at the discretion of the Engineer. Alternatively 270mm of sub-base overlaid with 80mm of dense bitumen base course to Clause 903 of the Highways Agency Specification may be used.

Intergrid(s) †

SC Intergrid

DBM Running Course

To be 20mm dense base binder course manufactured with 100/150 grade bitumen to BS4987. The DBM shall conform with the requirements of BS 4987.

Membrane †

Generally a taped membrane will be suitable for most applications of the tanked system. If a guaranteed watertight system is required a fully welded system should be installed. Examples of this type of application would be sites with a high water table, methane contamination, areas above basements or retaining walls. Further advice should be sought from the Hanson Formpave design team.

Fin drain †

300mm Hydraway Fin Drain to BBA Number 95/85.

Seal †

Formpave top hat seal

Sub-grade

Where the structure is to be over-run by heavy vehicles the sub-grade should have, or be improved to have, a CBR of at least 15%. Poor sub-grades with low CBR's may be improved by

incorporating a capping layer of cement, lime or bituminous bound materials. Alternatively granular materials in accordance with clause 613 of the Highways Agency specification may be used.

Inbitex®

Thermally bonded nonwoven developed to optimise the cleansing of water entering the system. The various characteristics have been combined to create a unique geotextile that aids the development of the naturally occurring microbes, and offers them refuge during periods of drought.

Alternative colours finishes

Special colours and finishes are available to order. Please contact sales office details.

Samples

Sample blocks are available from your nearest Hanson Formpave Stockist upon request.

Method of accessing services and reinstatement

General

It is important that access to services in or underneath the Formpave Sustainable urban drainage system is undertaken in a disciplined and progressive way.

Procedure

Uplift Aquaflow blocks 1m either side of the line of relevant underground services. Take up the laying course stone and cut the underlying geotextile membrane along either side of the line of services and parallel with them. Dispose of the laying course stone and geotextile.

Excavate sub-base stone and cut the underlying geotextile membrane along either side of the line of services and parallel with them. Dispose of the laying course stone and geotextile. Excavate sub-base stone and place adjacent to the excavation on plastic membrane. The subbase stone can be re-used.

Cut intergrid(s) in the same way as the geotextile and dispose of it. Cut layer of geotextile or waterproof membrane at reduced level along the line of the services in the same way as the higher layer of geotextile and dispose of it.

Excavate material over and around services and put on plastic membrane ready for
re-use.

Carry out repair on services. Once repairs have been completed replace and fully compact the excavated material around the services.

Cut fresh geotextile or waterproof membrane to size allowing additional 300mm extra width either side of the remaining geotextile membrane. Tape new geotextile/membrane in place. If a heavy duty welded waterproof membrane is installed due to a high water table or the presence of methane the replacement membrane will need to be rewelded to the existing membrane. Replace the first 250mm depth of sub-base and thoroughly compact, cut and install fresh itergrid(s) allowing 300mm of extra width either side.

Spread and compact final 100mm depth of sub-base. Cut fresh geotextile membrane to size again allowing 300mm overlap using double sided tape.

Lay and loose screed to level approximately 50mm depth of
2-6mm crushed stone to BS EN

13242: 2002. Replace surface blocks, vibrate surface blocks to level and dress the surface with 2-4mm clean gritstone and vibrate again.

Brush off and dispose of any debris before final vibration.

Colour and finish variation

Hanson Formpave products are manufactured from naturally occurring materials and consequently may show slight variations in finish and colour.

It is strongly recommended that products are taken from two or more packs and mixed during laying to minimise any colour variation.

All concrete products may suffer from efflorescence. This occurs naturally and will disappear with use. It is in no way detrimental to the performance of the product. No responsibility can be accepted for this natural reaction.

Maintenance

The surface blocks have a design life equivalent to standard block paving.

All paved surfaces will require occasional cleaning. In normal circumstances, regular sweeping will be sufficient.

It is recommended that this should be carried out in the spring and after leaf fall in autumn.

It should be noted that lighter coloured blocks may exhibit tyre marks and will therefore require more cleaning and maintenance when used in certain situations.

Following routine maintenance it may be necessary to re-dress the surface with 2-4mm clean gritstone.

Ultimately, perhaps after 25 years or more, areas of the laying course may become filled with silts and toxins. If this occurs the surface blocks should be uplifted and the affected areas of laying course material and geotextile disposed of. The existing subbase can be left in situ. Fresh geotextile and laying course stone should be installed and the existing surface blocks re-used.

Construction

Laying generally

All construction work on pavements should be carried out following completion of general site works and after topsoiling of adjacent areas to prevent wash down of fine materials.

Sub Grade

Excavate to sub grade appropriate levels shown on site drawings to provide a minimum fall of 1:1000 to fin drain. The sub grade should be compacted with a vibrating plate. Prior to compaction all soft areas should be removed and filled with suitable replacement material to provide a stable sub grade.

Kerbs/Edgings

The paved areas must be firmly restrained. Where the pavement is designed for heavy use the concrete kerb haunching must extend to a minimum depth of 150mm below the base of the kerb. The kerb/edging must extend with sufficient height above the haunching to accommodate the full laying course depth and block height.

SC Membrane

The SC Membrane must be watertight therefore a taped joint will be insufficient. To ensure the integrity of the membrane the joints should be fully welded, this can be completed on site or
pre-formed off site and delivered ready for installation.

For further information contact: WTB Geotextiles
0845 6005505

Sub-base

The lower layer of sub-base
(10-63mm) should be placed in 2 separate layers, each layer being compacted with a vibrating roller or heavy duty vibrating plate to the requirements of Clause 802 of the Highways Agency specification. The final pass should be undertaken with no vibration. Compaction should continue until 97% of the compacted bulk density achievable under laboratory conditions has been reached. This can be measured with a nuclear density gauge. The specified 350mm depth of
sub-base may be varied by the Engineer to suit site requirements.

SC Intergrid

Where required the Intergrid should be incorporated at the interface between the two layers of sub-base. The Intergrid should be laid on the sub-base and joints should be overlapped by 300mm. The upper sub-base layer
(5-20mm) should then be laid on top of the Intergrid and compacted as before.

A second intergrid can be incorporated underneath or within the sub-bse at the engineers discretion. This should be laid in the same way as the first intergrid.

Inbitex ®

Lay geotextile on top of the
sub-base overlapping joints by 300mm. Inbitex should be brought up to the haunched kerb/edging and cut-off flush with the surface of the paving.

Laying Course

Lay and screed to level approximately 50mm depth of
2-6mm single sized crushed stone to BS EN 13242: 2002. It is important that the final level of the 2-6mm stone is accurate as the stone will compact down much less than sand when the surface blocks are vibrated.

The particle shape of the 2-6mm stone will also affect the degree of compaction. It is recommended that a small trial area should be laid prior to construction to determine the accuracy of final levels.

Block laying

It is advisable to pre-set the block level by 6mm to allow for the ffects of settlement when laid gainst fixed edgings. The blocks and slabs must be tightly butt jointed ensuring that a good fit is achieved.

A single or double stretcher course of Aquaflow blocks must be used around the periphery of the paved areas and also at the edges of any separately restrained areas, such as tree pits. It is recommended that lateral restraints (such as forest edging)should be installed in areas where vehicles turn and/or brake, such as bends and junctions and on large areas of paving. The lateral restraints should be properly constructed and haunched with concrete.

Where blocks need cutting, they should be cut to a tight fit and none are to be smaller than 30% of the unit block size with three machined edges. Where Aquaflow blocks are cut they must be cut across the 100mm and not the 200mm dimension. Blocks should be cut vertically and not under-scored. All block cutting should be carried out with a disc cutter.

Surface Finish

The blocks should be vibrated with a vibrating plate Type DVP75/22'' or similar. Following the first pass with a vibrating plate, 2-4mm clean quartzite or gritstone should be applied to the surface and brushed in. (Available from Formpave in 25 kg bags). The tapers and slots between the blocks should be fully filled. Blocks should again be vibrated and any debris brushed off.

The existing sub-base can be left in situ. Fresh geotextile and laying course stone should be nstalled and the existing surface blocks re-used.