In the UK, the new European

Transcription

1 In the UK, the new European Standards for asphalts came into force on 1 January 2008 and the previous standards, BS 4987 and BS 594, were withdrawn from use in December 2007.This paper gives an overview of the main requirements of the new standards and, in particular, the differences compared with the previous standards.while the asphalt mixtures themselves do not change, the descriptions and the methodology leading up to their manufacture, supply and conformity differ from those previously applicable. The new European Standards for asphalt comprise two families of standards: the EN family of product and associated standards the EN family of testing standards. These ENs (the UK versions of the ENs are designated BS EN and are published by BSI) replace the current Part 1 of BS , which addresses coated macadams, and Part 1 of BS 594 2, which deals with hot-rolled asphalts. Additionally, the BS EN series of testing standards will, at the same time, replace the majority of those parts of BS 598 where an equivalent European test Standard exists.a list of the mixture standards is shown in table 1 with the testing standards listed in table 2. European Standards (ENs) are drafted using a similar process to that used by the British Standards Institution. However, as a result of their wide applicability across the 27 member states of Europe that have agreed to adopt the European Standards for asphalt, European Standards for Asphalt An introduction to the new European Standards and PD document, and their application in the UK By John B-Bullock, Aggregate Industries (technical Manager - Yeoman Asphalt) their practical use without national guidance for individual countries would be almost impossible and would inevitably lead to the selection of inappropriate mixture compositions, resulting in performance levels that would be unacceptable to clients, producers and laying contractors. To address this, the UK has published a national guidance document (designated Published Document or PD) to address the applicability of the new EN series in the UK. The guidance document PD 6691, Asphalt - Guidance on the use of BS EN Bituminous Mixtures - Material specifications is particularly important as issues such as climate, traffic density and road safety demand specific properties and performance criteria to be selected and applied within the UK. Development of the ENs started after the issue of the Construction Products Directive (CPD) in December 1988 with the work on harmonizing the standards commencing in The first EN construction standard published was that for cement in 2000.The bitumen standard EN was published later the same year.the European Standards for aggregates were published in 2002 and implemented in January It has taken until this year QM January

2 Table 1. European asphalt mixture standards BS EN Bituminous mixtures. Material specifications. Asphalt Concrete BS EN Bituminous mixtures. Material specifications. Asphalt Concrete for very thin layers BS EN Bituminous mixtures. Material specifications. Soft Asphalt BS EN Bituminous mixtures. Material specifications. Hot Rolled Asphalt BS EN Bituminous mixtures. Material specifications. Stone Mastic Asphalt BS EN Bituminous mixtures. Material specifications. Mastic Asphalt BS EN Bituminous mixtures. Material specifications. Porous Asphalt BS EN Bituminous mixtures. Material specifications. Reclaimed Asphalt BS EN Bituminous mixtures. Material specifications. Type Testing BS EN Bituminous mixtures. Material specifications. Factory Production Control to reach a point where the asphalt standards can be implemented, some 18 years after work commenced. The principle involves the harmonization of individual European countries specifications and test methods. While there are currently 27 countries represented and bound to implement the ENs, in 1989 there were only 12.Their implementation will remove the geographical barriers to trade within Europe and introduce a common approach to testing and performance assessment. Key differences between the old British Standards and the new European Standards for asphalts It is very important to note that the new standards have greater authority and legal standing than the previous British Standards, therefore requiring particular attention to the detail of product certification through CE marking. The British Standards left compliance to be a requirement of the contract, whether directly with the customer/user of the road or pavement, or through other contractual supply arrangements including Sector Scheme 14, whereas the European Standards bring product compliance and conformity into the materials standards. The ENs relate to the product in the back of the lorry, but in the UK some properties are installation trial dependent (the protocols for the trials are annexes within the new BS , which addresses the issues covered in Part 2 of both BS 4987 and BS 594 and is discussed below). However, there will still be requirements written into contracts including, for example, proof of adequate compaction, and the same protocols applicable to what is called type testing, proof of conformity prior to supply, will be utilized. The grading and binder content for the asphalt products are based on the principle of selecting specific target values and then applying the production control tolerances to these individual target values.this concept was first introduced in BS 4987 and BS 594 in 2005 as a lead in to the new standards but only against the 2mm sieve.the Table 2. BS EN Bituminous mixtures - Test methods for hot asphalt BS EN Soluble binder content BS EN Determination of particle size distribution BS EN Bitumen recovery. Rotary evaporator BS EN Bitumen recovery. Fractionating column BS EN Determination of the maximum density BS EN Determination of bulk density of bituminous specimens BS EN Determination of the bulk density of bituminous specimens by gamma rays BS EN Determination of void characteristics of bituminous specimens BS EN Determination of the reference density BS EN Compactability BS EN Determination of the affinity between aggregate and bitumen BS EN Determination of the water sensitivity of bituminous specimens BS EN Temperature measurement BS EN Water content BS EN Determination of the segregation sensitivity BS EN Abrasion by studded tyres BS EN Particle loss of porous asphalt specimen BS EN Binder drainage BS EN Permeability of specimen BS EN Indentation using cube or Marshall specimens BS EN Indentation using plate specimens BS EN Wheel tracking BS EN Determination of the indirect tensile strength of bituminous specimens BS EN Resistance to fatigue BS EN Cyclic compression test BS EN Stiffness BS EN Sampling BS EN Preparation of samples for determining binder content, water content and grading BS EN Determination of the dimensions of a bituminous specimen BS EN Specimen preparation by impact compactor BS EN Specimen preparation by gyratory compactor BS EN Laboratory compaction of bituminous mixtures by vibratory compactor BS EN Specimen prepared by roller compactor BS EN Marshall test BS EN Laboratory mixing BS EN Determination of the thickness of a bituminous pavement BS EN Hot-sand test for the adhesivity of binder on pre-coated chippings for HRA BS EN Test equipment and calibration BS EN Binder content by ignition BS EN In-situ drainability BS EN Resistance to de-icing fluids BS EN Amount of coarse foreign matter in reclaimed asphalt BS EN Resistance to fuel 18 QM January 2008

3 specification tolerances for grading and binder content are not included in the individual product standards; they sit within EN and, of course, PD Target binder contents are adjusted according to the relative density of the aggregate combination used, thereby ensuring that the more critical aspect of the binder volume of the mixture is fully taken account of in the design of the mixture. Within PD 6691 the example specifications found in the annexes already take the nature of the aggregate into account and, therefore, state the actual binder contents that should be found on analysis. In terms of product conformity, binder and filler contents are not adjusted to allow for any sampling bias.while this is particularly relevant to the larger 32mm lean binder content mixtures, in respect of all mixtures it increases the importance of ensuring that representative samples are taken from the material, whether it be in the lorry, a heap or even from the laid mat, for contractual audit testing. There are provisions for the use of reclaimed asphalt in each of the asphalt product standards and reclaimed asphalt is formally recognized as an ingredient and covered under EN , where it is identified and categorized according to any contaminants and the properties of the binder. EME2 (Enrobé à Module Élevé), the very stiff and resilient base and binder course material that has now replaced HMB35 and which utilizes approximately 5.5% of a very hard 15/20 or 20/25 pen binder, is now officially covered by a national standard in addition to its inclusion in the Specification for Highway Works 4,5. SMA (stone-mastic asphalt), which again was not covered under a British Standard specification, is now addressed by EN (SMAs also feature in a number of proprietary BBA/HAPAS-certified mixtures 6 for use in a number of motorway and trunk road applications). All mixtures supplied in compliance with one of the EN product standards are prefixed by an abbreviation which identifies the mixture type, the principal ones being: AC (asphalt concrete), HRA (hot-rolled asphalt) and SMA (stone-mastic asphalt). More details on mixture designations are given below. The national guidance document for asphalt mixtures PD 6691 This is the indispensable document for engineers, specifiers, contractors and suppliers, ie for all those involved in asphalt in the UK. It facilitates the selection of the appropriate asphalt mixture for the majority of paving applications and must be read and understood before attempting to grasp the contents of the individual standards in the BS EN series.without the advice given in PD 6691 it would be almost impossible to specify asphalt mixtures capable of handling and performing in an equivalent manner to the mixtures used previously. PD 6691 principally covers BS EN Asphalt Concrete, BS EN Hot Rolled Asphalt and BS EN Stone Mastic Asphalt, with limited reference to BS EN Asphalt Concrete for Thin Layers, which is covered primarily through BBA/HAPAS certification. PD 6691 does not cover BS EN Soft Asphalt, which is principally used in the Nordic countries, BS EN Porous Asphalt or BS EN Mastic Asphalt.While the use of porous asphalt on motorways and trunk roads is now limited in the UK, guidance can still be sought from the Specification for Highway Works. For mastic asphalt, contact should be made with the Mastic Asphalt Council 7 and for asphalt specifically to be used on airfields, reference should be made to the series of Defence Estates Standards 8. For ease of use, the format of PD 6691 has been made very similar to that of BS 4987 and BS 594.While it provides guidance on the use and selection of asphalt mixtures, full details of the specification requirements for each of the principle mixture types used in the UK (AC, HRA Asphalt Technology and SMA) are covered and these take account of the requirements associated with UK climate, traffic and safety issues. Importantly, it also contains stand-alone example specifications for the most commonly used asphalts from BS 4987, BS 594 and from the Specification for Highway Works for SMA and EME2. The UK will continue to follow the empirically-based recipe approach to mixtures with, initially, few ancillary property tests; the principal tests being voids content and, where necessary, wheel-tracking and stiffness. Some of the EN test methods will change, eg wheeltracking, where the method used is dependant on the material being tested and a different format is used for reporting the results of AC and SMA.As a result, testing against the new BS EN test method will be carried out alongside testing undertaken in accordance with BS This will continue until sufficient data are available to correlate the results from the two methods, which, in time, will permit the specification of limits applicable to the new EN methods. The more fundamental approach to mixture design will take a number of years to be introduced and can only be considered once the required experience with the new European Standard tests and how they relate to performance in the pavement has been gained. As previously stated, target binder contents are adjusted according to the relative density of the aggregate combination used to ensure the binder volume relationship for the mixture is maintained. However, in the UK allowance has always been made for another key attribute of the aggregate its microtexture. Accordingly, target binder contents in PD 6691 are recommended depending on the type and nature of aggregate used. For CE marking purposes, the binder content by mass used in the manufacture of the asphalt is back-calculated to ensure that it is declared in the correct format, in line with the requirements of the EN.This binder content is quoted as Bmin on the CE mark and is likely to QM January

4 be a different figure to the actual binder content used in the manufacture of the asphalt, which is known as Bact and is the binder content against which product conformity is adjudged. With regard to the use of reclaimed asphalt, it is classified in terms of its content of foreign matter and the properties of its binder. Recommended maximum limits for its use in mixtures are 10% for surface course and 50% for bases and binder courses. Where more than 10% and 20% of reclaimed asphalt is used in surface courses or bases and binder courses, respectively, the recovered binder from the mixture is evaluated by penetration testing.thus, there is little difference from the current requirements given in the Specification for Highway Works. In the UK the normative product designations of the asphalt concretes have been further expanded to permit identification of the full grading range of the mixtures used.these descriptions will be familiar to the users of BS 4987 materials as: dense (dense) open (open graded) close (close graded) med (medium graded) fine (fine graded). The terms HDM (heavy-duty macadam) and HMB (highmodulus base) will also continue to be used to differentiate between the mixtures providing improved performance characteristics in use. Additionally, the PSV of the aggregate can be added to the designation for surface course and binder courses exposed to traffic in their early life.this is not a mandatory requirement within the ENs but must be considered a safeguard from the customer s perspective ensuring that appropriate skid-resistant mixtures are supplied.to identify design mixtures from recipe mixtures, as applicable to HRA and AC dense mixtures, the designation des will be used. Examples of these product designations are: AC 32 HDM base 40/60 AC 10 close surf 100/150 PSV60 HRA 35/14F surf 40/60 des PSV50 SMA 10 surf 40/60 PSV65. It should be noted that individual asphalt producers may add further information to the product designation/description. In most cases, the description of proprietary asphalts will be unchanged. Product conformity (Attestation of Conformity) is evidenced by CE marking, which is similar to a product conformity certificate and works on similar principles to those applicable to the ENs for aggregates. However, it is anticipated that the CE marking for asphalt will be more rigidly applied and more widely used in the UK. PD 6691 contains four very important annexes which provide detailed information and guidance on the mixture specifications. These annexes occupy some two-thirds of the document and are the key reference areas for the selection of appropriate target gradings and binder contents for the type of mixture that is required.the use of the tables in the annexes ensures that the mixture composition and performance do not change significantly when transferring the specification of the asphalts to the new EN Standards.The contents of the annexes are: Annex A:The importance of example mixture specifications; Annex B: Asphalt Concrete; Annex C: Hot Rolled Asphalt (including PCC); and Annex D: Stone Mastic Asphalt The fundamental differences between specifying the grading using the European Standards and the UK method contained in BS 4987 and BS 594, and other documents, is easier to understand by way of an example.table 3 identifies the process for selecting target gradings and binder content from the target grading ranges and applying the FPC tolerance using 32mm asphalt concrete dense binder course as an example. Readers should note the use of a comma, which replaces the decimal point traditionally used in the UK. For the purposes of Table 3. Example of a declared specification (AC 32 HDM dense bin 40/60) Test sieve mm Target composition Annex B Table B.11 Declared target grading/binder Tolerances from Table 8 Conformity specification , ± , ± ± , ± , ±3 5,0-11,0 Binder (Limestone Aggregate) 4,0 4,0 ±0,6 3,4-4,6 Notes 1. Test sieves from the appropriate table in Annex B, together with the appropriate binder content as allowed in BS EN are included in the table. 2. The target grading ranges and binder content limiting values have been taken from the relevant table in Annex B. 3. The specific target grading values and target binder content are selected from the values in the column headed Target composition Annex B.Where the latter column contains only a single value, as is the case for the percentage passing the 6,3mm sieve, only this value can be selected.where a range is shown, eg for the percentage passing the 2mm sieve, any value between 27 and 33 can be selected as the target grading value. 4. The values shown in the column headed Tolerances from Table 8 are the tolerances taken from PD 6691 (BS EN ) to be applied to the individual target grading values and the target binder content and used to formulate the compliance specification. 5. The conformity specification is similar to the equivalent specification that would be found within BS QM January 2008

5 monitoring quality and checking on the deviation of the results from the declared target values used for type testing, the compliance specification is better reported as the declared target values with the tolerances alongside in a similar format to that shown in table 4. To convert the Bact target values within PD 6691 back to the regulatory Bmin value required by the BS EN Standard, the following formula is used: Bmin declared = b x Bact 2,650 where b is the mean particle density of the aggregate mixture in Mg/m 3, determined in accordance with BS EN , with the resultant binder content being declared to the nearest 0,2%. Thus, if the mean particle density of the aggregate in a mixture is 2,730Mg/m 3, the binder content for CE marking purposes (Bmin) would be calculated from the selected target binder content (Bact) used to manufacture the mixture using the above formula as follows: Bmin declared = 2,730 4,0% Bact 2,650 = 4,2% (4,12 rounded to the nearest 0,2%) The process for the approval of CE-marked asphalt mixtures on contracts is formalized through type testing disciplines covered by EN and the factory product control covered by EN The asphalt industry is identifying this process using the acronym CE MAP, which stands for the CE Marking and Approval Process. The CE MAP - The methodology for type testing and factory production control Section 13 of PD 6691 details the requirements for the Evaluation of Conformity and the obligations of the asphalt producer.target grading values and the target binder content are selected from the tables in annexes B, C or D in PD 6691 and type testing is carried out in accordance with BS EN Table 4. Conformity specification alternative format (AC 32 HDM dense bin 40/60) Test sieve mm to prove mix conformity with the EN/PD requirements at the selected target composition.the protocols identified in this section and used as part of the type testing procedure are found in BS The type test record is completed and includes: a declaration of the types and sources of constituent materials test data proving conformity of the constituents with the relevant requirements a declaration of the target composition of the mixture test data showing conformity of the mixture with any specified performance requirements. It is important to note that type testing is mixture specific and does not have to be repeated where the same type, source and proportion of constituents are used on another plant. However, certain type tests will not have to be repeated where the change in a constituent leads to a result which will be better than that obtained with the original constituent. For example, a mixture containing 100/150 pen for wheel-tracking would be assumed to comply if the binder grade was changed to 40/60 pen, providing no other mixture constituents nor any mixture proportions were altered. Under the requirements for factory production control covered in EN , the type testing procedure for an asphalt mixture has to be repeated at intervals not exceeding five years. The EN factory product control (FPC) tolerances are applied to the target composition to formulate the Conformity specification , ±9 6,3 52 ± ±7 0, ±5 0,063 8 ±3 Binder (Limestone Aggregate) 4,0 ±0,6 compliance specification for conformity assessment. The documented FPC requirements to manufacture the product are followed. It is noteworthy that these are narrower in scope than those contained in BS EN 9001 as customer-related issues and continuous improvement are not covered in EN Industry Sector Scheme refers to EN and expands on the FPC requirements.the FPC system, including the additional requirements of Sector Scheme14, is currently third party assessed by registered notified bodies (NoBo s). The Sector Scheme 14 requirements are considered in addition to those from the ENs and the FPC procedures are followed to check conformity of the product supplied. Conformity is checked against the single result criteria within PD 6691 (EN ).The mean deviation from target is a new concept in the UK and is determined as a check on product consistency to ensure production results do not wander too far from the target values proposed under type testing. In place of the Q level previously used in the UK, a system to determine the OCL (operating compliance level) is used.this is determined from the last 32 results (Q level utilized the last 30 results). However, the OCL is also marked down by a failure in mean deviation.the OCL determines the sample rates for groups of mixtures and linked to this are recommended minimum test frequencies identified within Sector Scheme 14. CE marking is carried out by self-certification with the CE QM January

6 marks being subject to examination by the notified bodies. To ensure that clients and customers are made fully aware of the supply specification, it is likely that the majority of asphalt suppliers will provide an additional product information sheet for each of their mixtures, which will show the types and sourcing of all the ingredients along with the compliance specification and any ancillary test data. BS Asphalt for roads and other paved areas specification for transport, laying and compaction and design protocols This new standard replaces Parts 2 of BS and BS and covers all the EN asphalt mixtures found in PD It has been produced for UK use because there is no European Standard that addresses the issues of transport, laying and compaction. In a similar format to Parts 2 of BS 4987 and BS 594, it must be considered as the baseline document for all hot asphalt pavement applications. It details minimum and maximum compacted thicknesses along with the accuracy of finish required for each of the pavement layers, and it provides improved clarity on laying, the formation of joints and all the other key issues associated with site preparation. Readers should note that, at the same time as the full implementation of the European Standards for Asphalt, the Highways Agency have had to amend their documents and have produced two Interim Advice Notes covering the European Standards for asphalt and the amended 900 series. These are covered in summary below. The application of pre-coated chippings to hot-rolled asphalt surface course is detailed along with the rates of spread and the measurement of texture depth. As previously, the importance and the requirements for achieving compaction are detailed. An area not previously covered which is now included is the sampling and testing for type testing the asphalt through the use of trial strips.this is detailed within a series of very important informative annexes, a number of which cover protocols previously found within the Specification for Highway Works, as indicated by the SHW clause references in brackets. The annexes are: Annex A: Details delivery and rolling temperatures for a full range of mixtures including SMA Annex B: Details the rates of spread including the range of Asphalt Concretes, Hot Rolled Asphalts, Stone Mastic Asphalt and EME2 Annex C: Details the procedure for the determination of DBM/HDM/HMB design voids (SHW 929) Annex D: Details the procedure for the determination of DBM/HDM/HMB deformation resistance (SHW 952) Annex E: Details of the EME2 design procedure and the properties testing (extracted from TRL 636) Annex F: Details of the procedure for the determination of performance HRA properties (SHW 943) Annex G: Details of the procedure for the determination of SMA binder course properties (SHW 937) Annex H: Details of the procedure for the determination of the HRA surface course design (including the requirements of BS ) Annex I: Calibration and operation of indirect density gauges including both nuclear and other indirect gauges. Changes to the Highways Agency Specification for Highway Works During November 2007 two Interim Advice Notes (IANs) were published by the Highways Agency covering the introduction of the European Standards for Asphalt: IAN 102/07 13, entitled The introduction of BSEN standards for bituminous mixtures site supervision aspects, and IAN 101/07 14, entitled Revised MCHW specification 900 series. IAN 102/07 introduces the changes taking effect from 1 January 2008 focusing on product description changes, the introduction of reclaimed asphalt and, of course, the implications of initial type testing, factory production control and CE marking.the IAN also identifies and details the transitional arrangements on contracts and explains that CE mark certification from all suppliers will not necessarily be available from January due to the assessment work needing to be carried out by the notified bodies before certification can be issued by suppliers. The significant changes to the 900 series are covered in IAN 101/07 with references to PD6691 in respect to all the key areas of the changes, including the important product designation/description changes. However, further important changes have been brought in by the Highways Agency since 1 January concerning the durability of base and binder course layers.these have arisen from joint collaborative work and have been fully supported by the asphalt industry in full recognition of the early-life failures and the resultant significant costs arising from water ingress to the lower layers of flexible asphalt pavements. Within clause 903, in summary, the following are the most significant additional requirements to the base and binder course layers to enhance those of the new BS A detailed method statement is required for each contract covering laying and compaction of each of the layers along with details of longitudinal and transverse joint formation. Full interlayer bonding required between all flexible pavement layers. All longitudinal joints will be outside defined wheeltrack zones and offset by 300m from any parallel joints in the underlying layer. Additional, and specifically for 26 QM January 2008

7 the base and binder course layers: Compaction will be measured within 100m of the joints in each of the layers with the voids content being not more than 2% higher than that required for the layer in the contract. All joints will be overbanded with a bitumen sealant to a width of 75mm either side of the joint. The same sealant will be applied to the whole of any freestanding edge on the outside of the finished pavement on the high side of the camber and on the low side when specified in App 7/1. These changes in clause 903 do involve significant additional costs and are therefore not mandatory for contracts that have already been priced, awarded or were under construction before 1 January References 1. BRITISH STANDARDS INSTITUTION: Coated macadam (asphalt concrete) for roads and other paved areas Part 1: Specification for constituent materials and for mixtures, BS :2005, BSI, London. 2. BRITISH STANDARDS INSTITUTION: Hot-rolled asphalt for roads and other paved areas, Specification for constituent materials and asphalt mixtures, BS 594-1:2005, BSI, London. 3. BRITISH STANDARDS INSTITUTION: Bitumen and bituminous binders, Specifications for paving grade bitumens, BS EN 12591:2000, BSI, London. 4. HIGHWAYS AGENCY et al: Manual of Contract Documents for Highway Works,Vols 0-6, various dates,the Stationery Office, London co.uk/index.htm 6. html 7. co.uk/ 8. estates.mod.uk/publications/airfiel d/airfields.php 9. BRITISH STANDARDS INSTITUTION: Bituminous mixtures for roads and other paved areas, Methods of test for the determination of texture depth, BS :2004, BSI, London. 10. UKAS: National Highways Sector Scheme for Quality Management in Highway Works, Sector Scheme Asphalt Technology 16, For the quality assurance of the production of asphalt mixes, March 2004, Sector Scheme Advisory Committee, Feltham, Middlesex. 11. BRITISH STANDARDS INSTITUTION: Coated macadam for roads and other paved areas, Specification for transport, laying and compaction, BS :2003, BSI, London. 12. BRITISH STANDARDS INSTITUTION: Hot rolled asphalt for roads and other paved areas, Specification for transport, laying and compaction, BS 594-2:2003, BSI, London. 13. HIGHWAYS AGENCY: Interim Advice Note 102/07 The introduction of BSEN standards for bituminous mixtures site supervision aspects, Nov Available for download from: ans/index.htm 14. HIGHWAYS AGENCY: Interim Advice Note 101/07, Revised MCHW specification 900 series, Nov Available for download from: ans/index.htm QM January