6. Kerbing and concrete
New roads and footpaths, and improvements shall be supported and restrained by kerbing and concrete.
Kerbing
Meaning road kerbs, channels and edgings which shall be in accordance with Figures NA1 and NA2 of BS EN 1340 and laid on a base of ST4 (20N/mm²) concrete.
Road kerbs shall be 125mm by 255mm half battered HB2 to create separation between roads and footpaths, and 125mm by 150mm BN2 dropped kerbs shall be used in vehicle and pedestrian crossing points.
Tapered kerbs to vehicle and pedestrian crossing points shall be 125mm by 255mm reducing to 125mm x 150mm.
Radius kerbs or radius channels shall be used in curves where the radius is 15 metres or less. For radii between 15m and 80m inclusive, straight kerbs of length 600mm shall be used, unless channels are required in which case radius kerbs and channels shall be used.
The minimum cut length of a kerb shall be 450mm and a trowel width gap shall be left at the front face of a radius.
Road kerbs shall be laid on a 150mm x 380mm concrete base.
Example standard kerb types drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Sustainable drainage system Kerbing
Sustainable drainage kerbing may utilise various inlet methods to promote water flow from new roads and footpaths into the drainage system.
The options below are provided as a typical detail for reference only. The method selected should be designed specifically to suit the layout of the new road and footpath.
Example inlet - intermittent kerb drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Example inlet - quadrant drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Example inlet - offlet and reverse bullnose kerb drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Channel blocks shall be used on impermeable roads with a longitudinal gradient between 1 in 150 and 1 in 250 along the face of the road kerb. Channel blocks should have a false slope for longitudinal gradients less than 1 in 250.
Channel blocks shall be 125mm x 255mm Type CS1 and should be laid on a 150mm x 300mm concrete base.
Footpath edgings, known as external flat (EF) precast concrete edgings should be used adjacent to footpaths and vehicle entrances. They should be laid on a 75mm x 330mm concrete base.
Bedding and backing of all kerbing shall be laid and bedded on a 25mm layer of cement mortar. Concrete bedding and haunching for all kerbing shall consist of ST4 (15N/mm²) concrete of low workability.
The kerb and channel bed on new roads shall always be laid separate to the backing. This is due to the high level of kerb damage experienced on development roads and the resulting need to replace kerbs at a late stage of construction whilst causing the minimum damage to the overall construction.
Alternative kerbing methods may be used on bituminous roads where the road kerbs are to be installed later, referred to as two-stage construction, and the initial layer of binder course shall be 70mm thick with the separate road kerb base utilised as level control.
Any sacrificial blocks or road kerbs shall be removed and the correct approved road kerb installed prior to laying a further 60mm layer of binder course and/or the installation of footpaths.
Should the road binder course not provide a suitable line for the road kerb to be laid, there may be a requirement to inlay plane part of the road to ensure a perfect seal between the kerb and road binder course.
Example alternative kerbing method drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Damaged kerbing shall be replaced prior to the application of the final road or footpath surface course. Road kerbs shall be removed from the footpath or verge side unless the road binder course is still to be laid or repaired.
Where it becomes necessary to replace kerbing following the application of final surface course to the road and footpath, a minimum two metre length of surface course, the full width of the footpath, shall be replaced. If damage is caused to the adjacent road surface course, the surface course shall be replaced for a minimum of five metres for half the width of the road.
Where more than four separate road kerbs, channels or edgings are damaged within any ten metre length, the entire ten metre length shall be replaced.
When all surfacing has finished and minor damage exists, a HAPAS approved dedicated epoxy kerb repair product, which preferably incorporates a priming system may be used except on conservation kerbing or any kerbing that have not received the final surfacing.
Concrete
Concrete shall be ready mixed concrete complying BS 8500-1:2023 and BS EN 206:2013. The maximum aggregate size shall be 20mm. Suppliers shall be members of the Quality Scheme for Ready Mixed Concrete (QSRMC) and have a quality management system in accordance with BS EN ISO 9001: 2015.
Concrete compressive strengths are defined in terms of both cylinder strength and cube strengths. The first (lower) number gives the cylinder strength requirement; the second (higher) number is the cube strength requirement.
Fresh concrete shall not be placed against concrete which has been in position for more than 30 minutes unless an approved construction joint is formed.
Standard prescribed concrete shall be in accordance with the required concrete mixes and strengths but shall not be used where:
- Sulphates or other aggressive chemicals are present in the ground water.
- Where concrete will be subjected to road de-icing salt.
In these circumstances a suitable mix, including admixtures and cement containing additives, shall be submitted to, and approved by, us.
|
Standardised prescribed concrete |
Strength Class for structural design |
Compressive cube strength at 28 days (N/mm2) |
|---|---|---|
|
ST1 |
C6/8 |
8 |
|
ST2 |
C8/10 |
10 |
|
ST3 |
C12/15 |
15 |
|
ST4 |
C16/20 |
20 |
|
ST5 |
C20/25 |
25 |
Site batched concrete may be acceptable where small quantities of concrete are required and the use of ready mix concrete would be prohibitively expensive. Site batched concrete will only be permitted in unreinforced applications and shall be in accordance with the table below.
|
Compressive Strength N/mm2 |
Coarse |
Fine |
Cement |
|---|---|---|---|
|
C12/15 |
4 |
2 ½ |
1 |
|
C16/20 |
4 |
2 |
1 |
|
C25/30 |
3 |
1 ½ |
1 |
Recycled low grade concrete mixes with 10% recycled aggregate may be used in footpath edgings and, sign and street name plate foundations. This should not be used for structural, drainage or kerbing works.
When recycled concrete aggregate is used, it shall not have more than 1% by mass of foreign materials including wood, plastic and metal nor a floating material in volume content exceeding 10cm³/kg when tested in accordance with BS EN 933-11.
Compaction shall be required for all concrete to produce a dense uniform mass. It shall be compacted with the assistance of vibrators, care being taken to avoid contact with reinforcement and inserts.
All concrete shall be compacted in its final position within 30 minutes of being discharged from the mixer unless carried in continuously operated purpose-made agitators, when the time shall not be more than 2 hours after the introduction of the cement.
Curing of all concrete shall be required for 24 hours before any fresh concrete is placed adjacent to the cured concrete.
Immediately after completion and for 7 days thereafter, concrete shall be protected against harmful effects of weather, including rain, rapid temperature changes, frost and from drying out.