S6 Flexible and Composite Roads
S6 Flexible and Composite Roads
General
1) The Undertaker shall carry out the reinstatement in accordance with one of the following methods and should endeavour to achieve the greatest degree of immediate permanent reinstatement. Reinstatement methods are listed in Appendix A2.10 Table A2.6.
2) Permitted materials and layer thickness are specified in Appendices A1 to A4, A9 and A11.
3) Where the Authority knows of any site with high sulphate levels, dangerous toxins or contaminants it should advise Undertakers in advance of the works so that appropriate measures may be taken. Ideally this information should be stored on the SRWR (as a Special Engineering Difficulty for dangerous toxins and contaminants) where it is available to all Undertakers and Roads Authorities. Similarly where an undertaker discovers any dangerous toxins or contaminants in the ground, it should inform the Local Authority such that they can update the register.
S6.1.1 Method A - All Permanent Reinstatement
The excavation shall be reinstated to a permanent standard at the first visit.
S6.1.2 Method B - Permanent Binder Course Reinstatement
1) The backfill, sub-base, Base and binder course shall be reinstated to a permanent standard at the first visit.
2) The permanent binder course material, or an alternative interim material, shall be extended to the surface as the interim surface course, with or without a thin separating material layer of sand at the position of the binder course/surface course interface.
3) On the second visit, all interim surfacing materials shall be removed, to the top of the binder course, typically by cold planing, and a permanent surface course shall be laid.
4) Where a sand separation layer is present, prior to the reinstatement of the permanent surface course the sand shall be removed, the surface brushed clean and a tack coat or bond coat applied.
S6.1.3 Method C - Permanent Base Reinstatement
1) The backfill, sub-base and Base shall be reinstated to a permanent standard at the first visit.
2) The interim surface course and part, or all, of the interim binder course, may be deferred set material. Part, or all, of the entire interim binder course may be an unbound granular material.
3) On the second visit, all interim surfacing materials shall be removed, to the top of the Base, and a permanent binder course and surface course shall be laid.
S6.1.4 Method D - Permanent Sub-base Reinstatement
1) The backfill and sub-base shall be reinstated to a permanent standard at the first visit
2) The interim Base shall be granular and the interim surfacing shall be in accordance with the relevant requirements of Section S6.1.4.
3) On the second visit, all interim materials shall be removed, to the top of the sub-base, and a permanent Base, binder course and surface course laid.
General
Permitted options are shown in Appendix A3.5, A4.4 & A4.5 - subject to the following exceptions:
a) Sub-base Equivalence: The thickness of granular sub-bases may be reduced, provided that the thickness of the bituminous binder course is increased proportionately, in accordance with S6.3.2.
b) Small Reinstatements: CBGM B sub-base of 150 mm thickness may be used in small excavations and narrow trenches regardless of whether the existing sub-base is cement bound. Where this option is utilised, the Base material shall also be a bound material.
c) Alternative Reinstatement Materials: Alternative Reinstatement Materials (ARMs) may be laid to the top of sub-base level, in accordance with Appendix A9, regardless of whether the existing sub-base is a bound material.
General
Permitted options are shown in Appendices A3 and A4, subject to the following provisions:
S6.3.1 CBGM B in Flexible and Composite Roads
1) In Types 0 & 1 roads, where a CBGM B Base is used, the reinstatement may either be surfaced on the same day or the CBGM B shall be allowed 7 days to cure before surfacing is undertaken. In either case, the CBGM B shall be allowed 7 days to cure before the road is opened to traffic.
2) In Types 2, 3 & 4 roads, where the reinstatement is surfaced on the same day that the CBGM B Base is placed, the road may be opened to traffic on the following day. Where the CBGM B Base is not surfaced on the same day, the reinstatement shall be allowed 3 days to cure before surfacing is undertaken.
3) All composite roads constructed with a Base of CBGM B lean-mix concrete or equivalent shall be reinstated with a CBGM B Base.
4) In composite roads, the reinstated CBGM B Base shall be laid flush with the top of the existing cement-bound Base.
5) Continuously reinforced concrete bases that have been connected with dowel bars are not covered by this clause S6.3.1. Special conditions will apply to the reinstatement and shall be agreed with the Authority.
In Type 3 and 4 flexible roads, the thickness of granular bases may be reduced provided that the thickness of the bituminous binder course is increased proportionately, in accordance with the following requirements:
1) Each 10 mm increase in bituminous binder course thickness is equivalent to a 35 mm decrease in thickness of Type 1 Granular Sub-Base at Base and/or sub-base levels and vice versa.
2) This equivalence rule may be applied to include the total replacement of all granular materials at both sub-base and Base levels, subject to the following restrictions:
a) Binder course and surface course thickness in Type 3 and 4 roads are minimum values and shall not be reduced by application of the 10:35 equivalence of bituminous/granular materials; and
b) Where part of a granular Base and/or sub-base is to be replaced by additional binder course material, the remaining total thickness of granular material at Base and/or sub-base level shall not be less than 150 mm.
S6.3.3 Modular Materials within the Excavation
1) Where cobbles or setts are encountered during excavation, they may be recovered and re-used for reinstatement of the relevant layer. Alternatively, at the discretion of the Undertaker, the layer may be reinstated using CBGM B laid to a thickness of 100 mm, or to match the original thickness, whichever is greater.
2) Layers of modules, cobbles/setts, stones, rocks, or other large aggregate particles laid upright, in an interlocking fashion, often termed 'penning', will exhibit a greater stiffness than an equivalent layer of cobbles/setts laid horizontally. Where such upright interlocking modules are encountered, the layer shall be reinstated using CBGM B laid to a thickness of 100 mm, or to match the original thickness, whichever is greater.
3) Where surplus modules, cobbles or setts are removed from site, they shall remain the property of the Authority. The Undertaker shall notify the Authority and retain them for 10 days following such notification. Thereafter, the Undertaker shall be free to dispose of all remaining modules, cobbles and setts.
4) Where CBGM B is used at base level, it shall be used in accordance with Section S6.3.1.
S6.3.4 Alternative Reinstatement Materials
Alternative Reinstatement Materials (ARMs) may be laid to the top of Base level, in accordance with Appendix A9, regardless of whether the existing Base is a bound material.
Permitted options are shown in Appendices A2 to A4 inclusive, subject to the following provisions:
S6.4.1 Hot Rolled Asphalt (HRA) Surface
Where the existing Surface Course material is HRA, it shall be reinstated with HRA as per Appendix A2 to A4.
S6.4.2 Stone Mastic Asphalt (SMA) and Thin Surface Course Systems
1) Where the existing surface course material is SMA or a thin surface course (TS) system the road shall be reinstated either with SMA surface course or, at the Authority's request, with thin surface course, subject to the following requirements:
a) Generic SMA or thin surface course mixtures shall match the existing nominal aggregate size of the existing surface course material. Reduction in nominal aggregate size shall only be where agreed with the Authority and shall take into account texture depth requirements.
b) The standard combined thickness of binder course and SMA surface course shown in Appendices A3.0 to A3.4 shall be 100mm.
2) Edge and base preparation for permanent SMA reinstatements shall be as follows:
a) All edges shall be saw cut or trimmed by saw, to a depth of 40 mm or the thickness of the surface course, prior to permanent reinstatement.
b) A K1-40 tack coat or BBA HAPAS certified bond coat shall be applied in accordance with Section S6.5.1. In the event that no such approvals have been issued they shall not be used without approval of the Authority. Approval shall not unreasonably be withheld.
c) An edge sealant shall be applied in accordance with Section S6.5.2.2.
3) Where the existing surface is a thin surface course material and the Authority does not want the reinstatement to be completed using SMA, the Authority shall contact the Undertaker in accordance with Section S6.4.5.5.
4) Where the Authority has a policy to grit or otherwise treat newly laid Stone Mastic Asphalt surfacings, it should advise the Undertaker of the required method and materials and the Undertaker shall comply.
S6.4.3 Asphalt Concrete Surface Course Materials
Where the existing surface course material is asphalt concrete it may be reinstated with any of the surface course options in Appendix A2 to A4.
Where used, asphalt concrete surface course materials shall be AC 10 close surf, laid 40 mm thick.
S6.4.4 Asphalt Concrete Binder Course Materials
Where Asphalt concrete binder course is to be used as the running surface for a period in excess of 6 months the usual supplier declared target binder content shall be increased by 0.5%.
S6.4.5 Other Bituminous Materials
Where it is necessary to use bituminous materials not included in Appendix A2, they shall be used in accordance with the following:
1) Where existing road surfaces have been treated or constructed with high friction surfacings, porous asphalt or coloured surfacings and local custom and practice has been to complete all previous resurfacing with like materials, their permanent reinstatement shall be carried out in accordance with the following requirements:
a) High friction surfacings shall be permanently reinstated with like materials, or an agreed alternative material, in accordance with Section S6.4.5.2.
b) In the event of notification by the Authority the reinstatement of any existing porous asphalt surface course (excluding small reinstatements) shall be carried out in accordance with the Authority's requirements. Small reinstatements shall be reinstated as detailed in Section S6.4.5.3.
c) Coloured surfacings shall be permanently reinstated with like materials, or an agreed alternative material, in accordance with Section S6.4.5.4.
2) When requested by the Undertaker, the Authority shall identify an appropriate source of suitable like or alternative materials, wherever possible. Where the Authority is unable to identify an appropriate source of suitable material, the Undertaker shall provide a suitable material on the basis of best reasonable endeavours.
3) Where existing road surfaces have been treated or constructed with high friction surfacings, porous asphalt or coloured surfacings and local custom and practice has not been to complete all previous resurfacing with like materials, the Undertaker shall consult with the Authority to determine appropriate reinstatement requirements.
4) Where other specialist surfacing materials not included in Appendix A2 or Section S6.4.5.1 (1) above have been used, they may generally be permanently reinstated in accordance with Section S6.4.5.5.
S6.4.5.2 High Friction Surfacings
1) High friction surfacings shall be permanently reinstated with a like material within 15 working days following the date of completion of the reinstatement, unless the prevailing weather conditions or other site circumstances mitigate against the successful application of the high friction surfacing. Where this occurs, the permanent reinstatement shall be deferred until such time as the unfavourable weather conditions or other site circumstances abate. Site circumstances justifying delaying the reinstatement of the High Friction Surfacing include the need for the new surface course material to be trafficked and/or aged prior to the application of a cold-applied material if this is specified by the system supplier.
2) Prior to the application of the permanent, or any interim, friction surfacing, warning signs shall be displayed indicating a potential slippery road surface.
3) All High Friction Surfacing applied to any roads shall have a current Type 1 BBA/HAPAS Roads and Bridges certificate. These materials shall be laid by a contractor certificated by the BBA, and being a Certificate holder for the application of that material, with the exception of small or narrow excavations in Types 2, 3 & 4 roads where the material shall have a current Type 1 BBA/HAPAS Roads and Bridges certificate, but may be applied by a contractor not approved by the BBA/HAPAS, but with experience in applying such materials strictly in accordance with the manufacturer's instructions.
4) Some high friction surfacing materials have a limited manufacturer's guarantee and may be subject to wear and abrasion during the guarantee period. However, the reinstated area shall not be inferior to the adjoining surface during the guarantee period.
S6.4.5.3 Porous Asphalt (small reinstatements)
Small reinstatements which do not adversely affect the overall drainage characteristics of the site, may be reinstated using SMA subject to the following:
a) Multiple small reinstatements using SMA shall not be closer than 3 m to each other in the principal direction of fall or surface drainage flow.
b) Porous asphalt surface courses shall be reinstated to nominally match the thickness of the existing layer.
c) The binder course of porous asphalt reinstatements shall be hot rolled asphalt.
d) All edges shall be saw cut, or trimmed by saw, to a minimum depth of 50 mm (or the thickness of the surface course, if greater), prior to permanent reinstatement.
e) For permanent reinstatements using porous asphalt, all edges shall be cleared of all contamination and treated with a light application of tack coat material, not edge sealant. A K1-40 tack coat or BBA HAPAS certified bond coat shall be applied at a minimum rate of 0.5 to 0.7 l/m², in accordance with Section S6.5.1.
f) For permanent reinstatements using SMA, all edges shall be treated with edge sealant, preferably a non-rubberised sealant applied by spray. A K1-40 tack coat or BBA HAPAS certified bond coat shall be applied to the base of the reinstatement in accordance with Section S6.5.1.
Coloured surfacings used to highlight highway features such as speed warnings, bus or cycle lanes, 'gateways' etc. shall be permanently reinstated using like materials of equivalent type and similar colour, subject to the following requirements:
a) Where the coloured surfacing is overlaid onto a road surface, a coloured overlay shall be applied to the same thickness.
b) Where the coloured surfacing is laid full depth, a coloured material shall be laid to the same thickness, wherever possible and practical. Where it is not possible or practical, the coloured surfacing material shall be reinstated by agreement.
c) Some high friction surfacing materials that are coloured have a limited manufacturer's guarantee and may be subject to wear and abrasion during the guarantee period. However, the reinstated area shall not be inferior to the adjoining surface during the guarantee period.
S6.4.5.5 Other Specialist Surfacing Materials
1) Specialist surfacings not included in Appendix A2 or Section S6.4.5.1 (1) shall generally be reinstated with SMA. Such surfaces shall be recorded as a Special Engineering Difficulty for notification purposes.
2) Where the overall area is sufficiently large to facilitate machine laying and the local custom and practice has been to complete all previous resurfacing with like materials and the Authority wishes to request the use of like materials, the Authority shall:
a) Notify the Undertaker accordingly at the planning or notice stage, or in the case of immediate works, before the permanent reinstatement.
b) Identify an appropriate source of suitable like or equivalent materials.
3) All other surfacing materials not covered above, including grouted bituminous materials, traffic calming materials, surface treatments etc., shall be permanently reinstated by agreement.
S6.4.6 Surface Treatments
1) In Types 0, 1 & 2 roads,
a) where an existing surface dressing is readily apparent, the Undertaker shall reinstate in accordance with S6.4.1 to S6.4.5.
b) where an existing surface treatment is readily apparent, the Undertaker shall apply an equivalent surface treatment.
If requested by the Authority, an appropriate timing and methodology for the works shall be jointly agreed in accordance with national specifications and Codes of Practice
2) In Types 3 & 4 roads either:
a) Surface dressing or other surface treatment is not required when any binder course and surface course option permitted by Section S6.4 is laid, or
b) The surfacing layers and equivalent surface dressing or other surface treatment shall be reinstated by agreement.
S6.4.7 Coated Chippings
1) All pre-coated chippings shall be as specified in Appendix A2.
2) Where pre-coated chippings are to be embedded into a road surface, they shall meet the requirements for surface texture specified in Section S2.6.
S6.4.8 Composite Roads
The total combined thickness of the reinstated binder course and surface course shall match the existing bituminous thickness. Wherever practicable, the required surface course thickness should be maintained by adjustment of the binder course thickness.
S6.4.9 Single Course Construction
NOT USED
S6.4.10 Small Excavations, Narrow Trenches and Access Chamber Covers
1) In types 3 and 4 roads a permanent surface course material in accordance with Appendix A2 may be laid in place of a permanent binder course material at Base and/or binder course level in:
i) small excavations and narrow trenches (as defined in Sections S1.5.1 & S1.5.2);
ii) within 350mm of access chamber covers
2) Where this option is used there shall be no substitution of bitumen binder equivalence, as permitted under Appendix A11.
S6.4.11 Large Diameter Cores (>150 mm diameter for Undertaking Works)
Undertakers may extract large diameter cores of bound layers and reinsert the core into the opening as part of the reinstatement. This is a new procedure within the UK and the Undertaker shall obtain the prior agreement of the Authority before proceeding. There shall be no departure from the performance requirements during the guarantee period.
S6.5 Base and Edge Preparation
1) All surfaces shall be free of contamination prior to the application of a tack coat or bond coat. This is especially important after the removal of a sand separation layer.
2) A tack coat or bond coat shall be applied to the surface of all bound layers prior to overlaying in all circumstances.
3) The tack coat or bond coat shall be applied at a rate to ensure a residual bitumen content of 0.15 kg/m2.
4) Multiple lifts of the same material laid during a single visit on the same day do not require treatment between lifts. However, a tack coat or bond coat shall be applied prior to placement of the permanent surface course layer in work carried out under Section S6.4.10.
5) A bitumen emulsion edge sealant may be used as a tack coat or bond coat in small excavations and narrow trenches.
The edges of excavations may need to be trimmed, at binder course and/or surface course level, to meet the following requirements:
1) All bound edges shall be essentially straight, smooth and vertical.
Edge regularity requirements are intended to provide a shape that will not hinder the compaction of material adjacent to the reinstatement edge. Overlapping edge cuts and corner cut outs should be minimal and all cuts extending into the existing surface shall be filled with flexible bituminous sealant. A circular excavation shall be considered a regular shape.
2) The internal corners and edges of a reinstatement shall be as square as possible. Internal corners and edges shall not be less than a nominal 90o.
3) There shall be no requirement to trim the sides of trench excavations solely to provide a uniform width, provided that individual projections are not less than 250 mm length, measured parallel to the nominal centreline of the trench. See also Figure S6.1 (Example 1).
4) There shall be no requirement to trim a small excavation solely in order to provide a square or rectangular shape. Any shape, in any excavation, with included angles which may be less than 90º, with no projection less than 250 mm length, may be considered to be regular. See also Figure S6.1 (Example 2).
5) Where the existing surfacing material is sound at the corners of an excavation, there shall be no necessity to cut out to a corner; a regular chamfer may be preferable.
The final shape of the excavation when viewed from above should be governed by the above principles rather than by aesthetic considerations (see Figure S6.1).
1) All edges shall be adequately prepared prior to application of edge sealant e.g. free of contamination, loose material, and the like. In all cases the manufacturer's instructions shall be followed.
2) At any interim stage and at the time of permanent reinstatement, the top 100 mm, at least, of all bound vertical edges at surface course and binder course levels, and the equivalent area on kerbs and exposed fixed features, shall be painted with a bitumen based edge sealant or otherwise prepared with an edge sealing system or equivalent material There shall be no significant splashing, spillage or any deliberate over painting of the adjacent road surface, subject to the requirements of Section S11.7.
3) Tack coat, bond coat or overbanding material shall not be used as an edge sealant unless otherwise specified in Section S6.4.5.3.
4) There should be visible evidence of the use of sealant. The fact that a core may separate is not, on its own, evidence that no edge sealant has been used.
S6.5.2.3 Proximity to Road Edges, and Fixed Features
1) Where the "trimmed" edge of any excavation is within 250 mm of the road edge, kerbing, other fixed features or another reinstatement, the trim-line shall be extended to the interface with the road edge, kerbing etc. See Figure S6.2
2) The additional reinstatement area required by extending the trim-line may be confined to the surface course, provided the lower layers have not been damaged.
3) Where an existing fixed feature is immediately adjacent to another fixed feature (e.g. road gully, valve cover, etc.) material selection shall be appropriate to ensure adequate compaction and surface profile - Section S2.2.1 (4) refers.
1) All bound edges shall be essentially smooth and vertical with no significant undercutting, as shown in Figure S6.3.
S6.5.2.5 Stepped Joints
On Type 0 and 1 roads where it is the custom and practice of an Authority to cut-back the surface and/or binder course to provide a stepped profile then this shall be notified to the Undertaker. Subject to the agreement of the Authority the stepped joint shall be applied to reinstatements in Type 0 and 1 roads subject to the following:
i) Small reinstatements and narrow transverse trenches shall be excluded
ii) The stepped profile shall match the Authority's policy subject to a maximum of 75mm step - see Figure S6.4
1) Tolerances for all bituminous materials permitted in Appendix A2 are contained in that Appendix.
2) Tolerances for bituminous materials not included in Appendix A2 shall be by agreement.