Guidance Document on Surfacing Options for Highways Edition

Transcription

1 Guidance Document on Surfacing Options for Highways 2010 Edition Technical Advice Group Hampshire County Council Capital House Andover Road Winchester Hampshire SO23 7BH

2 HAMPSHIRE COUNTY COUNCIL ENVIRONMENT DEPARTMENT TECHNICAL ADVICE GROUP GUIDANCE DOCUMENT ON SURFACING OPTIONS FOR HIGHWAYS CONTENTS Page Number 1 INTRODUCTION SCOPE SURFACING GENERAL Preliminary Works Effect of Existing Substrate on Material Choice Ironwork Overlay or Inlay? Inter-layer Bonding Joints Quality Assurance Materials Testing Strategy (MTS) Layer Thicknesses and Weather Considerations for Hot Applied Materials Deferred Set Materials Traffic Noise SELECTION OF AGGREGATES AND BINDERS Aggregate Properties Aggregate Selection for Surface Courses Binders SELECTION OF APPROPRIATE SURFACING TYPE Relative Properties of Surfacing Materials Guidance on Choice of Surfacing Sites with a Speed Limit of 40 mph or Greater Sites with a Speed Limit of Less than 40 mph Detailed Consideration Of Alternative Surfacing Materials SURFACE DRESSING Surface Dressing on Carriageways Surface Dressing on Footways REHABILITATION OF THE EXISTING SURFACE Pothole Repairs and Patching Reinstatements Within Special Surfacings...51

3 7.3 Retexturing Repave/Remix Crack Sealing Techniques Asphalt Rejuvenation ROAD RECYCLING In-situ Recycling Ex-Situ Recycling ( Cold Recycled Bituminous Bound Material) CONCRETE SLAB CARRIAGEWAYS Joints Exposed Slabs Overlaying HIGH FRICTION AND DECORATIVE SURFACINGS High Friction Surfacings (decorative surfacings derived from HFS systems) Coloured 'Gateway' Surfacings - General Resin Bonded Surfacing Resin Bound Surfacings Decorative Asphalts BLOCK PAVING AND NATURAL STONE PAVING General Guidance Block Paving for Vehicular Areas Block Paving for Pedestrian Areas Block Paving for Shared Areas Improving Skid/Slip Resistance Natural Stone Paving ASPHALT REINFORCEMENT GRIDS Choice of Grid Reinforcement Thermal cracking Cracking with some anticipated Vertical Displacement expected Clay Shrinkage cracking Concrete Joint problems/severe Clay Shrinkage cracking GridSeal Guide to Successful Installation FOOTWAYS General Guidance A note on Slurry Treatment of Footways...69 APPENDIX A: PERMITTED PAVEMENT OPTIONS Appendix 7/1/A...75 Appendix 7/1/B...76 Appendix 7/1/C...77 Appendix 7/1/D...79

4 Appendix 7/1/E...80 Appendix 7/1/F...81 Appendix 7/1/G...82 Appendix 7/1/H...83 Appendix 7/1/J...85 Appendix 7/1/K...87 Appendix 7/1/L...88 Appendix 7/1/M...90 APPENDIX B : KEY CHANGES SINCE 2002 EDITION B.1 Revised Bituminous Material Standards...93 B.2 New Materials and Processes...98

5 1 INTRODUCTION The last 50 years have seen significant changes to road legislation and automotive technology. Higher traffic loadings now impose greater stresses on road materials and have highlighted some weaknesses in traditional surfacing materials. There is a need now also to consider the sustainable use of materials and the potential influence of climate change on the future performance of materials. The highways industry has responded by both improving the specification and properties of traditional materials and by developing new surfacings However, there is no one surfacing material that is "perfect" for all applications and some, whilst ideal in certain circumstances, would be totally unsuitable in others. Additionally, the costs between materials can vary significantly. Purpose of this Document The purpose of this document (first published in February 1989) is to provide Highway Engineers with guidance on the various highway surfacing materials/products on the market so that the most suitable and cost-effective material is selected on a site specific basis. As far as is possible, all the guidance is based upon practical experience both within Hampshire and nationally. The Highway & Transport Branch strongly support the use of environmentally sustainable or 'green' alternatives to conventional maintenance operations. Many 'green' solutions are now incorporated into standard maintenance treatments. This document aims to provide Engineers with a combination of information, advice, guidance and Departmental policies/standards. All guidance/ information is given in normal type and Engineers are encouraged to use their judgement on a scheme specific basis. All text in bold type, however, are requirements with which Engineers must comply unless a departure has been agreed at SMG level in advance. The requirements noted are generally due to National/County Standards or because specialist advice is crucial to obtain a satisfactory product and for ' best value' in the particular activity concerned. Failure to comply with these requirements could produce sub-standard works and possibly even leave the County liable to legal action. Since the previous edition of this document there have been numerous changes to Standards, Specifications, Materials and Practice and it is these changes which have prompted this revised edition. Many staff will already be familiar with the changes and it is not necessary to know the full detail in order to use this document. Accordingly these are not dwelled upon but have been summarised as Appendix B for those new staff who may appreciate the background. Page 1 of 101

6 . Both the Highways and Transport Branch Management Team and the Highways Technical Group (formerly Departmental Standards Committee) have endorsed this document prior to publication. This heavily revised edition has only been published after a comprehensive internal consultation process. However, it is recognised that the document may contain errors, omissions, contradictions, etc. It is also likely that particular scenarios may not be covered. For these reasons, feedback from Engineers (both positive and constructively negative!) would be welcome. Any such feedback should be sent to the Technical Advice Group - Tel , Fax or colin.norris@hants.gov.uk 2 SCOPE Whilst this document has been formulated primarily as a guide to the selection of surface treatments for highway maintenance works in areas not subject to special requirements, the concepts are equally valid for new works in similar areas. The document complements but is not intended to replace The Highways Environment - Design guidelines for Special Areas or Traditional Materials a guide to the use of natural materials in the Highway, both of which remain current and should be referred to when considering surfacing works in special areas. The purpose of this document is to provide sufficient guidance for Engineers to enable them to specify safe and durable surface treatments which will give an adequate level of performance over their service life. Reconstruction and similar treatments are generally outside the scope of this document and hence materials primarily involved in such operations (e.g. Base and sub-base) are not covered. Eight basic groups of surface treatment are covered: Bituminous surfacings - HRA, AC, Thin Surface Courses, SMA, etc. Surface dressing Rehabilitation of existing surfacing Road recycling Treatment of concrete roads Special surfacings (High Friction Surfacing, Coloured Surfacing, etc) Block paving and Natural Stone Paving. Footway surfacings Flow charts are used to guide users to the most appropriate group for any given maintenance scenario. Within each group, the merits of a range of possible treatments are discussed and the preferred option is suggested for any particular set of circumstances. In all cases the preferred option has been selected for its engineering properties. Page 2 of 101

7 However, there may well be over-riding environmental conditions which will affect the choice of treatment/material e.g. Conservation Areas. The intention is that this document should have a long life and therefore no attempt has been made to quantify prices. Prices can be influenced by many factors and specifiers are encouraged to evaluate prices at scheme level. Prices for most of the processes covered will be available through the Term Highway Contract. 3 SURFACING GENERAL 3.1 Preliminary Works Whilst all the materials quoted should perform adequately under the circumstances discussed, it should be borne in mind that any surfacing/surface treatment is only as good as the base upon which it is laid. THERE CAN BE NO SUBSTITUTE FOR ADEQUATE PREPARATORY WORKS. This is particularly the case where the surfacing selected is potentially permeable. As may be the case with negative textured surfacing, see section 3.2 and Effect of Existing Substrate on Material Choice When resurfacing, the nature and performance of the existing surfacing should be considered carefully and the new material specified to overcome any deficiencies (e.g. if the existing surfacing has rutted badly then it would be wise to consider removing all the rutted material - Binder Course and Base as well if affected - and replacing it with more deformation resistant materials). If the works are sufficient to justify it, an investigation or testing should be carried out to establish the extent and cause of any deficiencies. In maintaining County roads it must be remembered that many have evolved over time and are not constructed to modern standards. A consequence of this is that they are relatively thin and can exhibit more flexibility than a modern designed carriageway. Any surfacing to be applied needs to be able to accommodate this movement if it is to provide a durable running surface. It is essential also that evolved highways are sealed effectively to prevent deterioration. Where a potentially porous surfacing e.g. a Thin Surface Course is being considered, an investigation should be undertaken to determine the potential for water penetration and the consequent need for additional waterproofing measures e.g. a dense binder course or a thick seal/bond coat. Additionally, where a thin surfacing has been used previously consideration should be given to the potential for increased noise arising from maintenance in accordance with section 3.11 below Page 3 of 101

8 3.3 Ironwork It is highly desirable that ironwork is raised BEFORE any surfacing work is undertaken. This provides a surface with a better riding quality and is usually more pleasant aesthetically. Further, by raising ironwork before surfacing no patching is needed and this prevents the normal problems associated with fretting and potholing of reinstated material near ironwork. If, for whatever reason, ironwork cannot be raised until after surfacing has been completed, consideration should be given to the use of the Paco-Patch process or an infra red repair in order to ensure a good weatherproof joint. 3.4 Overlay or Inlay? Overlaying should be the first process considered when renovating a carriageway as this takes advantage of the materials already in place, strengthens the road and is the least disruptive. Where the situation requires an inlay the excavated surface must be cleaned free of any loosely bonded material and should be as uniform in depth and surface profile as possible. 3.5 Inter-layer Bonding A good bond is essential between pavement layers in order to realise the maximum structural potential. A tack coat or bond coat shall be applied in association with all bituminous layers to promote adhesion (ref SHW Cl 903.4). The Specification for Highway Works (Clause 920) requires all tack coats and bond coats to be applied by metered spray tanker. However, it must be recognised that this is not always practical for works on the County network including footways and indeed the BBA/HAPAS certificates for some proprietary products still permit manual spraying. As a consequence, although application by tanker is to be preferred the Engineer will be allowed discretion to consider all reasonable means of application provided care is exercised to ensure the recommended rate is applied uniformly. 3.6 Joints Careful consideration must be paid to joints in the surfacing. Any joint can be considered to be a weakness in the system. The fewer the number of joints the better. Where joints cannot be avoided they shall be positioned to avoid areas of stress away from vehicle wheel paths and as much as possible away from turning movements or acceleration and braking zones. Page 4 of 101

9 When surfacing bends, care should be taken to ensure that consistent road surface properties are provided throughout. There should be no significant change in surfacing type within such bends. This would present drivers and particularly motorcyclists with different road surface properties which could lead to accidents. If necessary, surfacing should be extended to move surface changes into a generally straight section of carriageway. Finally any joints must be properly formed, prepared and constructed in accordance with the requirements of the Specification for Highway Works and BS The width of joint cut back or offset from layer joints beneath is the one exception to this. Generally on County works the minimum width of cut-back for B and C roads shall be 150mm and for A and Trunk roads 300mm. The requirement should be stated in Appendix 7/ Quality Assurance It should be noted that all suppliers of coated materials into Hampshire are required to operate quality systems complying with QA Sector Scheme No. 14 Production of Asphalt Mixtures to assure the quality of their products. Sector Scheme No. 14 Production of Asphalt Mixtures came into operation with effect from 1 April This scheme is now routinely called up in the 'Specification for Highway Works' (SHW) and is implicitly required under the IWF 1 and THC Contracts which refer to SHW. Other forms of contracts will need to make specific reference to this scheme (or to SHW). Plants not-registered under Sector Scheme 14 shall not be approved for supply to any works within Hampshire. If in doubt contact TAG. Under Sector Scheme 14, the ability of a production plant to mix material of consistent quality can be judged in terms of an Operating Compliance Level (OCL) value based on compliance rates for the last 32 samples tested. The lower the OCL value the greater the compliance rate. No 'minimum' OCL value has been set so a production plant can still claim accreditation under Sector Scheme 14 even though the material produced may not be of consistently good quality. Accordingly, Engineers are strongly advised not just to rely on a Suppliers QA status but to also require sight of OCL values pertinent to the anticipated period of supply and to consider the need for specific scheme testing (see Section 3.8 re HCC's Materials Testing Strategy). Any failures by the contractor to comply with their own quality procedures should be reported formally to them and if no satisfactory reply is received, a complaint should be made to their accreditation body. Page 5 of 101

10 In addition to quality assured supplies, the SHW requires that companies laying asphalts be accredited under Sector Scheme 16. This move is supported by HCC with a view to making the requirement mandatory from In the meantime, where a company not accredited to Sector Scheme 16 is proposed, Engineers should satisfy themselves through taking up references that the company is competent to undertake the work. 3.8 Materials Testing Strategy (MTS) Contractor making best use of routine quality control data. For larger one-off schemes the testing strategy to be employed in each instance will be determined on a scheme by scheme basis considering the nature of the works, although in general terms it is likely the majority of responsibility will rest with the Contractor. Engineers supervising works should be demanding sight of the appropriate evidence on a routine basis. Experience shows however, that it can take some time for this data to be made available and many Engineers require the sanction to call up a limited amount of audit testing to provide early confidence. To facilitate audit testing, or to challenge quality control data in the event of a dispute on THC works, a centrally held budget has been established to enable the County Highways Laboratory to undertake spot sampling work on an ad-hoc basis. Call off against this budget is apportioned annually in line with the RS/SM budget for each Highway Unit. For larger works and/or where full monitoring of laying operations is needed then provision for testing should be made within the scheme budget. To call up sampling and testing under the Materials Testing Strategy, contact the County Highways Laboratory Layer Thicknesses and Weather Considerations for Hot Applied Materials Unless constrained by special circumstances all material thicknesses and temperatures shall be specified to comply with the requirements of BS or the appropriate BBA HAPAS Certificate. Page 6 of 101

11 The requirements for wind speed and air temperatures in Clause 945 of the SHW (Specification for Highway Works) shall be adhered to whenever bituminous materials are laid. Failure to do so can severely affect material compaction and chipping embedment especially in cold weather. During periods of cold weather bituminous materials cool down rapidly and if adverse conditions are anticipated and cannot be avoided an increase in layer thicknesses may prove advantageous where this can be accommodated. However, where considering thicker layers it may be necessary to alter the grading or nominal size of aggregate to prevent other problems arising. The laying of high stability HRA mixtures in thin lifts in cold weather can give rise to particular problems with workability and chipping retention/embedment. Accordingly the preferred thickness for HRA surfacing is now 45mm. Where this cannot be accommodated and adverse conditions cannot be avoided it may be necessary to reduce the nominal size of chippings ( subject to meeting texture criteria ) or even preheat the substrate in order to achieve a satisfactory result. Some binder modifiers can be used to improve the workability/'cold weather working' properties of a mixture e.g. EVA, SBS, SBR, Wax, etc. Any such proposal shall be discussed first with TAG ( ) because such modifiers can have significant implications on many aspects of a materials performance - see also Section 3.2. The suppliers/applicators of some proprietary products will not guarantee their product/work if laid during winter months. This should be taken into account by Engineers when planning works. Conversely, if subject to trafficking at elevated temperatures many materials can be subject to fatting and deformation. This is particularly the case if trafficked before the freshly laid mat has cooled sufficiently. Spraying the rolled surface with a fine spray of cold water can reduce delays but should only be used where really necessary. Even after initial cooling, freshly laid materials with dark binder rich surfaces are likely to absorb more solar radiation than matured surfaces and can thus be subject to elevated temperatures in service until the aggregate becomes exposed. With climatologists predicting hotter summers, it would seem sensible to programme resurfacing of heavily trafficked sites during the autumn as this will reduce the number of hot days the material will be subjected to during its early life. Page 7 of 101

12 3.10 Deferred Set Materials Deferred set material shall not generally be used for permanent works in footways or carriageways to avoid subsequent instability, deformation or tacky binder being tracked, particularly to un-wanted locations. Deferred set material may be used for temporary works or very small scale potentially permanent works such as pothole repairs as directed in TAG Report TAG/P262 (August 2002) - 'Investigation into Improving the Performance of Pothole Repairs in Hampshire (Phase 2). The distinctive smell of deferred set materials (creosote or kerosene) makes them easy to identify. In addition the delivery note should include the letters DS in the description of the material e.g. AC 6 med surf 100/150 DS. Whilst deferred set material should not have been used for anything other than temporary works since 2002 it may occur in older works or as part of specialist applications (e.g. car parks). Where deferred set material has been used and overlaid before the flux oils have evaporated the material often remains mobile and is liable to excessive deformation. Where such issues are identified any underlying deferred set material should be removed and replaced with conventional hot material prior to surface repairs to avoid repetition. If it is suspected that deferred set material may have been used in contravention of policy then any investigation to determine the extent of deferment should be carried out sooner rather than later as it becomes more difficult to quantify the initial degree of deferment as time goes by Traffic Noise When planning resurfacing or surface dressing operations, engineers should consider the implication of road traffic noise arising from the new surface in accordance with the relevant procedure in HMMP. Noise is unlikely, generally, to be an issue where; Traffic speeds are likely to be less than 30MPH, Vehicle flows are likely to be less than 32,000 vehicles per 18 hour day, There are no properties within the immediate vicinity of the surfacing works, The texture depth of the new surface is likely to be the same as or less than existing and/or roadside noise levels are predicted to be less than 78dB(A) after the works. However, since the introduction of the Environmental Noise (England ) Regulations in 2006, plans are being developed nationally to manage and reduce environmental noise generally. Arising from this exercise a Page 8 of 101

13 number of major road sites in Hampshire have been flagged as first priority locations for detailed study with a view to introducing noise mitigation measures where possible. These first priority locations are shown on maps available at and particular attention should be paid to the specification of surfacing at these locations with a presumption in favour of low-noise materials where this is feasible and appropriate. See Appendix A 7/1/H to 7/1/L. 4 SELECTION OF AGGREGATES AND BINDERS 4.1 Aggregate Properties The physical requirements for aggregates are stated in BS EN and the associated guidance document PD These requirements are much as previously although the terminology and the test method may have changed. The following are the essential criteria and test methods: Resistance to fragmentation, measured by the Los Angeles test method. Freeze-thaw resistance determined by measuring the water absorption value as a screening test or more specifically using the magnesium sulfate soundness test. Resistance to polishing of coarse aggregate for surface courses, measured by the polished stone value (PSV). Resistance to surface abrasion, measured by the aggregate abrasion value (AAV). Further detailed guidance for the polished stone value (PSV) and aggregate abrasion value (AAV) required are given in section Aggregate Selection for Surface Courses In order to provide adequate levels of skid resistance and durability Engineers must specify an aggregate which is appropriate to site conditions and traffic flow. Hampshire County Council s policy on the management of skid resistance is described in the documents Skid Resistance Policy (Strategy) and HCC Procedure for Management of Skid Resistance. As well as monitoring the network by means of skid testing, a key factor in the provision and maintenance of adequate levels of skid resistance is Page 9 of 101

14 the selection and specification of aggregates with regard to Polished Stone Value (PSV). Although surface texture is an important property of a road surface, particularly at higher speeds, it is the ability of the aggregate to resist the polishing effects of traffic which has the greatest effect on skid resistance and safety in the wet, particularly in the medium to long term life of a surfacing or dressing. Table 4/1 PSV and Table 4/2 AAV should be used to select the appropriate aggregate properties with respect to Site Category and commercial traffic flow. As in previous editions of this guide the tables are based on advice given in Highways Agency standards, currently HD 36/06 Surfacing Materials for New and Maintenance Construction, amended for use on the local road network. In the table the Site Categories and target skid resistance values reflect the level of risk or difficulty of the site while the traffic flow is proportional to the intensity of polishing the aggregate is likely to be subjected to. Unless specific growth rates are known the commercial traffic flow at the end of life of the proposed surfacing should be estimated assuming a nominal growth rate of 2% per annum. For Asphalt mixes (including TSCs where appropriate preservative treatments are applied) a service life of 20 years may be assumed whereas for surface dressings a life of 10 years would be a more realistic assumption. However it is advisable to err on the side of safety when estimating design life as future maintenance frequency cannot be predicted with certainty. The main differences from earlier versions of this table concern site category definitions and target skid resistance values, mostly those for approaches to junctions, roundabouts, signals and the bend categories. These changes reflect amendments to site category definitions and changes in risk levels introduced in HD36/06 as a result of continuing research by TRL. Additionally for non-event sites the very lowest PSV aggregates permitted in HD 36/06 have been excluded, reflecting the increased risks associated with the un-designed nature of many of our roads. It is important that the Notes for Guidance accompanying the PSV table are read before finalising specifications as the selection of the appropriate site category is more complex than in previous versions. An additional traffic category of 0-50 cv/day has now been introduced to the table as an HCC amendment to cover the lesser used C class and unclassified roads which make up a large proportion of our local network. Occasionally a blend of coarse aggregates are proposed for incorporation into a mixture and in such cases the assessment of the overall material's skid resistance cannot be determined with certainty unless both aggregates comply with the minimum value specified. TAG shall be consulted in all cases where a supplier proposes combining different coarse aggregates, chippings or pre-coated chippings. Page 10 of 101

15 Aggregates shall be specified in terms of Polished Stone Value (PSV) and Aggregate Abrasion Value (AAV). The term "Hardstone" shall NOT be used in isolation as this is ambiguous. Occasionally a supplier will suggest that an aggregate performs better than the PSV results indicate. This may be the case but this should not be accepted without suitable evidence being provided and TAG approving. Conversely some aggregates, particularly those with an AAV of less than 6, tend not to perform as well as their PSV result would suggest when subjected to high stress traffic situations. TAG can advise on which sources have been found to react in this manner. It should be noted that whilst aggregates come in a variety of colours and PSV grades it is not always possible to obtain the exact colour/psv combination that may be desired on some schemes (e.g. in conservation areas). It is important that all Environment Department staff note that safety issues are of paramount importance and PSV requirements shall not be reduced just to allow a particular coloured aggregate to be used. Not withstanding this, if there is a choice of aggregates with a suitable PSV for the particular scheme then colour should be taken into consideration, especially in conservation areas TAG is available to advise on required aggregate properties and also holds further records relating to this matter. Page 11 of 101

16 Table 4/1 MINIMUM PSV OF CHIPPINGS OR COARSE AGGREGATE IN UNCHIPPED SURFACINGS FOR NEW SURFACE COURSES Site Description Dual Carriageways non-event sections. As above elevated risks. See note 1 Single carriageways non-event sections. As above elevated risks. See note 1 Gradients 5% - 10% Gradients > 10% As above elevated risks Approaches to pedestrian crossings and other high risk situations. See note 2 Approaches to major and minor junctions on dual and single carriageways. Approaches to roundabouts. See note 3. Roundabout circulation areas and exits (incl. mini). As above elevated risks. See note 4. Dual C/way bends, radius < 500m ( >=50mph) See note 5. Single C/way bends, radius m ( >=50mph) Single C/way bends, radius < 100m ( >=50mph) As above elevated risks. See note 6. Site Category Target Skid Resistance (SFC) B C G1/G K Q1 Q2 Q R S S Estimated commercial traffic flow at end of life of surface ( cv/lane/day ) * * 60* * HFS 60* 60 60* HFS HFS 65 HFS HFS HFS 68+ HFS HFS 60 HFS 60 HFS 65 HFS HFS 0-50# * HFS HFS HFS HFS HFS HFS 68+ HFS HFS 65 HFS 65 HFS 68+ HFS HFS > 2000 Consult TAG # This category is intended to cover the lightly used rural and urban C class and unclassified network. * May be lowered to 55 based on local experience and if there is no evidence of above average wet-skid accidents (consult Safety Engineering) Page 12 of 101

17 Notes for Guidance : - Table 4/1 1. For dual and single carriageway non-event sections (B and C) the default target skid resistance appropriate for average conditions, where traffic is free flowing and braking does not regularly occur, is as shown in bold. Where there are felt to be additional hazards (eg restricted sight lines, regular overtaking, poor geometry etc) or the site has an above average wet skid accident history, select the higher level. 2. For approaches to pedestrian crossings, etc. (site category K) use the lowest target skid resistance (bold) in situations where approach speeds are slow and visibility is good. For crossings in 40mph or greater zones or where, for other reasons, heavy braking may be anticipated use the higher level. 3. Site category Q covers a wide range of junction approaches:- Q1 applies to:- Approaches to roundabouts (incl. mini roundabouts) and signals in 40mph or less zones; Approaches to junctions on major roads in 40mph zones and Approaches to junctions on minor roads any speed limit. Q2 applies to roundabout and signal approaches and to and across junctions on major roads in 50mph or greater zones. Q3 applies to Q1 and Q2 categories where there are significantly higher risks. Definition: Major Rd = traffic has permanent priority; Minor Road = traffic is required to give way. 4. For roundabout circuits (R) generally use the default level in bold. However, where circulation speeds are high, where there is frequent use by cyclists and motorcyclists or where there is an absence of signalised control on grade-separated junctions select the higher level. 5. For S1 bends raise the target skid resistance to 0.50 where traffic needs to slow down to safely negotiate the bend, where there is adverse camber or where the road geometry presents an increased hazard. Otherwise select the default target skid resistance shown in bold. 6. For S2 bends the default target skid resistance of 0.50 can be lowered to 0.45 if a detailed site investigation shows the bend to have a reduced accident risk. The higher target of 0.55 band should be used only where a risk assessment identifies enhanced risks such as adverse camber or where the road geometry presents an increased hazard. 7. For all site categories the higher target skid resistance should be selected where a site has a known history of wet skid accidents showing a significantly higher level than the county average for a given site or length of road. 8. For sites which encompass multiple hazards, a target skid resistance appropriate to the feature with the highest level of risk should be selected. Page 13 of 101

18 Table 4/2 MAXIMUM AAV OF CHIPPINGS, OR COARSE AGGREGATES IN UNCHIPPED SURFACES, FOR NEW SURFACE COURSES (HD 36/06) Traffic (cv/lane/day) at design life Max AAV for chippings for hot rolled asphalt and surface dressing, and for aggregate in slurry and microsurfacing systems Max AAV for aggregate in thin Surface Course systems, SMA, exposed aggregate concrete surfacing and Asphalt Concrete Surface Course < > Note 1: For roads carrying less than 1750 cv/lane/day, aggregate of higher AAV may be used where experience has shown that satisfactory performance is achieved by an aggregate from a particular source. 4.3 Binders For surfacing materials generally 40/60 pen binder will be adequate for Hot Rolled Asphalt (HRA) and Thin Surface Course (TSC) mixtures, 100/150 pen for Asphalt Concrete (AC) mixtures including footways and 70/100 where stiffer AC mixes are required. The use of 160/220 pen binder is now generally limited to materials for footway works only at particularly cold periods. However, consideration must be given to the effect of subsequent high temperatures. There are also many binder additives, e.g. polymers and waxes, available which improve specific aspects of a bituminous materials performance. Before approving the use of any additive, the advice of TAG shall be sought. 5 SELECTION OF APPROPRIATE SURFACING TYPE Selection of the most appropriate surface treatment in any given situation involves consideration of numerous factors. There will often be more than one potential option and opinions will inevitably vary. The Technical Advice Group can assist with complex problems, however, the key issues have been mapped into a series of flow charts below, the combination of which should steer engineers in the right general direction. Outcomes from the flow charts direct engineers to the relevant more detailed sections of this document which will provide the guidance necessary to identify the criteria required to specify/order the appropriate process/material effectively. Page 14 of 101

19 MAINTENANCE TREATMENT CHART Does Deflectograph indicate low residual life or Is road showing signs of structural distress (SCANNER/CVI) Yes No Undertake Investigation to determine most appropriate course of action Is surface Profile/Drainage generally good Yes No Select Treatment from Surface Treatment Chart Consider need for regulating/profile planning and select surfacing from Resurfacing chart Page 15 of 97

20 RESURFACING CHART Does road carry high speed traffic - >40mph Yes No Refer to Table 5/2 Refer to Table 5/3 Does layout comply with modern geometric design criteria See Yes Is noise an issue See Section 4.11 No Yes Does site include Steep Gradient Use Positive Textured Surfacing eg HRA Yes No Regulate/resurface using positive texture surfacing eg HRA Regulate/resurface using a negative textured surfacing + initiate programme of Preventive Maintenance Referring to Tables 4/1 and 4/2 to provide a surfacing incorporating the appropriate aggregate (depends upon traffic flow, actual gradient etc) Page 16 of 97

21 SURFACE TREATMENT CHART Is surface deterioration limited to minor defects only, ie no significant cracking present Yes No Is skid resistance adequate? Refer to SCRIM data or commission survey Consider patch and surface dress or Microasphalt Surface Clause 960AR Yes No Consider rejuvenation to extend life See Section 7.6 and Clause 990AR Has existing surface polished rapidly? Yes No Consider Surface Dressing See section 6.1 (may require warning signs or retexturing as a temporary measure) Consider Retexturing See section 7.3 Page 17 of 97

22 5.1 Relative Properties of Surfacing Materials As mentioned in the introduction to this document not all surfacings are created equal. Table 5/1 gives a general overview of the relative properties of the 'common' surfacing materials when applied to carriageways. It is subjective and may not be unanimously accepted but nonetheless represents a considered judgement based on the typical type of site each material will be used on and the typical aggregate and texture properties specified. Since the publication of the previous edition of this guide in 2002 experience of negative textured surfacings such as Porous Asphalt, Stone mastic Asphalt (SMA), Thin Surface Courses and Ultra Thin Surface Courses on County roads has matured somewhat. Experience shows that the life expectancy of generic SMAs can be relatively short. It is evident that the technology is still evolving and the industry is moving away from generic mixes in favour of proprietary Thin Surface Courses, the performance of which is regulated through the BBA/HAPAS approvals process. The relative values given for these materials have been tweaked since 2002 to reflect this broader experience. More detailed guidance on the issues to be considered when using such materials are contained in sections 5.5.1, 5.5.2, 5.5.3, 7.1 and 7.2, B1.10 of this document. It is now recommended that proprietary thin surface course materials be used rather than generic SMAs (those specified in BS EN ). The full requirements of SHW clause 942 should be called up in order to specify these products. Page 18 of 97

23 TABLE 5/1 - RELATIVE PROPERTIES OF TYPICAL SURFACING MATERIALS FOR CARRIAGEWAYS MATERIAL (In descending order of typical layer thicknesses from 50mm-3mm) Skid Resistance Durability Deformation Resistance RELATIVE PROPERTIES Cracking Resistance Riding Quality/ Profiling Ability Structural Contribution Noise Characteristic Spray Control Hot Rolled Asphalt Performance Mixture Clause Marshall Design Recipe Mixture High Stone Content* Porous Asphalt Asphalt Concrete Thin Surface Course Clause * Micro- asphalt Surface Course (12-18mm) Surface Dressing, Single Surface Dressing, Racked in High Skid Resistance Surface Treatment n/a n/a n/a n/a n/a 1 n/a n/a 3 2 Block Paving Poor Good Excellent n/a n/a *The higher value for skid resistance of High Stone Content Asphalt only applies where speed limit < 40mph Reducing over time increased risk of icing Page 19 of 97

24 5.2 Guidance on Choice of Surfacing Detailed guidance on material selection is presented in tabular form with one table for sites with speed limits and/or 85th percentile speeds of '40mph (64kph) or greater' and one table for sites with 'speed limits and/or 85th percentile speeds of less than 40mph (64kph)'. This distinction is made due to the greater need for macrotexture at higher speeds where the risk of aquaplaning is elevated. The previous concerns regarding use of Generic Stone Mastic Asphalt (SMA) on any road with a speed limit of 40mph or greater have to a degree been overcome by the evolution of proprietary Thin Surface Courses (TSC) which can retain an adequate macrotexture in service. However, caution still needs to be exercised in the use of TSC in recognition of potential low early life skid resistance, slip resistance issues for horses and the potential increase in vehicle speeds arising from the low noise /smooth ride provided. TSCs shall not generally be used on evolved highways with geometry outside the parameters set down in Volume 6 of the DMRB. Under exceptional circumstances e.g. where there is no viable alternative, TSCs may be used at such sites in combination with other measures to reduce risk with the approval of the appropriate Area Director. In recognition of the developments in TSCs, the former HCC specification for Thin Surface Course Systems (Clause 960AR and previously Clause 942SR) has been withdrawn in favour of the new Clause 942 included in the latest 900 Series of SHW. Clause 942 and the new BS , which is called up therein, have addressed the issues which previously concerned HCC including requiring a 5 year guarantee. Similarly Clause 970AR for Generic SMA is withdrawn. Further guidance on use of TSCs is set out in Section of this document 6mm TSC is a relatively new material although feedback from a Highways Agency trial on the A34 trunk road near Winchester suggests it could be a more highly textured yet more durable alternative to 6mm Dense Surface Course (AC 6 dense surf), being better able to resist the scuffing actions of tyres on vehicles with power steering. This potentially makes it suitable for residential locations. It is not referred to in Tables 5/2 and 5/3 but is included within the mixtures in the THC. In addition to 6mm TSC, many manufacturers offer industrial versions of their 10 and 14mm TSCs with a denser grading aimed at reducing scuffing on low speed sites where requirements for macrotexture are less critical. Guidance on the preferred surfacing materials and any surface texture requirements are given based on the combination of site category and projected commercial vehicle traffic flow at the design life (i.e. in 20 years time allowing for the projected growth rate) - see Section 3 also. Page 20 of 97

25 Tables 5/2 and 5/3 set out the information referred to above. Subsequent to the tables are notes giving additional information and guidance on the various materials and their specifications. It is important that the supplementary information is considered fully to ensure that the selected material is specified appropriately. The 'Site Categories' in Tables 5/2 and 5/3 are derived from HD36 in the Design Manual for Roads and Bridges (DMRB) with minor amendments applicable to County roads. Tables 5/2 and 5/3 also include reference to the 'Road Hierarchy' introduced in the 1989 edition of the LAA Code of Good Practice (COGP) and reinforced in the latest revision Well Maintained Highways. The Hierarchy correlates reasonably well with Reinstatement Categories as defined in the New Roads and Street Works Act (NRSWA). However, there is an element of overlap and the traffic flows noted in the COGP are current, whereas those in Tables 5/2 and 5/3 are the anticipated flows at the end of 'Design Life' (i.e. 20 years). Engineers should therefore exercise caution in selecting the most appropriate surfacing material, assessing traffic flows at design life (see section 3.1) rather than just use the road hierarchy bands in a simplistic manner. Page 21 of 97

26 Section Site Category (HD36) Table 5/ C Estate Roads B Dual carriageway (non-event sections and minor junctions) C Single carriageway (non-event sections and minor junctions) Classification of Sites by Traffic and Stress Condition - Speed Limit 40mph or Greater Road Hierarchy - COGP Category 4a + 4b 3a + 3b 2 Traffic Design Life (20 yrs) Site Definition (Commercial vehicles per lane per day) As and above, but with channelised/slow moving traffic anticipated during summer months Q1,Q2,Q3 G1 Approaches to and across major junctions (all limbs) Dual and single carriageways Gradient 5% to 10%, longer than 50m: As above, but with channelised/slow moving traffic anticipated during summer months or in a south-facing cutting G2 Gradient steeper than 10%, longer than 50m: Dual and single carriageway R Roundabouts (including exits) As 5.3.7, above, but with channelised/slow moving traffic anticipated during summer months or in a south-facing cutting As 5.3.8, but with channelized/slow moving traffic anticipated during summer months or in a south-facing cutting K Approach to roundabout, traffic signals pedestrian crossings, railway level crossings and similar features Up to 50 Recipe HRA or Thin S/C Level 3 Recipe HRA or Thin S/C Level 3 or AC 14 CGSC kN HRA or Thin S/C Level 1 7kN HRA or Thin S/C Level 1 7kN HRA or Thin S/C Level (45 C) or Thin S/C Level (45 C) or Thin S/C Level (45 C) or Thin S/C Level 1 7kN HRA or Thin S/C Level (45 C) or Thin S/C Level 1 7kN HRA or Thin S/C Level (45 C) or Thin S/C Level (60 C) or Thin S/C Level 2 7kN HRA 943 (45 C) 943 (60 C) 7kN HRA or 943 (45 C) or Thin S/C Level 1 Thin S/C Level 1 7kN HRA (up to 250 cv/l/d) 7kN HRA otherwise 943 (45 C) 7kN HRA or Thin S/C Level 1 7kN HRA or Thin S/C Level 1 7kN HRA (up to 250 cv/l/d) Otherwise 943 (45 C) or Thin S/C Level (45 C) or Thin S/C Level 1 (i) A TEXTURE DEPTH OF 1.5 mm (SANDPATCH) OR 1.03 (MINI TEXTURE METER) SHALL BE SPECIFIED FOR ALL MATERIALS UNLESS MARKED *, or. SEE THE RELEVANT SECTION FOR FURTHER ADVICE (ii) NO TEXTURE DEPTH NEED BE SPECIFIED FOR MATERIALS MARKED (iii) SEE SECTION (iv) GUIDANCE ON THE SURFACING OF BENDS IS GIVEN IN SECTIONS AND (60 C) or Thin S/C Level (60 C) 943 (60 C) or Thin S/C Level (60 c) or Thin S/C Level 2 > 2500 Consult TAG Page 22 of 97

27 GENERAL NOTES TO TABLE 5/2 1 Where TSC (Thin Surface Course) is considered on evolved highways with questionable geometry (see 5.5.2) in areas with speed limits of 40 mph or greater, guidance from the Technical Advice Group should be sought and the approval of the appropriate Area Director, or his nominated representative, shall be obtained as necessary. 2 Where Clause 943 HRA (45ºC), 943 (60ºC) or TSC 942 Level 1, 942 Level 2 - is proposed, guidance from the Technical Advice Group (TAG) shall be sought and design information passed to TAG for comment. 4 Where the existing surface has rutted it may be necessary for the affected construction to be planed out prior to laying Clause 943 HRA, or Thin Surface Course mixtures. Failure to do this is likely to lead to continuing deformation under the new, deformation, resistant, material. Key AC 14 CGSC = Asphalt Concrete 14mm Close Graded Surface Course 7kN HRA = 30/14 HRA - 6-8kN stability Thin S/C = Thin Surface Course 943 (45 C) = HRA meeting 45 C wheel tracking specification 943 (60 C) = HRA meeting 60 C wheel tracking specification Page 23 of 97

28 5.3 Sites with a Speed Limit of 40 mph or Greater Shared Surface and Residential Roads serving up to 50 Dwellings (C) - these roads should never have a speed limit of 40mph or greater and hence are not covered by Table 5/2. In the unlikely event that such a road is the subject of surfacing works it should be considered to be within the most appropriate of the other site categories covered by Table 5/ Dual Carriageway (non-event sections and minor junctions) (B) - these site categories have been considered jointly as it is likely that any scheme involving a dual carriageway will also include at least minor junctions. Generally, this type of site will require a material resistant to deformation (rutting) and with the ability to maintain a relatively high level of surface texture. The traditional and preferred option is an HRA 30/14F surf 40/60 des with a Marshall Stability specified appropriate to the traffic flow of the site. On very heavily trafficked sites traditional HRA is liable to rut and hence a Clause 943 asphalt should be specified. On very lightly trafficked sites rutting is unlikely to be a problem and durability is the main requirement. In such circumstances a lower stability (4kN-8kN) mix HRA (with a higher binder content) is to be preferred. A proprietary Thin Surface Course may be an alternative, see also Section for more detailed guidance. The PSV required is also related to traffic flow and the class of site. Refer to Table 4/1 to select the appropriate level. Summary Traffic Flow at Design Life (comm. veh/lane/day) Preferred Material /Specification THC/IWF Appendix Up to 50 HRA 30/14F surf 40/60 rec + PCCs BS EN Table 4 7/1/M 51 to 1500 HRA 30/14F surf 40/60 des + PCCs BS EN , Table 4 Marshall Stability = 7± 1kN 1501 to 2500 HRA 35/14F surf 40/60 des + PCCs to Clause C wheel tracking Level 1 >2500 HRA 35/14F surf 40/60 des + PCCs to Clause C wheel tracking Level 2 7/1/B 7/1/C 7/1/C Up to 2500 Thin Surface Course System 45 C wheel tracking Level 1 7/1/H or 7/1/L N.B. For HRA and 14mm TSC a 1.5mm (sand patch) surface texture shall be specified. A 1.2mm texture depth may be appropriate for 10mm TSC material subject to an appropriate risk assessment. The PSV and AAV of Precoated Chippings (PCCs) and the coarse aggregate in a Thin Surface Course shall be specified in accordance with section 4 of this document. Page 24 of 97

29 5.3.3 Single Carriageway (non-event sections and minor junctions) (C) these site categories have also been considered jointly as it is likely that any single carriageway site will also include minor junctions. The selection of materials for these site categories is almost identical to those for dual carriageways. The only exception being in the 'up to 50 cv/l/day' band where a AC14 close surf 100/150 is considered as an acceptable alternative surfacing. It does not have the same degree of macrotexture as HRA and chippings and this should be considered when selecting a material for a particular site - if in doubt specify the 4kN to 8kN HRA 30/14F mixture. Summary Traffic Flow at Design Life (com veh/lane/day) Preferred Material/ Specification THC/IWF Appendix Up to 50 HRA 30/14F surf 40/60 rec + PCCs - BS EN , Table 4 or, AC 14 close surf 100/150 - BS EN to 1500 HRA 30/14F surf 40/60 des + PCCs BS EN Table 4 Marshall Stability = 7±1 kn 1501 to 2500 HRA 35/14F surf 40/60 des + PCCs to Clause C wheel tracking Level 1 >2500 HRA 35/14F surf 40/60 des + PCCs to Clause C wheel tracking Level 2 7/1/M 7/1/D 7/1/B 7/1/C 7/1/C Up to 2500 Thin Surface Course System 45 C wheel tracking Level 1 7/1/H or 7/1/L N.B. For HRA and 14mmTSC a 1.5mm (sand patch) surface texture shall be specified. For 10mmTSC A 1.2mm texture depth may be appropriate subject to an appropriate risk assessment. AC14 shall only be used on sites where a surface texture of 1.0mm or less is deemed acceptable. The PSV and AAV of Precoated Chippings (PCCs) and the coarse aggregate in an Asphalt Concrete or Thin Surface Course shall be specified in accordance with section 4 of this document Dual/Single Carriageways (include. minor junctions) with channelised/slow moving traffic anticipated during summer months - in summer when road temperatures are higher surfacing materials can approach the softening point of the bitumen in the mixture. Slow moving traffic results in longer loading times and hence the road surface is more liable to deform and rut. Channelised traffic results in more concentrated wheel track loading. Due to these factors, sites of these types need stiffer, more deformation resistant, mixtures than would otherwise be required. Page 25 of 97