MATERIALS IN N IRELAND A DRD ROADS SERVICE

Transcription

1 Presentation to the Joint Meeting of the IHT and IAT on Monday19 January THE USE OF THIN SURFACING MATERIALS IN N IRELAND A DRD ROADS SERVICE EXPERIENCE By Geoff Lester Roads Service Consultancy MEAS

2 Introduction Background to the Project Project Brief What the Project looked at What Are Thin Surfacings BBA HAPAS Approval of TSCS Visual Inspections and Coring Skid Resistance Texture Depth Road Noise Durability Patching and Utility Reinstatements Conclusions Questions

3 Project Brief To establish: How well they are performing and whether their use is offering good value for money; Compare observed performance with any tests/ information provided by the Contractor; Determine whether the material was laid on a suitable base material; Establish the opinions of Roads Service Engineers and Suppliers; Investigate issues re patching and reinstatements in Thin Surfacing; and Investigate, where there are issues about noise, if Thin Surfacing Systems would be preferable to HRA.

4 What the Project Looked At 120 TSCS sites and 32 HRA sites that had been laid since 2004 were identified by RS Engineers. Details included: Location Type of material used Contractor details Date laid Average depth of surface course specified Average cost /m2 Reasons for use of TSCS Comments re performance

5 What the Project Looked At On site assessments included: Visual inspections to identify any failures / problems; Coring; Comparisons of SCRIM data and texture t depth readings; Establish traffic volumes (cv/lane/day); Opinions and experience of Roads Service Engineers/ contractors / manufacturers/ and other Local Authorities on mainland UK. TRL report TRL660 Durability of Thin Asphalt Surfacing Systems. TRL report PPR205 Early Life Skid Resistance An Assessment of Accident Risk. CSS report ENG 1/2003 Advice Note for the Specification of Thin Surfacing. UK Roads Board Best Practice Guidelines for Specification of Modern Negative e Texture Surfaces (NTS) on Local Authority Highways.

6 What Are Thin Surfacings Thin Surface Course Systems (TSCS) are proprietary products and include: Thin Asphalt Concrete systems (TAC); Thin Stone Mastic Asphalt systems (TSMA); Paver-laid Surface Dressings; Multiple Surface Dressings; Micro-surfacing. BBA HAPAS has classified TSCS into 3 types depending on thickness laid: Type A <18mm Type B 18-25mm Type C >25 to 40mm TSCS are also known as Negative Texture Surfaces

7 What Are Thin Surfacings Typical Details of Negative and Positive Textures

8 What Are Thin Surfacings SMA was originally developed in Germany in the 1970 s but there were no requirements for macrotexture. Developments in the UK increased the nominal aggregate size to 14mm to provide high speed skid resistance. A high binder content is essential to achieve the durability and laying characteristics required.

9 What Are Thin Surfacings Typical UK SMA Compared to Typical German SMA

10 What Are Thin Surfacings The perceived benefits of TSCS v HRA are: Improved resistance to rutting by heavy traffic at high temperatures; Speed of installation reduces road user costs; Reduction in working area required; Quieter generates less noise at speeds above 50kph; Reduced surface spray in wet conditions. SHW cl. 942 provides guidance on the specification and use of TSCS. The new European Standards BS EN now include material specifications for TSCS: BS EN Asphalt Concrete for very thin layers; BS EN Stone Mastic Asphalt. TSCS are used extensively el on mainland UK and are said to account for at least 80% of pre-mixed surface course installed.

11 BBA HAPAS Approval of TSCS Highways Authorities Product Approval System (HAPAS) operated by the British Board of Agrément (BBA). HAPAS identifies appropriate criteria to measure the performance of Thin Surfacing installations and sets out categories of performance. The HAPAS assessment and certification process is undertaken in six stages. Each Thin Surfacing System undergo tests t & site trials over 2 years. The BBA Guidelines Document for the Assessment and Certification of Thin Surfacing Systems for Highways, details procedures for enhancing conditions encountered. A Certificate shall only be awarded on the systems successful completion of all 6 stages HAPAS Certificates for all approved TSCS can be viewed at

12 Details Typical Details Included on HAPAS Certificates Name of Supplier / Material Approved Aggregates Mix Tack / Bond Coat Details Information AN Other 14mm Something-phalt Gritstones, granites, limestones & basalts Polymer modified binder (Cariphalte TS) or 40/60 grade bitumen & cellulose fibres K1-40 or Colbond 50 bond coat Nominal Thickness 25 50mm Classification Type C Texture Depth Perf. Level 3 Wheel Tracking Perf. Level 3 Assessed Traffic Levels C Max Site Stress Level 1 Site Stress Level 2 Site Stress Level 3 >5000 cv/l/d Mainline/non event sections >5000 cv/l/d Major junctions >2500 cv/l/d Roundabouts Site Stress Level 4 >2500 cv/l/d Approaches to Roundabouts

13 Visual Inspections and Coring Of the 120 No TSCS sites identified: 75No 63% - had been laid since No - 54% - were on A class and above The most common reason given for using TSCS was traffic management/avoidance of road closures Summary of TSCS Sites Identified Division No of Sites Total A Class Avg cv/l/d A Class Avg Depth SC Avg Depth Below SC Eastern (68%) mm 154mm Northern (69%) mm 131mm Southern (46%) mm 99mm Western (50%) mm 148mm Total/Avg (54%) mm 132mm

14 Visual Inspections and Coring Summary of HRA Sites Identified Division No of Total A Avg cv/l/d Avg Depth Avg Depth Sites Class A Class SC Below SC Eastern 8 7 (87%) mm 153mm Northern 8 5 (62%) mm 136mm Southern 8 8 (100%) mm 145mm Western 8 7 (87%) mm 197mm Total/Avg (86%) mm 159mm

15 Visual Inspections and Coring The average cost of TSCS was 4.12/m² /m² for HRA sites. Average depth of surface course on TSCS sites was 39mm - 46mm on HRA sites. The average depth of blacktop on TSCS sites below the surface course was 132mm - 159mm on HRA sites. Average traffic volumes for A class roads with TSCS was 719 cv/l/day average in Western was 1097 cv/l/day. 7No suppliers in NI have HAPAS approved products. 3No suppliers use polymer-modified modified binder. All HAPAS certificates stipulate that TSCS are used in conjunction with either a bitumen emulsion or polymer-modified bond/tack coat: Majority of NI suppliers use K1-40 although some also include for a polymer-modified bond coat.

16 Visual Inspections and Coring Results of the visual inspections on the TSCS sites were as follows: The majority of sites were performing well although 75No (63%) were laid less than 2 years; Major failures were identified at 2No sites with serious fretting of the surface course at high stress areas; Failures around ironwork were identified at 26No sites; At 7No locations there was evidence of some texture loss/fretting/fattening up over isolated patches; 1No location rutting and potholing as a result of poor underlying layers rather than a problem with TSCS; There were no problems identified at any of the 32 HRA sites.

17 Visual Inspections and Coring Example of failures at high stress sites

18 Visual Inspections and Coring Example of failures at high stress sites

19 Visual Inspections and Coring Typical Ironwork Failures

20 Visual Inspections and Coring Typical Ironwork Failures

21 Visual Inspections and Coring Rutting / Potholes as a result of poor underlying layers:

22 Visual Inspections and Coring On 2No sites where major failures occurred, the failures were similar to those on the Toome Bypass. The initial failures at both sites occurred within the first 2 years. The Best Practice Guidelines for Specification of Modern Negative Texture Surfaces On Local Authority Highways identifies fretting as the most important and frequent single source of deterioration on TSCS. Max Traffic Volumes, as detailed in the HAPAS Certificate, for the 14mm TSCS used are: Site Stress Level 1 > 5000 cv/lane/day Mainline/non event sections Site Stress Level 2 > 5000 cv/lane/day Major Junctions Site Stress Level 3 > 2500 cv/lane/day Roundabouts Site Stress Level 4 > 2500 cv/lane/day Approaches to Roundabouts Current traffic volumes on these 2 sites are 1150 and 1700 cv/l/day.

23 Visual Inspections and Coring Would a 10mm TSCS be more appropriate at such sites. HAPAS details for the 10mm version of the TSCS used indicate that it would not have been suitable: Site Stress Level 1 > 3500 cv/lane/day Mainline/non event sections Site Stress Level 2 > 1500 cv/lane/day Major Junctions Site Stress Level 3 > 1000 cv/lane/day Roundabouts Site Stress Level 4 > 900 cv/lane/day Approaches to Roundabouts The high texture depth achieved by 14mm TSCS is an important factor to be considered when carrying out future designs.

24 Visual Inspections and Coring The results of a survey of Local Authorities included in The Best Practice Guidelines for Modern NTS concludes that: surface serviceability, in general, was good or better than traditional materials where the right material has been installed in the right site, but performance in high stress situations was indicated not to be quite so good.

25 Visual Inspections and Coring

26 Skid Resistance Texture Depth Road Noise SCRIM measurements were available for a number of TSCS sites from when they were first laid. Results obtained for others from the annual survey program. One off SCRIM survey carried out on 30No of these roads. Results from previous SCRIM surveys where also extracted for 13No of the HRA sites identified. Texture Depth Results: Year Avg. Texture Laid Depth Texture e Depth mm (San nd Patch) Typical Texture Depth Changes Over 2 Years Duration in Months

27 Skid Resistance Texture Depth Road Noise SCRIM Results: On majority of sites SCRIM results were good 2No TSCS sites and 2No HRA sites were significantly below Investigatory t Levels (IL). TSCS with polymer-modified binder appear to give higher SCRIM results than those with unmodified binder and cellulose fibres, but then reduce to comparable levels after this. Initial SCRIM results are similar for TSCS and HRA, however TSCS appear to retain their skid resistance better with time. Year Laid Avg. SCRIM TSCS Avg SCRIM HRA n/a

28 Skid Resistance Texture Depth Road Noise The data currently available within Roads Service is insufficient i to determine how well TSCS will retain their skid resistance with time. Results comparable to the findings contained within the TRL Report TRL660, which concludes that: While there are significant differences in SCRIM between sites with different aggregates, PSV category and thin surfacing type, there was no apparent reduction in skid resistance for TSCS up to 14yrs in service.

29 Skid Resistance Texture Depth Road Noise Early Life Skid Resistance: TRL Reports PPR060 The Early Life Skid Resistance of Asphalt Surfaces and PPR205 Early Life Skid Resistance An Assessment of Accident Risk conclude that: Dry friction on new asphalt can be lower, by up to about 20% at low speeds and by about 30-40% at intermediate and higher speeds. Early life skid resistance issues are not widespread but there is evidence of a small increased accident risk on newly laid asphalt surfaces - on both TSCS and HRA; Additional accidents are in the slight severity category and there is a significant decrease in fatal accidents; IAN 49/03 remains the best advice regarding the management of new surfacings.

30 Skid Resistance Texture Depth Road Noise Road Noise: Where traffic speeds are >50 km/hr the major component of traffic noise comes from the tyre/road interface. TSCS can be significantly quieter than conventional surfacings such as HRA.

31 Durability This is the area which gives the greatest cause for concern amongst Engineers across Roads Service. The reasons for this are: Sites where HAPAS Approved SMA products have been laid are still relatively new and their durability in comparison to HRA has still to be proved; Failures that occurred with thin surfacing materials used in the mid/late 1990 s within 4-5 years; Failures of TSCS on high profile sites; Reported failures of thin surface course materials on mainland UK. TSCS have been used extensively across Europe from the 1970 s and have demonstrated satisfactory working lives of years.

32 Durability Developments in UK to provide the required surface texture requirements are likely l to limit it the lives: Thicker SMA derived systems to about 15 years; Very thin systems to approx. 10 years. DEM 67/04 specifies a design life of 8 12 years. The TRL Report TRL660 concludes that: Thin Asphalt Concrete systems - maintain an acceptable performance for years with 0/14mm and 0/10mm. Thin Stone Mastic Asphalt systems - maintain an acceptable performance for 15 years with 0/14 mm and possibly more with 0/10 mm. When looking at the performance of HRA in trials on the A38 (Nicholls, 2005), the longevity of HRA was greater to that found here for thin surfacing systems.

33 Patching and Utility Reinstatements Possible problems identified with Utility reinstatements in TSCS as: They are difficult to hand lay; and Should only be laid by HAPAS Approved contractors. As a result most are being reinstated t using HRA. The NIRAUC Specification for the Reinstatement of Openings in Roads (2 nd Edition) allows for hand laying and is in conflict with details in the HAPAS Certificates and HD 37/99. Amendments to the NIRAUC Specification are required in relation to the reinstatement of Utility openings in TSCS. Careful consideration should be given to the use of TSCS on sites where Utility activity is likely.

34 Patching and Utility Reinstatements Typical Example of a Utility HRA Reinstatement in TSCS

35 Conclusions The use of TSCS are increasing Benefits of TSCS over HRA include: Quieter where road speeds >50kph; Reduced surface water spray; Easier and faster to lay and avoids problems with chipper, particularly during inclement weather; More resistant to rutting; Maintains better skid resistance throughout life; Early life skid resistance issues are not widespread but evidence of small increased accident risk on both TSCS and HRA. Average cost of TSCS comparable with cost of HRA. The majority of the TSCS sites identified are performing well. Problems with failures around ironwork: Need to work with contractors to resolve these problems Problems with utility reinstatements requires changes to NIRAUC specification.

36 Conclusions From the evidence available, TSCS can perform as well as HRA provided: Sites are properly designed; Care is taken when specifying materials in high stress areas; Choose the right material for the right site; TSCS are laid on a sound structure; Quality aggregates are used throughout the mix; A high standard of workmanship is used in the placement and compaction of the material particularly around ironwork. In terms of durability/service life, evidence not conclusive that TSCS available are a suitable long term alternative to HRA. TRL reports indicate TSCS can maintain acceptable performances of 15 yrs with 0/14mm gradings & possibly more with 0/10mm - but also concludes that from trials HRA will last longer.

37 Conclusions Major problems identified with the performance of 14mm TSCS on high h stress areas with high h traffic volumes. Similar problems not seen in Germany. SHW Series 900 cl 921 Table 9/3 now specifies a reduced initial texture depth on TSCS of: High speed 50mph NLT 1.3mm Roundabouts high speed Lower speed 40mph Roundabouts lower speed NLT 1.2mm NLT 1.0mm NLT 1.0mm Roads Service designers need to implement new standards and avoid over specifying texture depth. Need to consider specifying a maximum texture depth. Consider use of 10mm TSCS on high stress areas possible trial sites for suitable products.

38 Conclusions Developments in the UK of the original German SMA were carried out in order to provide the required surface texture requirements for skid resistance. Manufacturers need to consider further development of existing HAPAS approved products to provide an easy to compact low air void material to provide high durability. To allow this Roads Service may need to consider giving a commitment to the industry regarding the use of TSCS in the future in order to justify the additional costs which h these developments would incur.

39 Thank You for Listening Any Questions